RULEMAKING ISSUE 

COMMISSION MEETING 

September 28, 2009 SECY-09-0140

FOR: The Commissioners 

FROM: R. W. Borchardt 

 Executive Director for Operations 

SUBJECT: RULEMAKING RELATED TO DECOUPLING AN ASSUMED 

LOSS OF OFFSITE POWER FROM A LOSS-OF-COOLANT 

ACCIDENT, 10 CFR PART 50, APPENDIX A, GENERAL DESIGN 

CRITERION 35 (RIN 3150-AH43) 

PURPOSE: 

To seek a Commission decision on the staff’s recommended option to discontinue the 

rulemaking effort to decouple the analysis assumption that a loss of offsite power (LOOP) 

occurs coincident with a large-break loss-of-coolant accident (LOCA). 

SUMMARY: 

The Nuclear Regulatory Commission (NRC) staff recommends that the Commission discontinue 

the LOOP/LOCA rulemaking. The staff’s recommendation is based on the lack of a fully 

developed regulatory basis and expenditures of staff time to develop one would not be expected 

to result in a quantifiable safety improvement. This recommendation is, to some extent, driven 

by a decision made by the Boiling Water Reactors Owners Group (BWROG) to withdraw a 

BWROG topical report that the NRC staff was using to develop the regulatory basis for a 

LOOP/LOCA rule. 

BACKGROUND: 

On March 31, 2003, in the staff requirements memorandum (SRM) responding to 

SECY-02-0057, “Update to SECY-01-0133, ‘Fourth Status Report on Study of Risk-Informed 

Changes to the Technical Requirements of 10 CFR Part 50 (Option 3) and Recommendations 

on Risk-Informed Changes to 10 CFR 50.46 (ECCS Acceptance Criteria),’” the Commission 

CONTACT: Barry W. Miller, NRR/DPR 

 301-415-4117 
The Commissioners 2 

directed the staff to proceed with rulemaking to risk-inform the emergency core cooling system 

(ECCS) functional reliability requirements in General Design Criterion (GDC) 35, “Emergency 

Core Cooling,” of Appendix A, “General Design Criteria for Nuclear Power Plants,” to Title 10 of 

the Code of Federal Regulations (10 CFR) Part 50, “Domestic Licensing of Production and 

Utilization Facilities,” and thus relax the current analysis requirements for considering a LOOP 

to occur coincident with a large-break LOCA. 

In SECY-04-0037, “Issues Related to Proposed Rulemaking to Risk-Inform Requirements 

Related to Large Break Loss-Of-Coolant Accident (LOCA) Break Size and Plans for Rulemaking 

on LOCA with Coincident Loss-of-Offsite Power,” dated March 3, 2004, the staff proposed to 

review a topical report and pilot exemption request that would be submitted by the BWROG to 

relax the assumed coincident LOOP required for LOCA analysis. If found acceptable and 

approved by the NRC staff, this BWROG topical report was intended to substantially serve as 

the technical portion of the regulatory basis for the LOOP/LOCA rulemaking. The Commission 

approved this proposal in its subsequent SRM dated July 1, 2004. 

In December 2007 (COMSECY-07-0041), the staff informed the Commission that if either the 

BWROG topical report NEDO-33148, “Separation of Loss of Offsite Power from Large Break 

LOCA” (Agencywide Documents Access and Management System (ADAMS) accession number 

ML041210900) or the 10 CFR 50.46a final rule are not approved, it would be unlikely that a 

LOOP/LOCA rule would be worth pursuing. In its February 4, 2008, response, the Commission 

approved the staff’s request to defer the schedule for the LOOP/LOCA rulemaking and directed 

the staff to keep the existing Commission action on the rule open pending review of the 

decisions on the 10 CFR 50.46a final rule and the BWROG topical report. 

The following timeline reflects the history of activities related to the review of the BWROG 

topical report: 

April 27, 2004 BWROG submits licensing topical report NEDO-33148, 

“Separation of Loss of Offsite Power from Large Break LOCA.” 

July 20, 2004 NRC staff accepts NEDO-33148 for comprehensive review but 

twice defers start of review until January and then October 2005 

because of resource limitations (ML042030516, ML050870389). 

December 2, 2005 NRC issues requests for additional information (RAIs) 

(ML053330380). 

February 14, 2006 NRC holds a public meeting to discuss the RAIs. BWROG decides 

to revise NEDO-33148 to be a methodology document with 

respect to the risk assessment, rather than a generic risk 

assessment intended to be referenced by licensees with minimal 

need to do plant-specific analyses (ML060550493). 
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April 20, 2006 NRC issues revisions to the December 2, 2005, RAIs based on 

the February 14, 2006, public meeting (ML061030403). 

June 14, 2006 NRC holds a public meeting to discuss the revised RAIs 

(ML061790565). 

August 25, 2006 BWROG submits NEDO-33148, Revision 2, as a methodology 

document rather than a generic result document (ML062480321). 

June 15, 2007 NRC staff issue RAIs on NEDO-33148, Revision 2 

(ML071630548). 

July 25, 2007 NRC holds a public meeting to discuss the RAIs (ML072700668). 

September 28, 2007 BWROG submits a response to the June 15, 2007, RAIs 

(ML072750041). 

March 14, 2008 NRC staff issues additional RAIs (ML080720484). 

March 24, 2008 NRC issues a letter of outstanding issues on NEDO-33148 to the 

BWROG. The letter includes proposed limitations and conditions 

for approval of NEDO-33148 (ML080230696). 

June 12, 2008 BWROG withdraws NEDO-33148 from further NRC review and 

discontinues its effort, stating that “if ultimately approved in the 

form presently desired by NRC staff, adoption by licensees would 

most likely be prohibitively expensive” (ML081680048). 

December 19, 2008 The Commission is notified of the withdrawal of NEDO-33148 and 

of the staff’s plan to reassess the need for this rulemaking 

(ML082950233, currently nonpublic). 

DISCUSSION: 

The LOOP/LOCA rulemaking has been pursued in parallel with the rulemaking for a new 

10 CFR 50.46a, which presents a risk-informed redefinition of large-break LOCA ECCS analysis 

requirements. The 10 CFR 50.46a rule is currently available for public comment as a revised 

proposed rule. When promulgated as a final rule, the alternative 10 CFR 50.46a rule would 

allow both pressurized water reactors (PWRs) and boiling water reactors (BWRs) to decouple a 

LOOP from a LOCA for certain break sizes. For PWRs, this size is any break larger than about 

11 inches in diameter; for BWRs, it is any break larger than about 21 inches. The NRC staff 

intended to derive a rule from NEDO-33148 to benefit BWR licensees by further decreasing the 

break size to about 10 inches in diameter. Such a rule would allow BWR licensees to make the 

following seven specific design changes (as sought after in NEDO-33148) that otherwise could 

not be made without exemptions from the current 10 CFR 50.46 or the new alternative 

10 CFR 50.46a: 

 

 (1) optimized emergency diesel generator (EDG) loading; 
The Commissioners 4 

 (2) maintenance of one residual heat removal loop in a suppression pool cooling 

 mode; 

 (3) elimination of loop select logic for the low-pressure coolant injection system; 

 (4) allowance for slow starting EDGs; 

 (5) allowance for starting EDGs only upon a LOOP; 

 (6) simplification of EDG startup; and 

 (7) increased stroke times for motor-operated valves. 

The BWROG initially chose to pursue an approach that relied on a generic probabilistic risk 

assessment (PRA) and on other published reports, authored by both the NRC and industry, for 

justification of several important assumptions made in NEDO-33148 (e.g., large-break LOCA 

probability, consequential/delayed LOOP, and double sequencing1

 of electrical loads). The 

staff, however, expects topical reports to contain complete and detailed information on the 

specific subject presented. The staff also noted that many of the “other published reports” had 

not been reviewed by the NRC. The BWROG proposed to address these issues in Revision 2 

of NEDO-33148 submitted on August 25, 2006. Revision 2 was modified to present the risk 

analyses as risk assessment methodologies rather than a generic risk assessment. Double 

sequencing and other issues were purportedly addressed through conservative assumptions. 

The staff’s March 24, 2008, letter details the conditions and limitations that the staff concluded 

were required for approval of NEDO-33148. Some of the outstanding technical issues include 

LOOP/LOCA frequency determinations, seismic contributions to break frequency, the 

maintenance of defense in depth, and the treatment of delayed LOOP and double sequencing 

issues. These issues would need to be adequately addressed in order to complete a regulatory 

basis that could support a LOOP/LOCA rulemaking. 

With regard to risk and safety, the NRC staff does not believe that the seven specific BWR 

design changes discussed in NEDO-33148 would result in either a quantifiable safety 

improvement or a significant increase in risk (i.e., they are essentially “risk neutral”), provided 

that the proposed conditions and limitations are met. 

The BWROG’s withdrawal letter stated that further development of NEDO-33148 “is no longer 

cost effective and, if ultimately approved in the form presently desired by NRC staff, adoption by 

licensees would most likely be prohibitively expensive.” The withdrawal of NEDO-33148 and 

discontinued effort by the BWROG demonstrates a loss of industry support for a LOOP/LOCA 

rulemaking given the conditions and limitations required by the staff in its March 24, 2008, letter. 

In both SECY-01-0133 and SECY-02-0057, the NRC staff recommended developing a possible 

risk-informed alternative to reliability requirements in 10 CFR 50.46/GDC 35. In support of this 

 

1

 Double sequencing is defined as the unintended sequence of operations at a nuclear power plant during 

which safety and accident mitigation loads automatically start, shut down, and restart in rapid succession 

when called on to operate. Double sequences can have a range of detrimental effects from simple delay 

of function success because of restarts to causing unrecoverable failure of pumps and generators. 
The Commissioners 5 

potential alternative to GDC 35, the staff performed substantial work in a number of technical 

areas, including LOCA frequency estimation and conditional probability of LOOP given a LOCA 

(see memorandum from A. Thadani to S. Collins, “Transmittal of Technical Work to Support 

Possible Rulemaking on a Risk-Informed Alternative to 10 CFR 50.46/GDC 35,” dated 

July 31, 2002; ML022120661). As part of this work, the NRC staff identified a number of areas 

of uncertainty associated with estimating the conditional probability of a LOOP given occurrence 

of a LOCA (e.g., very limited data on major ECCS actuations and LOOPs after such actuations, 

incomplete knowledge about all of the factors that can impact the probability of consequential 

LOOP due to plant-centered or transient factors,2

 and the impact on offsite system voltage due 

to deregulation of the electric utility industry). With the withdrawal of NEDO-33148, in order to 

complete a fully developed regulatory basis for the LOOP/LOCA rulemaking, the staff would 

need to ensure that these areas of uncertainty are adequately addressed. 

In May 2002, the NRC received a petition for rulemaking (PRM) related to this topic. The 

petition, docketed as PRM-50-77 in June 2002 (67 FR 40622), requested that the NRC amend 

its regulations in Appendix A to 10 CFR Part 50 to eliminate the requirement to assume a LOOP 

coincident with postulated accidents. The petition was resolved by a decision to consider its 

issues within this rulemaking activity (NUREG-0936, Vol. 26, No. 2), but the petition remained 

open because of the ongoing developments related to this rule. However, in late 2007, the NRC 

Executive Director for Operations approved changes to the PRM process to enhance the 

efficiency and effectiveness of PRM dispositions. As a result, the NRC closed this petition in 

April 2009 (74 FR 16802) with a commitment to follow through with the original resolution to 

consider it within the LOOP/LOCA rulemaking. Therefore, if the Commission decides to 

discontinue this rulemaking, the NRC must publish a document in the Federal Register that 

addresses why the agency did not adopt the petitioner’s requested rulemaking changes. The 

NRC communicated this possibility to the petitioner and to the public when it closed the PRM 

docket. Because the petition did not present any technical information beyond what the NRC 

staff has already considered, the basis for a decision on the rulemaking should be the same 

basis for a final disposition of the petition’s requested changes. 

REQUESTED ACTION: 

The NRC staff requests that the Commission choose one of the following rulemaking options. 

OPTIONS: 

Option 1: Discontinue the rulemaking 

Pros: The NRC would take definitive action on the rule. 

The NRC staff would not incur the significant resource expenditures needed to 

independently complete the development of a regulatory basis that, in the end, might be 

“prohibitively expensive” for licensees to implement. 

Cons: The significant industry and NRC resources already expended to develop and to review 

 

2

 As used here, transient factors include the electrical disturbance triggered by the LOCA and the 

conditions of the offsite transmission system grid. 
The Commissioners 6 

NEDO-33148 would not result in a regulatory change. 

 The NRC would not develop a complete regulatory basis to support LOOP/LOCA 

rulemaking for the smaller break size LOCAs for BWRs. 

Option 2: Proceed with the rulemaking 

Pros: The expended resources and lessons learned during the review of NEDO-33148 would 

supplement the previous staff efforts in support of a potential risk-informed alternative to 

GDC 35 and produce a regulatory change. 

Cons: This option requires the NRC to expend significant additional resources to complete a 

fully developed regulatory basis to support the rule. 

 The rule is expected to be essentially “risk neutral.” 

 The rule would be an alternative regulatory approach that licensees might not choose to 

adopt since it might not provide licensees with cost-effective operational benefits. 

Option 3: Defer the decision until the 10 CFR 50.46a rule is implemented (estimated to be late 

2012) 

Pros: This option allows time to obtain feedback on the implementation of 10 CFR 50.46a and 

to determine if there is sufficient incremental benefit to be obtained from a separate 

LOOP/LOCA rulemaking. 

Cons: This option delays the decision on the rulemaking. 

The NRC would not develop a complete regulatory basis to support LOOP/LOCA 

rulemaking for the smaller break size LOCAs for BWRs. 

This option would not alleviate the Cons under Option 2. 

RECOMMENDATION: 

The staff recommends that the Commission approve Option 1 to discontinue the LOOP/LOCA 

rulemaking. 

Option 1 is recommended because the lack of a fully-developed regulatory basis and apparent 

loss of industry support does not justify continued NRC effort on this rulemaking. The rule 

would be an alternative regulatory approach, and its implementation would not be expected to 

result in either a quantifiable safety improvement or a significant increase in risk (i.e., it is 

essentially “risk neutral”), provided that the proposed conditions and limitations are met. There 

is currently no technical concern with the existing rule. When the 10 CFR 50.46a rule is 

promulgated as a final rule, licensees will then have the opportunity to decouple LOOP from a 

large-break LOCA. Finally, the staff believes that a LOOP/LOCA rule is unlikely to be widely 

adopted because of the BWROG’s belief that it would be “prohibitively expensive” to do so. 
The Commissioners 7 

Under Option 2, completion of a regulatory basis would necessitate a significant expenditure of 

staff resources to fully define and address areas of uncertainty associated with the issues 

identified in the staff’s March 24, 2008, letter to the BWROG. The staff estimates that the 

regulatory basis development and rulemaking process would take approximately 5 to 6 FTE 

(including any necessary contract support) assuming a standard three-year period for these 

activities. Approval of Option 2 may still not result in the timely development of the rule because 

of the low priority status it was accorded by the NRC’s rulemaking common prioritization 

methodology and the lack of resources currently allocated to this project. 

Given the BWROG’s decision to no longer support the initiative, Option 3 now appears to have 

little incremental regulatory benefit. As currently proposed, the alternative 10 CFR 50.46a rule 

would not address the LOOP/LOCA issue for the smaller break size LOCAs for BWRs. 

Therefore, a LOOP/LOCA regulatory basis would have to be independently developed by the 

staff even if the 10 CFR 50.46a rule is approved. 

Based on the foregoing discussion, the staff recommends that the Commission approve 

Option 1 to discontinue the LOOP/LOCA rulemaking. The staff would support resumption of 

LOOP/LOCA rulemaking in the future if licensees should express new interest and support for 

such an effort. 

RESOURCES: 

There are currently no resources funded or budgeted for this rulemaking. If either Option 1 or 

Option 3 is chosen, then no new resources would need to be budgeted. However, if Option 2 is 

chosen, the staff estimates that approximately 5 to 6 FTE would need to be budgeted and 

funded over a three-year period to support regulatory basis development and the rulemaking 

process. 

COORDINATION: 

The Office of the General Counsel has reviewed this paper and has no legal objection. The 

current resource implications do not meet the threshold for review by the Office of the Chief 

Financial Officer. 

 /RA Bruce S. Mallett for/ 

 R. W. Borchardt 

 Executive Director 

 for Operations 
The Commissioners 7 

identified in the staff’s March 24, 2008, letter to the BWROG. The staff estimates that the 

regulatory basis development and rulemaking process would take approximately 5 to 6 FTE 

(including any necessary contract support) assuming a standard three-year period for these 

activities. Approval of Option 2 may still not result in the timely development of the rule because 

of the low priority status it was accorded by the NRC’s rulemaking common prioritization 

methodology and the lack of resources currently allocated to this project. 

Given the BWROG’s decision to no longer support the initiative, Option 3 now appears to have 

little incremental regulatory benefit. As currently proposed, the alternative 10 CFR 50.46a rule 

would not address the LOOP/LOCA issue for the smaller break size LOCAs for BWRs. 

Therefore, a LOOP/LOCA regulatory basis would have to be independently developed by the 

staff even if the 10 CFR 50.46a rule is approved. 

Based on the foregoing discussion, the staff recommends that the Commission approve 

Option 1 to discontinue the LOOP/LOCA rulemaking. The staff would support resumption of 

LOOP/LOCA rulemaking in the future if licensees should express new interest and support for 

such an effort. 

RESOURCES: 

There are currently no resources funded or budgeted for this rulemaking. If either Option 1 or 

Option 3 is chosen, then no new resources would need to be budgeted. However, if Option 2 is 

chosen, the staff estimates that approximately 5 to 6 FTE would need to be budgeted and 

funded over a three-year period to support regulatory basis development and the rulemaking 

process. 

COORDINATION: 

The Office of the General Counsel has reviewed this paper and has no legal objection. The 

current resource implications do not meet the threshold for review by the Office of the Chief 

Financial Officer. 

 /RA Bruce S. Mallett for/ 

 R. W. Borchardt 

 Executive Director 

 for Operations 

WITS 200800120/EDATS: SECY-2008-0110 

WITS 200900168/EDATS: OEDO-2009-0539 

ADAMS Accession No.: ML092151078 *via e-mail 

OFFICE NRR/DPR/PFPB NRR/DPR/PFPB TECH EDITOR* NRR/DPR/PFPB 

NAME BMiller RDudley KAzariah-Kribbs RCarlson 

DATE 08/07/09 08/24/09 08/06/09 09/08/09 

OFFICE NRR/DPR NRR/DE/EEEB NRR/DE/EEEB NRR/DE 

NAME TMcGinty RMathew GWilson PHiland 

DATE 09/21/09 08/19/09 08/20/09 08/20/09 

OFFICE NRR/DRA/APLA NRR/DRA/APLA NRR/DRA* RES* 

NAME SDinsmore DHarrison MCunningham CLui 

DATE 08/24/09 09/01/09 09/21/09 09/18/09 

OFFICE NRO* ADM* OGC NRR 

NAME CAder MLesar(CBladey for) BJones (NLO) ELeeds 

DATE 09/18/09 09/21/09 09/22/09 09/23/09 

OFFICE EDO 

NAME RBorchardt 

(BMallett for) 

DATE 09/28/09 

OFFICIAL RECORD COPY