Cotet

In tro d u ctio n ....................................................................... 1 

Fuel Behavior and High Burnup Fuel ................................... 2 

P la n t A g in g ................................................................................ 3 

Plant Material Conditions ...................................................... 4 

Spent Fuel and W aste Storage ............................................ 4 

Digital Instrumentation and Controls .................................... 4 

Thermal Hydraulics and Severe Accident Codes ................. 5 

Probabilistic Risk Analysis ................................................... 6 

New Reactor Designs .......................................................... 7 

Radiation Protection ............................................................. 8 

Decommissioning ............................................................... 8 

Operational Data Assessment .............................................. 8 

Human Performance ............................................................. 9 

Use of Technical Standards and Codes .............................. 9 

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I0 I

Nuclear Safety Research

T, he Nuclear 

Regulatory 

Commission is 

responsible for 

assuring safety 

- : in the design, 

construction, and 

operation of 

commercial 

nuclear facilities 

... -and in the other 

uses of nuclear 

materials, such 

as in medicine 

and industrial 

activities. As a 

key component 

of nuclear safety, 

, the NRC carries 

out a research 

program to 

NRC Headquarters provide 

independent 

information and expertise needed to 

support the NRC's decision-making 

process and to identify and characterize 

technical questions that may become 

important safety issues in the future. 

NRC's regulatory research is designed to 

improve the agency's knowledge in 

areas where uncertainty in knowledge 

exists, where safety margins are not well 

characterized, and where regulatory 

decisions need, or will need to be 

confirmed. Thus, the development of 

sound technical bases allows proper 

focus on safety issues and more 

realistic decisions. 

The NRC's research program is carried 

out by the Office of Nuclear Regulatory 

Research (RES). RES develops its 

program with consideration of 

Commission direction and input from 

program offices and other stakeholders, 

including the academic and international

communities. Its mission includes: (1) 

complementing the front-line regulatory 

activities of licensing, inspection and 

oversight, (2) independently examining 

evolving technology and anticipated 

issues, (3) striving to be a center of 

excellence, and (4) having a major role in 

every strategic arena in implementing 

key strategies of NRC's Strategic Plan. 

RES contributes to the agency's 

regulatory decision-making by providing 

technical advice, analytical tools and 

information for staff to identify and 

resolve safety issues, make regulatory 

decisions, develop regulations and 

guidance, conduct independent analyses 

to support decisions to grant or deny 

licensee proposed changes, renew plant 

operating licenses, evaluate operating 

experience, and evaluate proposed 

designs and technologies, and enhance 

efficiency and effectiveness of NRC 

programs and processes. 

As part of its critical role at the agency, 

the office coordinates research activities 

within the NRC and leads the agency's 

initiative for cooperative research with 

the U.S. Department of Energy, the 

nuclear industry, universities, and 

international partners. Research 

sponsored by the office is performed 

primarily by national laboratories of the 

Energy Department, but universities and 

private firms also are used. Further, the 

RES staff possess broad knowledge in 

many scientific and engineering fields 

and is frequently called upon for its 

expertise by other offices of the NRC. 

RES' efforts focus on a wide range of 

technical issues such as those discussed 

in this booklet.

me-
Fuel Behavior and 

High Burnup Fuel

Reactor accidents involving a large 

release of radioactivity can only happen 

when fuel melts. There are only two 

ways to melt fuel: (1) too much power, 

and (2) not enough coolant (water). Too 

much power can develop if there is a loss of reactivity control and insufficient 

coolant, and insufficient coolant can result from a large water leak in the 

reactor. The NRC 

requires that 

reactors be 

designed such that 

they can withstand 

major reactivity 

accidents and loss

of-coolant accidents 

with very limited fuel 

damage such that 

melting could not 

occur. Postulated 

accidents of these 

types are studied 

using experiments 

and analyses to 

demonstrate that 

fuel damage will be 

adequately limited. 

These accidents are 

being reexamined to 

confirm that recent 

increases in nuclear 

power plant output 

or newer alloys used Examination off 

in metal rods 

housing nuclear reactor fuel preserve 

the original low limits on fuel damage. 

Nuclear fuel for light water reactors 

release energy through fission (the 

splitting of a uranium atom). The fuel 

consists of uranium dioxide ceramic 

pellets that contain both fissile and fertile 

materials. Fissile material is material in 

which fission can be caused by neutrons 

with low energy. A fertile material is a substance which can be converted into 

fissionable material by absorption of a

EU

:U(

neutron. The fissile material is used up 

and converted to energy and fission 

products. This process causes changes 

in the structure of the fuel and results in a gradual deformation of the fuel and a reduction in the neutron population and 

thus a less efficient nuclear reaction. 

The total energy released in fission by a given amount of nuclear fuel is called 

the fuel burnup and is 

i measured in 

megawatt days 

(Mwd). The fission 

Aý energy released per 

unit rhass of the fuel 

is termed specific 

burnup of the fuel and 

is usually expressed 

in megawatt days per 

metric ton (Mwd/t). 

Fuel damage criteria, 

established in the 

1970s, were 

developed for normal 

operation and several 

postulated accidents. 

The fuel damage 

criteria were defined 

in terms of the 

amount of energy 

released from the 

fuel. The industry, for 

el Rods economic reasons, 

has requested and, 

the NRC has approved, fuel burnup to 

higher levels than was originally 

anticipated. RES is focused on a reevaluation of NRC regulatory criteria 

for fuel damage and modification of 

related analytical tools for higher burnup 

fuels. It is essential to investigate the 

behavior of the fuel and fuel rods under 

high burnup conditions to confirm fuel 

integrity and reliability under these 

conditions.
Plant Aging 

A better 

understanding of 

the effect of age

related 

degradation on 

structures and , . 

passive 

components (e.g., 

buried piping, 

masonry walls, 

and flat bottom 

tanks) is needed Measuring a crack d, 

to ensure that a reactor coolant sy,, 

adequate margins 

are maintained under all design load 

conditions for the current and any 

extended operating life of nuclear power 

plants. This research assembles the 

age-related degradation data base for 

structures and passive components, 

identifies their age-related degradation 

mechanisms, develops a technical 

evaluation of the effects of their 

degradation and the significance to risk, 

for more risk-informed licensing 

decisions. 

Steam Generator Tube Integrity 

Steam generators are devices which 

use the heat of water circulating 

through the reactor core to generate 

non-radioactive steam to drive 

turbines. The hot radioactive water 

flows through steam generator tubes 

heating the non-radioactive water 

which is outside the tubes. Thus, the 

tubes form a critical boundary, 

preventing the release of 

radioactivity and, therefore, are 

designed to maintain their structural 

integrity under operating and 

postulated accident conditions. 

Various forms of degradations have 

occurred in steam generator tubes. 

With safety paramount, the steam 

generator integrity research program 

assesses the adequacy of inspection 

for identification and characterization

iscovere 

stem pip

S~ of degraded tubes,causes degradations, 

and methods 

.. for evaluating 

and maintaining 

integrity. This 

helps ensure 

that the tubes 

are designed 

to maintain 

.d in a weld in structural 

e. integrity under 

operating and 

postulated accidental conditions. 

Reactor Pressure Vessel Internals 

The cylindrical, steel reactor vessel 

and its internal equipment that 

houses the fuel rods provide the 

heat source for the generation of 

steam to turn a turbine for the 

production of electricity. Cracking of 

reactor pressure boundary 

components, such as piping, 

continues to be observed. 

Degradation of these components 

could cause leaks or breaks that 

could impair the ability to shut down 

and cool the reactor core. Issues 

being addressed by RES include: 

(1) crack initiation and growth, (2) 

cracking due to stress corrosion, 

and the effects of irradiation on 

stainless steel. 

Structures 

Aging structures can lead to 

changes in structural properties, 

which could lead to weakening and 

failure. Degraded structures are of 

particular concern when subjected 

to external loads such as 

earthquakes. Risk studies for 

degraded structures are being 

conducted.

I Nuclear Research PrograrnsTo, Ensure Public Hen-ith and SafeN I
Plant Material 

Conditions

This research area focuses on the 

evaluation of structural integrity and 

material conditions of components and 

systems in nuclear power plants and 

other nuclear facilities under normal 

operating and accidental conditions. The 

research addresses material exposure to 

reactor operating temperatures, stresses, 

irradiation environments, water coolant 

chemistry, cyclic loading, and general 

wear. Research also includes evaluation 

of non-destructive examination methods 

for performing in-service inspections of 

plant components and systems. 

Spent Fuel and Waste 

Storage 

There are two licensing issues associated 

with the long-term storage of spent

Storage casks at the Surry Nuclear 

Power Plant in Virginia

nuclear fuel. The first is the renewal of 

existing dry cask storage licenses and

=

Certification of Compliance for 

intermediate burnup fuel. The second is 

the licensing of dry cask storage for high 

burnup fuel. RES is developing the 

technical basis for ensuring the 

continued safe performance of dry 

storage systems for long-term storage 

of spent nuclear fuels and high-level 

radioactive waste under extended 

service conditions, 20 to 100 years. 

Digital Instrumentation 

and Controls 

The general direction of the nuclear 

industry is to replace their analog 

instrumentation and control equipment 

with digital equipment because of the 

difficulty in replacing analog equipment 

modules and the advantages of newer 

equipment. It is expected that plants will 

retro-fit their protection systems, control 

systems, and eventually the majority of 

their control rooms. This will result in a mixture of analog and digital (hybrid) 

equipment that will require complex 

interfaces with an increased potential 

for errors. For example, industry is 

currently developing new modern control 

and diagnostic systems to improve 

reliability, and advanced neutron and 

flow sensors to reduce the uncertainty of 

power measurements. While digital 

technology has the capability to improve 

both operational performance and 

safety, there are challenges to the 

introduction of this technology into 

nuclear power plants. The ever

changing digital technology with its 

complexity and unique failure modes 

requires research programs to provide a safety focus and guidance to the 

industry with sufficient lead time.
Thermal Hydraulics and 

Severe Accident Codes

Thermal-Hydraulics 

Thermal-hydraulic research involves 

development of computer codes and data 

that are used to model the reactor system 

to ensure that a balance is achieved and 

to assess the consequences of such an 

imbalance and mitigating actions taken if 

an imbalance occurs. 

The energy source of nuclear power 

reactors is the nuclear fission process that 

occurs within the fuel. Water is pumped 

into the reactor and passes over the fuel 

elements. 

In passing 

over the fuel 

elements 

the coolant 

(water) is 

heated, 

which is 

then used to 

generate 

steam. 

Various . 

forms of 

steam 

generators 

are used in , ,,., 

nuclear 

reactors. An illustration of a Boiling

The nuclear 

reactor itself 

is the steam generator in the case of 

boiling water reactors, where the steam is 

formed directly within the reactor core. 

The steam generator is fed with water, 

which is totally or partially evaporated to 

steam. The steam is then passed through 

the turbine, which drives the electrical 

generator. The very low pressure exhaust 

steam from the turbine is passed to a 

condenser, where it is converted back into 

water and recirculated to the steam 

generator. The removal of energy in the 

fuel and the production of the energy must

Wa

be balanced. The situation of either too 

little coolant flow or too much energy 

production can result in the fuel 

overheating and potentially melting. 

Additionally, RES maintains and 

continues to improve the usefulness of 

computer codes that are used to analyze 

reactor operations and functions. These 

codes are used in analyzing many types 

of transients and accidents. They also 

are used to resolve fuel behavior 

technical issues. 

Severe 

Accidents 

Severe 

accident 

> >research 

studies the 

detailed 

behavior of 

• ,K. reactors and 

the radiation 

-w•im released 

during such 

accidents and 

~ '..examines 

•\'" , means to 

prevent such 

'ter Reactor accidents and 

protect the 

public. 

Severe accidents are that highly 

improbable group of accidents that 

involve serious, prolonged overheating of 

most of the nuclear fuel which could then 

result in the release of large amounts of 

radiation and radioactive materials to the 

containment and possibly the 

environment. For some of these severe 

accidents, the radiation may escape from 

the nuclear power plant and be carried 

by the wind exposing people in the 

surrounding area.

I4 e -'--
Probabilistic Risk 

Analysis (PRA)

PRA is an important element of the 

NRC's regulatory processes. PRA is a 

systematic method for incorporating 

realistic information on the design and 

operation of a facility into a logical and 

integrated model. Using this model, both 

the overall reliability and risk of the 

facility, as well as the relative importance 

of components, human actions and 

errors, and potential accident initiators, can be estimated. Research is important 

to risk-informed decision-making, 

providing information on the likelihood, 

consequences, or mode of progression of 

postulated accidents and providing a risk 

context for regulatory decisions. 

Plant Operating Data 

Nuclear power plant operational data 

provide information on relevant operating 

experience that is used to enhance plant 

inspections of risk-important systems, to 

perform technical reviews of proposed 

license amendments, and to support 

improvements in the reactor oversight 

process. Therefore, RES operates and 

maintains the Sequence Coding and 

Search System (SCSS) that contains 

information about events at nuclear 

power plants in a computer-searchable 

framework. RES also operates and 

maintains the Common-Cause Failure 

(CCF) database. Common-cause 

failures have the potential to adversely 

impact the safety of nuclear power plants. 

Thus, review of operating events at 

power reactors can disclose risk

significant interactions, phenomena, and 

behavior in the design and operating of 

power reactors that were not previously 

recognized or analyzed. 

The Accident Sequence Precursor (ASP) 

program provides analyses of the risk

significance of operating experience on 

a plant-specific basis. It also provides 

trending information on industry and 

group-specific risk performance. Thus, 

the ASP program provides a risk 

perspective of nuclear power plant 

events to inform agency response and 

regulatory decisions. Analytical tools to 

support these analyses are also 

developed and maintained. 

Risk-Informed Regulation 

RES prepared guidance for making 

risk-informed regulatory decisions. The 

guidance describes acceptable means 

for assessing the nature and impact of 

licensing changes when the change 

request is supported by risk information. 

Another RES effort focuses on 

providing a better balance to nuclear 

plant technical requirements among 

those needed to provide defense-in

depth, to maintain appropriate safety 

margins, and to limit risk. For example, RES is working to develop the technical 

basis to improve the realism of 

evaluations of reactor pressure vessel 

(RPV) integrity to support risk-informed 

modifications to the associated 

regulations. The results of probabilistic 

fracture calculations and PRA 

considerations will be integrated to 

develop revised pressurized thermal 

shock screening criteria for incorporation 

into the nuclear plant regulations. 

Risk-informing may involve relaxing 

requirements in some areas in 

combination with increasing 

requirements in other areas to 

achieve a better balance. 

PRA Standards 

The increased use of PRA in the 

regulatory decision-making process
requires high-quality analyses 

(i.e., scope, methodology and data 

used in such analyses). This applies to 

PRAs developed by industry to support 

specific, risk-informed licensing actions 

as well as to PRAs developed by NRC 

staff to analyze specific technical issues 

or to support risk-informed Commission 

decisions. To this end, NRC has been 

working with the American Society of 

Mechanical Engineers (ASME) and the 

American Nuclear Society (ANS) to 

develop national consensus standards 

on PRA. When developed, such 

standards on PRA quality will help to 

ensure that PRAs developed in 

accordance with the standards are 

robust, consistent, and defensible and 

provide a suitable basis upon which 

regulatory decisions can confidently be 

made. While the ASME and ANS 

maintain overall responsibility for this 

effort, active NRC and industry 

participation has been, and will 

continue to be, essential to the 

development of such standards. 

PRA Methods 

RES is continuing to develop and 

improve methods for risk analysis to 

better support realistic, risk-informed 

decision making. Areas where work is 

currently underway to improve methods 

are plant aging, human reliability, fire, 

and digital instrumentation and control 

systems. Uncertainty exists concerning 

the nature and magnitude of the 

contributions of these aspects to plant 

risk. The new methods will complement 

the methods developed to-date, further 

reducing uncertainties and improving 

realism and improving agency 

decision making.

New Reactor Designs 

There is a possibility that in the next 

five to 10 years orders for new nuclear 

power plants will become a reality. 

However, for such orders to be realized, 

future reactor designs must be attractive 

from an economic and safety 

perspective. Many of these designs 

will propose features very different 

than current reactor designs. Since 

safety and licensing are major 

considerations for any future designs, 

it is most efficient, timely, and in the 

national interest for NRC to prepare 

for licensing future designs by having 

early interactions with the designers 

and developers as encouraged by the 

Nuclear Regulatory Commission's 

Policy Statement on Advanced 

Reactors. 

Early interaction would be to: 

- Understand reactor designs 

- Identify safety issues and plans for 

their resolution 

- Establish a framework for licensing 

that recognizes the unique features 

of these designs 

RES plays a key role in the agency 

efforts to prepare for reviews of future 

reactors for licensing in the U.S. This 

includes developing analytical tools, 

data, and guidance to support licensing 

reviews as well as evaluating new 

technologies, such as that associated 

with the proposed Pebble Bed Modular 

Reactor (PBMR). 

Some key issues that need to be 

addressed through research, so as to 

facilitate the licensing of future reactors 

are: qualification of the fuel and its 

fabrication; development of the 

radiological source term; performance 

of high temperature materials;

I Nuclear Research Programs Ib Ensure Public Health and Safety
verification and validation of design and 

safety analysis codes; probabilistic risk 

assessment; use of commercial-grade 

components; and new digital systems, 

hardware and software. 

Radiation Protection 

With regard to the NRC's current 

regulations on radiation exposure based 

on risk estimates, RES accumulates data 

on the effects of radiation on the human 

body through several types of studies. 

RES uses this data to re-evaluate the 

current health effects of computer models 

and to evaluate health effects caused by 

long-term exposures to low levels 

of radiation. 

Decommissioning 

For reactors and other facilities that are 

nearing the end of their productivity, RES 

has initiated studies on safe and effective 

means of decommissioning nuclear

Dismantlement of the Trojan Nuclear 

Power Plant in Oregon. 

power plants and other nuclear facilities. 

Decommissioning is the process of safely

-mm -

removing a facility from service followed 

by reducing residual radioactivity to a 

level that permits the release of the 

property for unrestricted use and, under 

certain conditions, restricted use. This 

includes removal of all intact radioactive 

materials and the clean-up of any 

residual contamination to acceptable 

regulatory levels. Additionally, RES 

examines environmental contamination 

associated with a nuclear facility in 

terms of potential off-site transport of 

radioactive material and compliance with 

any standards for termination of the 

operating license. 

Operational Data 

Assessment 

Data from operating reactors is 

continually assessed to learn more 

about operational safety. RES collects, 

analyzes, and disseminates data 

accumulated during operations and 

assesses trends in performance from 

these data. It evaluates operating 

experience to provide insights into and to 

improve the understanding of the risk 

significance of events that have occurred 

at licensed facilities. The evaluation may 

disclose risk-significant interactions, 

phenomena, and behaviors at power 

reactors that have not previously been 

recognized or analyzed. For example, 

data accumulated from many operating 

reactors can show trends in aging of the 

reactors. Examinations of individual 

plants and events at nuclear plants is 

also used to develop guidance and 

standards on the use of risk 

assessments that are needed for the 

agency's reactor oversight program.
Nucea ReerhPorm oEsr Pbi elha0ýft

Human Performance 

Human Performance research activities 

at the NRC focus on the interaction of 

people with the systems and the 

environments in which they work. The 

importance of these interactions is that 

they can strongly affect personnel 

performance and thus overall system 

safety at a nuclear facility. Indeed there 

is considerable operational evidence that 

poor human performance has been a 

factor in more than 50% of the incidents 

at nuclear power plants and an even 

greater percentage of incidents involving 

the use of nuclear materials for medical 

and industrial applications. 

At NRC we look at the performance 

of people in normal and abnormal 

conditions, and at the effects of the work 

environment, including physical and 

cognitive effects, on both individual and 

team performance. 

This includes human

system interfaces, 

training, procedures, 

shift working hours, I 

and a safety

conscious work 

environment. In 

addition, human per

formance research 

addresses human 

characteristics, such . 

as knowledge, skills, 

and abilities, fatigue, An NRC inspectoi 

and fitness for duty. ficensed facility. 

It is important that 

human performance is supported by an 

organizational environment that promotes 

a culture of safety and provides its 

personnel with the programs, support, 

staffing, and tools necessary to perform 

the jobs safely and comfortably.

NRC's research program in human 

performance is anticipatory in that it

CO

addresses emerging technology's 

potential effect on human performance. 

In addition, human performance research 

develops and establishes the technical 

bases for NRC initiatives, such as, 

inspection guidance for evaluating 

emergency operating procedures, a 

systems approach to training, human 

system interface design for current and 

advanced control station design, human 

performance contributors in events, 

communications-related corrective action 

plans, shift working hours and fatigue 

management programs. 

Use of Technical 

Standards and Codes 

RES coordinates the development of 

consensus and voluntary standards for 

agency use. 

Consensus 

standards are 

technical standards 

that support 

regulatory needs 

pertaining to 

materials, 

components, and 

processes. They 

are developed by 

experts from 

industry, 

liects data at a universities, or

government 

agencies. The 

agency serves on committees of the 

national and international organizations 

(i.e., American Society of Mechanical 

Engineers, the American National 

Standard Institute, the International 

Commission on Radiation Units and 

Measurements, and the National Council 

on Radiation Protection) that develop

---------------- L_ EVAIII11-

r
these standards. The NRC frequently 

endorses these standards as guidance or 

adopts them into its regulations. 

In short, the NRC's Office of Regulatory 

Research goals are to maintain safety, 

increase public confidence, make NRC 

activities and decisions more effective, 

efficient, and realistic, and reduce

unnecessary regulatory burden on 

stakeholders. It carries out the agency's 

research program to provide independent 

information and expertise needed to 

support the Commission's decision

making process and to identify and 

characterize technical questions in 

anticipation of safety issues that may 

arise in the future.

FOR ADDITIONAL INFORMATION 

CONTACT: 

Office of Public Affairs 

U.S. Nuclear Regulatory Commission 

Washington, D.C. 20555 

(301) 415-8200 

E-mail: opa@nrc.gov 

Visit our website at www.nrc.gov

-i