61256 Federal Register / Vol. 73, No. 200 / Wednesday, October 15, 2008 / Rules and Regulations 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 197 

[EPA–HQ–OAR–2005–0083; FRL–8724–9] 

RIN 2060–AN15 

Public Health and Environmental 

Radiation Protection Standards for 

Yucca Mountain, Nevada 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Final rule. 

SUMMARY: We, the Environmental 

Protection Agency (EPA), are 

promulgating amendments to our public 

health and safety standards for 

radioactive material stored or disposed 

of in the potential repository at Yucca 

Mountain, Nevada. Congress directed us 

to develop these standards and required 

us to contract with the National 

Academy of Sciences (NAS) to conduct 

a study to provide findings and 

recommendations on reasonable 

standards for protection of the public 

health and safety. The health and safety 

standards promulgated by EPA are to be 

‘‘based upon and consistent with’’ the 

findings and recommendations of NAS. 

Originally, these standards were 

promulgated on June 13, 2001 (66 FR 

32074) (the 2001 standards). 

On July 9, 2004, the U.S. Court of 

Appeals for the District of Columbia 

Circuit vacated portions of the 2001 

standards concerning the period of time 

for which compliance must be 

demonstrated. The Court ruled that the 

compliance period of 10,000 years was 

not ‘‘based upon and consistent with’’ 

the findings and recommendations of 

the NAS and remanded those portions 

of the standards to EPA for revision. 

These remanded provisions are the 

subject of this action. 

This final rule incorporates 

compliance criteria applicable at 

different times for protection of 

individuals and in circumstances 

involving human intrusion into the 

repository. Compliance will be judged 

against a standard of 150 microsieverts 

per year (μSv/yr) (15 millirem per year 

(mrem/yr)) committed effective dose 

equivalent (CEDE) at times up to 10,000 

years after disposal and against a 

standard of 1 millisievert per year (mSv/ 

yr) (100 mrem/yr) CEDE at times after 

10,000 years and up to 1 million years 

after disposal. This final rule also 

includes several supporting provisions 

affecting the projections of expected 

disposal system performance prepared 

by the Department of Energy (DOE). 

DATES: Effective Date: This final rule is 

effective on November 14, 2008. 

ADDRESSES: EPA has established a 

docket for this action under Docket ID 

No. EPA–HQ–OAR–2005–0083. All 

documents in the docket are listed on 

the http://www.regulations.gov Web 

site. Although listed in the index, some 

information is not publicly available, 

e.g., Confidential Business Information 

(CBI) or other information whose 

disclosure is restricted by statute. 

Certain other material, such as 

copyrighted material, is not placed on 

the Internet and will be publicly 

available only in hard copy form. 

Publicly available docket materials are 

available either electronically through 

http://www.regulations.gov, for 

purchase or access from sources 

identified in the docket (Docket Nos. 

EPA–HQ–OAR–2005–0083–0086 and 

EPA–HQ–OAR–2005–0083–0087), or in 

hard copy at the Air and Radiation 

Docket, EPA/DC, EPA Headquarters 

West Building, Room 3334, 1301 

Constitution Ave., NW., Washington, 

DC. The Public Reading Room is open 

from 8:30 a.m. to 4:30 p.m., Monday 

through Friday, excluding legal 

holidays. The telephone number for the 

Air and Radiation Docket is (202) 566– 

1742. 

FOR FURTHER INFORMATION CONTACT: Ray 

Clark, Office of Radiation and Indoor 

Air, Radiation Protection Division 

(6608J), U.S. Environmental Protection 

Agency, 1200 Pennsylvania Ave., NW., 

Washington, DC 20460–0001; telephone 

number: 202–343–9360; fax number: 

202–343–2305; e-mail address: 

clark.ray@epa.gov. 

SUPPLEMENTARY INFORMATION: 

I. General Information 

A. Does This Action Apply to Me? 

DOE is the only entity regulated by 

these standards. Our standards affect 

NRC only to the extent that, under 

Section 801(b) of the EnPA, 42 U.S.C. 

10141 n., NRC must modify its licensing 

requirements, as necessary, to make 

them consistent with our final 

standards. Before it may construct the 

repository or accept waste at the Yucca 

Mountain site and eventually close the 

repository, DOE must obtain 

authorization for these activities from 

NRC. DOE will be subject to NRC’s 

modified regulations, which NRC will 

implement through its licensing 

proceedings. 

B. How Can I View Items in the Docket? 

1. Information Files. EPA is working 

with the Lied Library at the University 

of Nevada-Las Vegas (http:// 

www.library.unlv.edu/about/ 

hours.html) and the Amargosa Valley, 

Nevada public library (http:// 

www.amargosalibrary.com) to provide 

information files on this rulemaking. 

These files are not legal dockets; 

however, every effort will be made to 

put the same material in them as in the 

official public docket in Washington, 

DC. The Lied Library information file is 

at the Research and Information Desk, 

Government Publications Section (702– 

895–2200). Hours vary based upon the 

academic calendar, so we suggest that 

you call ahead to be certain that the 

library will be open at the time you 

wish to visit. The other information file 

is in the Public Library at 829 East Farm 

Road in Amargosa Valley, Nevada 

(phone 775–372–5340). As of the date of 

publication, the hours are Monday and 

Thursday (9 a.m.–7 p.m.); Tuesday, 

Wednesday, and Friday (9 a.m.–5 p.m.); 

and Saturday (9 a.m.-1 p.m.). The 

library is closed on Sunday. These 

hours can change, so we suggest that 

you call ahead to be certain when the 

library will be open. 

2. Electronic Access. An electronic 

version of the public docket is available 

through the Federal Docket Management 

System at http://www.regulations.gov. 

You may use http:// 

www.regulations.gov to view comments, 

access the index listing of the contents 

of the official public docket, and to 

access those documents in the public 

docket that are available electronically. 

To access the docket go directly to 

http://www.regulations.gov and select 

‘‘Advanced Docket Search’’ under 

‘‘More Search Options.’’ In the Docket 

ID window, type in the docket 

identification number EPA–HQ–OAR– 

2005–0083 and click on ‘‘Submit.’’ 

Please be patient since the search could 

take several minutes. This will bring 

you to the ‘‘Docket Search Results’’ 

page. From there, you may access the 

docket contents (e.g., EPA–HQ–OAR– 

2005–0083–0002) by clicking on the 

icon in the ‘‘Views’’ column. 

C. Can I Access Information by 

Telephone or Via the Internet? 

Yes. You may call our toll-free 

information line (800–331–9477) 24 

hours per day. By calling this number, 

you may listen to a brief update 

describing our rulemaking activities for 

Yucca Mountain, leave a message 

requesting that we add your name and 

address to the Yucca Mountain mailing 

list, or request that an EPA staff person 

return your call. In addition, we have 

established an electronic listserv 

through which you can receive 

electronic updates of activities related to 

this rulemaking. To subscribe to the 

listserv, go to https://lists.epa.gov/read/ 


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Federal Register / Vol. 73, No. 200 / Wednesday, October 15, 2008 / Rules and Regulations 61257 

all_forums. In the alphabetical list, 

locate ‘‘yucca-updates’’ and select 

‘‘subscribe’’ at the far right of the screen. 

You will be asked to provide your email address and choose a password. 

You also can find information and 

documents relevant to this rulemaking 

on the World Wide Web at http:// 

www.epa.gov/radiation/yucca. The 

proposed rule for today’s final rule 

appeared in the Federal Register on 

August 22, 2005 (70 FR 49014). We also 

recommend that you examine the 

preamble and regulatory language for 

the earlier proposed and final rules, 

which appeared in the Federal Register 

on August 27, 1999 (64 FR 46976) and 

June 13, 2001 (66 FR 32074), 

respectively. 

D. What Documents are Referenced in 

This Final Rule? 

We refer to a number of documents 

that provide supporting information for 

our Yucca Mountain standards. All 

documents relied upon by EPA in 

regulatory decision-making may be 

found in our docket (EPA–HQ–OAR– 

2005–0083). Other documents, e.g., 

statutes, regulations, and proposed 

rules, are readily available from public 

sources. The documents below are 

referenced most frequently in today’s 

final rule. 

Item No. (EPA–HQ–OAR–2005–0083– 

xxxx). 

0076 Technical Bases for Yucca 

Mountain Standards (the NAS Report), 

National Research Council, National 

Academy Press, 1995. 

0086 DOE Final Environmental 

Impact Statement, DOE/EIS–0250, 

February 2002. 

0383 ‘‘Geological Disposal of 

Radioactive Waste,’’ International 

Atomic Energy Agency Final Safety 

Requirements (WS–R–4), 2006. 

0417 ‘‘Radiation Protection 

Recommendations as Applied to the 

Disposal of Long-Lived Solid 

Radioactive Waste,’’ International 

Commission on Radiological Protection 

Publication 81, 2000. 

0408 ‘‘Regulating the Long-Term 

Safety of Geological Disposal: Towards 

a Common Understanding of the Main 

Objectives and Bases of Safety Criteria,’’ 

OECD Nuclear Energy Agency, NEA– 

6182, 2007. 

0421 ‘‘1990 Recommendations of the 

International Commission on 

Radiological Protection,’’ ICRP 

Publication 60. 

0423 ‘‘2007 Recommendations of the 

International Commission on 

Radiological Protection,’’ ICRP 

Publication 103. 

0431 Response to Comments 

Document for Final Rule, EPA–402–R– 

08–008, June 2007. 

Acronyms and Abbreviations 

We use many acronyms and 

abbreviations in this document. These 

include: 

BID—background information document 

CED—committed effective dose 

CEDE—committed effective dose equivalent 

CFR—Code of Federal Regulations 

DOE—U.S. Department of Energy 

EIS—Environmental Impact Statement 

EnPA—Energy Policy Act of 1992 

EPA—U.S. Environmental Protection Agency 

FEIS—Final Environmental Impact Statement 

FEPs—features, events, and processes 

FR—Federal Register 

GCD—greater confinement disposal 

HLW—high-level radioactive waste 

IAEA—International Atomic Energy Agency 

ICRP—International Commission on 

Radiological Protection 

NAS—National Academy of Sciences 

NEA—Nuclear Energy Agency 

NEI—Nuclear Energy Institute 

NRC—U.S. Nuclear Regulatory Commission 

NRDC—Natural Resources Defense Council 

NTS—Nevada Test Site 

NTTAA—National Technology Transfer and 

Advancement Act 

NWPA—Nuclear Waste Policy Act of 1982, 

as amended 

NWPAA—Nuclear Waste Policy 

Amendments Act of 1987 

OECD—Organization for Economic 

Cooperation and Development 

OMB—Office of Management and Budget 

RMEI—reasonably maximally exposed 

individual 

SSI—Swedish Radiation Protection Authority 

SNF—spent nuclear fuel 

TRU—transuranic 

UK—United Kingdom 

UMRA—Unfunded Mandates Reform Act of 

1995 

U.S.C.—United States Code 

WIPP LWA—Waste Isolation Pilot Plant Land 

Withdrawal Act of 1992 

Outline of This Action 

I. What Is the History of This Action? 

A. Promulgation of 40 CFR Part 197 in 

2001 

B. Legal Challenges to 40 CFR Part 197 

II. Summary of Proposed Amendments to 40 

CFR Part 197 and Public Comments 

A. How Did We Propose To Amend Our 

2001 Standards? 

B. What Factors Did We Consider in 

Developing Our Proposal? 

C. In Making Our Decisions, How Did We 

Incorporate Public Comments on the 

Proposed Rule? 

D. What Public Comments Did We 

Receive? 

III. What Final Amendments Are We Issuing 

With This Action? 

A. What Dose Standards Will Apply? 

1. What Is the Dose Standard Between 

10,000 Years and 1 Million Years? 

2. What Is the Dose Standard for 10,000 

Years After Disposal? 

3. How Does Our Final Rule Protect Public 

Health and Safety? 

4. How Did We Consider Uncertainty and 

Reasonable Expectation? 

5. How Did We Consider Background 

Radiation in Developing the Peak Dose 

Standard? 

6. How Does Our Rule Protect Future 

Generations? 

7. What is Geologic Stability and Why Is 

it Important? 

8. Why Is the Period of Geologic Stability 

1 Million Years? 

9. How Will NRC Judge Compliance? 

10. How Will DOE Calculate the Dose? 

B. How Will This Final Rule Affect DOE’s 

Performance Assessments? 

IV. Statutory and Executive Order Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review 

B. Paperwork Reduction Act 

C. Regulatory Flexibility Act 

D. Unfunded Mandates Reform Act 

E. Executive Order 13132: Federalism 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

G. Executive Order 13045: Protection of 

Children From Environmental Health & 

Safety Risks 

H. Executive Order 13211: Actions That 

Significantly Affect Energy Supply, 

Distribution, or Use 

I. National Technology Transfer and 

Advancement Act 

J. Executive Order 12898: Federal Actions 

To Address Environmental Justice in 

Minority Populations and Low-income 

Populations 

K. Congressional Review Act 

I. What Is the History of This Action? 

Radioactive wastes result from the use 

of nuclear fuel and other radioactive 

materials. Today, we are revising certain 

standards pertaining to spent nuclear 

fuel, high-level radioactive waste, and 

other radioactive waste (we refer to 

these items collectively as ‘‘radioactive 

materials’’ or ‘‘waste’’) that may be 

stored or disposed of in the Yucca 

Mountain repository. When we discuss 

storage or disposal in this document in 

reference to Yucca Mountain, we note 

that, while Public Law 107–200 

approved the site at Yucca Mountain for 

the development of a repository for the 

disposal of spent nuclear fuel and highlevel radioactive waste, no licensing 

decision has been made regarding the 

acceptability of the proposed Yucca 

Mountain facility for storage or disposal 

as of the date of this publication. To 

save space and to avoid excessive 

repetition, we will not describe Yucca 

Mountain as a ‘‘potential’’ repository; 

however, we intend this meaning to 

apply. 

Once nuclear reactions have 

consumed a certain percentage of the 

uranium or other fissionable material in 

nuclear reactor fuel, the fuel no longer 

is useful for its intended purpose. It 


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61258 Federal Register / Vol. 73, No. 200 / Wednesday, October 15, 2008 / Rules and Regulations 

1EnPA, Public Law No. 102–486, 102 Stat. 2776, 

42 U.S.C. 10141 n. (1994). 

then is known as ‘‘spent’’ nuclear fuel 

(SNF). It is possible to recover specific 

radionuclides from SNF through 

‘‘reprocessing,’’ which is a process that 

dissolves the SNF, thus separating the 

radionuclides from one another. 

Radionuclides not recovered through 

reprocessing become part of the acidic 

liquid wastes that the Department of 

Energy (DOE) plans to convert into 

various types of solid materials. Highlevel radioactive waste (HLW) is the 

highly radioactive liquid or solid wastes 

that result from reprocessing SNF. The 

SNF that does not undergo reprocessing 

prior to disposal remains inside the fuel 

assembly and becomes the final waste 

form for disposal in the repository. 

In the United States, SNF and HLW 

have been produced since the 1940s, 

mainly as a result of commercial power 

production and national defense 

activities. Since the inception of the 

nuclear age, the proper disposal of these 

wastes has been the responsibility of the 

Federal government. The Nuclear Waste 

Policy Act of 1982, as amended (NWPA, 

42 U.S.C. Chapter 108) sets forth the 

framework for the disposal of SNF and 

HLW. In general, DOE is responsible for 

siting, constructing, and operating an 

underground geologic repository for the 

disposal of SNF and HLW and the 

Nuclear Regulatory Commission (NRC) 

is responsible for licensing the 

construction and operation of this 

repository, including permanent closure 

and decommissioning of the surface 

facilities. In making this licensing 

decision for the Yucca Mountain 

repository, NRC must utilize radiation 

protection standards that EPA 

establishes pursuant to section 801(a) of 

the Energy Policy Act of 1992 (EnPA, 

Pub. L. 102–486).1 Thus, today we are 

promulgating amendments to our public 

health protection standards at 40 CFR 

part 197 (which, pursuant to EnPA 

section 801(a), apply only to releases of 

radioactive material stored or disposed 

of at the Yucca Mountain site, rather 

than generally applicable). NRC will 

amend its regulations to be consistent 

with these standards. 

On June 3, 2008, pursuant to the 

NWPA, as amended, DOE submitted a 

license application to NRC seeking a 

license to construct the repository. NRC 

will determine whether DOE has met 

NRC’s requirements, including those 

implementing 40 CFR part 197, and 

whether to grant or deny authorization 

to construct the repository and a license 

to receive radioactive material at the 

Yucca Mountain site. 

In 1985, we established generic 

standards for the management, storage, 

and disposal of SNF, HLW, and 

transuranic (TRU) radioactive waste (see 

40 CFR part 191, 50 FR 38066, 

September 19, 1985), which were 

intended to apply to facilities utilized 

for the storage or disposal of these 

wastes, including Yucca Mountain. In 

1987, the U.S. Court of Appeals for the 

First Circuit remanded the disposal 

standards in 40 CFR part 191 (NRDC v. 

EPA, 824 F.2d 1258 (1st Cir. 1987)). We 

later amended and reissued those 

standards to address issues that the 

court raised. Also in 1987, the Nuclear 

Waste Policy Amendments Act 

(NWPAA, Pub. L. 100–203) amended 

the NWPA by, among other actions, 

selecting Yucca Mountain, Nevada, as 

the only potential site that DOE should 

characterize for a geologic repository for 

SNF and HLW. In October 1992, 

Congress enacted the EnPA and the 

Waste Isolation Pilot Plant Land 

Withdrawal Act (WIPP LWA, Pub. L. 

102–579). These statutes changed our 

obligations concerning radiation 

standards for the Yucca Mountain 

candidate repository. The WIPP LWA: 

(1) Reinstated the 40 CFR part 191 

disposal standards, except those 

portions that were the specific subject of 

the remand by the First Circuit; 

(2) Required us to issue standards to 

replace the portion of the challenged 

standards remanded by the court; and 

(3) Exempted the Yucca Mountain site 

from the 40 CFR part 191 disposal 

standards. 

We issued the amended 40 CFR part 191 

disposal standards, which addressed the 

judicial remand, on December 20, 1993 

(58 FR 66398). 

The EnPA set forth our 

responsibilities as they relate to Yucca 

Mountain and directed us to set public 

health and safety radiation standards for 

Yucca Mountain. Specifically, section 

801(a)(1) of the EnPA directed us to 

‘‘promulgate, by rule, public health and 

safety standards for the protection of the 

public from releases from radioactive 

materials stored or disposed of in the 

repository at the Yucca Mountain site.’’ 

Section 801(a)(2) directed us to contract 

with the National Academy of Sciences 

(NAS) to conduct a study to provide us 

with its findings and recommendations 

on reasonable standards for protection 

of public health and safety from releases 

from the Yucca Mountain disposal 

system. Moreover, it provided that our 

standards shall be the only such 

standards applicable to the Yucca 

Mountain site and are to be based upon 

and consistent with NAS’s findings and 

recommendations. On August 1, 1995, 

NAS released its report, ‘‘Technical 

Bases for Yucca Mountain Standards’’ 

(the NAS Report) (Docket No. EPA–HQ– 

OAR–2005–0083–0076). 

A. Promulgation of 40 CFR Part 197 in 

2001 

Pursuant to the EnPA, we developed 

standards specifically applicable to 

releases from radioactive material stored 

or disposed of in the Yucca Mountain 

repository. In doing so, we considered 

the NAS Report, our generic standards 

in 40 CFR part 191, and other relevant 

information, precedents, and analyses. 

We evaluated 40 CFR part 191 

because those standards were developed 

to apply to sites selected for storage and 

disposal of SNF and HLW. Thus, we 

believed that 40 CFR part 191 already 

included the major components of 

standards needed for any specific site, 

such as Yucca Mountain. However, we 

recognized that all the components 

would not necessarily be directly 

transferable to the situation at Yucca 

Mountain, and that some modification 

might be necessary. We also considered 

that some components of the generic 

standards would not be carried into sitespecific standards, since not all of the 

conditions found among all potential 

sites are present at Yucca Mountain. See 

66 FR 32076–32078, June 13, 2001 

(Docket No. EPA–HQ–OAR–2005–0083– 

0042), for a more detailed discussion of 

the role of 40 CFR part 191 in 

developing 40 CFR part 197. 

We also considered the findings and 

recommendations of the NAS in 

developing standards for Yucca 

Mountain. In some cases, provisions of 

40 CFR part 191 were already consistent 

with NAS’s analysis (e.g., level of 

protection for the individual). In other 

cases, we used the NAS Report to 

modify or draw out parts of 40 CFR part 

191 to apply more directly to Yucca 

Mountain (e.g., the stylized drilling 

scenario for human intrusion). See the 

NAS Report for a complete description 

of findings and recommendations 

(Docket No. EPA–HQ–OAR–2005–0083– 

0076). 

Because our standards are intended to 

apply specifically to the Yucca 

Mountain disposal system, we tailored 

our approach to consider the 

characteristics of the site and the local 

populations. Yucca Mountain is in 

southwestern Nevada approximately 

100 miles northwest of Las Vegas. The 

eastern part of the site is on the Nevada 

Test Site (NTS). The northwestern part 

of the site is on the Nevada Test and 

Training Range (referred to in our 

proposal as the Nellis Air Force Range). 

The southwestern part of the site is on 

Bureau of Land Management land. The 


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area has a desert climate with 

topography typical of the Basin and 

Range province. Yucca Mountain is 

made of layers of ashfalls from volcanic 

eruptions that happened more than 10 

million years ago. There are two major 

aquifers beneath Yucca Mountain. 

Regional ground water in the vicinity of 

Yucca Mountain is believed to flow 

generally in a south-southeasterly 

direction. For more detailed 

descriptions of Yucca Mountain’s 

geologic and hydrologic characteristics, 

and the disposal system, please see 

Chapter 7 of the 2001 Background 

Information Document (BID) (Docket 

No. EPA–HQ–OAR–2005–0083–0050) 

and the preamble to the proposed rule 

(64 FR 46979–46980, August 27, 1999, 

Docket No. EPA–HQ–OAR–2005–0083– 

0041). 

We proposed the original standards 

for Yucca Mountain on August 27, 1999 

(64 FR 46976). In response to our 

proposal, we received more than 800 

public comments and conducted four 

public hearings. After evaluating public 

comments, we issued final standards (66 

FR 32074, June 13, 2001). See the 

Response to Comments document from 

that rulemaking for more discussion of 

comments (Docket No. EPA–HQ–OAR– 

2005–0083–0043). 

The final standards issued in 2001 as 

40 CFR part 197 included the following: 

• A standard to protect the public 

during management and storage 

operations on the Yucca Mountain site; 

• An individual-protection standard 

to protect the public from releases from 

the undisturbed disposal system; 

• A human-intrusion standard to 

protect the public after disposal from 

releases caused by a drilling penetration 

into the repository; 

• A set of standards to protect ground 

water from radionuclide contamination 

caused by releases from the disposal 

system; 

• The requirement that compliance 

with the disposal standards be shown 

for 10,000 years; 

• The requirement that DOE continue 

its projections for the individualprotection and human-intrusion 

standards beyond 10,000 years to the 

time of peak (maximum) dose, and place 

those projections in the Environmental 

Impact Statement (EIS) for Yucca 

Mountain; 

• The concept of the Reasonably 

Maximally Exposed Individual (RMEI), 

defined as a hypothetical person whose 

lifestyle is representative of the local 

population living today in the Town of 

Amargosa Valley, as the individual 

against whom the disposal standards 

should be assessed; and 

• The concept of a ‘‘controlled area,’’ 

defined as an area immediately 

surrounding the repository whose 

geology is considered part of the natural 

barrier component of the overall 

disposal system, and inside of which 

radioactive releases are not regulated. 

More detail on these aspects of the 

2001 final rule may be found at 66 FR 

32074–32134, June 13, 2001, and 70 FR 

49019–49020, August 22, 2005. 

B. Legal Challenges to 40 CFR Part 197 

Various aspects of our standards were 

challenged in lawsuits filed with the 

U.S. Court of Appeals for the District of 

Columbia Circuit in July 2001. These 

challenges and the Court’s subsequent 

ruling are described briefly here, 

emphasizing the aspects leading to 

today’s final rule, and in more detail in 

the preamble to the proposed rule (70 

FR 49014, August 22, 2005). 

The State of Nevada, the Natural 

Resources Defense Council (NRDC), and 

several other petitioners challenged 

various aspects of our final standards on 

the grounds that they were 

insufficiently protective and had not 

been adequately justified. The focus of 

this challenge was the 10,000-year 

compliance period. Nevada and NRDC 

claimed that EPA’s promulgation of 

numerical standards that applied for 

10,000 years after disposal violated the 

EnPA because such standards were not 

‘‘based upon and consistent with’’ the 

findings and recommendations of the 

NAS. NAS recommended standards that 

would apply to the time of maximum 

risk, within the limits imposed by the 

long-term geologic stability of the site, 

and stated that there is ‘‘no scientific 

basis for limiting the time period of the 

individual-risk standard to 10,000 years 

or any other value.’’ (NAS Report p. 55) 

The Nuclear Energy Institute (NEI) 

challenged the ground-water protection 

standards as unnecessary to protect 

public health and safety, contrary to 

recommendations of the NAS, and 

outside our authority under the EnPA. 

The DC Circuit Court’s July 9, 2004 

decision dismissed NEI’s challenge, and 

all of the challenges by Nevada and 

NRDC, except one. On the question of 

EPA’s 10,000-year compliance period, 

the Court upheld the challenge, ruling 

that EPA’s action was not ‘‘based upon 

and consistent with’’ the NAS Report, 

and that EPA had not sufficiently 

justified on policy grounds its decision 

to apply compliance standards only to 

the first 10,000 years after disposal. 

Nuclear Energy Institute v. 

Environmental Protection Agency, 373 

F.3d 1251 (D.C. Cir. 2004) (NEI ). 

The Court concluded that ‘‘we vacate 

40 CFR part 197 to the extent that it 

incorporates a 10,000-year compliance 

period * * *.’’ (Id. at 1315) The Court 

did not address the protectiveness of the 

150 μSv/yr (15 mrem/yr) dose standard 

applied over the 10,000-year 

compliance period, nor was the 

protectiveness of the 15 mrem/yr 

standard challenged. It ruled only that 

the compliance period was not 

consistent with or based upon the NAS 

findings and recommendations and, 

therefore, was contrary to the plain 

language of the EnPA. 

As the Court noted, NAS stated that 

it had found ‘‘no scientific basis for 

limiting the time period of the 

individual-risk standard to 10,000 years 

or any other value,’’ and that 

‘‘compliance assessment is feasible 

* * * on the time scale of the long-term 

stability of the fundamental geologic 

regime—a time scale that is on the order 

of 106 years at Yucca Mountain.’’ As a 

result, and given that ‘‘at least some 

potentially important exposures might 

not occur until after several hundred 

thousand years * * * we recommend 

that compliance assessment be 

conducted for the time when the 

greatest risk occurs.’’ (NAS Report pp. 

6–7) Today’s action addresses this 

recommendation and the DC Circuit 

ruling. 

II. Summary of Proposed Amendments 

to 40 CFR Part 197 and Public 

Comments 

The primary goal of our proposal 

issued in 2005 was to gather public 

comment on the appropriate response to 

the Court decision and NAS 

recommendation to assess compliance 

at the time of maximum dose (risk). 

Therefore, our proposed amendments 

centered on extending the compliance 

period to capture the peak projected 

dose from the Yucca Mountain disposal 

system ‘‘within the limits imposed by 

the long-term stability of the geologic 

environment.’’ (NAS Report p. 2) Of 

course, establishing a radiological 

protection standard to apply at the time 

of peak dose is a uniquely challenging 

task. Only a small number of countries 

have established standards of any kind 

for the geologic disposal of SNF and 

HLW. Of these, only Switzerland has 

established a quantitative standard 

applicable for as long as 1 million years, 

although we are aware that other 

regulatory bodies outside the U.S. are 

contemplating the need to establish 

some type of regulation addressing these 

extremely long time frames. Comments 

received in the course of this 

rulemaking have been helpful given the 

extraordinary technical complexity of 

this task. 


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2For example, the ICRP’s most recent 

recommendations note that ‘‘both the individual 

doses and the size of the exposed population 

become increasingly uncertain as time increases. 

The Commission is of the opinion that in the 

decision-making process, owing to the increasing 

uncertainties, giving less weight to very low doses 

and to doses received in the distant future could be 

considered.’’ (Publication 103, 2007, Docket No. 

EPA–HQ–OAR–2005–0083–0423, Paragraph 222) 

A. How Did We Propose To Amend Our 

2001 Standards? 

We considered carefully the language 

and reasoning of the Court’s decision in 

revising our 2001 standards. As 

originally promulgated in 2001, 40 CFR 

part 197 contained four sets of standards 

against which compliance would be 

assessed. The storage standard applies 

to exposures of the general public 

during the operational period, when 

waste is received at the Yucca Mountain 

site, handled in preparation for 

emplacement in the repository, 

emplaced in the repository, and stored 

in the repository until final closure. The 

three disposal standards apply to 

releases of radionuclides from the 

disposal system after final closure, and 

include an individual-protection 

standard, a human-intrusion standard, 

and a set of ground-water protection 

standards. 

The Court’s ruling vacated only one 

aspect of 40 CFR part 197: The 10,000- 

year compliance period applicable to 

the disposal standards. Therefore, the 

storage standard, which is applicable 

only for the period before disposal, is 

not affected by the ruling. Further, the 

Court recognized that the ground-water 

protection standards were issued as an 

expression of EPA’s overall groundwater protection policies and were not 

among the standards addressed by the 

NAS, either in form or purpose (‘‘NAS 

treated the compliance-period and 

ground-water issues quite differently 

* * * NAS made no ‘finding’ or 

‘recommendation’ that EPA’s regulation 

could fail to be ‘based upon and 

consistent with’ ’’ (NEI, 373 F.3d at 

1282)). Therefore, we concluded that the 

Court’s vacature of the 10,000-year 

compliance period, which was 

explicitly tied to recommendations 

concerning the individual-protection 

standard, does not extend to the groundwater provisions. As a result, we did not 

propose to amend the ground-water 

protection standards. Nothing in today’s 

final rule affects those standards. 

We proposed to revise only the 

individual-protection and humanintrusion standards, along with certain 

supporting provisions related to the way 

DOE must consider features, events, and 

processes (FEPs) in its compliance 

analyses (70 FR 49014, August 22, 

2005). In addition, we proposed to 

adopt updated scientific factors for 

calculating doses to show compliance 

with the storage, individual-protection, 

and human-intrusion standards. We 

requested comments only on those 

aspects of the individual-protection and 

human-intrusion standards which were 

to be amended. Specifically, we 

proposed to: 

• Extend the compliance period for 

the individual-protection and humanintrusion standards to 1 million years 

after disposal (closure), consistent with 

NAS estimates regarding the ‘‘long-term 

stability of the geologic environment’’; 

• Retain the dose standard of 150 

μSv/yr (hereafter, 15 mrem/yr) 

committed effective dose equivalent 

(CEDE) for the first 10,000 years after 

disposal, as promulgated in 2001; 

• Establish a dose standard of 3.5 

mSv/yr (hereafter, 350 mrem/yr) CEDE 

for the period between 10,000 years and 

1 million years; 

• Clarify that the arithmetic mean of 

the distribution of projected results will 

be compared to the dose standard for 

the initial 10,000 years, and specify use 

of the median of the distribution of 

projected results between 10,000 and 1 

million years; 

• Retain the probability threshold (1 

in 10,000 chance of occurring in 10,000 

years, or 1 in 100 million chance of 

occurring per year) below which ‘‘very 

unlikely’’ FEPs may be excluded from 

consideration; 

• Allow FEPs with a probability of 

occurring above the probability 

threshold to be excluded if they would 

not significantly affect the results of 

performance assessments in the initial 

10,000 years; 

• Require consideration of seismic 

and igneous events causing direct 

damage to the engineered barrier system 

during the 1 million-year period; 

• Require consideration of the effects 

of increased water flow through the 

repository resulting from climate 

change, which could be represented by 

constant conditions between 10,000 and 

1 million years; 

• Require consideration of the effects 

of general corrosion of the engineered 

barriers between 10,000 and 1 million 

years; and 

• Require use of updated scientific 

factors, based on Publications 60 and 72 

of the International Commission on 

Radiation Protection (ICRP), to calculate 

dose for comparison with the storage, 

individual-protection, and humanintrusion standards. 

B. What Factors Did We Consider in 

Developing Our Proposal? 

Of great concern in extending the 

compliance period to 1 million years is 

the increasing uncertainty associated 

with numerical projections of 

radionuclide releases from the Yucca 

Mountain disposal system and 

subsequent exposures incurred by the 

Reasonably Maximally Exposed 

Individual (RMEI). This uncertainty 

affects not only the projections 

themselves, but also the interpretation 

of the results. There is general 

agreement in the international 

community that dose projections over 

periods as long as 1 million years 

cannot be viewed in the same context or 

with the same confidence as projections 

for periods as ‘‘short’’ as 10,000 years. 

As a result, the nature of regulatory 

decision-making fundamentally changes 

when faced with the prospect of 

compliance projections for the next 1 

million years. International guidance 

from the International Atomic Energy 

Agency (IAEA) and Nuclear Energy 

Agency (NEA), as well as geologic 

disposal programs in other countries, 

recognize this difficulty and 

accommodate it by viewing longer-term 

projections in a more qualitative 

manner, to be balanced and 

supplemented by other considerations 

that would provide confidence in the 

long-term safety of the disposal system. 

In effect, numerical dose projections are 

given less weight in decision-making at 

longer times.2 Such approaches 

discourage comparison of projections 

against a strict compliance limit. 

This uncertainty was the overriding 

reason for limiting the compliance 

period to 10,000 years in our 2001 rule. 

We supplemented that 10,000-year 

compliance period by requiring DOE to 

continue projections through the time of 

peak dose, consistent with the approach 

favored by the international community. 

However, while we believed this 

approach was consistent with the NAS 

recommendation to assess compliance 

at the time of maximum dose (risk) and 

the committee’s acknowledgment that 

policy considerations would also play a 

role in determining the compliance 

period, the Court concluded that it was 

inconsistent with the NAS 

recommendation. We concluded that 

the most direct way to address the 

Court’s ruling would be to establish a 

numeric compliance standard for the 

time of peak dose, within the period of 

geologic stability at Yucca Mountain, 

which NAS judged to be ‘‘on the order 

of one million years.’’ (NAS Report p. 2) 

In establishing our final standards, we 

have considered that the level of 

uncertainty increases as the time period 

covered by DOE’s performance 


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3 ‘‘We recognize that there are significant 

uncertainties in the calculations and that these 

uncertainties increase as the time at which peak 

risk occurs increases.’’ (NAS Report p. 56) 

assessment increases.3 Therefore, it is 

reasonable for us to consider how the 

compliance standard itself might also 

need to change. Specifically, we do not 

believe that extending the 10,000-year 

individual-protection standard of 15 

mrem/yr to apply for 1 million years 

adequately accounts for the 

considerations outlined above or 

represents a reasonable test of the 

disposal system (more extensive 

discussion of uncertainty in 

performance assessments is in section 

III.A.4 of this document, ‘‘How Did We 

Consider Uncertainty and Reasonable 

Expectation?’’); see also 66 FR 32098. 

We turned back to the international 

technical literature for advice regarding 

appropriate points of comparison for 

doses projected over hundreds of 

thousands of years. A number of sources 

suggested that natural sources of 

radioactivity would provide an 

appropriate benchmark for such 

comparisons. In exploring this approach 

further, we found that the variation in 

background radiation across the United 

States covered a wide range (from 

roughly 100 mrem/yr to 1 rem/yr), 

primarily because of local variation in 

radon exposures. We chose for our 

proposal a level of 350 mrem/yr, which 

is close to a widely-cited estimate of 300 

mrem/yr for the national average 

background radiation exposure (NAS 

Report Table 2–1), but specifically 

represented the difference between 

estimated background levels in 

Amargosa Valley and the State of 

Colorado. This level was proposed for 

both the individual-protection and 

human-intrusion standards as offering 

both a reasonable level of protection and 

a sound basis for regulatory decisionmaking when exposures are projected to 

occur hundreds of thousands of years 

into the future. Selecting such a level 

would also provide an indication that 

exposures incurred by the RMEI in the 

far future from the combination of 

natural background radiation and 

releases from the Yucca Mountain 

disposal system would not exceed 

exposures incurred by residents of other 

parts of the country today from natural 

sources alone. Today’s final rule adopts 

a more stringent standard that is not 

derived from an analysis of background 

radiation, as explained in sections 

III.A.1 (‘‘What is the Peak Dose Standard 

Between 10,000 and 1 Million Years 

After Disposal?’’) and III.A.5 (‘‘How Did 

We Consider Background Radiation in 

Developing The Peak Dose Standard?’’) 

of this document. 

Uncertainty in long-term projections 

also influenced our proposal. Given the 

probabilistic nature of performance 

assessments, it is possible that some 

combinations of parameter values will 

result in very high doses, even if such 

combinations have an extremely low 

probability of occurring. Although there 

may be only a few results that are very 

high, extreme results have the potential 

to exert a strong influence on the 

arithmetic mean, which could make the 

mean less representative of all 

performance projections. This 

possibility may be increased by the 

introduction of additional, and possible 

excessive, conservatisms as a way to 

account for uncertainties. We expressed 

a preference for a statistical measure 

that would not be strongly affected by 

either very high- or low-end estimates, 

believing it appropriate to focus on the 

‘‘central tendency’’ of the distribution, 

where the bulk of the results might be 

expected to be found. We proposed the 

median of the distribution as being most 

representative of central tendency. 

Because it is always located at the point 

where half the distribution is higher and 

half lower, the median depends only on 

the relative nature of the distribution, 

rather than the absolute calculated 

values. Given our concerns about 

specifying a peak dose compliance 

value against which performance would 

be judged for a period up to 1 million 

years, we believed the median might 

also provide a reasonable test of longterm performance. Today’s final rule 

departs from the proposal by adopting 

the arithmetic mean as the statistical 

measure of compliance to be applied at 

all times, as explained in section III.A.9 

of this document (‘‘How Will NRC Judge 

Compliance?’’). 

Our consideration of FEPs also was 

affected to some extent by uncertainty, 

as well as by conclusions of the NAS 

committee. In our proposal, the overall 

probability threshold for inclusion of 

FEPs remained the same as in the 2001 

rule, which we believe provides a very 

inclusive initial screen that captures 

both major and minor factors potentially 

affecting performance. Uncertainty 

plays a role in the sense that very 

gradual or infrequent processes and 

events may begin to influence 

performance only at times in the 

hundreds of thousands of years, when 

the overall uncertainty of assessments is 

increasing. The additional uncertainty 

introduced by these slow-acting FEPs 

led us to propose the exclusion of FEPs 

if they were not significant to the 

assessments in the initial 10,000 years. 

We believed this would still provide for 

robust assessments that would address 

the factors of most importance over the 

entire 1 million-year period. We did 

consider in our proposal whether 

significant FEPs might not be captured 

using this approach. In evaluating 

whether excluded FEPs might become 

more probable or more significant after 

10,000 years, and therefore should not 

be eliminated, we identified general 

corrosion as a FEP that is certain to 

occur and represents a significant 

failure mechanism at longer times, even 

though it is less significant in the initial 

10,000 years. 

We also consulted the NAS Report for 

advice on handling long-term FEPs. 

NAS identified three ‘‘modifiers’’ that it 

believed could reasonably be included 

in assessments: seismic events, igneous 

events, and climate change. (NAS 

Report p. 91) We developed provisions 

addressing these FEPs that incorporated 

the views expressed by the NAS. For 

seismic and igneous events, we 

proposed that DOE focus its attention on 

events causing direct damage to the 

engineered barriers. We took this 

approach because failure of the 

engineered barrier system, particularly 

the waste packages, is the predominant 

factor in determining the timing and 

magnitude of the peak dose, and is the 

overriding uncertainty in assessing 

performance of the disposal system. To 

address climate change, we required 

DOE to focus on the effects of increased 

water flow through the repository, 

which is the climatic effect with the 

most influence on release and transport 

of radionuclides. We determined that 

such a focus would provide the basis for 

a reasonable test of the disposal system, 

and that climate change beyond 10,000 

years could be represented by constant 

conditions reflecting precipitation levels 

that differ from current conditions, 

which eliminates unresolvable 

speculation regarding the timing, 

magnitude, and duration of climatic 

cycles over this time frame. We also 

directed that NRC establish the exact 

nature of future climate characteristics 

to be used in performance assessments. 

NRC subsequently issued a proposal to 

specify a range of values for deep 

percolation into the repository, which 

DOE would use as another parameter in 

its probabilistic performance 

assessments. (70 FR 53313, September 

8, 2005) 

Finally, we proposed to update the 

factors used to calculate dose for the 

storage, individual-protection, and 

human-intrusion standards. Our generic 

standards in 40 CFR part 191, and by 

inference our Yucca Mountain 

standards in 2001, specified the factors 

associated with ICRP Publications 26 


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4 ICRP published its most recent 

recommendations in Publication 103, issued in 

2007 (Docket No. EPA–HQ–OAR–2005–0083–0423). 

EPA has not determined the impact of these 

recommendations on its current dose and risk 

estimates, but may decide to adopt them in the 

future. Today’s final rule will incorporate the ICRP 

60 recommendations as consistent with EPA’s 

current federal guidance; however, we have 

provided some flexibility for use of newer 

dosimetry in the future if deemed appropriate by 

NRC. 

5 5 U.S.C. 553. 

and 30 (Docket Nos. EPA–HQ–OAR– 

2005–0083–0425 and 0428, 

respectively). Since we issued 40 CFR 

part 191, ICRP has modified the models 

and associated organ-weighting factors 

to more accurately calculate dose. See 

ICRP Publications 60 and 72 (Docket 

Nos. EPA–HQ–OAR–2005–0083–0421 

and 0427, respectively). We used this 

newer method in 1999 to develop our 

Federal Guidance Report 13, ‘‘Cancer 

Risk Coefficients from Exposure to 

Radionuclides’’ (Docket No. EPA–HQ– 

OAR–2005–0083–0072). Where 

possible, we believe it is appropriate to 

adopt the latest scientific methods.4

C. In Making Our Final Decisions, How 

Did We Incorporate Public Comments 

on the Proposed Rule? 

Section 801(a)(1) of the EnPA requires 

us to set public health and safety 

radiation protection standards for Yucca 

Mountain by rulemaking. Pursuant to 

Section 4 of the Administrative 

Procedure Act (APA), regulatory 

agencies engaging in informal 

rulemaking must provide notice of a 

proposed rulemaking, an opportunity 

for the public to comment on the 

proposed rule, and a general statement 

of the basis and purpose of the final 

rule.5 The notice of proposed 

rulemaking required by the APA must 

‘‘disclose in detail the thinking that has 

animated the form of the proposed rule 

and the data upon which the rule is 

based.’’ (Portland Cement Association v. 

Ruckelshaus, 486 F. 2d 375, 392–94 (DC 

Cir. 1973)) The public thus is enabled to 

participate in the process by making 

informed comments on the proposal. 

This provides us with the benefit of ‘‘an 

exchange of views, information, and 

criticism between interested persons 

and the agency.’’ (Id.) 

There are two primary mechanisms by 

which we explain the issues raised in 

public comments and our reactions to 

them. First, we discuss broad or major 

comments in the succeeding sections of 

this preamble. Second, we are 

publishing a document, accompanying 

today’s action, entitled ‘‘Response to 

Comments’’ (Docket No. EPA–HQ– 

OAR–2005–0083–0431). The Response 

to Comments document provides more 

detailed responses to issues addressed 

in the preamble. It also addresses all 

other significant comments on the 

proposal. We gave all the comments we 

received, whether written or oral, 

consideration in developing the final 

rule. 

D. What Public Comments Did We 

Receive? 

The public comment period ended 

November 21, 2005. We received more 

than 300 individual submittals, 

although any particular submittal could 

contain many specific comments. We 

also received many more submissions as 

part of mass comment efforts, in which 

organizations encourage commenters to 

use prepared texts or comment on 

specific aspects of the proposal. All, or 

representative, comments are available 

electronically through the Federal 

Document Management System (FDMS), 

available at http://www.regulations.gov. 

See the ‘‘General Information’’ section 

of this document for instructions on 

how to access the electronic docket. 

Some submittals may be duplicated in 

FDMS, as a commenter may have used 

several methods to ensure the comments 

were received, such as fax, e-mail, U.S. 

mail, or directly through FDMS. 

A significant number of comments 

addressed the proposed peak dose 

standard of 350 mrem/yr, which would 

apply between 10,000 and 1 million 

years. Most commenters opposed our 

proposal, arguing that it is much higher 

than any previous standard, is not 

protective, is not equitable to future 

generations, and is based on 

inappropriate use of background 

radiation data. Many commenters also 

took issue with our proposal to use the 

median of the distribution of results as 

the statistical measure between 10,000 

and 1 million years, viewing this 

measure as inconsistent with NAS 

recommendations to use the mean. 

Commenters also viewed the median as 

too ‘‘lax’’ and likely to discount 

scenarios that would result in high 

exposures. We also received comment 

on our proposal concerning the 

assessment of FEPs beyond 10,000 

years, with some comments expressing 

the opinion that we had inappropriately 

constrained the analyses, leaving out 

potentially significant FEPs. Some 

commenters disagreed with our general 

premise that uncertainty increases with 

assessment time and further disagreed 

that we should take uncertainties into 

account when considering standards 

applicable to the far future. These 

specific comments, and our responses to 

them, will be discussed in more detail 

in section III of this document and in 

the Response to Comments document 

associated with this action (Docket No. 

EPA–HQ–OAR–2005–0083–0431). 

Some commenters also questioned 

our conclusion that extending the 

compliance period is the appropriate 

way to respond to the Court ruling. 

These commenters point out that the 

Court’s opinion could be interpreted to 

permit us to justify the approach taken 

in our 2001 standards. They cite 

statements by the Court such as ‘‘[i]t 

would have been one thing had EPA 

taken the Academy’s recommendations 

into account and then tailored a 

standard that accommodated the 

agency’s policy concerns’’ and ‘‘[h]ad 

EPA begun with the Academy’s 

recommendation to base the compliance 

period on peak dosage and then made 

adjustments to accommodate policy 

considerations not considered by NAS, 

this might be a very different case’’ (NEI, 

373 F.3d at 1270 and 1273, respectively) 

to support the thesis that the Court’s 

judgment was based primarily on the 

presentation of our case, rather than the 

substance. In the commenters’ view, the 

Court would have been receptive to our 

arguments had they been presented 

differently, and the Court provided a 

clear ‘‘road map’’ to justify keeping our 

original standards in place. In addition, 

these and other commenters viewed 

extending the compliance period to 1 

million years as not justifiable either 

scientifically or as a matter of public 

policy. We believe that the approach we 

are taking is the most appropriate way 

to address the concerns raised by the 

Court’s decision, particularly given the 

weight accorded by the Court to the 

NAS technical recommendations 

concerning the period of geologic 

stability. As we stated in our proposal, 

‘‘it is not clear how EPA’s earlier 

explanation of its policy concerns might 

be reconciled with NAS’s technical 

recommendation.’’ (70 FR 49032) 

Accordingly, today’s final rule 

implements the NAS technical 

recommendation with regard to the 

length of time for the compliance period 

while still accommodating our policy 

concerns in the provisions related to the 

peak dose standard, and FEPs. 

We received some comments that 

suggested we should have provided 

more or better opportunities for public 

participation in our decision making 

process. For example, comments 

suggested that we should have 

rescheduled public hearings, extended 

the public comment period, and 

provided alternatives to the public 

hearing process. We provided numerous 

opportunities and avenues for public 

participation in the development of 

these standards. For example, we held 

public hearings in Washington, DC; Las 


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6We noted in our 2001 rule: ‘‘Focusing upon a 

10,000-year compliance period forces more 

emphasis upon those features over which humans 

can exert some control, such as repository design 

and engineered barriers. Those features, the 

geologic barriers, and their interactions define the 

waste isolation capability of the disposal system. By 

focusing upon an analysis of the features that 

humans can influence or dictate at the site, it may 

be possible to influence the timing and magnitude 

of the peak dose, even over times longer than 

10,000 years.’’ (66 FR 32099) 

Vegas, NV; and Amargosa Valley, NV. 

We also opened a 60-day public 

comment period and met with key 

stakeholders before and during that 

time. In response to requests from 

stakeholders, we extended the public 

comment period by 30 days and held an 

additional public hearing in Las Vegas. 

We conducted targeted outreach to 

Native American tribal groups and have 

fully considered all comments received 

through December 31, 2005, after the 

end of the extended public comment 

period. These measures are in full 

compliance with the public 

participation requirements of the 

Administrative Procedure Act. 

Several commenters supported our 

role in setting standards for Yucca 

Mountain. Other commenters thought 

that aspects of our standards duplicate 

NRC’s implementation role. We believe 

the provisions of this rule clearly are 

within our authority and they are 

central to the concept of a public health 

protection standard. We also believe our 

standards leave NRC the necessary 

flexibility to adapt to changing 

conditions at Yucca Mountain or to 

impose additional requirements in its 

implementation efforts, if NRC deems 

them to be necessary. 

We also received many general 

comments, and others addressing topics 

that are outside the scope of our 

authority under the EnPA. For example, 

several commenters simply expressed 

their support for, or opposition to, the 

Yucca Mountain repository. Other 

comments suggested our standards 

should explicitly consider radiation 

exposures from all sources because of 

the site’s proximity to the Nevada Test 

Site (NTS) and other sources of 

potential contamination. Also, a number 

of commenters suggested that we should 

explore alternative methods of waste 

disposal, such as neutralizing 

radionuclides. Comments also 

expressed concern regarding risks of 

transporting radioactive materials to 

Yucca Mountain. These comments all 

raise considerations that are outside the 

scope of our authority and this 

rulemaking. 

Many comments touched on issues 

related to our authority and standards, 

but outside the limited scope of this 

rulemaking. In particular, many 

comments urged us to extend the 

ground-water protection limits to the 

time of peak dose within the 1 millionyear compliance period. Many of these 

commenters disagreed with our position 

that the ground-water standards were 

not the subject of the Court’s ruling, and 

that in fact the Court left us with 

discretion regarding the content and 

application of those standards. Others 

believed that we are obligated to accept 

comments on this topic, since we were 

proposing not to change the standards. 

We stated clearly in our proposal that 

we were not soliciting, and would not 

consider, comments on this issue. 

III. What Final Amendments Are We 

Issuing With This Action? 

This section describes the provisions 

of our final rule, our rationale, and our 

response to public comments on various 

aspects of our proposal. Today’s final 

rule establishes the dose standards 

applicable for a period up to 1 million 

years after disposal, the statistical 

measures used to determine compliance 

with those standards, the methods to be 

used to calculate the dose, and the 

requirements for including features, 

events, and processes (FEPs) in the 

performance assessments. 

A. What Dose Standards Will Apply? 

Today’s final rule includes an 

individual-protection standard 

consisting of two parts, which will 

apply over different time frames. The 

post-10,000-year public health 

protection standard limits the long-term 

peak dose to the RMEI from the Yucca 

Mountain disposal system to 1 mSv/yr 

(100 mrem/yr) committed effective dose 

equivalent (CEDE). This post-10,000- 

year (also referred to as the ‘‘peak dose’’) 

standard addresses and responds to the 

DC Circuit ruling that our 2001 

standards, with the compliance period 

limited to 10,000 years, were 

inconsistent with the recommendations 

of the NAS. The post-10,000-year 

standard was the focus of our proposal 

and will apply after 10,000 years 

through the period of geologic stability, 

up to 1 million years after disposal. The 

other part of the individual-protection 

standard, which will apply over the 

initial 10,000 years after disposal, 

consists of the 150 μSv/yr (15 mrem/yr) 

CEDE individual-protection standard 

promulgated in 2001 as 40 CFR 197.20. 

We believe this approach maintains an 

appropriate emphasis on the initial 

condition of the repository and its 

critical early evolution, including the 

period when thermal stresses will be 

most significant.6 As the disposal 

system evolves, today’s final rule 

establishes a peak dose standard for the 

period up to 1 million years that is 

responsive to the Court’s ruling, 

consistent with the NAS 

recommendation to establish a 

compliance standard for the time of 

peak risk, and satisfies our statutory 

mandate to protect public health and 

safety. The final rule also provides a 

reasonable test of disposal system 

performance by appropriately 

recognizing the relatively more difficult 

challenge in treating the uncertainties 

associated with projecting performance 

to such distant times, and the resulting 

lessened level of confidence that can be 

derived from such performance 

projections. 

As we noted in our proposal, there 

was no legal challenge to, and the Court 

made no ruling on, the protectiveness of 

our standards up to 10,000 years. 

Further, the Court ruled that we must 

address peak dose, but did not state, and 

we do not believe intended, that we 

could not have additional measures to 

bolster the overall protectiveness of the 

standard. We believe that promulgating 

the post-10,000-year peak dose standard 

to protect public health and safety while 

retaining a separate individualprotection standard that focuses 

attention on the early evolution of the 

repository in the pre-10,000-year period 

enhances the overall protectiveness of 

our rule and is consistent with the 

findings and recommendations of the 

NAS committee. As the Court noted, the 

EnPA requires that EPA ‘‘establish a set 

of health and safety standards, at least 

one of which must include an EDEbased, individual protection standard’’ 

(NEI, 373 F.3d at 1281), but does not 

restrict us from issuing additional 

standards. Thus, as long as we address 

the NAS recommendation regarding 

peak dose, as we are doing today by 

issuing the post-10,000-year standard, 

we are not precluded from issuing other, 

complementary, standards to apply for a 

different compliance period. The 

Court’s concern was whether we had 

been inconsistent with the NAS 

recommendation by not extending the 

period of compliance to capture the 

peak dose ‘‘within the limits imposed 

by the long-term stability of the geologic 

environment.’’ (NAS Report p. 2) 

Today’s final rule defines the period of 

geologic stability for purposes of 

compliance as ending at 1 million years 

after disposal. We believe our decision 

to retain a separate standard applicable 

for the first 10,000 years after disposal 

during this period, along with ‘‘at least 

one * * * EDE-based, individual 

protection standard’’ applying to the 

peak dose during the period of geologic 


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61264 Federal Register / Vol. 73, No. 200 / Wednesday, October 15, 2008 / Rules and Regulations 

7 In discussing an alternative subsistence-farmer 

receptor, the committee noted that ‘‘it makes the 

most conservative assumption that wherever and 

whenever the maximum concentration of 

radionuclides occurs in a ground water plume 

accessible from the surface, a farmer will be there 

to access it.’’ (NAS Report p. 102) We have defined 

the RMEI to incorporate this same assumption. 

stability between 10,000 years and 1 

million years, protects public health and 

safety pursuant to the EnPA, complies 

with the Court’s decision, falls well 

within our policy discretion and is 

supported by scientific considerations 

concerning the impact of uncertainties 

in projecting doses over extremely long 

time frames, as discussed in Section 

III.A.4 of this document (‘‘How Did We 

Consider Uncertainty and Reasonable 

Expectation?’’). 

The NAS Report recognized the 

possible outcome of a rulemaking 

establishing separate standards that 

apply over different time periods. As 

discussed in more detail in Section 

III.A.6 (‘‘How Does Our Rule Protect 

Future Generations?’’), the committee 

contrasted an approach in which ‘‘a 

health-based risk standard could be 

specified to apply uniformly across time 

and generations’’ with ‘‘some other 

expression of the principle of 

intergenerational equity’’ to be 

determined by ‘‘social judgment.’’ (NAS 

Report pp. 56–57) The committee also 

recognized, as we have just explained, 

that ‘‘the scientific basis for analysis 

changes with time’’ in potentially 

significant ways as the time to peak 

dose increases. (NAS Report pp. 30–31) 

We also find it useful to consider the 

testimony of Mr. Robert Fri, chair of the 

NAS committee, before the Senate 

Environment and Public Works 

Committee on March 1, 2006, in his 

personal capacity, wherein he pointed 

out that ‘‘the specification of the time 

horizon and the selection of the person 

to be protected are intimately 

connected.’’ As a result, he explained 

that retaining the RMEI as the receptor 

(which the NAS committee recognized 

as more conservative than, but ‘‘broadly 

consistent’’ with, its preferred 

probabilistic critical group 7) while at 

the same time extending the compliance 

period ‘‘runs the risk of excessive 

conservatism,’’ potentially putting the 

rule where the ‘‘committee specifically 

did not want to be.’’ He noted that the 

committee had considered and rejected 

such an approach. (See NAS Report pp. 

100–103) Mr. Fri viewed our proposal of 

a higher dose limit between 10,000 and 

1 million years as a way ‘‘to avoid 

becoming overly conservative.’’ 

Therefore, while he (like the NAS 

committee itself) offered no opinion on 

the level of the proposed post-10,000- 

year standard, he indicated that, in his 

opinion, our approach was not in 

conflict with the committee’s intention, 

and would be closer to the committee’s 

overall goal than would applying the 15 

mrem/yr standard to the 1 million-year 

compliance period. He concluded by 

stating ‘‘the committee recognized that 

EPA properly had considerable 

discretion in applying policy 

considerations outside the scope of our 

study to the development of the health 

standard for Yucca Mountain.’’ (See 

generally NAS Report p. 3) See the 

hearing transcript at Docket No. EPA– 

HQ–OAR–2005–0083–0380 and Mr. 

Fri’s prepared testimony at Docket No. 

EPA–HQ–OAR–2005–0083–0402. We 

believe the decision to establish two 

compliance standards falls well within 

our policy discretion and in that context 

the 10,000-year individual-protection 

standard is analogous to our groundwater protection standards, which were 

also not addressed by NAS 

recommendations. 

1. What Is the Peak Dose Standard 

Between 10,000 and 1 Million Years 

After Disposal? 

In establishing a public health and 

safety standard applicable at the time of 

peak dose, as required by the EnPA and 

recommended by the NAS, and after 

considering public comments on the 

issue, today’s final rule adopts a more 

stringent standard than the proposed 3.5 

mSv/yr (350 mrem/yr) standard. 

Specifically, we are today establishing 

an individual-protection standard of 1 

mSv/yr (100 mrem/yr) to apply beyond 

10,000 years and up to 1 million years 

after disposal. 

As discussed in more detail later in 

this section, NAS expressly refrained 

from recommending any specific dose 

or risk limit for the compliance 

standard, but instead described ‘‘the 

spectrum of regulations already 

promulgated that imply a level of risk, 

all of which are consistent with 

recommendations from authoritative 

radiation protection bodies’’ for EPA’s 

consideration. (NAS Report p. 49) 

Further, while NAS stated that a single 

standard ‘‘could be specified to apply 

uniformly over time and generations,’’ it 

also recognized that other approaches 

are possible as ‘‘a matter for social 

judgment.’’ (NAS Report pp. 56–57) 

NAS also recognized that the level of 

protection was a matter best left to EPA 

to establish through rulemaking: ‘‘We do 

not directly recommend a level of 

acceptable risk.’’ (NAS Report p. 49) 

NAS further noted that, while ‘‘there is 

a considerable body of analysis and 

informed judgment from which to draw 

in formulating a standard for the 

proposed Yucca Mountain repository,’’ 

‘‘EPA’s process for setting the Yucca 

Mountain standard is presumably not 

bound by this experience.’’ (NAS Report 

p. 39) Thus, the NAS Report contains no 

finding or recommendation as to the 

dose limit at the time of peak dose in 

our Yucca Mountain standards. 

In selecting this final standard, we 

started with a range of annual fatal 

cancer risk (10¥5 to 10¥6) that 

encompassed the 15 mrem/yr standard 

established in 2001 for the initial 10,000 

years after disposal. We also considered 

the ‘‘starting range’’ identified by NAS 

in determining the appropriate level for 

the individual-protection standard to 

apply in the time period beyond 10,000 

years. (NAS Report p. 49 and Tables 2– 

3 and 2–4) For the reasons discussed 

below, we determined that it would not 

be reasonable to apply a standard within 

that starting range for the entire millionyear compliance period. Rather, we 

identified dose levels that are protective 

of public health and safety and that 

reasonably accommodate our policy 

concerns regarding the implementation 

of a compliance standard for 1 million 

years. For the same reasons, the Agency 

has determined that it is not reasonable 

to apply its traditional risk-management 

policies when establishing a compliance 

standard applicable for periods beyond 

10,000 years and up to 1 million years 

(see section III.A.3, ‘‘How Do Our 

Standards Protect Public Health and 

Safety?’’). EPA does not believe it is 

realistic to demand that projections for 

such complex systems over this far 

future time frame be readily 

distinguishable at the level of 

incremental risk customarily addressed 

by the Agency in situations where 

results can be confirmed, modeling is 

utilized on a more limited scale, or 

institutional controls are more 

applicable. 

In selecting 100 mrem/yr as the peak 

dose standard for the period beyond 

10,000 years, we took particular note of 

the NAS’s discussion of that dose level: 

‘‘Consistent with the current 

understanding of the related 

consequences, ICRP, NCRP, IAEA, 

UNSCEAR, and others have 

recommended that radiation doses 

above background levels to members of 

the public not exceed 1 mSv/yr (100 

mrem/yr) effective dose for continuous 

or frequent exposure from radiation 

sources other than medical exposures. 

Countries that have considered national 

radiation protection standards in this 

area have endorsed the ICRP 

recommendation of 1 mSv per year 

radiation dose limit above natural 

background radiation for members of 


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8NAS cited an estimate of 300 mrem/yr as the 

national average for natural background radiation 

(cosmic, terrestrial, radon, and radioactive isotopes 

internal to the human body). (NAS Report Table 2– 

1) This is the best-known estimate of average 

natural background in the U.S., but does not use the 

more conservative radon dose conversion factor 

provided by public comments. 

the public.’’ (NAS Report pp. 40–41) We 

also note that the 100 mrem/yr level is 

included in the range of regulations 

offered by NAS for EPA’s consideration. 

(NAS Report Table 2–3) 

Therefore, as we discussed in our 

proposal, a dose level of 100 mrem/yr 

level is well-established as protective of 

public health under current dose limits, 

and, as such, represents a robust public 

health protection standard in the 

extreme far future. (70 FR 49040) As 

noted by NAS, international 

organizations such as ICRP, IAEA, and 

NEA recommend its use as an overall 

public dose limit in planning for 

situations where exposures may be 

reasonably expected to occur. Although 

it had used the concept of public dose 

limits previously, ICRP first described 

its recommendations for a 

comprehensive system of radiation 

protection in Publication 60 (‘‘1990 

Recommendations of the ICRP’’) (Docket 

No. EPA–HQ–OAR–2005–0083–0421). 

ICRP considered two referents in 

recommending a public dose limit: 

health detriment and ‘‘variation in the 

existing level of dose from natural 

sources.’’ ICRP concluded that estimates 

of health detriment ‘‘suggest a value of 

the annual dose limit not much above 

1 mSv.’’ Similarly, ‘‘[e]xcluding the very 

variable exposures to radon, the annual 

effective dose from natural sources is 

about 1 mSv, with values at high 

altitudes above sea level and in some 

geological areas of at least twice this. On 

the basis of all these considerations, the 

Commission recommends an annual 

limit on effective dose of 1 mSv.’’ 

(Paragraphs 190–191) ICRP re-affirmed 

this position in its most recent 

recommendations: ‘‘For public exposure 

in planned exposure situations, the 

Commission continues to recommend 

that the limit should be expressed as an 

effective dose of 1 mSv in a year.’’ 

(Publication 103, Paragraph 245, Docket 

No. EPA–HQ–OAR–2005–0083–0423) 

This recommendation as to a 100 

mrem/yr public dose limit was adopted 

in the 1996 ‘‘International Basic Safety 

Standards for Protection Against 

Ionizing Radiation and for the Safety of 

Radiation Sources,’’ which was jointly 

sponsored by IAEA, NEA, the Food and 

Agriculture Organization of the United 

Nations, the International Labor 

Organization, the Pan American Health 

Organization, and the World Health 

Organization. (IAEA Safety Series 115, 

Schedule II, Docket No. EPA–HQ–OAR– 

2005–0083–0409) It should also be 

noted that the European Union requires 

its Member States to incorporate this 

100 mrem/yr public dose limit into 

national law or regulation (Council 

Directive 96/29/EURATOM of 13 May 

1996, Docket No. EPA–HQ–OAR–2005– 

0083–0410). Non-EU countries such as 

Argentina, Australia, Canada, and Japan 

also incorporate this public dose limit 

into their systems of regulation, as 

shown by their national reports under 

the Joint Convention on the Safety of 

Spent Fuel Management and on the 

Safety of Radioactive Waste 

Management (see http://wwwns.iaea.org/conventions/wastejointconvention.htm). The United States 

is also a Contracting Party to the Joint 

Convention (Docket No. EPA–HQ– 

OAR–2005–0083–0393). 

Domestically, both NRC and DOE 

incorporate the 100 mrem/yr level into 

their systems of regulation (10 CFR 

20.1301 and DOE Order 5400.5, 

respectively), and NCRP also endorses 

the ICRP system of protection (NCRP 

Report 116, ‘‘Limitation of Exposure to 

Ionizing Radiation,’’ Docket No. EPA– 

HQ–OAR–2005–0083–0407). In setting 

today’s peak dose standard, EPA 

acknowledges and concurs in the broad 

consensus in the protectiveness of the 

100 mrem/yr level and, furthermore, 

considers it especially suitable for 

application to the extreme far future, 

when planning for and projecting public 

exposures is much less certain. 

For all these reasons, we conclude 

that the 100 mrem/yr peak dose 

standard we are establishing today for 

the period beyond 10,000 years will 

protect public health and safety. By 

considering international guidance and 

examples, we have derived a final peak 

dose limit that balances the competing 

factors highlighted by NAS and 

acknowledged by us as important: the 

dual objectives of promulgating a 

standard that is protective of the health 

and interests of future generations, and 

also effectively addressing the effects of 

uncertainty on compliance assessment. 

Moreover, the 100 mrem/yr level is 

comparable to the domestic and 

international standards NAS suggested 

that EPA consider. (NAS Report p. 49 

and Tables 2–3 and 2–4) 

Our selection of a 100 mrem/yr 

standard is therefore protective and 

reasonable in that it effectively 

addresses the factors it is necessary to 

consider when projecting exposures 

very far into the future. By applying this 

standard over the entire period of 

geologic stability beyond 10,000 years 

(up to 1 million years), our approach is 

consistent with the NAS 

recommendation to have a standard 

with compliance measured ‘‘at the time 

of peak risk, whenever it occurs, within 

the limits imposed by the long-term 

stability of the geologic environment, 

which is on the order of one million 

years.’’ (NAS Report p. 2) 

Although we have not used specific 

estimates of background radiation in 

determining our final peak dose 

standard, as we had proposed, we note 

that the 100 mrem/yr level reasonably 

comports with such an analysis as well. 

For example, it is comparable to outdoor 

(unshielded) measurements of cosmic 

and terrestrial radiation in Amargosa 

Valley. When shielding from buildings 

is considered and indoor radon doses 

are estimated using a more conservative 

conversion factor suggested by some 

commenters, 100 mrem/yr is at the low 

end of overall background radiation 

estimates in Amargosa Valley and 

nationally.8 Within the State of Nevada, 

the difference in average estimates of 

background radiation for counties is 

greater than 100 mrem/yr. (Docket No. 

EPA–HQ–OAR–2005–0083–0387) This 

suggests that 100 mrem/yr can be 

considered to be a level such that the 

total potential doses incurred by the 

RMEI from the combination of 

background radiation and releases from 

Yucca Mountain will remain below 

doses incurred by residents of other 

parts of the country from natural 

sources alone. See Section III.A.5 of this 

document for more discussion of 

background radiation (‘‘How Did We 

Consider Background Radiation in 

Developing the Peak Dose Standard?’’). 

Our proposal discussed several factors 

that we considered to be important in 

setting a dose standard for the time of 

peak dose within the period of geologic 

stability. We emphasized the 

cumulative and increasing uncertainty 

in projecting potential doses over great 

time periods, and argued against 

viewing projected doses as predictions 

of disposal system performance. This is 

consistent with the position taken by 

the NAS committee: ‘‘The results of 

compliance analysis should not, 

however, be interpreted as accurate 

predictions of the expected behavior of 

a geologic repository.’’ (NAS Report p. 

71) 

We also have considered how the role 

of quantitative projections in making 

compliance decisions must change as 

the time covered by those projections 

increases to the extreme far future. We 

noted that emphasizing incremental 

dose increases when such increases may 

be overwhelmed by fundamental 

uncertainties inappropriately takes 

attention away from an evaluation of the 


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9The 2007 NEA document on ‘‘Consideration of 

Timescales in Post-Closure Safety of Geological 

Disposal of Radioactive Waste,’’ which is based on 

surveys of NEA Member Countries, states 

‘‘Calculated values of dose and risk are therefore 

viewed in regulations not as predictions but rather 

as indicators or measures of protection that are used 

to test the capability of the system to provide 

isolation of the waste and containment of 

radionuclides (the ‘dose’ that is being calculated is 

what radio-protectionists refer to as ‘potential 

dose’). These indicators are to be evaluated on the 

basis of models that include certain stylized 

assumptions, in particular regarding the biosphere 

and human lifestyle or actions.’’ (Docket No. EPA– 

HQ–OAR–2005–0083–0411, p. 38) NEA also notes: 

‘‘There is agreement that calculations of dose and 

risk in the future are illustrations of possible system 

behaviour rather than predictions of outcomes, and 

there is consensus that, in the long term, numerical 

criteria for radioactive waste disposal should be 

considered as references or indicators, addressing 

the ultimate safety objectives, rather than as 

absolute limits in a legal context.’’ (‘‘Regulating the 

Long-Term Safety of Geological Disposal: Towards 

a Common Understanding of the Main Objectives 

and Bases of Safety Criteria,’’ NEA–6182, Docket 

No. EPA–HQ–OAR–2005–0083–0408, p. 24) 

Similarly, ICRP Publication 81 contrasts the 

approach of ‘‘consideration of quantitative 

estimates of dose or risk on the order of 1000 to 

10,000 years’’ with ‘‘consideration of quantitative 

calculations further into the future making 

increasing use of stylized approaches and 

considering the time periods when judging the 

calculated results. Qualitative arguments could 

provide additional information to this judgmental 

process.’’ (Docket No. EPA–HQ–OAR–2005–0083– 

0417, Paragraph 71) The IAEA consensus document 

for geologic disposal (‘‘Safety Requirements for 

Geological Disposal of Radioactive Waste,’’ WS–R– 

4, 2006) states: ‘‘It is recognized that radiation doses 

to individuals in the future can only be estimated 

and that the uncertainties associated with these 

estimates will increase for times farther into the 

future. Care needs to be exercised in using the 

criteria beyond the time when the uncertainties 

become so large that the criteria may no longer 

serve as a reasonable basis for decisionmaking.’’ 

(Docket No. EPA–HQ–OAR–2005–0083–0383, 

Paragraph 2.12) 

10Such considerations are not unusual in other 

applications. For example, in making plans based 

on weather forecasts, one can expect the next-day 

forecast to be fairly accurate. However, one has to 

recognize that the same degree of accuracy cannot 

be expected from longer-range forecasts. In that 

case, one would want to have confidence that the 

forecast is based upon the most current scientific 

understanding of weather patterns. 

11For example, IAEA notes that in modeling over 

longer time frames, ‘‘The emphasis of assessment 

should therefore be changed so that the calculations 

relating to the near-surface zone and human activity 

are simplified by assuming present day 

communities under present conditions.’’ (TECDOC– 

767, Docket No. EPA–HQ–OAR–2005–0083–0044, 

p. 19) The French Basic Safety Rule III.2.f specifies 

that ‘‘The characteristics of man will be considered 

to be constant (sensitivity to radiation, nature of 

food, contingency of life, and general knowledge 

without assuming scientific progress, particularly in 

the technical and medical fields).’’ (Docket No. 

EPA–HQ–OAR–2005–0083–0389, Section 3.2) 

overall safety of the disposal system, 

which may rest equally on other lines of 

evidence, such as confidence in the 

long-term stability of the site or 

reference to natural analogues. In our 

view, in order to provide a reasonable 

test of the disposal system, the role of 

the peak dose standard in the overall 

decision of disposal system safety must 

be consistent with the relative 

confidence that can be placed in 

quantitative projections over extremely 

long times. We have recognized the 

strong consensus in the international 

radioactive waste community that dose 

projections extending many tens to 

hundreds of thousands of years into the 

future can best be viewed as qualitative 

indicators of disposal system 

performance, rather than as firm 

predictions that can be compared 

against strict numerical compliance 

criteria. In fact, international 

organizations have treated such 

numerical criteria in a more flexible 

way and supported their application in 

conjunction with other qualitative 

considerations in applying them to 

regulatory determinations over very 

long time frames.9 Further, we agree 

that confidence in the way the 

projections were performed, and the 

consideration of supporting qualitative 

information, may be more important to 

an overall judgment of safety at longer 

times.10 However, our task is to 

establish a numerical compliance limit, 

rather than a qualitative standard or 

dose target. Therefore, we believe it is 

appropriate in setting that limit to 

evaluate and apply the considerations 

that have led the international radiation 

protection community to view long-term 

projections in a more qualitative 

manner. 

We conclude that a peak dose 

standard of 100 mrem/yr for the Yucca 

Mountain disposal system for the period 

between 10,000 and 1 million years 

protects public health and safety. 

Setting the standard as we have is also 

consistent with the NAS committee’s 

decision not to recommend a level for 

the final peak standard and EPA’s broad 

discretion to establish standards that are 

protective while accommodating 

technical and policy concerns inherent 

in projecting and evaluating potential 

events hundreds of thousands of years 

into the future. See section III.A.3 of this 

document for more discussion of the 

protectiveness of our standards (‘‘How 

Does Our Final Rule Protect Public 

Health and Safety?’’). 

The ICRP recommendation for a 

public dose limit of 100 mrem/yr relates 

to the total exposure to members of the 

public from all manmade sources 

(excluding occupational, accidental, and 

medical, which can be significantly 

higher). A number of comments took 

issue with our approach and suggestion 

that it might be reasonable to 

‘‘apportion’’ the entire 100 mrem/yr to 

the Yucca Mountain disposal system 

because of the lack of other potential 

sources in the region, and that this 

could be considered consistent with the 

NAS recommendation to rely on current 

conditions and present knowledge. The 

comments expressed the view that such 

an approach would be entirely contrary 

to the NAS recommendation to apply 

apportionment, as well as to the 

principle of apportionment itself, which 

recognizes the potential for new or 

additional sources of exposure to be 

developed. 

NAS made no recommendation or 

finding regarding apportionment. In its 

discussion of apportionment, NAS 

noted that the concept had been widely 

adopted (NAS Report pp. 40–41). NAS 

also noted that ‘‘guidance to date has 

been for expected exposures from 

routine practices. There is little 

guidance on potential exposures in the 

far distant future.’’ (NAS Report p. 41). 

NAS made no specific recommendation 

that EPA apply the concept to Yucca 

Mountain, let alone how the concept 

should be applied. 

Further, given our statutory obligation 

under the EnPA to establish a sitespecific standard, allocating 100 mrem/ 

yr to a single source at the time of peak 

dose is reasonable because other 

contributors currently in the Yucca 

Mountain area are negligible by 

comparison (FEIS, DOE/EIS–0250, 

section 8.3.2, Docket No. EPA–HQ– 

OAR–2005–0083–0086). By relying on 

current conditions, as recommended by 

NAS, rather than speculating on 

potential future sources of exposure to 

the local population, it is reasonable for 

EPA to allocate the entire 100 mrem/yr 

to the Yucca Mountain disposal system. 

By assuming that current conditions 

will apply in the future, we are applying 

an approach routinely applied 

internationally, as well as by EPA in its 

WIPP compliance criteria (the ‘‘future 

states’’ assumption at 40 CFR 194.25).11

EPA’s application of the concept of 

apportionment is, moreover, reasonable. 

We addressed the apportionment 

approach in conjunction with our 

10,000-year standard of 15 mrem/yr as 

consistent with EPA’s overall risk 

management approach and past actions. 

However, we do not agree that it is 

either required or reasonable to follow 

the apportionment approach over 

hundreds of thousands of years, when 

the level of uncertainty in dose 

projections is significantly increased 

and the ability to project the 

performance of engineered barriers and 

the overall disposal system with a high 

degree of certainty decreases. This 

position is consistent with general 


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12 In describing criteria relevant to 

apportionment, IAEA states: ‘‘It is recognized that 

radiation doses to individuals in the future can only 

be estimated and that the uncertainties associated 

with these estimates will increase for times farther 

into the future. Care needs to be exercised in using 

the criteria beyond the time when the uncertainties 

become so large that the criteria may no longer 

serve as a reasonable basis for decision making.’’ 

(Paragraph 2.12, emphasis added) Similarly, NEA 

cites IAEA and ICRP in noting that ‘‘Generally 

speaking, these documents recommend that the 

same criteria should be used as are applied for 

radiation protection from current practices. These 

documents also recognise, however, that such 

criteria cannot be applied in the same way for the 

distant future as they are for current practices.’’ 

(NEA–6182, Docket No. EPA–HQ–OAR–2005– 

w0083–0408, p. 19, emphasis added) 

13 ICRP clearly expresses this view in Publication 

81: ‘‘To evaluate the performance of waste disposal 

systems over long time scales, one approach is the 

consideration of quantitative estimates of dose or 

risk on the order of 1000 to 10,000 years. This 

approach focuses on that period when the 

calculation of doses most directly relates to health 

detriment and also recognises the possibility that 

over longer time frames the risks associated with 

cataclysmic geologic changes such as glaciation and 

tectonic movements may obscure risks associated 

with the disposal system. Another approach is the 

consideration of quantitative calculations further 

into the future making increased use of stylised 

approaches and considering the time periods when 

judging the calculated results. Qualitative 

arguments could provide additional information to 

this judgmental process.’’ (Docket No. EPA–HQ– 

OAR–2005–0083–0417, Paragraph 71) Similarly, 

IAEA suggests that within 10,000 years, ‘‘While it 

is recognized that considerable uncertainty can 

exist during this time period, it is still reasonable 

to attempt to make quantitative estimates of the 

indicators to be used.’’ However, beyond that time, 

‘‘While it may be possible to make general 

predictions about geological conditions, the range 

of possible biospheric conditions and human 

behaviour is too wide to allow reliable modeling 

* * * Such calculations can therefore only be 

viewed as illustrative and the ‘doses’ as indicative.’’ 

(‘‘Safety Indicators in Different Time Frames for the 

Safety Assessment of Underground Radioactive 

Waste Repositories,’’ TECDOC–767, Docket No. 

EPA–HQ–OAR–2005–0083–0044, pp. 18–19) 

14France applies a dose standard for the first 

10,000 years that ‘‘will be applied for determining 

the acceptability of the radiological consequences.’’ 

However, at later times, ‘‘the same [25 mrem/yr] 

limit shall be used as a reference value.’’ (Basic 

Safety Rule III.2.f, Section 3.2.1, Docket No. EPA– 

HQ–OAR–2005–0083–0389, emphasis added) 

Sweden specifies quantitative analyses to be judged 

against a numerical standard for the first 1,000 

years, but requires examination of ‘‘various possible 

sequences for the development of the repository’s 

properties, its environment and the biosphere’’ after 

that time. (SSI FS 1998:1, Docket EPA–HQ–OAR– 

2005–0083–0047) Similarly, Finland applies a dose 

standard for ‘‘at least several thousands of years,’’ 

but when ‘‘human exposure’’ is no longer 

‘‘adequately predictable,’’ an activity release 

standard is in place. (YVL 8.4, Docket EPA–HQ– 

OAR–2005–0083–0392) 

international practice and guidance, in 

which regulatory judgments rely less on 

compliance with quantitative standards 

and more on other qualitative factors 

supporting the overall safety case. Thus, 

for example, IAEA recognizes in the 

consensus document ‘‘Safety 

Requirements for Geological Disposal of 

Radioactive Waste’’ (WS–R–4, Docket 

No. EPA–HQ–OAR–2005–0083–0383) 

the general agreement of the geologic 

disposal community that, while 

apportionment is pertinent to geologic 

disposal, it cannot be assumed to apply 

indefinitely.12 Moreover, IAEA reaches 

this conclusion on the basis of 

uncertainty in projecting exposure from 

a specific long-term source, without 

regard to the presumed knowledge, or 

lack thereof, of other potential sources 

of exposure. We believe our approach is 

consistent with the long-held 

international view of 10,000 years 

generally as a demarcation point prior to 

which quantitative dose projections can 

be reasonably well-managed, but 

beyond which those projections become 

progressively more uncertain and less 

valuable.13 In our view, it is preferable 

to follow this well-established 

precedent rather than to attempt to 

define a different transition point based 

on the level and timing of uncertainty 

in dose projections. As discussed in 

more detail later in this section, 

countries that have established dose or 

risk standards for geologic disposal have 

typically applied them for 10,000 years 

or less, suggesting that this is a period 

of time within which standards 

comparable to those applied to current 

practices can ‘‘serve as a reasonable 

basis for decision making.’’ Beyond that 

time, the initial ‘‘criteria,’’ or dose 

standards, are viewed more qualitatively 

or entirely different criteria that are not 

expressed in terms of risk or dose are 

applied.14

Moreover, we note that under 10 CFR 

20.1301, NRC requires that licensees 

conduct operations so that the total 

effective dose equivalent to individual 

members of the public from ‘‘the 

licensed operation’’ does not exceed 100 

mrem/yr. Thus, this regulatory limit 

applies to individual licensees operating 

today, without reference to other 

potential sources of exposure to the 

public. Of course, some types of NRC 

licensees, such as fuel cycle facilities 

subject to our standards in 40 CFR part 

190, must meet dose constraints lower 

than the 100 mrem/yr limit. 

Nonetheless, 100 mrem/yr is the public 

dose limit from licensed operations 

imposed in NRC regulations. 

We disagree with those comments 

generally questioning both the legality 

and the protectiveness of our proposal 

to establish a long-term standard higher 

than 15 mrem/yr. As described 

previously in section III.A (‘‘What Dose 

Standards Will Apply?’’), commenters 

stated that the NAS Report and Court 

decision required us to retain a single 

dose standard (i.e., 15 mrem/yr) for the 

entire 1 million-year compliance period, 

equivalent to the period of geologic 

stability defined in our rule. 

Commenters pointed out that the 

proposed level was well above the range 

identified by NAS as a starting point for 

our rulemaking, and therefore stated 

that only the 15 mrem/yr level could be 

considered consistent with the 

committee’s recommendation. 

Similarly, some commenters interpreted 

the Court ruling to require us to adjust 

the time period covered by the existing 

15 mrem/yr standard, which was not 

challenged. We do not believe this 

interpretation to be correct. It should be 

emphasized that NAS identified a range 

of risks represented by current national 

and international standards, ‘‘all of 

which are consistent with 

recommendations from authoritative 

radiation protection bodies,’’ suggested 

only a ‘‘reasonable starting point’’ for 

our rulemaking, and that none of the 

regulatory precedents considered by 

NAS applied for periods approaching 1 

million years. (NAS Report pp. 5 and 

49, respectively) In fact, NAS explicitly 

declined to recommend a level of 

protection, recognizing that this was a 

matter best left to EPA to establish 

through rulemaking: ‘‘We have not 

recommended what levels of risk are 

acceptable * * * The specific level of 

acceptable risk cannot be identified by 

scientific analysis, but must rather be 

the result of a societal decision-making 

process. Because we have no particular 

authority or expertise for judging the 

outcome of a properly constructed 

social decision-making process on 

acceptable risk, we have not attempted 

to make recommendations on this 

important question.’’ (NAS Report p. 20) 

Indeed, NAS explicitly acknowledged 

‘‘that determining what risk level is 

acceptable is not ultimately a question 

of science but of public policy.’’ (NAS 

Report p. 5) Further, NAS noted that the 

final outcome of the rulemaking might 

diverge substantially from the starting 

point suggested by NAS: ‘‘Finally we 

have identified several instances where 

science cannot provide all of the 

guidance necessary to resolve an issue 

* * * In these cases, we have tried to 

suggest positions that could be used by 

the responsible agency in formulating a 

proposed rule. Other starting positions 

are possible, and of course the final rule 

could differ markedly from any of 

them.’’ (NAS Report p. 3, emphasis 

added) Thus, we agree with NAS that 

the selection of a level for the peak dose 

standard is one of the regulatory policy 

issues left to EPA’s discretion by the 

EnPA. As stated earlier, we find that the 

annual risk associated with the final 

peak dose standard of 100 mrem/yr is 


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15The standard issued by the Swedish Radiation 

Protection Authority (SSI, formerly the Swedish 

Radiation Protection Institute) (SSI FS 1998:1, 

‘‘Regulations on the Protection of Human Health 

and the Environment in Connection with the Final 

Management of Spent Nuclear Fuel and Nuclear 

Waste,’’ Docket EPA–HQ–OAR–2005–0083–0047) 

includes a numerical standard during the initial 

period after disposal and adopts a more qualitative 

approach at later times. Specifically, for the first 

1,000 years following closure of a repository, ‘‘the 

assessment of the repository’s protective capability 

shall be based on quantitative analyses of the 

impact on human health and the environment.’’ 

(Section 11) Thus, initially the performance 

projections may be used to make decisions 

regarding the protectiveness of the disposal system. 

However, beyond the first thousand years, ‘‘the 

assessment of the repository’s protective capability 

shall be based on various possible sequences for the 

development of the repository’s properties, its 

environment and the biosphere.’’ (Section 12) 

Similarly, the Finnish Radiation and Nuclear Safety 

Authority’s (STUK) regulations for ‘‘Long-term 

Safety of Disposal of Spent Nuclear Fuel’’ (YVL 8.4, 

May 2001, Docket EPA–HQ–OAR–2005–0083– 

0392) include two primary protection standards. 

The first is an individual-protection standard of 10 

mrem/yr (0.1 mSv/yr), which applies to ‘‘an 

assessment period that is adequately predictable 

with respect to assessments of human exposure but 

that shall be extended to at least several thousands 

of years.’’ (Section 2.2) The second protection 

standard, which is implied to cover periods beyond 

the time for which ‘‘human exposure’’ is 

‘‘adequately predictable,’’ is a radionuclide release 

standard similar to that included in 40 CFR part 191 

and applied at WIPP. We also refer readers to the 

French standard (Basic Safety Rule No. III.2.f, 

‘‘Disposal of Radioactive Waste in Deep Geological 

Formations,’’ 1991, Docket No. EPA–HQ–OAR– 

2005–0083–0389). For the initial period, which is 

to last ‘‘at least 10,000 years * * * The limit of [25 

mrem/yr] will be applied for determining the 

acceptability of the radiological consequences.’’ 

However, ‘‘[b]eyond this period’’ when 

‘‘uncertainty concerning the evolution of the 

repository increases progressively with time * * * 

Quantified estimates of the individual dose 

estimates must then be made. These may be 

supplemented, by more qualitative assessments of 

the results of these estimates, as regards the 

geological barrier evolution factors, so as to verify 

that the release of the radionuclides does not result 

in an unacceptable individual dose. In this 

verification, the same [25 mrem/yr] limit shall be 

used as a reference value.’’ (Section 3.2.1, emphasis 

added) 

protective of public health and 

comparable to the domestic and 

international standards NAS suggested 

that EPA consider, particularly when 

considering the extended time frames 

under consideration for this rulemaking. 

(NAS Report p. 49 and Tables 2–3 and 

2–4) 

We also find it instructive to consider 

again the personal Senate testimony of 

NAS committee chair Robert Fri, as 

described in Section III.A (‘‘What Dose 

Limits Will Apply?’’) (Docket Nos. EPA– 

HQ–OAR–2005–0083–0380 and 0402). 

Mr. Fri noted that simply extending the 

compliance period in our 2001 rule to 

1 million years ‘‘runs the risk of 

excessive conservatism’’ and could 

place our standard where the 

‘‘committee specifically did not want to 

be.’’ He recognized that a higher 

standard at the time of peak dose would 

be one way to reduce that conservatism. 

Mr. Fri did not address the consistency 

of our proposed dose level with the 

NAS findings and recommendations; 

however, he indicated that, in his view, 

retaining the 15 mrem/yr standard at the 

time of peak dose would not be 

consistent with those findings and 

recommendations if other aspects of our 

rule remained unchanged (specifically, 

the choice of receptor). We find this 

perspective noteworthy, in that it 

suggests that there are circumstances in 

which applying 15 mrem/yr throughout 

the 1 million-year compliance period 

could result in a standard contrary to 

the committee’s overall goals, which 

emphasized the use of ‘‘cautious, but 

reasonable’’ assumptions and care in the 

use of ‘‘pessimistic scenarios and 

parameter values.’’ (NAS Report pp. 100 

and 79, respectively) 

Further, we do not believe the Court’s 

decision provides direction 

independent of the NAS Report; rather, 

the decision requires only that we 

ensure that our standards are consistent 

with the NAS committee’s findings and 

recommendations, as required by the 

EnPA. 

In considering appropriate dose 

standards for periods approaching 1 

million years, we also considered the 

development of our generic standards in 

40 CFR part 191. In both our 1985 and 

1993 rulemakings establishing those 

generic standards, we emphasized that 

the 10,000-year compliance period for 

both the containment requirements and 

individual-protection limit would lead 

to a combination of site characteristics 

and engineered barriers that would be 

capable of providing containment and 

isolation of the waste for these long 

periods of time. We did not, however, 

anticipate that such performance could 

be maintained indefinitely. Our generic 

technical analyses, in fact, suggested 

that significant releases and doses to 

individuals could result at later times, 

depending on the characteristics of the 

site in question and the presumed 

location of the receptor. (See 58 FR 

66401, December 20, 1993) 

We note that sites whose natural 

features alone did not provide total 

containment were not necessarily 

considered unsuitable, but we 

recognized that in those instances, the 

focus would have to be on ‘‘the design 

of more robust engineered barrier 

systems capable of significantly 

impeding radionuclide releases.’’ We 

believe that it is unrealistic to assume 

that these sites would then exhibit 

better performance after the failure of 

those barriers than they would in the 

initial 10,000-year period. 

Consequently, we believe that the 

potential for doses higher than 15 

mrem/yr to individuals in the far future 

has always been implicit in the concept 

of geologic disposal. Over time, the 

initial static system consisting of intact 

waste packages and other engineered 

barriers in the natural geologic setting 

gives way to a more dynamic system in 

which episodic and gradual processes 

combine to transport radionuclides to 

the accessible environment. The 

sequence and timing of barrier failures 

strongly influence, and introduce 

considerable uncertainty into, the 

timing and magnitude of projected 

doses over the 1 million-year period. 

The range of projected doses widens 

considerably as the containment 

capability of the engineered barriers 

diminishes. Interpreting the safety of the 

disposal system for regulatory purposes, 

in our judgment, involves more than 

comparison of projected doses to a 

regulatory standard, and a single 

standard applicable to the initial static 

system would not adequately capture 

the essential nature of a system that will 

evolve over 1 million years. 

In developing our final standards, we 

have given much attention to guidance 

from international organizations and 

examples from specific national 

programs. In general, we find few 

similarities in the details of the 

international approaches that are 

directly applicable, and no clear basis 

for comparing the different approaches. 

At the same time, we did find broad 

points of similarity in the overall 

approach to long-term projections, and 

referred in our proposal to organizations 

such as IAEA and NEA, as well as 

specific countries, such as Sweden. The 

more typical approach internationally is 

to require compliance with quantitative 

performance assessment for only a 

limited period of time (in some cases, 

less than 10,000 years). Longer-term 

dose projections may be compared to 

dose or risk targets or reference levels, 

but are viewed more as qualitative 

indicators of performance than as 

‘‘accurate predictions of the expected 

behavior of a geologic repository’’ (NAS 

Report p. 71), to be weighed in 

conjunction with other qualitative 

arguments for confidence in the overall 

safety of the facility. At longer times, the 

weight given to quantitative projections 

typically decreases.15 More detailed 

discussion of specific international 

approaches may be found in Section 4 

of the Response to Comments document 

for this final rule (Docket No. EPA–HQ– 

OAR–2005–0083–0431). 


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16The annual fatal cancer risk of 15 mrem is 8.6 

× 10¥6, based on a conversion factor of 5.75 × 10¥4

fatal cancers per rem. 

17 GCD is a group of 120-feet deep boreholes, 

located within the Nevada Test Site, which contain 

disposed transuranic wastes. 

18This document focuses on annual risk rather 

than lifetime risk because NAS identified annual 

risk as the appropriate metric, although it did not 

recommend a particular risk level. 

2. What is the Dose Standard for 10,000 

Years After Disposal? 

Section 801(a)(1) of the EnPA directs 

us to ‘‘promulgate, by rule, public 

health and safety standards’’ that 

‘‘prescribe the maximum annual 

effective dose equivalent to individual 

members of the public’’ from releases of 

radioactive material from the Yucca 

Mountain repository. Promulgation of 

the standard described in section III.A.1 

of this document, which will apply 

beyond 10,000 years and up to 1 million 

years, fulfills this statutory direction. 

Today’s final rule also retains the 

standard promulgated in 2001 as 

§ 197.20, which requires that DOE 

demonstrate a reasonable expectation 

that the RMEI will not incur annual 

doses greater than 15 mrem from 

releases of radionuclides from the Yucca 

Mountain disposal system for 10,000 

years after disposal. We believe this is 

an appropriate exercise of our policy 

discretion, protective of public health 

and safety, and consistent with our 

generic standards at 40 CFR part 191 

(now applied to the WIPP) and other 

applications in both our regulations for 

hazardous materials and internationally 

for radioactive waste. Further, this dose 

level is also within the range of risks 

identified by NAS as consistent with 

current national and international 

regulations. (NAS Report p. 49, Tables 

2–3 and 2–3) Moreover, the 15 mrem/yr 

standard for 10,000 years is consistent 

with EPA’s overall risk management 

policies 16 and serves as a logical 

foundation for us to incorporate 

concerns regarding far future projections 

(such as the specifications regarding 

seismic, igneous, and climatic events 

and processes discussed in section III.B 

of this document). 

As we stated in our proposal, an 

important reason for retaining a 

standard applicable for the first 10,000 

years is to address the possibility, 

however unlikely, that significant doses 

could occur within 10,000 years, even if 

the peak dose occurs significantly later, 

as NAS believed likely. (NAS Report p. 

2) We received some comments 

suggesting that DOE’s estimates of waste 

package performance are overly 

optimistic and that significant early 

package failures are possible, if not to be 

expected. Some commenters incorrectly 

argued that we had inappropriately 

‘‘ratified’’ DOE’s projections of waste 

package performance and our proposal 

‘‘would provide essentially no 

protection for the period before 10,000 

years,’’ because early failure of a system 

licensed against a post-10,000-year dose 

standard in excess of 15 mrem/yr would 

have greater consequences than would 

early failure of a system licensed against 

a 15 mrem/yr standard that applied at 

all times. We recognize that DOE’s 

estimates of waste package integrity rely 

heavily on extrapolations of laboratory 

testing data, which involve significant 

uncertainties, especially when 

considering time frames well in excess 

of all practical experience. It is not 

possible to claim unequivocally that no 

information will come to light that 

might cause a reassessment of the 

containers’ behavior and its effect on 

disposal system performance. However, 

while DOE must defend its estimates in 

licensing, our rulemaking is not 

dependent on resolution of this issue. 

DOE will have to demonstrate that there 

is a reasonable expectation that the dose 

to the RMEI will not exceed 15 mrem/ 

yr in the first 10,000 years after closure. 

Thus, the addition of the peak dose 

standard in no way weakens the 

protection provided by our 2001 

standards, since disposal system 

performance must still be assessed 

against the 15 mrem/yr limit during the 

relevant time period. 

In fact, the reverse is true. The peak 

dose standard adds a new level of 

public health protection for the post10,000-year period that was not defined 

in our 2001 standards. It may in fact be 

highly unlikely, if not impossible, for 

projected doses to exceed (or even 

approach) 15 mrem/yr within the first 

10,000 years without also exceeding 100 

mrem/yr at some other time during the 

compliance period (see section III.A.4, 

‘‘How Did We Consider Uncertainty and 

Reasonable Expectation?’’). In that case, 

the peak dose standard of 100 mrem/yr 

alone would provide the necessary 

public health protection at all times 

during the compliance period. The 

10,000-year standard would not, then, 

control projected doses during that 

period but would instead represent an 

explicit statement of the level of 

performance that is required to be 

achieved by the peak dose standard in 

that initial period. We believe it is 

important to structure our regulations to 

make it clear that the standard of 

protection at Yucca Mountain would 

not be less than that provided for WIPP 

or the Greater Confinement Disposal 

facility (GCD).17

3. How Do Our Standards Protect Public 

Health and Safety? 

The peak dose standard we are 

establishing today, 1 mSv/yr (100 

mrem/yr), will protect public health and 

safety for the period beyond 10,000 

years and up to 1 million years. This 

standard is consistent with the public 

dose limit recommended by ICRP and 

widely adopted internationally and 

nationally. Section 801(a)(1) of the 

EnPA directs us to ‘‘promulgate, by rule, 

public health and safety standards’’ that 

‘‘prescribe the maximum annual 

effective dose equivalent to individual 

members of the public’’ from releases of 

radioactive material from the Yucca 

Mountain repository. In promulgating 

these standards, we have given special 

consideration to the EnPA mandate that 

our standards be ‘‘based upon and 

consistent with’’ the recommendations 

of the NAS, which included setting a 

‘‘health-based individual standard’’ 

‘‘that sets a limit on risk to individuals 

of adverse health effects.’’ (NAS Report 

pp. 65 and 4) We understand this to 

mean that we should select the standard 

based, in part, on the level of risk, 

although NAS declined to recommend 

such a level. (NAS Report p. 49) We 

have chosen to express the standard in 

terms of dose, for the reasons described 

in our 2001 final rulemaking (66 FR 

32085–32086). In that rulemaking, we 

did consider both the NAS views on risk 

and EPA policies and precedents in 

establishing the dose standard. The risk 

associated with the 15 mrem/yr 

standard applicable for the initial 

10,000-year period is consistent with 

both the Agency’s overall risk 

management policies and the suggested 

NAS ‘‘starting point’’ (NAS Report p. 

49) The nominal annual risk associated 

with the final peak dose standard of 100 

mrem/yr, 5.75 × 10¥5, is comparable to 

the range of risks represented by 

domestic and international standards 

that NAS suggested for EPA to 

consider.18 This is a protective level of 

risk given the extremely long time 

frames contemplated for this standard, 

and reasonable in that it effectively 

addresses the associated uncertainty in 

projecting doses for up to 1 million 

years. Given this fact and the broad 

consensus regarding 100 mrem/yr as a 

protective public dose limit, EPA finds 

that the dose standard of 100 mrem/yr, 

with its associated risk, is protective of 

the RMEI over the period from 10,000 


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19 Dose can be converted to risk by use of either 

radionuclide-specific or overall conversion factors. 

The NAS committee referred only to overall 

conversions (i.e., risk per rem), which is the typical 

approach applied to dose standards when the 

specific mix of radionuclides is not well-defined in 

advance. The committee saw the direct use of risk 

as an advantage if the relationship should change 

in the future through new research on low-dose 

health effects, because the underlying risk could be 

viewed as representing the level of societal 

acceptance of health impacts, which the committee 

saw as less likely to change, whereas dose could 

become further removed from this level of societal 

acceptance. (NAS Report p. 64) In fact, we use a 

conversion factor slightly higher than that cited by 

the NAS committee (5.75 × 10¥4 fatal cancers per 

rem, compared to the committee’s figure of 5 × 10¥4

per rem). See 66 FR 32080–32081, for more 

discussion of health risks from ionizing radiation. 

20For example, a 2007 NEA document on 

‘‘Consideration of Timescales in Post-Closure Safety 

of Geological Disposal of Radioactive Waste’’ (NEA/ 

RWMC/IGSC/(2006)3), which was based on surveys 

of Member Countries, points out that ‘‘In evaluating 

compliance with regulatory criteria, or in 

formulating these criteria, extreme scenarios or 

parameter distributions can generally be assigned 

less weight. This is, for example, inherent in criteria 

expressed in terms of risk.’’ (Docket No. EPA–HQ– 

OAR–2005–0083–0411, p. 38) Similarly, the UK 

Environment Agency has stated: ‘‘In the 1995 White 

Paper, the Government stated that reliance cannot 

be placed exclusively on estimates of risk to 

determine whether the facility is safe. Whilst such 

calculations can inform a judgement on the safety 

of the facility, other technical factors, including 

some of a more qualitative nature, will also need 

to be considered. The Government therefore 

considers it inappropriate to rely on a specified risk 

limit or risk constraint as an acceptance criterion 

for a disposal facility after control is withdrawn. It 

is, however, considered appropriate to apply a risk 

target in the design process.’’ (Guidelines for 

Authorisation of Disposal Facilities for Low- and 

Intermediate-Level Radioactive Waste, Docket No. 

EPA–HQ–OAR–2005–0083–0063, Paragraph 6.14) 

years to 1 million years, as required by 

the EnPA. 

The Agency believes it important to 

emphasize two aspects of this decision. 

First, modeling of a complex system 

such as the Yucca Mountain disposal 

system over such time frames involves 

significant uncertainties in both the 

knowledge of characteristics of the site 

and the conceptual representation of the 

processes contributing to release and 

transport of radionuclides. The NAS 

recommendation has extended the 

application of regulatory judgment 

beyond the period when substantially 

complete containment might reasonably 

be provided, and through a period 

during which complete loss of 

containment cannot be discounted. The 

sequence and timing of scenarios 

resulting in waste package failure are 

highly dependent on initial assumptions 

and are the most significant factors in 

estimating the timing and magnitude of 

doses to the RMEI. Dose projections 

involve extrapolation of assumptions, 

models, and data over time periods 

much longer than those considered in 

other regulatory contexts. Such 

projections therefore cannot be 

confirmed in the usual sense (i.e., 

through measurements or monitoring), 

nor is it expected that long-term 

maintenance of the repository will be 

performed. Such considerations lead us 

to conclude that it would not be realistic 

to demand that projections from such 

complex systems be readily 

distinguishable from one another at the 

level of incremental risk customarily 

addressed by the Agency in situations 

where results can be confirmed, 

modeling is utilized on a more limited 

scale, or institutional controls are more 

applicable. 

The Agency’s second concern is the 

correlation of risk with health 

detriment. NAS specifically framed its 

recommendation to establish a risk 

standard in the context of health effects. 

(NAS Report pp. 4 and 65) In doing so, 

it explicitly extended the traditional 

reliance on ‘‘present knowledge’’ in the 

framing of performance assessments to 

assume that future societies would not 

have eliminated radiation cancer 

risks.19 (NAS Report p. 100) However, 

the reliance on risk to express the 

results of long-term safety assessments 

has been approached more cautiously, 

and it has primarily been viewed as a 

mechanism to incorporate the 

likelihood of scenarios affecting 

potential exposures, rather than as a 

direct measure of health impacts or as 

a firm compliance criterion.20

Risk correlations are highly 

dependent on population characteristics 

and baseline cancer rates, which change 

over time with dietary, lifestyle, 

medical, industrial, environmental, 

demographic, and other contributing 

factors. ICRP has expressed caution that 

‘‘[d]oses and risks, as measures of health 

detriment, cannot be forecast with any 

certainty for periods beyond around 

several hundreds of years into the future 

* * * Such estimates must not be 

regarded as predictions of future health 

detriment.’’ However, ICRP has also 

suggested that it is not unreasonable for 

shorter-term assessments to relate dose 

or risk to health effects: ‘‘To evaluate the 

performance of waste disposal systems 

over long time scales, one approach is 

the consideration of quantitative 

estimates of dose or risk on the order of 

1000 to 10,000 years. This approach 

focuses on that period when the 

calculation of doses most directly 

relates to health detriment * * *’’ (ICRP 

Publication 81, ‘‘Radiation Protection 

Recommendations as Applied to the 

Disposal of Long-Lived Radioactive 

Waste,’’ Docket No. EPA–HQ–OAR– 

2005–0083–0417, Paragraphs 41 and 71, 

respectively) Thus, the Agency finds 

that its requirements for the 

probabilistic calculation of doses 

effectively incorporates the issue of risk 

as it has customarily been considered in 

long-term safety assessments. Further, 

the Agency believes its decision to view 

the 10,000-year standard within its 

traditional risk-management framework 

is reasonable and consistent with views 

on shorter-term safety assessments. 

The nominal annual risk level for fatal 

cancer associated with the 100 mrem/yr 

dose standard is 5.75 × 10¥5. This is 

comparable to the range of risks 

represented by national and 

international regulations identified by 

NAS for EPA to consider, and is 

premised on a dose level the NAS has 

addressed favorably as a matter of 

international regulatory consensus (NAS 

Report pp. 40–41, Tables 2–3 and 2–4). 

Considering that this standard will 

apply for up to 1 million years, we 

believe this represents a level of risk 

that will protect public health and 

safety in the far future. However, for the 

reasons described above, we do not 

believe it is appropriate to view the 

standard through a strict risk 

perspective, and caution against doing 

so. Further, even if the risk correlations 

could be assumed valid over such times, 

the nominal risk represented by 

projected doses may be a reflection of 

the uncertainties inherent in such 

projections, and therefore overstated. 

ICRP states, for example, that ‘‘as the 

time frame increases, some allowance 

should be made for assessed dose or risk 

exceeding the dose or risk constraint 

* * * This must not be misinterpreted 

as a reduction in the protection of future 

generations, and, hence, as a 

contradiction of the principle of equity 

of protection, but rather as an adequate 

consideration of the uncertainties 

associated with the calculated results.’’ 

(ICRP Publication 81, Docket No. EPA– 

HQ–OAR–2005–0083–0417, Paragraph 

77). 

As a result of these considerations, for 

a standard covering periods up to 1 

million years, the Agency believes it is 

more appropriate to view protectiveness 

from a broader perspective. This 

perspective must include consideration 

of the modeling issues discussed earlier, 

as well as be cognizant of the regulatory 

context in which dose projections will 

be presented. NRC’s judgment of 

‘‘reasonable expectation’’ will not rely 

on a simple comparison of the mean 

projected dose with the regulatory 

standard, but will encompass the data, 

assumptions, and models underlying 

those projections, including the sources 

and treatment of uncertainties and 

conservatisms. We are also mindful that 

the post-10,000-year peak dose standard 


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21 ICRP Publication 81: ‘‘Demonstration of 

compliance with the radiological criteria is not as 

simple as a straightforward comparison of 

calculated dose or risk with the constraints, but 

requires a certain latitude of judgement.’’ (Docket 

No. EPA–HQ–OAR–2005–0083–0417, Paragraph 86) 

22For example, ‘‘data’’ uncertainty can cover 

broad issues such as whether sufficient data are 

available, whether the right kind of data are 

available, whether the data are of sufficient quality, 

and whether the available data adequately capture 

what NAS referred to as ‘‘the difficulties in spatial 

interpolation of site characteristics’’ which ‘‘will be 

present at all times’’ (NAS Report p. 72). Similarly, 

‘‘model’’ uncertainty includes not only whether the 

processes acting on the site have been correctly 

represented mathematically and coupled with each 

other, but also whether the basic understanding of 

which processes operate, whether there are 

competing mechanisms that must be considered 

(e.g., for corrosion or ground-water flow), and the 

extent to which and conditions under which one 

mechanism is dominant. 

covers an extremely wide time window, 

far beyond that for any previous 

regulatory situation in this country, and 

that a peak mean dose could be 

projected to occur at any point within 

that time span. Where the precision and 

predictive capabilities of performance 

assessment models diminish over such 

long times, we believe it is appropriate 

that NRC ‘‘weigh how the scientific 

basis for analysis changes with time’’ in 

reaching its judgment (NAS Report pp. 

30–31). 

In that context, the 100 mrem/yr 

public dose limit recommended by ICRP 

and widely adopted by national and 

international organizations and 

government agencies represents a key 

element of radiation protection practice 

that can be applied to the estimation of 

potential future exposures. It provides a 

standard for public protection today 

and, by extension in the far future. This 

judgment reflects our view that the 

selected level must take into account 

larger, less quantifiable factors such as 

the uncertainties involved in projecting 

doses over 1 million years and the 

meaning that can be assigned to such 

projections (both in terms of their value 

as predictions of expected behavior of 

the disposal system and in their 

correlation with health effects), as well 

as the relative importance they should 

assume, in a regulatory context. Having 

considered these factors, we conclude 

that the post-10,000-year dose standard 

of 100 mrem/yr is protective of the 

RMEI. It must also be emphasized that 

the 100 mrem/yr level applies to the 

RMEI, who is described as a person 

whose location, lifestyle, and 

characteristics cause that person to be 

subject to doses at the high end of the 

local population. As a result, the RMEI 

is among the most highly exposed 

members of the public. Most residents 

in the vicinity of Yucca Mountain 

would receive much lower doses from 

the disposal system than the RMEI, if 

any dose at all. 

Taken together, the dual standards 

provide a reasonable test of the disposal 

system that appropriately combines 

protectiveness with recognition of the 

limitations of modeling in predicting 

the evolution of that system over 

hundreds of thousands of years. The 

10,000-year standard is solidly 

grounded in the Agency’s riskmanagement framework and prior 

practice for geologic disposal facilities. 

The longer-term peak dose standard is 

widely-accepted domestically and 

internationally as protective of public 

health and safety, reasonable in its 

recognition of the regulatory context, 

and fulfills our EnPA mandate by 

extending to the time of peak dose up 

to 1 million years. However, the Agency 

also emphasizes the site-specific nature 

of this rulemaking, which should not be 

viewed as a precedent for other 

regulatory situations, but as a reasoned 

response to unique circumstances 

involving issuance of a compliance 

standard applicable for periods up to 1 

million years after disposal. 

4. How Did We Consider Uncertainty 

and Reasonable Expectation? 

In establishing our final standards 

pursuant to the EnPA, we have 

considered two important statements 

from the NAS committee: (1) ‘‘We 

recognize that there are significant 

uncertainties in the supporting 

calculations and that the uncertainties 

increase as the time at which peak risk 

occurs increases’’ and (2) ‘‘No analysis 

of compliance will ever constitute an 

absolute proof; the objective instead is 

a reasonable level of confidence in 

analyses that indicates whether limits 

established by the standard will be 

exceeded.’’ (NAS Report pp. 56 and 71, 

respectively) We have been mindful of 

these statements, as well as the fact that 

NAS deferred to our judgment in setting 

the level of the final compliance 

standard, as indicating that there are 

limits to the ability of science to provide 

definitive answers. ‘‘When all 

reasonable steps have been taken to 

reduce technical uncertainty * * * 

there still remains a residual, 

unquantifiable uncertainty * * * The 

only defense against it is to rely on 

informed judgment.’’ (NAS Report p. 80) 

We believe we have appropriately 

considered the NAS views in 

establishing 1 mSv/yr (100 mrem/yr) as 

the individual-protection standard for 

the period beyond 10,000 years and up 

to 1 million years. In order to approve 

DOE’s license application, NRC must 

determine, at a minimum, that there is 

a reasonable expectation that standard 

will be met (as well as determine 

compliance with other NRC 

requirements, such as a multiple-barrier 

system). The primary indicator of 

compliance with the individualprotection standard is the mean of the 

distribution of projected doses 

presented by DOE (see Section III.A.9 of 

this document, ‘‘How Will NRC 

Determine Compliance?’’). However, 

NRC’s compliance determination will 

consist of more than a simple 

comparison of the mean of projected 

doses with the dose standard. Rather, as 

stated in 40 CFR 197.14, NRC will reach 

its determination ‘‘based upon the full 

record before it.’’ Regardless of whether 

the mean of projected doses is well 

below the dose standard or not, NRC 

will examine the assumptions, data, 

models, and other aspects of DOE’s 

projections to ensure that it has an 

understanding of those projections 

sufficient to reach a ‘‘reasonable 

expectation’’ as to their compliance 

with the standard (40 CFR 197.13). 

While applying the principles of 

reasonable expectation at all times, NRC 

may also use its judgment as to whether 

it would apply the concept in exactly 

the same way for times as long as 1 

million years as it would for much 

shorter times. A key element of 

reasonable expectation is that it 

‘‘accounts for the inherently greater 

uncertainties in making long-term 

projections of the performance of the 

Yucca Mountain disposal system’’ 

(§ 197.14(b)), we would consider it 

logical as well as practical for NRC, in 

reaching its compliance decision, to 

evaluate the sources and effects of 

uncertainties in DOE’s analyses, as well 

as DOE’s treatment of them.21

Uncertainties can influence 

performance assessments in a number of 

ways. Some sources of uncertainty can 

be addressed, or at least accounted for, 

while in other areas our knowledge may 

be too limited to even characterize the 

uncertainty, much less explicitly 

account for it. Sources of uncertainty are 

often discussed in broad categories such 

as ‘‘data’’ or ‘‘model’’ uncertainty, 

although these can take on various 

forms within those broader categories 

that create individual challenges.22

NAS supported the use of 

probabilistic modeling as one way to 

address the effects of uncertainty. 

However, NAS noted that this process 

itself can involve significant 

uncertainties in defining the parameter 

value distributions from which the 

probabilistic selections would be made. 

(NAS Report pp. 78–79) As a result, 

interpretation of probabilistic results, 

which illustrate uncertainty through the 

distribution of calculated values, may 


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23This problem is not specific to quantitative 

performance assessment. Similar issues have been 

identified in analysis of different policy options for 

energy or other areas associated with technological 

risk. It has been noted that ‘‘The results of 

individual risk assessment studies are often 

reported with formidable precision, expressed as 

discrete numbers (rather than ranges) and presented 

to two, three and even four significant figures. Yet 

* * * such precision seems entirely to 

misrepresent the accuracy of this style of appraisal 

taken as a whole * * * the problem does not tend 

to be driven by any single factor in analysis, nor is 

it a simple matter of some studies being more 

‘accurate’ or ‘reasonable’ than others in any 

definitive sense. The manifest variability * * * is 

rather a simple reflection of * * * the adoption of 

different (but equally scientifically valid) 

assumptions and priorities concerning the 

multitude of different dimensions of risk. Where 

[different options cannot be clearly distinguished] 

in any absolute sense, then the value of appraisal 

lies in exposing the relationships between different 

assumptions in analysis and the associate pictures 

of the relative importance of different options. It is 

better to be roughly accurate in this task of mapping 

the social and methodological contextdependencies than it is to be precisely wrong in 

spurious aspirations to a one-dimensional 

quantitative expression of technological risk.’’ (‘‘On 

Science and Precaution in the Management of 

Technological Risk,’’ Volume 1, Institute for 

Prospective Technical Studies, 1999, Docket No. 

EPA–HQ–OAR–2005–0083–0413, pp 13–16, 

emphasis in original) 

24One might compare this situation to finding 

two proximate, but distinct, locations on a road 

map. In the first instance, the scale on the map is 

such that all individual roads and landmarks (e.g., 

schools, churches, libraries) can be seen. One can 

easily locate each site and circle it. Now consider 

a map of the same size, in which the scale is much 

smaller, showing only major thoroughfares and 

main local roads. One would still be able to 

approximate the desired location(s), but any 

attempt to circle them would likely encompass both 

(and may be deliberately larger to ensure that both 

are captured). Thus, the ability to distinguish the 

two locations hinges on the scale and detail of the 

map in question. The change in ‘‘scale’’ for our 

rulemaking is the extension of the compliance 

period to 1 million years. 

25Although it employed site parameter value 

distributions used by DOE, the model used in this 

analysis was simplified and ‘‘forced’’ to the 

boundary condition of a 15 mrem/yr mean dose at 

10,000 years. This analysis should in no way be 

compared to the modeling conducted to support 

DOE’s license application. 

26We considered release of radionuclides from 

the waste form as a natural process dependent on 

solubility parameters. The waste form itself (spent 

fuel assemblies or vitrified HLW) is often 

considered part of the engineered barrier system. 

also be affected by this underlying 

uncertainty, which may not be fully 

appreciated or understood. 

Selecting an appropriate dose limit for 

periods up to 1 million years must also 

consider the ability of performance 

assessments, and those who interpret 

them, to distinguish between differing 

repository designs, as well as different 

conceptualizations of total system 

performance over very long time frames. 

We have described the general view that 

the predictive capabilities of 

performance assessments diminish as 

the time periods covered by the 

assessments increase. It is also 

important to understand that, while 

mathematical calculations can result in 

very precise estimates of dose (to 

multiple significant digits), this 

precision is misleading in its 

presentation of the approximate 

outcomes of multiple interacting 

processes. We believe it is not 

appropriate to imply that there is a clear 

and immutable difference between two 

projections of dose, when it is 

understood that neither on its own is an 

unqualified representation of reality. 

Such representations may promise more 

than can be delivered by the model’s 

ability to ‘‘slice it thin.’’ 23 In our view, 

it makes little sense to assert that a 15 

mrem/yr dose limit for the period 

within 10,000 years is more 

‘‘protective’’ than a higher limit much 

later in time if, in the time frame of 

hundreds of thousands of years, the 

uncertainties in projecting disposal 

system performance cannot easily make 

distinctions at such incremental 

levels.24

In responding to comments on this 

issue, we considered how it might be 

possible to demonstrate the increase in 

projected uncertainties and provide a 

quantitative estimate of the degree of 

increased uncertainty that might be 

encountered as a result of variation in 

parameter values. To examine the longterm propagation of uncertainty in dose 

projections, we used a simplified Yucca 

Mountain site performance assessment 

model and constructed a hypothetical 

disposal system that would produce a 

mean dose to the RMEI of 15 mrem/yr 

at 10,000 years. That is, we estimated 

the number of waste package failures 

that would be necessary to produce a 

disposal system operating at the ‘‘edge 

of compliance’’ at 10,000 years. This 

disposal system, which would still meet 

the performance standard at 10,000 

years, was the reference base case for 

our uncertainty analyses. The number of 

‘‘failed’’ waste packages needed to 

produce the reference case dose (a mean 

of 15 mrem/yr at 10,000 years) was 

calculated using the simplified site 

model and parameters used in the DOE 

model, and assumed some components 

of the engineered barrier did not 

function to provide containment (i.e., 

the titanium drip shields designed to 

divert water from the waste packages, as 

well as other components of the 

engineered barrier system, were 

removed from the model).25 Further, 

upon ‘‘failure’’ of a waste package, the 

entire inventory of that package was 

assumed to be available for dissolution 

and transport, subject to solubility 

limits applied to each radionuclide. 

To assess the progressive effects of 

uncertainty, the number of ‘‘failed’’ 

packages was limited to the number 

necessary to produce 15 mrem/yr at 

10,000 years, and the hypothetical site 

model was used to make dose 

projections from 10,000 years (the 

reference base case) through the period 

of peak dose within the period of 

geologic stability. Thus, the system 

established as a starting point for the 

peak dose projections was one in which 

some degree of release and transport to 

the RMEI had already taken place 

within the initial 10,000 years, 

providing a basis for judging how the 

continuation of these processes would 

change the results over time. These 

analyses examined the effects of 

uncertainties from the natural barrier 

portion of the disposal system, since 

additional waste package failures were 

not considered.26 It should be 

recognized that the base case was 

determined using probabilistic methods, 

so the results at 10,000 years already 

showed some effects of uncertainty, as 

indicated by the range of projected 

doses with the mean at 15 mrem/yr. 

We found that the uncertainty in dose 

projections, from the base case (at 

10,000 years) to peak dose (as measured 

by the spread in dose estimates between 

the 5th and 95th percentiles at these 

times), increased by approximately two 

orders of magnitude. These results 

showed quantitatively that uncertainty 

in performance projections does 

increase with time for the Yucca 

Mountain system, and supports the 

premise that increasing uncertainty 

reduces the degree of confidence that 

can be assumed for very long-term 

performance assessments. We believe 

this supports the premise, discussed 

earlier, that increasing uncertainty in 

dose projections over very long time 

periods lessens the ability of 

performance assessment modeling to 

meaningfully distinguish among 

alternative (and equally ‘‘likely’’) 

‘‘futures’’ represented by individual 

model simulations, and ultimately to 

distinguish among alternate models and 

assumptions for site performance 

assessments. More detail on the site 

model we used, parameter databases, 

sensitivity analyses and discussion of 

the results, is provided in the technical 

reports describing this work (Docket No. 

EPA–HQ–OAR–2005–0083–0386). 

NRC must reach a determination of 

compliance based on the specific case 

presented by DOE. In order to conclude 

that there is a reasonable expectation 

that the Yucca Mountain disposal 

system will comply with our standard of 

100 mrem/yr, NRC must understand the 

technical basis for DOE’s projections, 


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27 It could also be considered consistent with the 

NEA statement that ‘‘[w]hat can be aimed at, 

however, is to leave future generations an 

environment that is protected to a degree acceptable 

to our own generation. It is also relevant to observe 

that this level of protection will ensure that any 

radiological impacts due to disposal will not raise 

levels of radiation above the range that typically 

occurs naturally.’’ (‘‘The Handling of Timescales in 

Assessing Post-Closure Safety: Lessons Learnt from 

the April 2002 Workshop in Paris, France,’’ p. 9, 

Docket No. EPA–HQ–OAR–2005–0083–0046) 

28 ‘‘This natural background may not be harmless 

* * * but the variations from place to place 

(excluding the large variations in the dose from 

radon in dwellings) can hardly be called 

unacceptable * * * Excluding the very variable 

exposures to radon, the annual effective dose from 

natural sources is about 1 mSv, with values at high 

altitudes above sea level and in some geological 

areas of at least twice this. On the basis of all these 

considerations, the Commission recommends an 

annual limit on effective dose of 1 mSv.’’ (ICRP 

Publication 60, Docket No. EPA–HQ–OAR–2005– 

0083–0421, Paragraphs 190–191) 

29 In its 1995 Collective Opinion, the NEA 

Radioactive Waste Management Committee 

concludes that ‘‘from an ethical standpoint, 

including long-term safety considerations, our 

responsibilities to future generations are better 

discharged by a strategy of final disposal than by 

reliance on stores which require surveillance, 

bequeath long-term responsibilities of care, and 

may in due course be neglected by future societies 

whose structural stability should not be presumed’’ 

and ‘‘after consideration of the options for 

achieving the required degree of isolation of such 

wastes from the biosphere, geological disposal is 

currently the most favoured strategy,’’ whereby ‘‘it 

is justified, both environmentally and ethically, to 

continue development of geological repositories for 

those long-lived radioactive wastes which should 

be isolated from the biosphere for more than a few 

hundred years.’’ (‘‘The Environmental and Ethical 

Basis of Geological Disposal of Long-Lived 

Radioactive Wastes,’’ Docket No. EPA–HQ–OAR– 

2005–0083–0412, pp. 5–6) Similarly, the NAS 

Board on Radioactive Waste Management stated: 

‘‘There is a strong worldwide consensus that the 

best, safest long-term option for dealing with HLW 

is geological isolation.’’ (‘‘Rethinking High-Level 

Radioactive Waste Disposal: A Position Statement 

of the Board on Radioactive Waste Management,’’ 

1990, Docket No. EPA–HQ–OAR–2005–0083–0420, 

p. 2) 

including the inherent uncertainties. We 

believe it is appropriate for NRC to 

examine uncertainty in its licensing 

review in order to achieve the necessary 

level of confidence in DOE’s 

understanding and depiction of the 

disposal system. Ultimately, in reaching 

its compliance determination, it is 

incumbent upon NRC to clearly state 

what it can or cannot conclude from the 

performance assessment results, within 

the limits of science. 

5. How Did We Consider Background 

Radiation In Developing the Peak Dose 

Standard? 

We are not adopting the proposed 3.5 

mSv/yr (350 mrem/yr) level as the 

compliance standard for the period 

beyond 10,000 years, nor have we 

adopted the reasoning used to support 

the proposed standard (i.e., 

considerations of specific background 

radiation estimates) to the selection of 

the 100 mrem/yr level. We received 

significant comment on this aspect of 

our proposal, much of it taking issue 

with the concept of using background 

radiation as an indicator of ‘‘safe’’ levels 

of exposure from an engineered facility. 

We also received additional information 

that provided insights into and refined 

our consideration of background 

radiation. For example, commenters 

referred to monitoring data collected by 

the Desert Research Institute indicating 

that the unshielded (outdoor) 

background radiation from cosmic and 

terrestrial sources in Amargosa Valley is 

roughly 110 mrem/yr. Commenters also 

informed us that roughly 90% of the 

population in Amargosa Valley lives in 

mobile homes, which has implications 

for indoor radon exposures. Other 

commenters supported the use of a 

different factor for converting radon 

concentrations into dose. 

In considering these comments, as 

well as those taking issue with the 

overall premise described in the 

proposal, we found the relatively simple 

approach used in the proposal evolving 

into a more complex undertaking 

requiring numerous decisions where 

science did not provide a definitive 

answer. Addressing indoor radon 

estimates presented the greatest 

challenge, as indoor radon represented 

the highest proportion of overall 

background radiation. Complicating 

factors included multiple ways of 

calculating radon dose, the prevalence 

of mobile homes in Amargosa Valley, 

limited data sets primarily from the 

early 1990s, and data for individual 

counties in a different format than statewide data. We concluded that there was 

no generally agreed-upon approach in 

the context of Amargosa Valley for 

incorporating indoor radon exposures 

into an analysis of background radiation 

that would lead to a regulatory standard, 

particularly given the fact that many 

commenters viewed the entire concept 

as arbitrary. Accordingly, we have 

decided not to adopt a standard derived 

from an analysis of background 

radiation estimates at specific locations 

or the differences between background 

radiation estimates at different 

locations. 

We continue to believe that references 

to natural sources of radiation can 

provide useful insights. IAEA has 

observed that ‘‘[i]n very long time 

frames * * * uncertainties could 

become much larger and calculated 

doses may exceed the dose constraint. 

Comparison of the doses with doses 

from naturally occurring radionuclides 

may provide a useful indication of the 

significance of such cases’’. (IAEA WS– 

R–4, Docket No. EPA–HQ–OAR–2005– 

0083–0383, Paragraph A.8) We note that 

the 100 mrem/yr level reasonably 

comports with such an analysis as well. 

For example, as noted above, 100 mrem/ 

yr is roughly the value reported by the 

Desert Research Institute for cosmic and 

terrestrial radiation at Amargosa Valley 

(unshielded). When shielding from 

buildings is considered and indoor 

radon doses are estimated using a more 

conservative conversion factor 

suggested by some commenters, 100 

mrem/yr is at the low end of overall 

background radiation estimates in 

Amargosa Valley and nationally. Within 

the State of Nevada, the difference in 

average estimates of background 

radiation for counties is greater than 100 

mrem/yr. (Docket No. EPA–HQ–OAR– 

2005–0083–0387) As previously stated, 

this suggests that 100 mrem/yr can be 

considered to be a level such that the 

total potential doses incurred by the 

RMEI from the combination of 

background radiation and releases from 

Yucca Mountain will remain below 

doses incurred by residents of other 

parts of the country from natural 

sources alone.27 It may also be noted 

that the 100 mrem/yr public dose limit 

recommended by ICRP is itself related 

to background radiation, so indirectly 

our peak dose standard does incorporate 

the concept of variations in background 

radiation.28 However, in the absence of 

compelling reasons for selecting specific 

background radiation estimates and 

points of comparison, we conclude that 

comparing background radiation 

estimates from specific locations does 

not provide a clear or sufficient basis for 

a regulatory compliance standard 

applicable to the Yucca Mountain 

disposal system. Discussion of specific 

issues raised in public comments is in 

Section 3 of the Response to Comments 

document. 

6. How Does Our Rule Protect Future 

Generations? 

Because of its long lifetime, high 

hazard, and potential for misuse, SNF 

and HLW present special challenges to 

those charged with protecting the 

health, safety, and security of the public 

and the environment. Geologic disposal 

has long been viewed by policymakers 

as the management option that best 

addresses all of these concerns.29 In the 

United States, geologic disposal was 

first endorsed by the NAS in 1957 (‘‘The 

Disposal of Radioactive Waste on 

Land’’) and established as national 

policy in the Nuclear Waste Policy Act 

of 1982. 

However, the fact that geologic 

disposal has potentially significant 


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30NEA states: ‘‘The design and implementation of 

a repository involves balancing of risks and 

responsibilities between generations. The 

obligations of the present generation toward the 

future are complex, involving not only issues of 

safety and protection but also of freedom of choice 

and of the accompanying burden of responsibility, 

and of the need to transfer knowledge and 

resources. Our capacity to deliver these obligations 

diminishes with distance in time, which 

complicates the setting of criteria to be used today 

in order to demonstrate that obligations to the 

future will be met.’’ NEA–6182, Docket No. EPA– 

HQ–OAR–2005–0083–0408, p. 25) 

31NEA–6182: ‘‘National programmes which have 

already established such criteria have generally 

found it possible to make cautious, but reasonable 

assumptions to extend the use of radiological limits 

already applied to contemporary activities for 

several thousands of years. The greater challenge 

lies in setting criteria for very long time frames, 

extending to a million years and beyond, for which 

safety analyses must account for high uncertainty 

and for which the understanding of the needs and 

impacts on future generations become increasingly 

speculative.’’ (Docket No. EPA–HQ–OAR–2005– 

0083–0408, pp. 20–21). 

impacts over times far in excess of 

recorded human history naturally raises 

concerns as to how the welfare of 

people living far in the future can and 

should be taken into account when 

societal institutions may no longer exist 

to provide oversight of a disposal 

facility.30

In considering how our standards 

reflect these intergenerational issues, we 

considered the guidance offered by the 

NAS committee. (See 70 FR 49036) In 

citing NRC and IAEA sources on the 

question of intergenerational equity, 

NAS wrote: 

A health-based risk standard could be 

specified to apply uniformly over time and 

generations. Such an approach would be 

consistent with the principle of 

intergenerational equity that requires that the 

risks to future generations be no greater than 

the risks that would be accepted today. 

Whether to adopt this or some other 

expression of the principle of 

intergenerational equity is a matter for social 

judgment. 

NAS Report pp. 56–57, emphasis added. 

We generally agree with the NAS 

statement. A single dose standard 

applicable at all times would typically 

be consistent with a close reading of the 

principle of intergenerational equity as 

stated by NAS. However, NAS clearly 

acknowledges that ‘‘some other’’ 

approach could also be consistent with 

that principle. We believe it is 

reasonable to conclude that ‘‘some 

other’’ approach must include situations 

where it may not be reasonable to apply 

the same dose standard at all times 

because of the extremely long 

compliance period. We believe 

establishing a peak dose standard for the 

Yucca Mountain disposal system is a 

situation in which ‘‘some other 

expression of intergenerational equity’’ 

is more appropriate than is applying a 

single dose standard of 15 mrem/yr 

throughout the compliance period. The 

rulemaking process we are following is 

the accepted way for ‘‘social judgment’’ 

to be incorporated into regulations. 

NAS made no recommendation 

regarding the appropriate expression of 

intergenerational equity, just as it made 

no recommendation regarding the level 

of the final peak compliance standard. 

Rather, NAS acknowledged EPA’s wide 

latitude to exercise its policy judgment. 

We emphasize that we do not 

question whether there is an obligation 

to future generations, but we believe 

there is no consensus regarding the 

nature of that obligation, for how long 

it applies, whether it changes over time, 

or how it can be discharged. Regarding 

radioactive waste management and 

geologic disposal, there is general 

agreement that assurances can be 

provided that the protections offered 

will be similar to those applied to 

current activities for periods 

approximating 10,000 years, which is a 

very long time. It also is generally 

accepted that engineered barriers cannot 

be relied upon indefinitely, and that 

projected doses may eventually exceed 

the initial regulatory levels. The 

question of equity is also raised by the 

fact that the repository is part of a 

passive disposal system that may 

provide complete containment for 

hundreds of generations without their 

knowledge, but present the greatest risks 

to equally unsuspecting generations 

beyond that time. However, it is unclear 

as to exactly how such long-term 

projected doses should be factored into 

a judgment of facility safety, if we are 

not confident they can be interpreted in 

the same way at all times.31 We are 

establishing today a standard consistent 

with a public dose limit of 100 mrem/ 

yr that is deemed protective today as a 

matter of international consensus, 

which would not affect the quality of 

life for future generations, even those 

hundreds of thousands of years distant. 

We believe this is a reasonable level of 

commitment for such long times, given 

the complexities of the situation and 

what we see as our responsibility to 

establish a level of compliance, not a 

soft target or reference level that could 

be exceeded for unspecified reasons and 

by unspecified amounts. 

In conclusion, EPA acknowledges and 

remains committed to the principles of 

intergenerational equity. However, we 

do not interpret these principles as 

requiring that the same compliance 

standard must apply at all times. Such 

an approach is overly simplistic in the 

circumstances and ignores the 

complexities involved in establishing 

radiological protection standards for 

periods approaching 1 million years. We 

believe that peak dose limits over such 

periods should be viewed as 

qualitatively different from limits 

applied at earlier times; in other words, 

the basis for judgment at different times 

is not the same. As a matter of public 

policy, a commitment to protect future 

generations over the next 10,000 years at 

levels consistent with standards applied 

for the current generation, and to protect 

more distant generations at levels 

consistent with the overall public dose 

limits deemed protective today and 

adopted nationally and internationally, 

protects public health and the 

environment across generations in a 

manner that comports with the objective 

of intergenerational equity. Under this 

approach, future generations will not 

face undue burdens or the irreversible 

loss of reasonable options arising from 

a decision by the current generation to 

pursue a policy of geologic disposal at 

Yucca Mountain, nor will the 

compliance demonstration demand 

more than can be provided by scientific 

analysis. The standards applicable to 

both time frames are protective of public 

health and safety and will offer 

comparable, if not identical, protections 

to the affected generations. See section 

9 of the Response to Comments 

document for more detailed discussion 

of these issues. 

7. What is Geologic Stability and Why 

is it Important? 

Underlying the NAS recommendation 

to assess compliance at the time of 

maximum risk is the concept of geologic 

stability (i.e., peak dose should be 

assessed ‘‘within the limits imposed by 

the long-term stability of the geologic 

environment,’’ NAS Report p. 2). NAS 

viewed this as an important 

consideration in assessing performance, 

both analytically and in regulatory 

review. Indeed, NAS discussed two 

important kinds of uncertainty in 

describing this concept, which are 

spatial and temporal uncertainty. The 

committee concluded that spatial 

uncertainties will always exist no matter 

what time frame is used for the 

performance assessments. Temporal 

uncertainties, on the other hand, will 

vary over different time frames, and the 

presence of such uncertainties indicates 

the advisability of defining a ‘‘period of 

geologic stability,’’ during which 

performance projections can be made 

with some degree of confidence. For 

time periods where conditions at the 

site would change dramatically in a 

relatively short time, projections of site 


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conditions would be highly speculative, 

and consequently performance 

assessments would have very limited if 

any validity. It is important to 

understand that ‘‘stable’’ in this context 

is not synonymous with ‘‘static and 

unchanging.’’ Rather, NAS recognized 

that many ‘‘physical and geologic 

processes’’ are characteristic of any site 

and have the potential to affect 

performance of the disposal system. 

NAS concluded that these processes 

could be evaluated as long as ‘‘the 

geologic system is relatively stable and 

varies in a boundable manner’’ (NAS 

Report p. 9). Thus, the site itself could 

be anticipated to change over time, but 

in relatively narrow ways that can be 

defined (‘‘bounded’’). Implicit in the 

NAS recommendation is the idea that 

the maximum risk might occur outside 

the period of geologic stability, but 

assessments performed at that time 

would have little credibility and would 

not be a legitimate basis for regulatory 

decisions: ‘‘After the geologic 

environment has changed, of course, the 

scientific basis for performance 

assessment is substantially eroded and 

little useful information can be 

developed.’’ (NAS Report p. 72) 

NAS judged this period of ‘‘long-term 

stability’’ to be ‘‘on the order of one 

million years.’’ (NAS Report p. 2) We 

describe in section III.A.8 (‘‘Why is the 

Period of Geologic Stability 1 Million 

Years?’’) the policy judgment on our 

part to explicitly equate the period of 

geologic stability with 1 million years. 

More important, however, is to 

understand the relationship among the 

regulatory definition, the physical 

reality of the site, and the performance 

assessment models. In reaching its 

conclusion, NAS considered 

information available on the site 

properties and the processes as they 

currently operate. This provides a basis 

for understanding how the site 

functions today, but would not be 

sufficient to project that understanding 

for periods of millions of years into the 

future. To do that, NAS also considered 

information obtained through studies of 

the geologic record at the site, to see if 

evidence existed for times when 

processes were either fundamentally 

different or they operated at different 

rates. This is similar to our 

recommendation that DOE consider at 

least the last two million years (the 

Quaternary period) in characterizing 

FEPs. In fact, examination of the 

Quaternary geologic record is an 

important component in understanding 

the evolution of the geologic setting over 

time. NAS expressed confidence that 

neither the processes active at the site, 

nor the site itself, had changed in 

fundamental ways over the Quaternary 

Period and longer, and probably would 

continue to behave much as it does 

today for the next million years. NAS 

therefore suggested that geologic 

conditions could be bounded with 

reasonable confidence for periods ‘‘on 

the order of one million years.’’ (NAS 

Report p. 2) 

Models used to assess performance 

need to incorporate a description of the 

bounds under which the model can be 

considered valid, so as to avoid 

physically impossible situations, as well 

as assure that the conceptual models 

upon which the performance 

assessments are based reasonably 

represent the way the site is expected to 

behave over the period of stability. They 

must be defined so that significant 

changes to the properties of the site and 

physical and geologic processes are not 

projected inadvertently to create 

conditions of ‘‘geologic instability.’’ 

That is, they must avoid crossing over 

into sets of conditions that would in 

reality not be a geologically stable 

situation, or are outside the bounds 

under which the model can be 

considered valid. Here again the 

examination of the geologic record at 

the site provides the means of 

constructing the models to adequately 

make simulations of future performance 

that reflect the range of potential 

expected conditions at the site over the 

regulatory compliance period. 

Parameter value distributions used in 

the simulations, which are the 

fundamental input information used to 

make the dose assessments, should not 

be limited only to data collected for the 

present situation at the site, but should 

consider how those parameter values 

could change over the period of 

stability. Expert judgment, where 

appropriate, based upon site-specific 

information and broader understanding 

of how these processes operate in 

general, plays an important role in 

defining such modeling input data. 

The geologic record is the primary 

source of information on the question of 

geologic stability and was considered by 

NAS in reaching its conclusions about 

the geologic stability period. We believe 

that the geologic record at the site 

clearly supports the position that the 

site will be stable over the course of the 

next million years. Conclusions based 

on extrapolation beyond what can be 

supported in the geologic record should 

be avoided. 

8. Why is the Period of Geologic 

Stability 1 Million Years? 

Today’s final rule includes a 

compliance period of 1 million years, 

over which DOE must project 

performance and demonstrate 

compliance with the individualprotection and human-intrusion 

standards. As discussed at length in our 

proposal and more briefly in Sections I 

and II of this document, our rulemaking 

is in response to the DC Circuit decision 

vacating the 10,000-year compliance 

period in our 2001 rule. The Court 

concluded that the 10,000-year 

compliance period was not based upon 

and consistent with the NAS 

recommendations, as the EnPA 

required. NAS recommended ‘‘that 

compliance with the standard be 

assessed at the time of peak risk, 

whenever it occurs, within the limits 

imposed by the long-term stability of the 

geologic environment, which is on the 

order of one million years.’’ (NAS 

Report p. 2) NAS found that 

‘‘compliance assessment is feasible for 

most physical and geologic aspects of 

repository performance on the time 

scale of the long-term stability of the 

fundamental geologic regime,’’ and 

accordingly ‘‘there is no scientific basis 

for limiting the time period of an 

individual-risk standard.’’ (NAS Report 

p. 6) As a matter of policy, we believe 

it is appropriate and necessary to define 

a compliance period within which our 

standards apply. This section discusses 

the considerations that led us to 

conclude that a compliance period of 1 

million years is appropriate from a 

policy perspective and consistent with 

NAS statements regarding geologic 

stability at Yucca Mountain. 

As discussed in section III.A.7 (‘‘What 

is Geologic Stability and Why is it 

Important?’’), the NAS introduced the 

concept of geologic stability in its report 

and referred to it repeatedly in its 

discussions (NAS Report, e.g., pp. 9, 55, 

69, 71, and 72). In discussing the 

physical properties and geologic 

processes leading to the transport of 

radionuclides away from the repository, 

the NAS committee concluded ‘‘that 

these physical and geologic processes 

are sufficiently quantifiable and the 

related uncertainties sufficiently 

boundable that the performance can be 

assessed over time frames during which 

the geologic system is relatively stable 

or varies in a boundable manner.’’ (NAS 

Report p. 9) While variation of site 

characteristics over time produces some 

uncertainty, NAS believed that such 

changes could be bounded during the 

period of geologic stability of the site, 

i.e., as long as the conditions do not 

change significantly. (NAS Report pp. 

72, 77) NAS also noted that ‘‘[a]fter the 

geologic environment has changed, of 

course, the scientific basis for 


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32For example, in general guidance documents, 

the IAEA has stated that ‘‘little credibility can be 

attached to assessments beyond 106 years.’’ (‘‘Safety 

Indicators in Different Time Frames for the Safety 

Assessment of Underground Radioactive Waste 

Repositories,’’ IAEA–TECDOC–767, p. 19, 1994, 

Docket No. EPA–HQ–OAR–2005–0083–0044) In its 

final 2006 Safety Requirements for Geological 

Disposal of Radioactive Waste, IAEA also states, 

‘‘Care needs to be exercised in using the criteria 

beyond the time where the uncertainties become so 

large that the criteria may no longer serve as a 

reasonable basis for decision making.’’ (Docket No. 

EPA–HQ–OAR–2005–0083–0383, page 11, 

paragraph 2.12) As a country-specific example, final 

guidelines from the Swedish Radiation Protection 

Authority state that ‘‘the risk analysis should be 

extended in time as long as it provides important 

information about the possibility of improving the 

protective capability of the repository, although at 

the longest for a time period of one million years.’’ 

(Docket No. EPA–HQ–OAR–2005–0083–0388) Also, 

in an example where the official guidelines specify 

a risk target that is of undefined duration, the 

United Kingdom’s National Radiological Protection 

Board has stated that ‘‘[o]ne million years is * * * 

the timescale over which stable geological 

formations can be expected to remain relatively 

unchanged,’’ while concluding that the scientific 

basis for risk calculations past one million years is 

‘‘highly questionable.’’ (‘‘Board Statement on 

Radiological Protection Objectives for the Landbased Disposal of Solid Radioactive Wastes,’’ 1992 

Documents of the NRPB, Volume 3, No. 3, p. 15, 

Docket No. EPA–HQ–OAR–2005–0083–0416) 

performance assessment is substantially 

eroded and little useful information can 

be developed.’’ (NAS Report p. 72) 

While NAS made no additional 

qualification on what constituted 

‘‘significant’’ changes, it made 

numerous references in its report to a 

stability period for the site ‘‘on the order 

of one million years.’’ The committee 

concluded that during this period it 

would be feasible to make projections of 

repository site conditions. We concur 

and believe that assessments can be 

made and bounded where uncertainty 

exists, and consequently performance 

assessments can be developed with 

adequate confidence for regulatory 

decision-making within the context of 

the requirements adopted in today’s 

final rule. We discuss some additional 

qualifications to this proposition in the 

remainder of this section. 

While the NAS characterized the 

length of the geologic stability period in 

loose terms (‘‘on the order of’’), we 

believe it is appropriate to fix the 

stability period duration as a matter of 

regulatory policy. We find support on 

this point from NAS: ‘‘It is important, 

therefore, that the ‘rules’ for the 

compliance assessment be established 

in advance of the licensing process.’’ 

(NAS Report p. 73). We believe, 

therefore, as a matter of regulatory 

philosophy and policy, that a relatively 

loosely defined stability period ‘‘on the 

order of’’ one million years is not 

sufficiently specific for regulatory 

purposes, i.e., implementing our 

standards and reaching a compliance 

decision. Indeed, NAS clearly 

considered that the compliance period 

could be one of the ‘‘rules’’ that should 

be established for compliance 

assessments. (NAS Report p. 56) Some 

commenters suggested that the period of 

geologic stability could be longer (or 

interpreted ‘‘on the order of one million 

years’’ as possibly as long as ten million 

years), and said our rule should allow 

consideration of longer timescales if 

justified by considerations of geologic 

stability. The actual period of geologic 

stability at Yucca Mountain is 

unknowable, and we disagree that an 

open-ended compliance standard is 

justified over such time frames. We 

believe that the applicant (DOE) and the 

compliance decision-maker (NRC) must 

have definitive markers to judge when 

compliance is demonstrated, and that a 

loosely defined time frame does not 

provide such a marker for 

implementation of our standards in a 

licensing process. We believe that the 

geologic stability period of 1 million 

years that we have defined provides the 

necessary marker, and is within our 

discretion to set as a matter of policy. 

(See generally NAS Report p. 3) To do 

otherwise we believe would leave the 

licensing process in a potentially 

untenable situation of dealing with 

possibly endless debate over exactly 

when a peak dose occurs in relation to 

a compliance period time limit. Such 

debate can arise because of the inherent 

uncertainty that exists in characterizing 

the complex processes and variables 

involved in projecting performance of 

the disposal system over very long 

periods of time. As the NAS explained, 

‘‘although the selection of a time period 

of applicability has scientific elements, 

it also has policy aspects we have not 

addressed.’’ (NAS Report p. 56) 

As commenters have pointed out, the 

rate of waste package failure is a 

dominant factor in determining when 

the peak dose for a probabilistic 

assessment will occur. With all the 

parameters (and the uncertainty in their 

values over time) involved in a total 

system performance assessment, as well 

as the assumptions necessary to select 

processes involved in projecting 

performance, it is quite possible that 

significant debate could result in the 

licensing process over selection of the 

parameter values and the resulting 

timing of the peak dose results. We do 

not believe such debate is constructive 

because it would not advance the goal 

of providing a reasonable test of the 

disposal system. We also believe that 

the 1 million year stability period 

provides the needed definitive marker 

for judging the time over which the 

standards apply and is an appropriate 

exercise of our policy discretion. 

Throughout our proposal and in this 

final rule we have cited a significant 

number of international references to 

support policy judgments such as the 

one discussed here. Readers may recall 

that we cited such references suggesting 

that dose projections beyond 1 million 

years have little credibility and believe 

that we used those arguments to justify 

proposing the 1 million-year 

compliance period (70 FR 49036, 

August 22, 2005). We did not explicitly 

discuss in the proposal our reasons for 

selecting 1 million years as the 

compliance period and equating it to the 

period of geologic stability, other than 

references to the NAS language that it is 

‘‘on the order of’’ 1 million years. 

However, these sources do generally 

reflect widespread acceptance of the 

proposition that quantitative 

performance projections at very long 

time frames have limited utility for 

regulatory decision-making, and that 1 

million years may be a reasonable 

reference point beyond which such 

projections either should not be 

required or should be considered only 

in their broadest sense.32 Further, while 

it should be clear that we agree with the 

thrust of those international sources 

regarding the effects of uncertainty on 

long-term dose projections and the 

relative level of confidence that can be 

placed in them for decision-making, we 

believe the post-10,000-year peak dose 

standard in today’s final rule 

appropriately accommodates those 

considerations and is protective of 

public health, meaningful, 

implementable, and provides a 

reasonable test of the disposal system 

that is consistent with the NAS Report, 

DC Circuit decision, and the principles 

of reasonable expectation. 

To support these general policy 

arguments, which would lead us to 

consider a time period of approximately 

1 million years as an appropriate 

regulatory time frame, it is necessary to 

address NAS’s scientific judgments. 

While NAS did not define with 

precision the period of time that the 

geologic environment likely would 

remain stable, for purposes of our 

regulation we believe scientific 

information can be relied upon to 

support a firm definition of that period 

as ending at 1 million years after 

disposal. Further, we believe that 

equating a specific time period with the 

‘‘period of geologic stability’’ is a sitespecific decision, as NAS’s statements 

regarding geologic stability were wholly 

in the context of Yucca Mountain. (See, 

for example, NAS Report p. 69: ‘‘The 

time scales of long term geologic 


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processes at Yucca Mountain are on the 

order of 106 years’’; and NAS Report p. 

85: ‘‘The geologic record suggests this 

time frame is on the order of about 106

years.’’) Therefore, we have considered 

how the natural processes and 

characteristics at the Yucca Mountain 

site would support defining the period 

of geologic stability as ending at a 

specified time after disposal. In 

considering the natural setting, many 

comments expressed the view that the 

site’s natural characteristics are so 

conducive to rapid release and transport 

of radionuclides, only the waste 

packages and other engineered barriers 

would make it possible for significant 

doses to be delayed much beyond 

10,000 years. We believe it is therefore 

also appropriate to consider the geologic 

stability period from the perspective of 

a reasonable length of time for 

significant events to act on the waste 

packages and engineered barriers, and 

ultimately lead to release of 

radionuclides. Natural processes and 

events would contribute to both the 

package failures and to the subsequent 

transport of radionuclides, even if such 

failures occur relatively late in the 

period under consideration. 

A consideration of the geologic 

history of the site, in the areas of 

igneous and seismic activity, also 

supports a 1 million year stability 

period. Information compiled by NRC 

(Docket No. EPA–HQ–OAR–2005–0083– 

0373) concerning basaltic igneous 

activity around the site shows that this 

type of activity has been the only 

activity around the site through the 

Pliocene (beginning roughly 5.4 million 

years ago), and that the volume of 

eruptive activity (both tuff and basaltic 

material) has decreased continually over 

the last 10 million years (Coleman et al., 

2004, Docket No. EPA–HQ–OAR–2005– 

0083–0378). From the identification of 

surface features as well as indicators of 

buried remnants of past volcanic 

activity, the episodes of basaltic activity 

around the site can be shown to have 

occurred in clusters of events around 1 

million and 4 million years ago (Hill, 

2004, Docket No. EPA–HQ–OAR–2005– 

0083–0373). The occurrence of these 

clusters indicates that the nature and 

extent of past volcanic activity can be 

reasonably well characterized and that 

annual probabilities for such events can 

be reasonably estimated from the 

geologic record around the site. Annual 

probabilities of volcanic disruptions to 

the repository have been estimated by 

various investigators, and range from as 

high as 10¥6 to as low as 5.4 × 10¥10

(Coleman et al., 2004, Docket No. EPA– 

HQ–OAR–2005–0083–0378). 

Further, while geologic stability may 

be viewed as being affected primarily by 

large-scale events, accumulations of 

small-scale changes over very long time 

periods also have the potential to alter 

the geologic setting and affect the 

technical basis for performance 

assessments. Tectonic events have such 

a potential at Yucca Mountain. Rates of 

displacement on the nearest potentially 

significant fault in the region average 

about 0.02 mm/yr. (DOE, Science & 

Engineering Report, 2002, p. 4–409, 

Docket No. EPA–HQ–OAR–2005–0083– 

0069) This means that in 10,000 years, 

there could be 20 cm (0.65 ft) of 

displacement, a relatively small change 

not likely to affect performance of the 

geologic system. However, in 1 million 

years, the same rate of movement results 

in 20 m (65 ft) of displacement on the 

fault. Using the larger estimates of 

movement within the range of potential 

movement, displacement could be as 

much as 30 m (100 ft) over 1 million 

years. Such changes in the geologic 

setting at Yucca Mountain have the 

potential to erode the scientific basis for 

performance assessment and possibly to 

affect the quality of the information the 

assessment can provide to decisionmakers. 

NAS also stated that ‘‘we see no 

technical basis for limiting the period of 

concern to a period that is short 

compared to the time of peak risk or the 

anticipated travel time.’’ (NAS Report p. 

56) This statement suggests that the 

stability period must be long enough to 

allow FEPs that pass the probability and 

significance screens to demonstrate 

their effects, if any, on the results of the 

performance assessments, even from 

waste package failures occurring 

relatively late in the period. In contrast 

to the accumulated small-scale changes 

discussed above, larger-scale seismic 

events are more likely to contribute 

directly to radionuclide releases through 

the effects of ground motion. Strong 

seismic events could damage waste 

package integrity by causing 

emplacement drift collapse or vigorous 

shaking of the packages themselves. 

Earthquake recurrence intervals for the 

site indicate that strong events could 

reasonably be assumed to test waste 

package integrity at various times 

within the 1 million-year period (Docket 

No. EPA–HQ–OAR–2005–0083–0374 

and 0379). In addition, we note that 

estimates of ground water travel time 

from the repository to the RMEI location 

are on the order of thousands of years 

(see the BID for the 2001 final rule, 

Docket No. EPA–HQ–OAR–2005–0083– 

0050). At these rates, the effects of 

disruptive volcanic and seismic effects 

on releases would not be delayed from 

reaching the RMEI location during the 

stability period, e.g., added releases 

from a low probability seismic event at 

800,000 years would have ample time to 

be captured by the performance 

assessments. Based on these 

considerations, the 1 million-year 

period is a sufficiently long time frame 

to evaluate the potential consequences 

of both gradual processes and disruptive 

events on disposal system performance. 

In summary, for regulatory policy as 

well as site-specific scientific 

considerations, we believe that fixing 

the period of geologic stability for 

compliance assessments at 1 million 

years provides a reasonable test for the 

disposal system performance. We 

believe a fixed time period is necessary 

both to provide a definitive marker for 

compliance decision-making and to 

prevent unbounded speculation 

surrounding the factors affecting 

engineered barrier performance and the 

ultimate timing of peak dose 

projections. Examination of site 

characteristics indicates that the 

influences of natural processes and 

events on release and transport of 

radionuclides would be demonstrated 

even for waste package failures 

occurring relatively late in the period. 

We believe that setting a 1 million year 

limit is a cautious but reasonable 

approach consistent with the NAS 

position on bounding performance 

assessments for uncertain elements 

affecting disposal system performance. 

Finally, explicitly defining the period 

during which our standards apply will 

focus attention on times for which the 

geologic setting and associated 

processes are more quantifiable and 

boundable, rather than entering debate 

on disposal system performance in time 

periods where the fundamental geologic 

regime may have sufficiently changed so 

that the ‘‘scientific basis for 

performance assessment is substantially 

eroded and little useful information can 

be developed.’’ (NAS Report p. 72) 

9. How Will NRC Judge Compliance? 

Today’s final rule directs NRC to use 

the arithmetic mean of the distribution 

of projected doses to determine 

compliance with both the 150 μSv/yr 

(15 mrem/yr) dose standard applicable 

for the first 10,000 years after closure 

and the 1 mSv/yr (100 mrem/yr) peak 

dose standard applicable between 

10,000 and 1 million years after closure. 

In reaching this decision, we considered 

comments raising legal, technical, and 

policy points. Foremost among these 

were comments focusing on a statement 

by the NAS committee: ‘‘We 


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recommend that the mean values of 

calculations be the basis for comparison 

with our recommended standards.’’ 

(NAS Report p. 123) 

After considering public comments, 

the NAS Report, and the DC Circuit 

decision, we conclude that the use of 

the arithmetic mean to determine 

compliance at all times, without 

conditions or restrictions, is 

straightforward and clearly consistent 

with the NAS recommendation, 

pursuant to the EnPA. Consistent with 

our proposal, we are specifying that the 

‘‘mean’’ to be used is the arithmetic 

mean, as this is consistent with the 

intent of 40 CFR part 191 and its 

implementation at WIPP. See section 7 

of the Response to Comments document 

for more discussion of the points raised 

in public comments. 

10. How Will DOE Calculate the Dose? 

Today’s final rule requires DOE to 

calculate the annual committed effective 

dose equivalent (CEDE) for comparison 

to the storage, individual-protection, 

and human-intrusion standards using 

the radiation- and organ-weighting 

factors in ICRP Publication 60 (‘‘1990 

Recommendations of the ICRP’’), rather 

than those in ICRP Publication 26 

(‘‘1977 Recommendations of the ICRP’’). 

As we described in our proposal, this 

action will incorporate updated 

scientific factors necessary for the 

calculation, but will not change the 

underlying methodology. We explained 

in some detail the use of the terms 

‘‘effective dose equivalent’’ and 

‘‘effective dose’’ in the EnPA, the DC 

Circuit decision, the ICRP publications, 

and our previous actions to support our 

position that use of the weighting 

factors in ICRP 60 (and its follow-on 

implementing Publication 72) is 

consistent with calculation of effective 

dose equivalent, as required by the 

EnPA. (70 FR 49046–49047) 

We received some comment 

disagreeing with our conclusion that use 

of the term ‘‘effective dose equivalent’’ 

is consistent with the use of the ICRP 60 

weighting factors. As we discussed in 

our proposal, we believe a close reading 

of ICRP 60 supports our interpretation 

that effective dose equivalent and 

effective dose are synonymous concepts. 

ICRP defined two weighting factors in 

ICRP 26, the radiation quality factor, Q, 

and the tissue weighting factor, WT. In 

ICRP 60, the quality factor was replaced 

by the radiation weighting factor, WR, 

with the same values assigned to alpha, 

beta, and gamma radiation. In ICRP 26, 

the tissue weighting factor was 

presented as a rigid construct with 

defined values for specific organs. In 

ICRP 60, the tissue weighting factor was 

redefined as a set of recommended 

values for an expanded set of organs 

(which could be modified in cases 

where scientific information was 

available to support using alternative 

factors), and it was explained that the 

attributes of the tissue weighting factor 

include the components of detriment 

cited by the comments (fatal and nonfatal cancers, length of life lost, and 

hereditary effects). However, ICRP made 

a clear distinction between its renaming 

of the doubly weighted dose quantity 

from ‘‘effective dose equivalent’’ (ede) to 

‘‘effective dose’’ (E) and its redefining of 

WT. The association of effective dose 

equivalent with the ICRP 26 tissue 

weighting factors is thus coincidental 

but not required. We cited ICRP to that 

effect in our proposal: 

The weighted equivalent dose (a doubly 

weighted absorbed dose) has previously been 

called the effective dose equivalent but this 

name is unnecessarily cumbersome, 

especially in more complex combinations 

such as collective committed effective dose 

equivalent. The Commission has now 

decided to use the simpler name effective 

dose, E. The introduction of the name 

effective dose is associated with the change 

to equivalent dose, but has no connection 

with changes in the number or magnitude of 

the tissue weighting factors * * * 

ICRP Publication 60, p. 7, paragraph 27, 

Docket No. EPA–HQ–OAR–2005–0083– 

0421, emphasis added. 

Similarly, ICRP also states: 

The values of both the radiation and tissue 

weighting factors depend on our current 

knowledge of radiobiology and may change 

from time to time. Indeed, new values are 

adopted in these recommendations * * *. It 

is appropriate to treat as additive the 

weighted quantities used by the Commission 

but assessed at different times, despite the 

use of different values of weighting factors. 

The Commission does not recommend that 

any attempt be made to correct earlier values. 

It is also appropriate to add values of dose 

equivalent to equivalent dose and values of 

effective dose equivalent to effective dose 

without any adjustments. 

ICRP Publication 60, p. 9, paragraph 31, 

Docket No. EPA–HQ–OAR–2005–0083– 

0421, emphases added. 

In summary, we believe the intent of 

Congress in specifying effective dose 

equivalent is that the Yucca Mountain 

standards be based on a doubly 

weighted dose quantity, not that the 

assessment of that quantity be tied to 

factors developed at a particular time, 

when newer science indicates those 

factors should be updated. We use 

effective dose equivalent for consistency 

with the terminology used in the EnPA, 

but are adopting in today’s final rule the 

current recommended values for WT. 

Our approach is thus fully consistent 

with both the current ICRP 

recommendations and the EnPA. 

Today’s final rule does incorporate a 

change to the proposed definition of 

‘‘effective dose equivalent’’ in § 197.2 to 

make it consistent with language in 

Appendix A regarding the potential use 

of future ICRP recommendations. We 

received some comments suggesting that 

the appendix should not include 

specific weighting factors, but state only 

that doses are to be calculated in 

accordance with the methods of ICRP 

60/72. The commenter believes this is 

appropriate because NRC’s proposed 

licensing requirements included the 

tissue weighting factors, but not the 

radiation weighting factors. Further, the 

commenter points out that dose 

coefficients in ICRP 72 (and Federal 

Guidance Report 13) consider a 

somewhat different set of organs than do 

the tissue weighting factors. We prefer 

not to adopt the commenter’s 

suggestion, which we believe could lead 

to questions regarding the appropriate 

factors to use. We note that ICRP 60, 

unlike ICRP 26, is not tied to a specific 

set of weighting factors, and allows for 

the possibility that users will substitute 

their own preferred set of factors. 

Stating only that the methods of ICRP 

60/72 be used to calculate dose, without 

the additional stipulations in the 

appendix, would not provide sufficient 

clarity on this point. Therefore, we are 

adding language to the definition in 

§ 197.2 to the effect that NRC can direct 

that other weighting factors be used to 

calculate dose, consistent with the 

conditions presented in Appendix A. 

We believe this will effectively address 

the commenter’s concern. 

B. How Will This Final Rule Affect 

DOE’s Performance Assessments? 

Today’s final rule requires DOE to 

demonstrate compliance with the 

individual-protection standard through 

use of performance assessment. A 

performance assessment is developed by 

first compiling lists of features 

(characteristics of the disposal system, 

including both natural and engineered 

barriers), events (discrete and episodic 

occurrences at the site), and processes 

(continuing activity, gradual or more 

rapid, and which may occur over 

intervals of time) anticipated to be 

active during the compliance period of 

the disposal system. These items are 

collectively referred to as ‘‘FEPs’’ 

(features, events, and processes). Once 

FEPs are identified, they are evaluated 

for their probability of occurrence (i.e., 

how likely they are to occur during the 

compliance period) and their effect on 

the results of the performance 

assessment (i.e., do they significantly 


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33Only FEPs with an annual probability greater 

than or equal to 10¥5 need to be considered in 

performance assessments to show compliance with 

§§ 197.25(b) and 197.30. FEPs below this 

probability threshold, but still above 10¥8 per year, 

are defined by NRC as ‘‘unlikely’’. 

affect projected doses from the disposal 

system during the first 10,000 years after 

disposal). Addressing these aspects of 

performance assessment for a 

compliance period of 1 million years 

was a central aspect of our proposal and 

is the focus of this section. 

After considering public comments, 

we are retaining § 197.36 as proposed, 

with two modifications. First, the 

probability threshold for FEPs to be 

considered for inclusion in performance 

assessments conducted to show 

compliance with § 197.20(a)(1) is now 

stated as an annual probability of 1 in 

100 million (10¥8 per year).33 Because 

the same FEPs included in these 

performance assessments will also be 

included in performance assessments 

conducted to show compliance with 

§ 197.20(a)(2), the same probability 

threshold applies in all cases. Second, 

we are adding a provision to address a 

potential effect of seismicity on 

hydrology that was identified by NAS. 

The final rule now requires the potential 

effects of a rise in the ground-water 

table as a result of seismicity to be 

considered. If NRC determines such 

effects to be significant to the results of 

the performance assessment, it shall 

specify the extent of the rise for DOE to 

assess. 

Our 2001 rule set forth three basic 

criteria for evaluating FEPs for their 

potential effects on site performance 

and their incorporation into the 

scenarios used for compliance 

performance assessments (§ 197.36). 

These criteria retained the same 

limitations originally established in 40 

CFR part 191, which were developed to 

apply to any potential repository for 

spent nuclear fuel, high-level waste, or 

transuranic radioactive waste. We 

believe that approach remains 

reasonable for the site-specific Yucca 

Mountain standards, and we believe it 

is desirable to maintain consistency 

between the two regulations for geologic 

repositories in the basic criteria for 

evaluating FEPs. The criteria for 

evaluating FEPs are: 

• A probability threshold below 

which FEPs are considered ‘‘very 

unlikely’’ and need not be included in 

performance assessments; 

• A provision allowing FEPs above 

the probability threshold to be excluded 

from the analyses if they would not 

significantly change the results of 

performance assessments; and 

• An additional stipulation that in 

addition to ‘‘very unlikely’’ FEPs, 

‘‘unlikely’’ FEPs need not be considered 

in performance assessments conducted 

to show compliance with the humanintrusion and ground-water protection 

standards. 

As an initial step, a wide-ranging set 

of FEPs that potentially could affect 

disposal system performance is 

identified. The term ‘‘potentially’’ is key 

here, because at this early stage, the list 

is deliberately broad, focusing more on 

‘‘what could happen’’ rather than ‘‘what 

is likely to happen at Yucca Mountain.’’ 

Under the 2001 rule, each of these FEPs 

is then examined to determine whether 

it should be included in an assessment 

of disposal system performance over a 

10,000-year period by evaluating the 

probability of occurrence at Yucca 

Mountain and, as appropriate, the 

effects of the FEP on the results of the 

performance assessment. Based on these 

evaluations, a FEP may be excluded 

from the assessment of disposal system 

performance on the basis of probability, 

or if the results of the performance 

assessments would not be changed 

significantly by its exclusion. 

We included in our proposal 

provisions describing how FEPs should 

be incorporated into assessments of 

disposal system performance during the 

period of geologic stability, defined as 

ending at 1 million years after closure. 

Our purpose was to build upon the 

provisions applicable to the 10,000-year 

compliance period in our 2001 rule to 

address the complexities introduced by 

extending the compliance period to 1 

million years. In general, the database of 

FEPs applicable to Yucca Mountain 

should be the same, regardless of the 

period covered by the assessments. In 

developing our proposal, however, we 

considered how these general 

provisions might change when the 

compliance period extends to 1 million 

years. We also proposed specific 

provisions to address climate change, 

seismicity, and igneous events, which 

were identified by NAS as potential 

‘‘modifiers’’ whose effects could be 

bounded within the period of geologic 

stability. 

Some commenters questioned 

whether our authority to establish 

public health protection standards for 

Yucca Mountain extended to specifying 

how FEPs must be considered, 

contending that this function properly 

lies with the implementing authority 

(NRC). We disagree. While NRC clearly 

has authority to specify such provisions, 

it is also within our purview to stipulate 

such conditions as are necessary to 

place our regulations in context and 

ensure they are implemented as we 

intended. For analyses covering 1 

million years, it is important to focus on 

those factors most affecting 

performance, if necessary by excluding 

other aspects that are more likely to 

have little or no significance. We believe 

this approach is consistent with the 

direction from NAS. NAS was charged 

with providing advice to EPA on 

‘‘reasonable standards for protection of 

public health and safety’’ (EnPA section 

801(a)(2)). NAS provided its findings 

and recommendations in the context of 

standards to be developed by EPA, 

including discussion of FEPs, for 

example: ‘‘the radiological health risk 

from volcanism can and should be 

subject to the overall health risk 

standard to be required for a repository 

at Yucca Mountain.’’ (NAS Report p. 95) 

Further, NAS discussed the question of 

uncertainty in quantifying physical and 

chemical processes and their operation 

over long time periods and the 

inevitability of ‘‘residual, unquantifiable 

uncertainty,’’ stating ‘‘[t]he only defense 

against it is to rely on informed 

judgment.’’ (NAS Report p. 80) 

Therefore, we believe it appropriate to 

specify, where necessary, additional 

provisions for the treatment of FEPs in 

disposal system assessments to avoid 

boundless speculation. We have 

explained our understanding of the 

proper use of bounding performance 

scenarios, and we believe we are 

consistent with the NAS on this point. 

Bounding assessments addressing 

uncertainty in understanding the longterm behavior of the site should be 

constructed using informed judgment, 

not speculative assumptions without 

credible supporting evidence. 

Two of the criteria for evaluating 

FEPs, probability and significance of the 

impacts on performance assessments, 

are of primary importance in 

considering how the provisions 

applicable to the 10,000-year period 

might change when the compliance 

period is extended to 1 million years. In 

the proposed rule, we concluded that 

the 10,000-year FEPs screening could 

serve as an adequate basis for longerterm assessments because it is 

sufficiently inclusive to be appropriate 

for the entire 1 million-year compliance 

period, while at the same time 

reasonably bounding the scenarios that 

must be considered over the longer time 

frame. We thought our statements in the 

preamble on this point were sufficiently 

clear, but we understand that the way 

we structured § 197.36 of the proposal, 

essentially separating the two time 

periods, may have caused some 

confusion. For example, we did not 

intend to indicate or imply that the 


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post-closure performance assessments 

would consist of two separate and 

dramatically different calculations, with 

each having distinctly different scenario 

construction, parameter value 

distributions, or other attributes. 

Regardless of the standard against 

which compliance is being judged, the 

probability of occurrence and the 

significance of the impacts on 

performance assessment are the two 

primary criteria for including a FEP in 

the compliance analysis. The screening 

for FEPs is done for the 10,000-year 

performance assessment and then used 

with certain additions set forth in the 

rule for the 1 million-year peak dose 

performance assessment. The initial 

screening provides a database of FEPs, 

which is then used for both the 10,000- 

year and post-10,000-year peak dose 

analyses, with some additional 

stipulations for the period beyond 

10,000 years. The discussion that 

follows addresses each of these 

screening criteria in turn. 

Probability 

In the proposed standards, we defined 

the probability threshold for ‘‘very 

unlikely’’ FEPs as a 1 in 10,000 chance 

of occurrence within 10,000 years, or 

roughly a 1 in 100 million (10¥8) 

chance per year of occurring. In today’s 

final rule, the probability threshold is 

now stated only as an annual 

probability of 1 in 100 million (10¥8). 

We believe it is appropriate to clarify 

that FEPs have associated probabilities 

of occurrence that generally do not 

change over time. That is, the database 

of FEPs deemed sufficiently probable 

would serve equally well as the basis for 

assessments covering 1,000, 10,000, 

100,000, or 1 million years. These 

probabilities of occurrence are 

established by examining the geologic 

record and considering potential 

mechanisms for components of the 

repository and its natural setting to 

undergo changes. FEPs with a 

probability of occurrence greater than 1 

chance in 100 million per year should 

be considered for inclusion in the 

performance assessments to show 

compliance with the 10,000-year 

individual-protection standard, and the 

same FEPs included in those 

assessments should be used to develop 

the performance assessment scenarios to 

be analyzed for the peak dose 

performance assessments between 

10,000 and 1 million years. We believe 

that this is an inclusive threshold level 

that fully considers a range of lowprobability FEPs, while at the same time 

limiting speculation over highly 

improbable FEPs. We believe the 

probability screening threshold provides 

the foundation for a reasonable test of 

the disposal system, as discussed 

further below. 

Although we discussed the meaning 

of the probability threshold in some 

detail in our proposal, we emphasize it 

again as the foundation for constructing 

the performance assessment. A 1 in 100 

million annual probability of 

occurrence, when considered over a 

10,000-year period, includes FEPs with 

a cumulative chance of occurring of one 

one-hundredth of one percent (0.01%). 

Similarly, over 1 million years, the 

cumulative probability increases to only 

a one percent (1%) chance of occurrence 

within that time frame. We believe that 

the database of information necessary to 

assess FEPs at this low probability is the 

same as that necessary for examining 

their importance over the entire 1 

million-year compliance period. We 

believe this probability criterion leads to 

an inclusive set of potential FEPs for 

both the 10,000-year and peak dose 

assessments, and in our view would 

support a reasonable test of the disposal 

system that encompasses the climate 

change, seismic, igneous, and corrosion 

scenarios specified in our proposal. 

In our proposed rule, we concluded 

that the 10,000-year FEPs screening 

could serve as an adequate basis for 

longer-term assessments because it is 

sufficiently inclusive to be appropriate 

for use in developing performance 

scenarios applicable to the entire 1 

million-year compliance period. That is, 

we did not propose to require DOE to 

consider FEPs with an annual 

probability lower than 10¥8 to 

accommodate the lengthened 

compliance period. We believe 

excluding FEPs with less than a 1% 

chance of occurrence in 1 million years 

is consistent with the principles of 

reasonable expectation. We believe that 

lowering the annual probability level 

below 10¥8 would allow for speculative 

scenarios to be considered in the peak 

dose performance assessment, which 

would be neither reasonable nor 

justifiable, as explained below. 

Some commenters disagreed, stating 

that, because we are extending the 

compliance period by a factor of 100, 

the probability threshold for excluding 

FEPs should also be extended by a 

factor of 100, resulting in a threshold of 

1 chance in 10 billion of occurrence per 

year. Similarly, we received some 

comments questioning altogether the 

need for or validity of a probability 

threshold. The comments suggest that, 

because the effects are weighted by the 

probability of occurrence, any potential 

FEP, no matter how unlikely, should be 

characterized and assessed because its 

influence will be mitigated by its low 

probability. They cite NAS to the effect 

that ‘‘all these scenarios need to be 

quantified’’ with respect to probability 

and consequence. (NAS Report p. 72) 

Therefore, the commenters conclude 

that our concerns about introducing 

excessive speculation are unfounded. 

We disagree. We addressed this topic in 

our proposal, in the expectation that we 

would be encouraged to adjust the 

probability threshold by two orders of 

magnitude (i.e., widening the 

probability range by a factor of 100) to 

account for the similarly lengthened 

compliance period. We believe that 

simply extending the approach of using 

a one in 10,000 probability over a 1 

million-year period to give 1 in 10 

billion chance per year of occurring 

(10¥10) would result in the inclusion of 

FEPs that are so speculative as to be 

unreasonable (70 FR 49052). Nor do we 

believe it would be consistent with 

NAS’s view that the overall goal was ‘‘to 

define a standard that specifies a high 

level of protection but that does not rule 

out an adequately sited and welldesigned repository because of highly 

improbable events.’’ (NAS Report p. 28) 

Further, NAS itself suggested situations 

in which scenarios need not be 

quantified. NAS discusses, in the 

context of volcanism, a 10¥8 annual 

probability of occurrence as a level that 

‘‘might be sufficiently low to constitute 

a negligible risk’’ below which ‘‘it might 

not be necessary to consider’’ how the 

event might contribute to releases from 

the disposal system. (NAS Report p. 95) 

We believe this example is instructive, 

given that volcanism is the single 

scenario resulting in direct release of 

radioactive material from the repository 

into the biosphere, resulting in 

relatively immediate exposures. We 

believe it is reasonable to extend the 

concept expressed by NAS as 

‘‘negligible risk’’ to FEPs whose 

influences are seen in the gradual 

release and transport of radionuclides 

over long periods of time. Therefore, we 

believe that lowering the probability 

threshold, or eliminating it altogether, 

would be inconsistent with the 

important NAS cautions to focus 

assessment efforts on FEPs that can be 

bounded within the limits of geologic 

stability. 

In our view, were we to lower or 

eliminate the probability threshold, it 

would be necessary to consider and 

describe FEPs that might have been 

present or occurred only the initial 

years of the planet’s existence. 

Similarly, FEPs with an annual 

probability of 10¥10 may be only 

hypothetical, since the age of the Earth 

is generally considered to be ‘‘only’’ 4.6 


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× 109 years, suggesting that these FEPs 

may have less than a 50% chance of 

occurring within the entire history of 

the Earth. Indeed, the volcanic rocks 

comprising Yucca Mountain and its 

surroundings are only on the order of 

10–12 million years old (∼107 years). In 

determining the probability of particular 

FEPs, the geologic record at the site is 

the source of information to identify 

what FEPs have occurred at the site in 

the past and may occur in the future 

(through the period of geologic 

stability). Since the host rock formations 

at the site are only about 10 million 

years old, an annual probability cut-off 

of 10¥10 would mean that probability 

estimates for some FEPs would have to 

be made in spite of the fact that there 

is no evidence for their occurrence at 

the site in the past. As it is, the 10¥8

probability threshold presents a 

significant challenge to characterize 

FEPs with some degree of confidence, 

given the limits of today’s science and 

technology. ICRP makes a similar point 

in its 2007 recommendations: ‘‘The use 

of probability assessment is limited by 

the extent that unlikely events can be 

forecast. In circumstances where 

accidents can occur as a result of a wide 

spectrum of initiating events, caution 

should be exercised over any estimate of 

overall probabilities because of the 

serious uncertainty of predicting the 

existence of all the unlikely initiating 

events.’’ (Publication 103, Docket No. 

EPA–HQ–OAR–2005–0083–0423, 

paragraph 269) (Note that this 

discussion is in the context of 

‘‘potential’’ exposures, which include 

releases that may occur in the far future 

from disposal facilities. Therefore, the 

term ‘‘accidents’’ should not be taken as 

limited to operational activities.) 

Overall, we believe events with a lower 

annual probability than 10¥8 would 

introduce speculation beyond what is 

appropriate to define a reasonable test of 

disposal system performance. 

We also received comments stating 

that maintaining the probability 

screening criteria for the extended 

compliance period undermines our 

arguments for increasing uncertainty. To 

the contrary, we believe the physical 

meaning of the probability threshold 

(0.01% chance of occurrence within 

10,000 years, but a 1% chance within 1 

million years) appropriately 

incorporates the concept of uncertainty 

increasing with time, while still 

applying a substantially conservative 

screening criterion. 

We believe that the guidance we have 

provided for executing a FEPs 

evaluation and screening process 

assures that it is executed in a thorough 

manner. For example, we have stated 

that the geologic record through the 

Quaternary Period (a period extending 

back approximately 2 million years from 

today) at and around the site should be 

examined to identify relevant FEPs. 

While we believe that the Quaternary 

Period offers the most reliable data for 

identifying and characterizing site 

geologic FEPs, we do not believe that 

evidence preserved in older portions of 

the geologic record should be ignored in 

the FEPs identification process. We did 

not mean to imply that DOE need only 

consider the previous 10,000 years 

when developing evidence for the 

probability of occurrence of future 

events. Rather, our statements regarding 

the Quaternary Period as an appropriate 

geologic record were intended to 

confirm that, where available, reliable 

geologic records for earlier time periods 

should be consulted. For example, 

determining the probability of seismic 

and igneous events would make use of 

the geologic record at the site for as far 

back in time as reliable estimates of past 

events can be made so that defensible 

probability estimates can be made. We 

believe the Quaternary Period offers the 

best information to quantify the 

probabilities and consequences of 

geologic FEPs relevant to site 

performance. However, we did not 

intend that significant information 

about FEPs be ignored simply because 

that information appears in the geologic 

record at the site prior to the Quaternary 

Period. 

In fact, a longer portion of the 

geologic record has been examined by 

DOE and NRC in developing FEP 

probabilities. For example, to determine 

the nature and frequency of volcanic 

activity around Yucca Mountain, 

volcanic activity around the site through 

the Quaternary Period was extensively 

examined, as well as volcanic activity 

prior to that time (ACNW Workshop on 

Volcanism at Yucca Mountain, 

September 22, 2004—Docket No. EPA– 

HQ–OAR–2005–0083–0373 and 0378). 

We believe that the information 

necessary to evaluate FEPs against the 

probability threshold we established 

(10¥8 annual probability) will be 

extensive, and that increasing the 

compliance period from 10,000 to 1 

million years does not require that 

additional studies be performed beyond 

those necessary to derive the FEPs 

probabilities under the screening 

process done for the 10,000-year time 

frame assessments. As we have noted 

previously, the probabilities for 

individual FEPs are determined once, 

and the same probabilities are used in 

both the 10,000-year and 1 million-year 

assessments. 

On this last point, we stress that the 

revised § 197.36(a) issued today should 

not be interpreted as compelling DOE to 

extend the databases for its technical 

justifications. We are restating the 

probability screening criterion, not 

recasting the entire framework for the 

analysis. We recognize that in any 

licensing process the burden of proof is 

on the applicant to demonstrate that the 

necessary factors and influences have 

been evaluated. It must also be 

recognized that there will always be 

limits to the ability of science and 

technology to characterize FEPs and 

their effects on the disposal system. 

However, NAS has stated that many of 

these processes and their uncertainties 

are boundable. In our judgment, given 

the capabilities of today’s science and 

technology, it would be contrary to the 

principle of reasonable expectation to 

require DOE to demonstrate the same 

level of confidence in assessments 

covering 1 million years as it would for 

a much shorter 10,000-year analysis. 

Similarly, we believe that this 

clarification does not create the prospect 

of speculative scenarios of very low 

probability (from combinations of FEPs) 

being proposed, thereby opening the 

performance assessments to unbounded 

speculation. For example, if two low 

probability independent FEPs were 

proposed to occur simultaneously 

because of the longer time horizon 

under consideration, the probability of 

that combination would be the product 

of their respective probabilities. In other 

words, the probability of the combined 

FEPs occurring during the same year 

will be much lower, by possibly orders 

of magnitude, than the probability of 

either FEP occurring individually. 

Therefore, since the contributions of 

various FEPs (or scenarios) to the dose 

assessments is the product of their 

respective probabilities and 

consequences, the consequence of the 

combined FEPs would need to be 

inversely proportionally higher, 

typically by orders of magnitude, than 

the combined consequences of the 

individual FEPs considered separately, 

in order to make a significant change in 

the overall dose assessment. 

We did receive some comment 

suggesting that we had inappropriately 

excluded the type of volcanic events 

that created the Yucca Mountain tuff 

some 12 to 14 million years ago, instead 

focusing on the past several million 

years. However, as we stated in our 

proposal, the geologic record of the past 

several million years in the area around 

the site indicates that basaltic volcanism 

is the type of volcanism that has 

occurred recently and has the potential 

to recur in the future. The earlier events 


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were of a much different, cataclysmic 

nature, producing rock units more than 

6000 ft (1800 m) thick. The type of 

volcanic activity that created Yucca 

Mountain and the surrounding area has 

not recurred over the approximately 10 

million years since the deposits were 

originally laid down and is extremely 

unlikely to occur within the next 1 

million years (Docket No. EPA–HQ– 

OAR–2005–0083–0050, pp. 7–42 

through 7–49). Further, we question 

whether such cataclysmic events could 

be reasonably considered to fall within 

the bounds of geologic stability as 

envisioned by NAS. Inclusion of such 

events in the peak dose assessment up 

to 1 million years would be inconsistent 

with the intent of the NAS when it 

noted that long-term performance can be 

assessed (because physical and geologic 

processes are sufficiently quantifiable, 

and the related uncertainties sufficiently 

boundable) when the geologic system is 

relatively stable or varies in a boundable 

manner. (NAS Report p. 9) However, 

NAS noted that ‘‘[a]fter the geologic 

environment has changed, of course, the 

scientific basis for performance 

assessment is substantially eroded and 

little useful information can be 

developed.’’ (NAS Report p. 72) We 

believe that volcanism of that 

magnitude would result in fundamental 

change of the geologic environment and 

would not represent a reasonable test of 

the disposal system. Therefore, we 

continue to see no basis for requiring 

this type of event be included in the 

performance assessment. 

Some may view our approach using a 

single probability threshold for 

determining which FEPs should be 

considered for inclusion in the 

performance assessments as 

inconsistent with the application of 

different dose standards for the initial 

10,000 years and the period up to 1 

million years. We do not see an 

inconsistency primarily because the 

nature and effects of uncertainty on 

event probability and dose projections 

are dissimilar. The overall uncertainty 

in projecting doses using a model 

simulating the complex interplay of the 

disposal system components over long 

times, each of which has inherent 

uncertainties in their characteristics, 

and the associated difficulty in relying 

on such projections for regulatory 

decisions, should not be confused with 

the uncertainty implied in assigning a 

probability of occurrence to a particular 

FEP, which in many cases derives from 

an examination of the geologic record at 

the site. We have noted the difficulty in 

extrapolating performance to very long 

times, and believe it is appropriate to 

address this difficulty by establishing a 

somewhat higher, but still protective, 

dose limit for the period beyond 10,000 

years. FEP probabilities are assigned 

based on observations that may cover 

long periods of time, such as for 

geologic processes, or from laboratory 

testing and the extrapolation of such 

results to conditions that may exist in 

the distant future, such as for corrosion 

processes. In today’s final rule, the FEP 

probability threshold that must be 

considered in developing performance 

assessments represents a policy 

judgment about how such events should 

be addressed in order to meet the 

regulatory challenge recognized by 

NAS, supported by technical reasoning 

about the nature of the site database for 

identifying and characterizing FEPs. 

Significance 

The second criterion for evaluating 

FEPs, the evaluation of the significance 

of the impacts on performance 

assessment, allows FEPs above the 

probability threshold to be excluded 

from the analyses if they would not 

significantly change the results of 

performance assessments. In other 

words, this evaluation is intended to 

identify those FEPs whose projected 

probability would otherwise make them 

candidates for inclusion in the 

performance assessment, but whose 

effect on repository performance 

(however probable) can be demonstrated 

not to be significant. We are retaining 

the provisions presented in the 

proposed rule related to screening FEPs 

for their effects on the performance 

assessment results, and, for the reasons 

discussed below, are adding an 

additional provision regarding the 

analysis of seismic FEPs in § 197.36(c). 

Today’s final rule continues to focus 

on seismic and igneous events that 

cause direct damage to the engineered 

barrier system (e.g., repository drifts and 

waste packages). Regardless of other 

effects of these events on the disposal 

system, the timing and degree of waste 

package degradation has a significant 

effect on peak dose. The longevity of 

waste packages, when considering 

periods of hundreds of thousands of 

years, is uncertain and dependent on a 

number of factors. Therefore, the aspect 

of primary interest in evaluating seismic 

and igneous FEPs is their potential to 

breach waste packages and make 

radioactive material available for 

transport by infiltrating water (or, in the 

case of volcanic events, for direct 

release into the biosphere). 

We believe that the use of the 

significance criterion of § 197.36(a) 

would assure a reasonable test of 

disposal system performance through 

the period of geologic stability. We 

recognize that setting forth the 

significance screening criterion in 

§ 197.36(a) of our proposal as pertaining 

to the 10,000-year period could be 

construed as creating a situation in 

which important long-term processes 

could be excluded altogether from the 

analysis if they were not significant in 

the earlier period. However, we do not 

believe it is reasonable to interpret the 

significance criterion in this way. We 

have taken specific steps to ensure that 

significant long-term FEPs will be 

considered in the assessments. 

Consistent with NAS, we have 

addressed the long-term effects of 

seismic, igneous, and climatic FEPs. In 

addition, as described below, we have 

directed that the effects of general 

corrosion on the engineered barrier 

system be evaluated. Further, contrary 

to some comments, we explicitly 

required that FEPs included in the 

10,000-year analysis must continue to 

be included for the longer-term (10,000 

years to 1 million years) assessment. 

That is, FEPs included in the initial 

10,000-year assessments will continue 

to operate throughout the period of 

geologic stability. These FEPs are 

already identified as appropriate for 

inclusion, and include fundamental 

physical and geologic processes that 

play roles in the release and transport of 

radionuclides, regardless of the time 

period covered by the assessment. 

As noted above, to further bolster the 

significance screening criterion, in our 

proposal we considered whether it 

might be possible that FEPs eliminated 

from consideration during the first 

10,000 years should be included in the 

longer-term assessment if they would 

have a significant bearing on 

performance at later times, even if they 

could legitimately be dismissed for the 

initial 10,000-year period. We focused 

our attention on FEPs affecting the 

engineered barriers since, as noted 

above, waste package failure is the 

dominant factor in the timing and 

magnitude of the peak dose, and is the 

primary reason for considering time 

frames up to 1 million years. To 

illustrate one consideration, thermal 

conditions in the repository change 

dramatically within the initial 10,000- 

year period, affecting the relative 

importance of some FEPs during and 

after the thermal pulse. However, FEPs 

involved in release and transport of 

radionuclides would generally be the 

same, regardless of when the waste 

package fails. Further, while FEPs 

associated with the natural 

characteristics of the site are active 

today or can be observed in the geologic 


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record, FEPs related to engineered 

barrier longevity involve extrapolation 

of shorter-term testing data. The degree 

to which natural FEPs can contribute to 

the breaching of waste packages is 

dependent to a large extent on the 

condition of those packages over time, 

making FEPs specific to the engineered 

barriers of particular importance. We 

took this approach for two reasons. 

First, we needed to clearly outline the 

reasons why a FEP that could be 

excluded on the basis of significance 

from the performance assessments for 

the initial 10,000-year period might 

potentially need to be re-considered for 

the lengthened compliance period. 

Second, we wanted to further our goal 

of issuing an implementable standard by 

limiting potentially unconstrained 

speculation over the longer compliance 

period. By discussing the considerations 

involved in evaluating FEPs that could 

be previously excluded, we hoped to lay 

out clearly the reasoning that could be 

used to justify inclusion of additional 

FEPs beyond those identified by the 

NAS committee. 

We explicitly addressed general 

corrosion of the waste packages and 

other engineered barriers in our 

proposal because it is likely to be a 

significant degradation process at later 

times. We identified this FEP as being 

significant at times greater than 10,000 

years because we believe it is the 

principal process FEP that could lead to 

‘‘gross breaching’’ of the waste package 

over those extended time frames. 

Processes and events that could lead to 

‘‘gross breaching’’ are of greatest 

significance to long term performance 

because, as noted by the NAS, 

‘‘canisters are likely to fail initially at 

small local openings through which 

water might enter, but out of which the 

diffusion of dissolved wastes will be 

slow until the canister is grossly 

breached.’’ (NAS Report p. 86) It is the 

time of ‘‘gross breaching’’ that 

determines the time of more rapid 

release of dissolved wastes from the 

repository and hence may have a 

significant effect on the time and 

magnitude of the peak dose within 1 

million years. Although the general 

corrosion process is slow, tends to 

decrease with decreasing temperature, 

and may not lead to significant releases 

for the first 10,000 years (depending on 

DOE’s design of the waste package), we 

believe this FEP could be significant 

enough over the long term to require 

inclusion in the assessment of 

performance during the time of geologic 

stability, regardless of the screening 

decision in the first 10,000 years. 

Further, consideration of the 

uncertainties involved in extrapolating 

general corrosion data for the proposed 

waste package materials supports the 

inclusion of this potentially highly 

significant process (‘‘Assumptions, 

Conservatisms, and Uncertainties in 

Yucca Mountain Performance 

Assessments,’’ Docket No. EPA–HQ– 

OAR–2005–0083–0085, section 5.4.1). 

Therefore, we believe that general 

corrosion, in addition to those FEPs 

related to seismicity, igneous activity 

and climate change identified by NAS, 

requires explicit inclusion in the 

assessments during the time of geologic 

stability. 

We did, as one commenter pointed 

out, consider providing NRC more 

latitude to identify FEPs if they would 

significantly affect the peak dose. After 

further consideration, we decided 

against this approach, believing the 

provisions outlined above and the 

specification of general corrosion would 

adequately address this situation, 

provide a reasonable test of disposal 

system performance, and give DOE the 

necessary assurance that the important 

factors have been explicitly identified in 

the rule. As we noted above, we 

identified general corrosion of 

engineered barriers as a FEP potentially 

significant to the peak dose, and 

specified its inclusion because it is 

likely to be a significant degradation 

process at later times. Similarly, 

consistent with the NAS 

recommendations, we have specified 

the inclusion of climate change, 

seismicity, and igneous scenarios. We 

view the requirement to include general 

corrosion, as well as the climate, 

seismic, and igneous scenarios 

identified by NAS, as leading to an 

effective and extensive assessment, 

which can fairly be represented as a 

reasonable test of the disposal system. 

As we discussed in our proposal, the 

search for additional FEPs that might be 

significant at some point beyond 10,000 

years can rapidly become highly 

speculative and limited in benefit. 

Therefore, we continue to believe that 

our approach represents ‘‘informed 

judgment’’ and a reasonable test of 

repository performance over time frames 

as long as 1 million years for the Yucca 

Mountain disposal system. 

We also note that DOE submitted, as 

part of its comments on the proposed 

rule, the results of analyses based on a 

simplified peak dose model (Docket No. 

EPA–HQ–OAR–2005–0083–0352, 

Appendix 1). DOE states that it had 

compiled a database of FEPs, 

independent of compliance period, and 

evaluated them for inclusion in a 

10,000-year analysis. DOE 

‘‘subsequently re-evaluated the FEPs 

over the period beyond 10,000 years’’ 

and concluded that those FEPs excluded 

on the basis of significance within 

10,000 years would also not have 

significant effects on performance 

projections beyond 10,000 years. DOE 

reached its conclusion both for FEPs 

excluded ‘‘on a low consequence basis 

that is not affected by time’’ and for 

‘‘gradual and continuing processes’’ that 

‘‘are time dependent.’’ 

Also as part of its comments, DOE 

submitted an analysis that identified 

three reasons why gradual and/or 

infrequent FEPs excluded on the basis 

of significance within 10,000 years 

would also not have significant effects 

on performance projections beyond 

10,000 years: (1) An excluded FEP was 

determined to be of secondary 

importance to the primary significant 

degradation FEP, which was included in 

the analysis; (2) the inclusion of the FEP 

would tend to lower the peak dose 

during the time of geologic stability 

because it resulted in earlier and more 

diffuse releases (hence the exclusion of 

the FEP would be conservative from a 

peak dose perspective); or (3) the FEP is 

correlated in some way with 

temperature (e.g., in the rate with which 

it operates), so it would be less 

significant at later times due to the 

lower temperature in the repository over 

time. (Docket No. EPA–HQ–OAR–2005– 

0083–0352, Appendix 1, section 6.1 and 

Table 24) DOE considered FEPs of this 

nature associated with both the 

engineered and natural barrier systems. 

DOE concluded, for example, that some 

longer-term processes, such as general 

corrosion, may contribute to waste 

package failure, and disruptive seismic 

events may contribute to rockfall and 

other physical mechanisms leading to 

release. 

We also considered public comments 

on this topic. Most commenters who 

disagreed with our proposal cited the 

limited data available on various 

corrosion mechanisms that could affect 

the waste packages. Many of these 

commenters seem to believe that we 

have excluded all corrosion 

mechanisms except general corrosion. 

This is not the case. We have explicitly 

directed that general corrosion be 

considered because it is likely to be the 

most significant such process at longer 

times; however, other corrosion 

mechanisms (such as localized 

corrosion) are more likely in the early 

period after disposal when temperatures 

inside the repository are high. If DOE 

determines these processes to be 

insignificant within 10,000 years, they 

are not likely to be more significant than 

general corrosion at later times. If they 

are included in the 10,000-year analysis, 


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they must be included in the longerterm assessments. One commenter 

highlighted our discussion of criticality 

as excluding one of the ‘‘most 

worrisome threats to the repository’’ 

over the long term. We cited an NRC 

technical study to support our 

conclusion that such an event is 

unlikely to be significant to the results 

of the assessments. Further, the DOE 

reference cited above concludes that all 

criticality scenarios fall below the 

probability screening threshold. An 

alternative view on the FEPs screening 

process was expressed in a report by the 

Electric Power Research Institute (EPRI): 

‘‘Thus, the current EPA screening limit 

is very conservative compared to the 

[Negligible Incremental Dose] level 

suggested by [NAS]. It is likely that 

there are many FEPs that DOE has 

already included in their analysis using 

the EPA approach that would not have 

been included if the [NAS]- 

recommended approach had been 

followed. Given that many additional 

FEPs are already included, it should be 

unnecessary to include any additional 

FEPs if the regulatory compliance 

period is extended beyond 10,000 

years.’’ (‘‘Yucca Mountain Licensing 

Standard Options for Very Long Time 

Frames,’’ April 2005, pp. 3–5 and 3–6, 

Docket No. EPA–HQ–OAR–2005–0083– 

0087) Taking all of this information into 

account, we continue to believe it is 

reasonable that, with the exception of 

the specific FEPs identified in 197.36(c), 

a FEP determined to be insignificant in 

the first 10,000 years may continue to be 

excluded in the post-10,000-year 

analyses. 

As we noted above, we are modifying 

the proposed rule regarding the 

provisions related to seismic events in 

§ 197.36(c). We noted in our proposal 

the NAS statement that ‘‘[w]ith respect 

to the effects of seismicity on the 

hydrologic regime, the possibility of 

adverse effects due to displacements 

along existing fractures cannot be 

overlooked’’ but that ‘‘such 

displacements have an equal probability 

of favorably changing the hydrologic 

regime.’’ (NAS Report p. 93). We argued 

that these effects would likely be 

minimal given the many small-scale 

changes that would be possible in the 

connectivity of the fracture networks, 

and that these effects would likely be 

small compared to the effects of climate 

change on the hydrologic behavior of 

the disposal system. We did not mean 

to imply that the seismic and climate 

events would involve the same 

hydrologic characteristics and processes 

or produce the same effects on the 

ground-water flow regime, but that the 

effects of one were likely to outweigh 

the effects of the other. While we still 

believe that is likely, we have 

concluded, after further consideration, 

that the issue of hydrologic effects 

resulting from seismic events needs to 

be examined in sufficient detail to 

address the point made by NAS. We 

believe the effects of fault displacement 

on the hydrologic regime will be 

adequately addressed by the variation in 

parameters such as hydraulic 

conductivity (i.e., evaluating reasonable 

variation in ground-water flow 

parameter values, whether seismicallyinduced or not, will illustrate the range 

of effects that might result from 

seismicity). However, NAS also 

identified another seismic effect on 

hydrology, namely the potential for 

transient rise in the ground-water table. 

In this instance, NAS did not simply 

state that such potential could be 

bounded, but noted site-specific studies 

suggesting ‘‘a probable maximum 

transient rise on the order of 20 m or 

less.’’ (NAS Report p. 94) Therefore, we 

now require that the effects of a rise in 

the ground-water table as a result of 

seismicity be considered. We are not 

specifying the extent of the rise to be 

considered, but leave that conclusion to 

be determined by NRC. NRC may 

choose to estimate the magnitude of 

ground-water table rise itself, or require 

DOE to include such estimates in its 

license application. In this case, 

however, we are also allowing NRC to 

make a judgment as to whether such a 

rise in ground water would be 

significant to the results of the 

performance assessment. If NRC 

determines that such a reasonably 

bounded scenario would not be 

significant, DOE would not be required 

to evaluate its effects. 

We believe deferring to NRC on this 

point is the appropriate approach. The 

above quote from page 93 of the NAS 

Report makes it clear that changes to the 

hydrologic regime from seismic events 

would be equally likely to enhance or 

reduce transport of radionuclides. 

However, it would seem unlikely for 

changes to occur that would all combine 

to enhance transport to the saturated 

zone and then through the controlled 

area, such that concentrations of 

radionuclides at the RMEI location 

would be significantly increased. It 

seems more likely that localized 

changes would occur, which in sum 

would not significantly increase overall 

transport of radionuclides. Further, as 

noted above, we believe these 

seismically-induced changes are likely 

to be approximated by the normal 

variation in flow parameters. Changes in 

the hydrologic system from climate 

change (e.g., increases in infiltration) are 

expected to be quantitatively more 

significant than such changes resulting 

from seismic activity. We believe NRC 

is better positioned to make judgments 

regarding the significance and extent of 

such changes. We note that a dozen 

years of site characterization, scientific 

study, and performance assessments 

have been conducted since the NAS 

Report in 1995. NRC has conducted its 

own analyses as well as participated in 

ongoing technical exchanges with DOE 

over this period. We view deferring to 

NRC’s judgment in this case as 

comparable to the approach we have 

taken with climate change. In that 

instance, we outlined the primary issues 

and overall approach, but specified that 

NRC would establish the details 

required to implement our standard. 

Finally, we are retaining the provision 

related to climate change as it was 

proposed. We believe this is a 

reasonable approach, which allows NRC 

to characterize climate change beyond 

10,000 years using constant conditions. 

This approach has the advantage of 

avoiding speculation regarding the 

timing and magnitude of climatic 

cycles, while addressing the important 

aspects of climate change. We received 

some comments that appear to have 

misinterpreted our proposal. Some 

comments suggested that our citation of 

the NAS statement to the effect that 

‘‘climate changes on the time scale of 

hundreds of years would probably have 

little if any effect on repository 

performance’’ (NAS Report p. 92) as 

implying that we are ‘‘ignoring longerterm changes’’ such as ‘‘glacial periods 

covering thousands of years.’’ This 

represents a fundamental 

misunderstanding of our proposal, 

which would allow the future climate to 

be represented by what is essentially a 

glacial transition period lasting 990,000 

years, but in any event placed no limits 

on the duration of periods of increased 

precipitation. Similarly, some 

commenters expressed the view that we 

‘‘required’’ the future climate to be 

represented by constant conditions, or 

that we were suggesting that a single 

climate be used in all realizations. On 

the contrary, we cited the NAS 

conclusion that ‘‘a doubling of the 

effective wetness’’ might be significant 

as one justification for stating that it 

would be reasonable to represent farfuture climate by constant conditions. 

Today’s final rule, consistent with our 

proposal, leaves it to NRC to determine 

the parameter values that would define 

the future climate, including influential 

parameters other than precipitation, 


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Federal Register / Vol. 73, No. 200 / Wednesday, October 15, 2008 / Rules and Regulations 61285 

such as temperature. Our specification 

of the outcome of ‘‘increased water flow 

through the repository’’ provides NRC 

with the flexibility to specify basic 

parameters, such as precipitation and 

temperature, that must be assumed by 

DOE, or to derive estimates of water 

flow directly. This is consistent with 

our current belief that the dominant 

mechanisms and flow paths for water to 

move from the surface through the 

repository and beyond should be 

determined by NRC rather than EPA. 

Further, we anticipated that ‘‘constant 

climate conditions’’ would be used as 

another parameter in the probabilistic 

assessment. That is, each realization 

would select its constant conditions 

from among a distribution of such 

conditions developed to reflect 

estimates of different future climate 

states. This is exactly the approach that 

NRC has taken in its proposal, i.e., that 

a range of deep percolation values be 

used (70 FR 53313–53320, September 8, 

2005). 

Some commenters disagreed with the 

approach of specifying constant climate 

conditions leading to a higher rate of 

water flow through the repository, 

stating that the ‘‘non-linear’’ nature of 

the disposal system would be more 

sensitive to a dynamic, cyclical 

representation of climate. This is not 

necessarily true, as the effects on the 

disposal system would be highly 

affected by the timing of waste package 

failures (e.g., whether they fail during a 

wetter or drier cycle). Some comments 

cite recent climate research suggesting 

that anthropogenic climate influences 

will postpone the next glacial cycle by 

roughly 500,000 years, or that today’s 

climate at Yucca Mountain will actually 

be more representative of future 

climates than would the wetter 

conditions known to have occurred in 

the past. We believe that our final rule’s 

approach to climate change provides a 

reasonable approach to address a point 

of fundamental uncertainty regarding 

long-term climate change and its role in 

the performance assessments, an 

uncertainty that cannot be removed by 

additional research into past climate 

cycles or modeling of present or future 

climate behavior. We refer to NAS on 

this point: ‘‘Although the typical nature 

of past climate changes is well known, 

it is obviously impossible to predict in 

detail either the nature or the timing of 

future climate change.’’ (NAS Report p. 

77, emphasis added) Although 

continuing research will provide better 

understanding of past climate 

fluctuations, we believe that predicting 

with high confidence the timing and 

extent of climate fluctuations into the 

far future will remain an unrealistic 

goal. We believe that the understanding 

of past climate fluctuations and their 

potential effects on the Yucca Mountain 

hydrologic system is valuable 

information and should be applied to 

define the climate-related parameter 

values. As noted above, NRC has used 

such information to propose climaterelated parameter values, which DOE 

will use to project the behavior of 

hydrologic processes at the site. We 

believe that this approach to treatment 

of a ‘‘residual, unquantifiable 

uncertainty’’ by the application of 

‘‘informed judgment’’ is consistent with 

NAS guidance. (NAS Report p. 80) 

IV. Statutory and Executive Order 

Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review 

Under Executive Order 12866 (58 FR 

51735, October 4, 1993), this action is a 

‘‘significant regulatory action’’ because 

it raises novel legal or policy issues 

arising out of the specific legal mandate 

of section 801 of the Energy Policy Act 

of 1992. Accordingly, EPA submitted 

this action to the Office of Management 

and Budget for review under Executive 

Order 12866 and any changes made in 

response to OMB recommendations 

have been documented in the docket for 

this action. 

B. Paperwork Reduction Act 

This action does not impose an 

information collection burden under the 

provisions of the Paperwork Reduction 

Act, 44 U.S.C. 3501 et seq. Burden is 

defined at 5 CFR 1320.3(b). We have 

determined that this rule contains no 

information collection requirements 

within the scope of the Paperwork 

Reduction Act. This final rule 

establishes requirements that apply only 

to DOE. 

C. Regulatory Flexibility Act 

The Regulatory Flexibility Act (RFA) 

generally requires an agency to prepare 

a regulatory flexibility analysis of any 

rule subject to notice and comment 

rulemaking requirements under the 

Administrative Procedure Act or any 

other statute unless the agency certifies 

that the rule will not have a significant 

economic impact on a substantial 

number of small entities. Small entities 

include small businesses, small 

organizations, and small governmental 

jurisdictions. 

For purposes of assessing the impacts 

of today’s rule on small entities, small 

entity is defined as: (1) A small business 

as defined by the Small Business 

Administration’s (SBA) regulations at 13 

CFR 121.201; (2) a small governmental 

jurisdiction that is a government of a 

city, county, town, school district or 

special district with a population of less 

than 50,000; and (3) a small 

organization that is any not-for-profit 

enterprise which is independently 

owned and operated and is not 

dominant in its field. 

After considering the economic 

impacts of today’s final rule on small 

entities, I certify that this action will not 

have a significant economic impact 

upon a substantial number of small 

entities. This final rule will not impose 

any requirements on small entities. This 

final rule establishes requirements that 

apply only to DOE. 

D. Unfunded Mandates Reform Act 

Title II of the Unfunded Mandates 

Reform Act of 1995 (UMRA), Public 

Law 104–4, establishes requirements for 

Federal agencies to assess the effects of 

their regulatory actions on State, local, 

and tribal governments and the private 

sector. Under section 202 of the UMRA, 

EPA generally must prepare a written 

statement, including a cost-benefit 

analysis, for proposed and final rules 

with ‘‘Federal mandates’’ that may 

result in expenditures to State, local, 

and tribal governments, in the aggregate, 

or to the private sector, of $100 million 

or more in any one year. Before 

promulgating an EPA rule for which a 

written statement is needed, section 205 

of the UMRA generally requires EPA to 

identify and consider a reasonable 

number of regulatory alternatives and 

adopt the least costly, most costeffective or least burdensome alternative 

that achieves the objectives of the rule. 

The provisions of section 205 do not 

apply when they are inconsistent with 

applicable law. Moreover, section 205 

allows EPA to adopt an alternative other 

than the least costly, most cost-effective 

or least burdensome alternative if the 

Administrator publishes with the final 

rule an explanation why that alternative 

was not adopted. Before EPA establishes 

any regulatory requirements that may 

significantly or uniquely affect small 

governments, including tribal 

governments, it must have developed 

under section 203 of the UMRA a small 

government agency plan. The plan must 

provide for notifying potentially 

affected small governments, enabling 

officials of affected small governments 

to have meaningful and timely input in 

the development of EPA regulatory 

proposals with significant Federal 

intergovernmental mandates, and 

informing, educating, and advising 

small governments on compliance with 

the regulatory requirements. 


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Today’s final rule contains no Federal 

mandates (under the regulatory 

provisions of Title II of UMRA) for 

State, local, or tribal governments or the 

private sector. This final rule 

implements requirements specifically 

set forth by the Congress in section 801 

of the EnPA and establishes radiological 

protection standards applicable solely 

and exclusively to the Department of 

Energy’s potential storage and disposal 

facility at Yucca Mountain. The rule 

imposes no enforceable duty on any 

State, local or tribal governments or the 

private sector. Thus, today’s rule is not 

subject to the requirements of sections 

202 and 205 of UMRA. 

EPA has determined that this rule 

contains no regulatory requirements that 

might significantly or uniquely affect 

small governments. This final rule 

implements requirements specifically 

set forth by the Congress in section 801 

of the EnPA and establishes radiological 

protection standards applicable solely 

and exclusively to the Department of 

Energy’s potential storage and disposal 

facility at Yucca Mountain. The rule 

imposes no enforceable duty on any 

small governments. Thus, today’s rule is 

not subject to the requirements of 

section 203 of UMRA. 

E. Executive Order 13132: Federalism 

Executive Order 13132, entitled 

‘‘Federalism’’ (64 FR 43255, August 10, 

1999), requires EPA to develop an 

accountable process to ensure 

‘‘meaningful and timely input by State 

and local officials in the development of 

regulatory policies that have federalism 

implications.’’ ‘‘Policies that have 

federalism implications’’ is defined in 

the Executive Order to include 

regulations that have ‘‘substantial direct 

effects on the States, on the relationship 

between the national government and 

the States, or on the distribution of 

power and responsibilities among the 

various levels of government.’’ 

This final rule does not have 

federalism implications. It will not have 

substantial direct effects on the States, 

on the relationship between the national 

government and the States, or on the 

distribution of power and 

responsibilities among the various 

levels of government, as specified in 

Executive Order 13132. This final rule 

implements requirements specifically 

set forth by the Congress in section 801 

of the EnPA and establishes radiological 

protection standards applicable solely 

and exclusively to the Department of 

Energy’s potential storage and disposal 

facility at Yucca Mountain. Thus, 

Executive Order 13132 does not apply 

to this rule. In the spirit of Executive 

Order 13132, and consistent with EPA 

policy to promote communications 

between EPA and State and local 

governments, EPA specifically solicited 

comment on the proposed rule from 

State and local officials. 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

Executive Order 13175, entitled 

‘‘Consultation and Coordination with 

Indian Tribal Governments’’ (65 FR 

67249, November 9, 2000), requires EPA 

to develop an accountable process to 

ensure ‘‘meaningful and timely input by 

tribal officials in the development of 

regulatory policies that have tribal 

implications.’’ This final rule does not 

have tribal implications, as specified in 

Executive Order 13175. This final rule 

will regulate only DOE on land owned 

by the Federal government. The rule 

does not have substantial direct effects 

on one or more Indian tribes, on the 

relationship between the Federal 

Government and Indian tribes, or on the 

distribution of power and 

responsibilities between the Federal 

Government and Indian tribes. Thus, 

Executive Order 13175 does not apply 

to this rule. 

Although Executive Order 13175 does 

not apply to this rule, EPA specifically 

solicited additional comment on this 

proposed rule from tribal officials and 

consulted with tribal officials in 

developing this rule. EPA directly 

contacted more than 20 tribal 

governments and conducted three 

conference calls with members of tribal 

governments. In recognition of the 

importance of government-togovernment consultation with tribes and 

the significance of tribal governments as 

sovereign nations, EPA extended the 

public comment period for tribal 

governments to December 31, 2005. 

Comments related to tribal issues, and 

our responses to them, may be found in 

Section 13 of the Response to Comments 

document associated with this final rule 

(docket ref). 

G. Executive Order 13045: Protection of 

Children From Environmental Health & 

Safety Risks 

This final rule is not subject to 

Executive Order 13045 because it is not 

economically significant as defined in 

Executive Order 12866, and because the 

Agency does not have reason to believe 

the environmental health risks or safety 

risks addressed by this action present a 

disproportionate risk to children. 

H. Executive Order 13211: Actions That 

Significantly Affect Energy Supply, 

Distribution, or Use 

This action is not a ‘‘significant 

energy action’’ as defined in Executive 

Order 13211 (66 FR 28355 (May 22, 

2001)), because it is not likely to have 

a significant adverse effect on the 

supply, distribution, or use of energy. 

This final rule will apply only to DOE. 

Construction, operation, and closure of 

the repository at Yucca Mountain would 

fulfill the Federal government’s 

commitment to manage the final 

disposition of spent nuclear fuel from 

commercial power reactors. However, 

there is no direct link between operation 

of the repository and an increased use 

of nuclear power. Other economic, 

technical, and policy factors will 

influence the extent to which nuclear 

energy is utilized. 

I. National Technology Transfer and 

Advancement Act 

Section 12(d) of the National 

Technology Transfer and Advancement 

Act of 1995 (‘‘NTTAA’’), Public Law No. 

104–113, 12(d) (15 U.S.C. 272 note) 

directs EPA to use voluntary consensus 

standards in its regulatory activities 

unless to do so would be inconsistent 

with applicable law or otherwise 

impractical. Voluntary consensus 

standards are technical standards (e.g., 

materials specifications, test methods, 

sampling procedures, and business 

practices) that are developed or adopted 

by voluntary consensus standards 

bodies. NTTAA directs EPA to provide 

Congress, through OMB, explanations 

when the Agency decides not to use 

available and applicable voluntary 

consensus standards. 

This rulemaking involves technical 

standards. Therefore, the Agency 

conducted a search to identify 

potentially applicable voluntary 

consensus standards. In our original 

1999 proposal (64 FR 46976), we 

requested public comment on 

potentially applicable voluntary 

consensus standards that would be 

appropriate for inclusion in the Yucca 

Mountain rule. However, we identified 

no such standards, and none were 

brought to our attention in comments. 

Therefore, the standards promulgated in 

2001 and today’s final revisions are sitespecific and developed solely for 

application to the Yucca Mountain 

disposal facility. 


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J. Executive Order 12898: Federal 

Actions To Address Environmental 

Justice in Minority Populations and 

Low-income Populations 

Executive Order (EO) 12898 (59 FR 

7629 (Feb. 16, 1994)) establishes federal 

executive policy on environmental 

justice. Its main provision directs 

federal agencies, to the greatest extent 

practicable and permitted by law, to 

make environmental justice part of their 

mission by identifying and addressing, 

as appropriate, disproportionately high 

and adverse human health or 

environmental effects of their programs, 

policies, and activities on minority 

populations and low-income 

populations in the United States. 

EPA lacks the discretionary authority 

to address environmental justice in this 

final rulemaking. This final rule 

implements requirements specifically 

set forth by the Congress in section 801 

of the EnPA and establishes radiological 

protection standards applicable solely 

and exclusively to the Department of 

Energy’s potential storage and disposal 

facility at Yucca Mountain. Section 

801(a)(1) of the EnPA directs EPA to 

‘‘promulgate, by rule, public health and 

safety standards’’ that ‘‘ prescribe the 

maximum annual effective dose 

equivalent to individual members of the 

public’’ from releases of radioactive 

material from the Yucca Mountain 

repository. This final rule fulfills this 

statutory direction. 

K. Congressional Review Act 

The Congressional Review Act, 5 

U.S.C. 801 et seq., as added by the Small 

Business Regulatory Enforcement 

Fairness Act of 1996, generally provides 

that before a rule may take effect, the 

agency promulgating the rule must 

submit a rule report, which includes a 

copy of the rule, to each House of the 

Congress and to the Comptroller General 

of the United States. Section 804 

exempts from section 801 the following 

types of rules: (1) Rules of particular 

applicability; (2) rules relating to agency 

management or personnel; and (3) rules 

of agency organization, procedure, or 

practice that do not substantially affect 

the rights or obligations of non-agency 

parties. 5 U.S.C. 804(3). EPA is not 

required to submit a rule report 

regarding today’s action under section 

801 because this is a rule of particular 

applicability. This final rule will apply 

only to DOE, and is issued by EPA in 

response to direction from Congress in 

the EnPA. 

List of Subjects in 40 CFR Part 197 

Environmental protection, Nuclear 

energy, Radiation protection, 

Radionuclides, Uranium, Waste 

treatment and disposal, Spent nuclear 

fuel, High-level radioactive waste. 

Dated: September 30, 2008. 

Stephen L. Johnson, 

Administrator. 

■ 40 CFR part 197 is amended as 

follows: 

PART 197—PUBLIC HEALTH AND 

ENVIRONMENTAL RADIATION 

PROTECTION STANDARDS FOR 

YUCCA MOUNTAIN, NEVADA 

■ 1. The authority citation for part 197 

continues to read as follows: 

Authority: Sec. 801, Pub. L. 102–486, 106 

Stat. 2921, 42 U.S.C. 10141n. 

Subpart A—Public Health and 

Environmental Standards for Storage 

■ 2. Section 197.2 is amended by 

revising the definition of ‘‘Effective dose 

equivalent’’ to read as follows: 

§ 197.2 What definitions apply in Subpart 

A? 

* * * * * 

Effective dose equivalent means the 

sum of the products of the dose 

equivalent received by specified tissues 

following an exposure of, or an intake 

of radionuclides into, specified tissues 

of the body, multiplied by appropriate 

weighting factors. Annual committed 

effective dose equivalents shall be 

calculated using weighting factors in 

appendix A of this part, unless 

otherwise directed by NRC in 

accordance with the introduction to 

appendix A of this part. 

* * * * * 

Subpart B—Public Health and 

Environmental Standards for Disposal 

■ 3. Section 197.12 is amended by 

revising paragraph (1) of the definition 

of ‘‘Performance assessment’’ and the 

definition of ‘‘Period of geologic 

stability’’ to read as follows: 

§ 197.12 What definitions apply in Subpart 

B? 

* * * * * 

Performance assessment means an 

analysis that: 

(1) Identifies the features, events, 

processes, (except human intrusion), 

and sequences of events and processes 

(except human intrusion) that might 

affect the Yucca Mountain disposal 

system and their probabilities of 

occurring; 

* * * * * 

Period of geologic stability means the 

time during which the variability of 

geologic characteristics and their future 

behavior in and around the Yucca 

Mountain site can be bounded, that is, 

they can be projected within a 

reasonable range of possibilities. This 

period is defined to end at 1 million 

years after disposal. 

* * * * * 

■ 4. Section 197.13 is revised to read as 

follows: 

§ 197.13 How is Subpart B implemented? 

The NRC implements this subpart B. 

The DOE must demonstrate to NRC that 

there is a reasonable expectation of 

compliance with this subpart before 

NRC may issue a license. 

(a) The NRC will determine 

compliance, based upon the arithmetic 

mean of the projected doses from DOE’s 

performance assessments for the period 

within 1 million years after disposal, 

with: 

(1) Sections 197.20(a)(1) and 

197.20(a)(2) of this subpart; and 

(2) Sections 197.25(b)(1), 197.25(b)(2), 

and 197.30 of this subpart, if 

performance assessment is used to 

demonstrate compliance with either or 

both of these sections. 

(b) [Reserved] 

■ 5. Section 197.15 is revised to read as 

follows: 

§ 197.15 How must DOE take into account 

the changes that will occur during the 

period of geologic stability? 

The DOE should not project changes 

in society, the biosphere (other than 

climate), human biology, or increases or 

decreases of human knowledge or 

technology. In all analyses done to 

demonstrate compliance with this part, 

DOE must assume that all of those 

factors remain constant as they are at 

the time of license application 

submission to NRC. However, DOE must 

vary factors related to the geology, 

hydrology, and climate based upon 

cautious, but reasonable assumptions of 

the changes in these factors that could 

affect the Yucca Mountain disposal 

system during the period of geologic 

stability, consistent with the 

requirements for performance 

assessments specified at § 197.36. 

■ 6. Section 197.20 is revised to read as 

follows: 

§ 197.20 What standard must DOE meet? 

(a) The DOE must demonstrate, using 

performance assessment, that there is a 

reasonable expectation that the 

reasonably maximally exposed 

individual receives no more than the 

following annual committed effective 

dose equivalent from releases from the 

undisturbed Yucca Mountain disposal 

system: 


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61288 Federal Register / Vol. 73, No. 200 / Wednesday, October 15, 2008 / Rules and Regulations 

(1) 150 microsieverts (15 millirems) 

for 10,000 years following disposal; and 

(2) 1 millisievert (100 millirems) after 

10,000 years, but within the period of 

geologic stability. 

(b) The DOE’s performance 

assessment must include all potential 

pathways of radionuclide transport and 

exposure. 

■ 7. Section 197.25 is revised to read as 

follows: 

§ 197.25 What standard must DOE meet? 

(a) The DOE must determine the 

earliest time after disposal that the 

waste package would degrade 

sufficiently that a human intrusion (see 

§ 197.26) could occur without 

recognition by the drillers. 

(b) The DOE must demonstrate that 

there is a reasonable expectation that 

the reasonably maximally exposed 

individual will receive an annual 

committed effective dose equivalent, as 

a result of the human intrusion, of no 

more than: 

(1) 150 microsieverts (15 millirems) 

for 10,000 years following disposal; and 

(2) 1 millisievert (100 millirems) after 

10,000 years, but within the period of 

geologic stability. 

(c) The analysis must include all 

potential environmental pathways of 

radionuclide transport and exposure. 

■ 8. Section 197.35 is removed and 

reserved. 

§ 197.35 [Removed and Reserved] 

■ 9. Section 197.36 is revised to read as 

follows: 

§ 197.36 Are there limits on what DOE 

must consider in the performance 

assessments? 

(a) Yes, there are limits on what DOE 

must consider in the performance 

assessments. 

(1) The DOE’s performance 

assessments conducted to show 

compliance with §§ 197.20(a)(1), 

197.25(b)(1), and 197.30 shall not 

include consideration of very unlikely 

features, events, or processes, i.e., those 

that are estimated to have less than one 

chance in 100,000,000 per year of 

occurring. Features, events, and 

processes with a higher chance of 

occurring shall be considered for use in 

performance assessments conducted to 

show compliance with §§ 197.20(a)(1), 

197.25(b)(1), and 197.30, except as 

stipulated in paragraph (b) of this 

section. In addition, unless otherwise 

specified in these standards or NRC 

regulations, DOE’s performance 

assessments need not evaluate the 

impacts resulting from features, events, 

and processes or sequences of events 

and processes with a higher chance of 

occurring if the results of the 

performance assessments would not be 

changed significantly in the initial 

10,000-year period after disposal. 

(2) The same features, events, and 

processes identified in paragraph (a)(1) 

of this section shall be used in 

performance assessments conducted to 

show compliance with §§ 197.20(a)(2) 

and 197.25(b)(2), with additional 

considerations as stipulated in 

paragraph (c) of this section. 

(b) For performance assessments 

conducted to show compliance with 

§§ 197.25(b) and 197.30, DOE’s 

performance assessments shall exclude 

unlikely features, events, or processes, 

or sequences of events and processes. 

The DOE should use the specific 

probability of the unlikely features, 

events, and processes as specified by 

NRC. 

(c) For performance assessments 

conducted to show compliance with 

§§ 197.20(a)(2) and 197.25(b)(2), DOE’s 

performance assessments shall project 

the continued effects of the features, 

events, and processes included in 

paragraph (a) of this section beyond the 

10,000-year post-disposal period 

through the period of geologic stability. 

The DOE must evaluate all of the 

features, events, or processes included 

in paragraph (a) of this section, and also: 

(1) The DOE must assess the effects of 

seismic and igneous scenarios, subject 

to the probability limits in paragraph (a) 

of this section for very unlikely features, 

events, and processes. Performance 

assessments conducted to show 

compliance with § 197.25(b)(2) are also 

subject to the probability limits for 

unlikely features, events, and processes 

as specified by NRC. 

(i) The seismic analysis may be 

limited to the effects caused by damage 

to the drifts in the repository, failure of 

the waste packages, and changes in the 

elevation of the water table under Yucca 

Mountain. NRC may determine the 

magnitude of the water table rise and its 

significance on the results of the 

performance assessment, or NRC may 

require DOE to demonstrate the 

magnitude of the water table rise and its 

significance in the license application. If 

NRC determines that the increased 

elevation of the water table does not 

significantly affect the results of the 

performance assessment, NRC may 

choose to not require its consideration 

in the performance assessment. 

(ii) The igneous analysis may be 

limited to the effects of a volcanic event 

directly intersecting the repository. The 

igneous event may be limited to that 

causing damage to the waste packages 

directly, causing releases of 

radionuclides to the biosphere, 

atmosphere, or ground water. 

(2) The DOE must assess the effects of 

climate change. The climate change 

analysis may be limited to the effects of 

increased water flow through the 

repository as a result of climate change, 

and the resulting transport and release 

of radionuclides to the accessible 

environment. The nature and degree of 

climate change may be represented by 

constant climate conditions. The 

analysis may commence at 10,000 years 

after disposal and shall extend through 

the period of geologic stability. The NRC 

shall specify in regulation the values to 

be used to represent climate change, 

such as temperature, precipitation, or 

infiltration rate of water. 

(3) The DOE must assess the effects of 

general corrosion on engineered 

barriers. The DOE may use a constant 

representative corrosion rate throughout 

the period of geologic stability or a 

distribution of corrosion rates correlated 

to other repository parameters. 

■ 10. Appendix A to part 197 is added 

to read as follows: 

Appendix A to Part 197—Calculation of 

Annual Committed Effective Dose 

Equivalent 

Unless otherwise directed by NRC, DOE 

shall use the radiation weighting factors and 

tissue weighting factors in this Appendix to 

calculate the internal component of the 

annual committed effective dose equivalent 

for compliance with §§ 197.20 and 197.25 of 

this part. NRC may allow DOE to use updated 

factors issued after the effective date of this 

regulation. Any such factors shall have been 

issued by consensus scientific organizations 

and incorporated by EPA into Federal 

radiation guidance in order to be considered 

generally accepted and eligible for this use. 

Further, they must be compatible with the 

effective dose equivalent dose calculation 

methodology established in ICRP 26 and 30, 

and continued in ICRP 60 and 72, and 

incorporated in this appendix. 

I. Equivalent Dose 

The calculation of the committed effective 

dose equivalent (CEDE) begins with the 

determination of the equivalent dose, HT, to 

a tissue or organ, T, listed in Table A.2 below 

by using the equation: 

H Dw T

R

= ⋅ ∑ T,R R

where DT,R is the absorbed dose in rads (one 

gray, an SI unit, equals 100 rads) averaged 

over the tissue or organ, T, due to radiation 

type, R, and wR is the radiation weighting 

factor which is given in Table A.1 below. The 

unit of equivalent dose is the rem (sievert, in 

SI units). 


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TABLE A.1—RADIATION WEIGHTING

FACTORS, WR1

Radiation type and energy 

range 2 wR value 

Photons, all energies ................ 1 

Electrons and muons, all energies ........................................ 1 

Neutrons, energy 

< 10 keV ............................ 5 

10 keV to 100 keV ............ 10 

> 100 keV to 2 MeV .......... 20 

>2 MeV to 20 MeV ............ 10 

> 20 MeV ........................... 5 

Protons, other than recoil protons, > 2 MeV ....................... 5 

Alpha particles, fission fragments, heavy nuclei .............. 20 

1All values relate to the radiation incident 

on the body or, for internal sources, emitted 

from the source. 2See paragraph A14 in ICRP Publication 60 

for the choice of values for other radiation 

types and energies not in the table. 

II. Effective Dose Equivalent 

The next step is the calculation of the 

effective dose equivalent, E. The probability 

of occurrence of a stochastic effect in a tissue 

or organ is assumed to be proportional to the 

equivalent dose in the tissue or organ. The 

constant of proportionality differs for the 

various tissues of the body, but in assessing 

health detriment the total risk is required. 

This is taken into account using the tissue 

weighting factors, wT in Table A.2, which 

represent the proportion of the stochastic risk 

resulting from irradiation of the tissue or 

organ to the total risk when the whole body 

is irradiated uniformly and HT is the 

equivalent dose in the tissue or organ, T, in 

the equation: 

E wH = ⋅ ∑ T T .

TABLE A.2—TISSUE WEIGHTING

FACTORS, WT

Tissue or organ wT value 

Gonads ..................................... 0.20 

Bone marrow (red) ................... 0.12 

Colon ........................................ 0.12 

Lung .......................................... 0.12 

Stomach .................................... 0.12 

Bladder ..................................... 0.05 

Breast ....................................... 0.05 

Liver .......................................... 0.05 

Esophagus ................................ 0.05 

Thyroid ...................................... 0.05 

Skin ........................................... 0.01 

Bone surface ............................ 0.01 

Remainder ................................ a b 0.05 

a Remainder is composed of the following 

tissues: adrenals, brain, extrathoracic airways, 

small intestine, kidneys, muscle, pancreas, 

spleen, thymus, and uterus. bThe value 0.05 is applied to the massweighted average dose to the Remainder tissues group, except when the following ‘‘splitting rule’’ applies: If a tissue of Remainder receives a dose in excess of that received by 

any of the 12 tissues for which weighting factors are specified, a weighting factor of 0.025 

(half of Remainder) is applied to that tissue or 

organ and 0.025 to the mass-averaged committed equivalent dose equivalent in the rest of 

the Remainder tissues. 

III. Annual Committed Tissue or Organ 

Equivalent Dose 

For internal irradiation from incorporated 

radionuclides, the total absorbed dose will be 

spread out in time, being gradually delivered 

as the radionuclide decays. The time 

distribution of the absorbed dose rate will 

vary with the radionuclide, its form, the 

mode of intake and the tissue within which 

it is incorporated. To take account of this 

distribution the quantity committed 

equivalent dose, HT(t) where t is the 

integration time in years following an intake 

over any particular year, is used and is the 

integral over time of the equivalent dose rate 

in a particular tissue or organ that will be 

received by an individual following an intake 

of radioactive material into the body: 

H t dt T

t

( ) () τ

τ

=

+

∫ HT

t0

0

for a single intake of activity at time t0 where 

HT(t) is the relevant equivalent-dose rate in 

a tissue or organ at time t. For the purposes 

of this rule, the previously mentioned single 

intake may be considered to be an annual 

intake. 

IV. Internal Component of the Annual 

Committed Effective Dose Equivalent 

If the annual committed equivalent doses 

to the individual tissues or organs resulting 

from an annual intake are multiplied by the 

appropriate weighting factors, wT, from table 

A.2, and then summed, the result will be the 

internal component of the annual committed 

effective dose equivalent E(t): 

E wH T

T

T ( ) ( ). τ τ = ⋅ ∑

[FR Doc. E8–23754 Filed 10–14–08; 8:45 am] 

BILLING CODE 6560–50–P 


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