NUREG/BR-0303

Guidance for 

Performance-Based Regulation

U.S. Nuclear Regulatory Commission

Office of Nuclear Regulatory Research

Washington, DC 20555-0001
 NUREG/BR-0303

 

Guidance for

Performance-Based Regulation

Manuscript Completed: November 2002

Date Published: December 2002

Prepared by

N. P. Kadambi

Division of Systems Analysis and Regulatory Effectiveness 

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

iii

ABSTRACT

This document provides guidance on a

process for developing a performance-based

alternative for consideration, along with other

more prescriptive alternatives, in regulatory

decisionmaking. The U.S. Nuclear Regulatory

Commission (NRC) Management Directive

6.3, “Rulemaking,” calls for the consideration

of a performance-based alternative. Such an

alternative differs significantly from a

prescriptive one in which licensees are

provided detailed direction for obtaining safety

results. Performance-based approaches focus

primarily on results. They can improve the

objectivity and transparency of NRC

decisionmaking, promote flexibility that can

reduce licensee burden, and promote safety

by focusing on safety-successful outcomes.

These attributes are reflected in the process

described in this document. The process is

set up to develop answers to questions that, in

turn, provide the information to formulate an

alternative that can be compared against

others in a management review process. The

five steps in the process are (1) defining the

regulatory issue and its context, (2) identifying

the safety functions, (3) identifying safety

margins, (4) selecting performance

parameters and criteria, and (5) formulating a

performance-based alternative. Examples are

provided to illustrate the process. The formal

high-level guidelines for performance-based

activities are shown in Appendix A. For

broadly scoped and complex issues, a more

rigorous consideration of performance issues

may be appropriate; accordingly, Appendix B

provides supplementary guidance and

background information.

v

CONTENTS

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

ABBREVIATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

1 INTRODUCTION .......................................................... 1

1.1 Background ......................................................... 1

1.2 Frame of Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

 2 HIGH-LEVEL PERFORMANCE-BASED GUIDELINES ........................... 5

2.1 Viability Guidelines .................................................... 5

2.2 Assessment Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.3 Guidelines to Ensure Consistency with Other Regulatory Principles .............. 6

3 PROCESS ............................................................... 9

3.1 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.2 Process Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4 ILLUSTRATIVE EXAMPLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

APPENDICES

A HIGH-LEVEL GUIDELINES FOR PERFORMANCE-BASED ACTIVITIES . . . . . . . . . . . A-1

B SUPPLEMENTARY GUIDANCE FOR MORE COMPLEX ISSUES . . . . . . . . . . . . . . . . . B-1

FIGURES

1 Flow Chart To Address Regulatory Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

B-1 Overview of Objectives Hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-3

B-2 Reactor Oversight Process Objectives Hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4

B-3 More Detailed Decomposition of Means Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . B-5

vii

ABBREVIATIONS

ACRS Advisory Committee on Reactor Safeguards

AFWS auxiliary feedwater system

ALARA as low as reasonably achievable

ASME American Society of Mechanical Engineers

BWR boiling-water reactor

CDF core damage frequency

CFR Code of Federal Regulations

DG draft regulatory guide

GPRA Government Performance and Results Act

LERF large-early-release frequency

NRC U.S. Nuclear Regulatory Commission

PRA probabilistic risk assessment

PWR pressurized-water reactor

ROP Reactor Oversight Process

SRM staff requirements memorandum

1

1 INTRODUCTION

1.1 Background

A performance-based regulatory action

achieves defined objectives and focuses on

results. It differs significantly from a

prescriptive action in which licensees are

provided detailed direction on how those

results are to be obtained. For example, in the

reactor arena, one can envision a U.S.

Nuclear Regulatory Commission (NRC)

regulatory concern involving the reliability of

emergency backup diesels during station

blackout accidents. A prescriptive approach

would direct the licensee to perform specific

detailed maintenance operations, testing

procedures, and inspections at precise time

intervals. A performance-based approach

would simply set a performance objective

(e.g., diesel reliability of 95 percent) and allow

the licensee considerable freedom in how to

achieve that reliability objective. Similarly, the

as low as reasonably achievable (ALARA)

provisions of Title 10, Part 20, of the Code of

Federal Regulations (10 CFR Part 20), which

impact both materials and reactor licensees,

are performance-based in that they allow

licensees to meet the specified dose limits in a

manner that they deem most appropriate. If

the NRC had written a prescriptive Part 20, it

might have included specific time limits in

specific radiation areas, and required rigid

rules concerning the use of respirators and

protective suits under defined conditions. 

Performance-based regulatory approaches

possess inherent strengths that can lead to

more effective regulation. Examples include

improving the objectivity and transparency of

NRC decisionmaking, promoting licensee

flexibility in response to regulatory

requirements that can reduce licensee burden,

and promoting safety by focusing on safetysuccessful outcomes.

The history of NRC’s activity in performancebased regulation began with the staff

requirements memorandum (SRM) of January

22, 1997 (Ref. 1), in which the Commission

directed the staff to propose a plan to develop 

performance-based objectives that are not

amenable to probabilistic risk assessment.

Why must the staff consider performancebased regulatory approaches?

Performance-based regulatory approaches

are considered for policy and effectiveness

reasons. The policy considerations are

based on the 1993 Government

Performance and Results Act (GPRA).

NRC’s Strategic Plan, developed in

response to GPRA, provides specific

performance goals that drive the agency’s

regulatory program. Performance-based

approaches are mentioned in the goals for

reactors, materials, and waste. Regulatory

effectiveness has been found to improve

when such approaches are used

appropriately.

What is the basis for the guidance in this

document?

The basis for the guidance in this

document is the High-Level Guidelines for

Performance-Based Regulation (Ref. 4)

(hereafter referred to as “the high-level

guidelines”). The high-level guidelines

cover the three arenas (reactors,

materials, waste) and a broad range of

issues within each arena. Accordingly, the

high-level guidelines are formal and

abstract.

How will this guidance document

accomplish its objectives?

It provides simplified guidance for many of

the regulatory issues that NRC staff may

be tasked to resolve. It may not cover

complex considerations such as defense

in depth. Appendix B has been prepared

as a reference to support formulation of

performance-based alternatives to address

broader or more complex issues.
2

The initiative was given further definition by

Direction Setting Issue 12 (Ref. 2) and the

White Paper on “Risk-Informed and

Performance-Based Regulation,” SRM to

SECY-98-144 (White Paper) (Ref. 3). The

continuing efforts of the staff, which included

public workshops, led to the publication of

high-level guidelines for performance-based

activities (SECY-00-191 (Ref. 4) and 65 FR

26772 (Ref. 5)). These guidelines were

developed with interoffice participation by the

Performance-Based Regulation Working

Group. The developmental aspects of this

activity will end with the issuance of this

guidance document.

This document describes the use of high-level

guidelines for determining whether a

performance-based approach can be applied

to a given regulatory activity. In addition, it

provides insights into the formulation of

performance-based alternatives. Although a

tendency exits to characterize a regulatory

approach as either performance-based or

prescriptive, the reality is that the most likely

and preferred approach will often be a blend

of the two. Thus, when this document refers to

making an approach performance-based, the

intent is actually to make it as performancebased as possible. 

1.2 Frame of Reference

The NRC is heavily committed to the

identification and evaluation of regulatory

actions. Such activities are undertaken in

response to a wide array of regulatory issues,

and they typically focus on ways to improve

performance relative to NRC’s goals as

articulated in the Strategic Plan (Ref. 6).

These activities tend to involve concerns over

public health and safety; public confidence;

regulatory effectiveness, efficiency, and

realism; and unnecessary regulatory burden. 

When a decision is made to evaluate a

regulatory issue, it is standard practice for the

staff to use NUREG/BR-0058, Rev. 3,

“Regulatory Analysis Guidelines of the U.S.

Nuclear Regulatory Commission,” (Ref. 7) as

guidance. The regulatory analysis prescribed

therein is designed to determine whether a

regulatory action is needed, to provide

adequate justification for the proposed action,

and to explain why a particular action was

recommended. The heart of the regulatory

analysis is a cost-benefit assessment that

consists of a systematic evaluation of the

consequences associated with a range of

alternative responses and the selection of the

preferred alternative. It is clear that

consideration of the alternatives is critically

important in this overall decisionmaking

process. NUREG/BR-0058 recognizes the

desirability of including a performance-based

approach as one of the alternatives to be

evaluated. In NUREG/BR-0058, Section 4.2,

“Identification and Preliminary Analysis of

Alternative Approaches,” states –

If the objective or intended result of a

proposed generic requirement or staff

position can be achieved by setting a

readily quantifiable standard that has

an unambiguous relationship to a

What must the staff do?

In order to increase regulatory

effectiveness, the Commission has directed

the staff to consider risk-informed and

performance-based alternatives when a

choice is being made between different

regulatory approaches. The staff can use

this document to accomplish the

Commission’s objective.

How should the staff proceed?

The staff can begin with this document to

see if concepts such as safety function and

safety margin are relatively simple to

evaluate in the context of the specific

regulatory issue. If the resolution is

sensitive to where and how performance is

measured, Appendix B should be

considered for supplementary guidance.

The regulatory analysis, which considers

the costs and benefits of each alternative,

can document the preferred alternative.
3

readily measurable quantity1

 and is

enforceable, the proposed requirement

should merely specify the objective or

result to be obtained rather than

prescribe to the licensee how the

objective or result is to be attained. In

other words, requirements should be

performance-based, and highly

prescriptive rules and requirements

should be avoided absent good cause to

the contrary.

For many applications, the guidance in the

present document will suffice to support a

performance-based approach. For issues

whose resolution is sensitive to where and

how performance is measured, or in cases

involving cross-cutting issues, staff may need

to undertake a more considered development

as described in Appendix B.

1

The “readily measurable quantity” does not

necessarily imply that only direct measures of

physical parameters (such as length, weight,

temperature, pressure, flow rate) are acceptable.

Although direct measures (called natural

measures) are preferred, objective measures of

other sorts should also be considered. This

broader interpretation of the term “readily

measurable quantity” is based on more recent

work on performance-based approaches to

regulation.

5

2 HIGH-LEVEL PERFORMANCE-BASED GUIDELINES

In SECY-00-191, September 1, 2000, the

NRC issued high-level performance-based

guidelines for identifying and assessing

potential performance-based regulatory

actions. “High-level” means that the guidelines

are applicable across the full spectrum of NRC

regulatory activity, corresponding to the three

NRC arenas, reactor safety, material safety,

and waste safety.

The guidelines are meant to raise questions,

the answers to which should assist the staff in

determining whether and how to pursue a

performance-based alternative. The staff may

exercise discretion in applying these

guidelines, which are classified into three

groups (1) viability guidelines, (2) assessment

guidelines, and (3) guidelines to ensure

consistency with other regulatory principles. A

summary follows.

2.1 Viability Guidelines

Viability guidelines ask questions that enable

the regulator to determine whether a specific

regulatory issue is amenable to a

performance-based approach based on how

well the regulator can construct a regulatory

alternative that has the four attributes

discussed in the Commission’s White Paper.

These attributes are: 

• Failure to meet the predetermined

performance standard will not result in an

immediate safety concern. (Can margin be

estimated realistically, and if so, what is

known about it?)

• Measurable or calculable parameters are

available to determine whether the

performance standard is met. (Can

performance parameters be identified that

provide measures of performance and the

opportunity to take corrective action if

performance is lacking?) 

Can a “performance-based approach” have

prescriptive elements?

Appropriate regulatory decisionmaking

cannot exclude the possibility of

prescriptive elements. The characteristic of

a performance-based approach, as

described in the Commission’s White

Paper, is a reliance on performance and

results. This is evident from the following

statement in the White Paper, “A

performance-based regulatory approach is

one that establishes performance and

results as the primary basis for regulatory

decisionmaking....” The focus of a

performance-based approach is the use of

prescriptive elements only when

necessary.

How does “margin” enter into a

“performance-based approach?”

One of the White Paper attributes of a

performance-based approach is that, “...a

framework exists in which the failure to

meet a performance criterion, while

undesirable, will not in and of itself

constitute or result in an immediate safety

concern.” Such a framework contains the

concept of “margin.” In this construct,

“margin” is a quantity that expresses the

difference between performance within the

limits of a “criterion” and performance that

is representative of a “concern.” The word

“immediate” requires that a time element

be considered in the development of a

performance-based approach. The highlevel guidelines incorporate this

understanding. They are also consistent

with the NRC’s regulatory responsibility to

monitor potential erosion of margin, as well

as licensee responsibility for prompt

corrective actions. These interpretations

have been discussed with the public and

presented to the Commission.
6

• The performance standard is based on

objective criteria. (Can objective criteria be

developed that are indicative of

performance?)

• The licensee or the NRC has flexibility in the

method used to achieve the desired

performance level. (Is flexibility for the NRC

or licensees available consistent with the

level of margin?)

If a regulatory alternative can be designed

with these three attributes, a performancebased approach is judged to be feasible. This

assessment would be applied on a case-bycase basis and would be based on an

integrated consideration of these guidelines,

rather than on strict adherence to each

individual guideline. 

In terms of relative importance, the guideline

concerned with performance failure leading to

an immediate safety concern is pre-eminent. A

performance-based requirement is justified

only if assurance exists that adequate safety

margins can be preserved to meet regulatory

needs. A safety margin is adequate for this

purpose when, if there is a failure to meet the

performance objective, sufficient time will be

available to take corrective action to avoid a

more serious condition associated with a

safety concern. The importance of safety

margin considerations justify placing this

guideline as the first among the viability

guidelines. Hence, if sufficient margin exists

under the first viability guideline, a broad

range of less-prescriptive approaches become

viable, including performance-based

approaches. The three subsequent viability

guidelines characterize the performancebased approach.

The White Paper associates flexibility with the

concept of incentives. It states that one of the

attributes of a performance-based approach is

that licensees have flexibility to determine how

to meet the established performance criteria in

ways that will “encourage and reward

improved outcomes.” The coupling of flexibility

and licensee incentives has been addressed

in the formal guidelines in Appendix A.

2.2 Assessment Guidelines

If a performance-based approach is deemed

viable, the regulatory activity would be

evaluated against guidelines that assess

whether such an approach results in

opportunities for regulatory improvement.

Regulatory improvement is a positive

contribution to NRC’s performance goals and

achievement of a net societal benefit. Thus,

the assessment guidelines question whether

the regulatory alternative achieves the

following: 

• maintains safety

• increases public confidence

• increases effectiveness, efficiency, and

realism

• reduces unnecessary regulatory burden

• results in a net benefit

Additional assessment guidelines include the

ability of the proposal to be incorporated into

the regulatory framework and the ability to

accommodate new technology. This

evaluation is to be based on an integrated

assessment of the individual guidelines within

this grouping. 

Many of the considerations that apply to this

set of guidelines are also pertinent to the costbenefit evaluation performed as part of the

regulatory analysis. Hence, information

developed here could also support the

alternatives analysis described in the

Regulatory Analysis Guidelines.

2.3 Guidelines to Ensure Consistency with

Other Regulatory Principles

These guidelines take into account

fundamental regulatory principles that have

been articulated by the Commission, such as,

the Principles of Good Regulation (Ref. 6).

The intent is to ensure that a performancebased regulatory alternative that conforms to

the viability and assessment guidelines does

not compromise any of NRC’s basic regulatory

principles. Although it is not generally

necessary to remind staff of these principles,

this third set of guidelines provides a

reasonable check.
7

The third set of guidelines need only be

applied if the candidate activity passes the first

two sets of guidelines. 

A complete presentation of the guidelines

appears in Appendix A.

9

3 PROCESS

3.1 Objectives

The objective of this document is to provide a

process that can be widely used for decisions

concerning performance-based regulatory

alternatives. As noted above, the

performance-based guidelines are articulated

at a high level and are applicable to regulatory

issues involving the reactor, materials, and

waste arenas. The process must be relatively

general for it to have such wide relevancy.

More detailed guidance, tailored specifically to

individual arenas, is beyond the scope of this

document. It is anticipated that each of the

major arenas will have additional guidance in

the form of office procedures that will

effectively supplement this document.

Nevertheless, for many regulatory actions, the

nature and objectives of the regulatory issue

will be clear and the knowledge base large

enough that a relatively modest process, such

as the one described here, will be sufficient. 

Although applicable across all regulatory

arenas, considerable leeway exists in the level

of adherence to the general process outlined

here. For example, in certain instances it may

be so clear that a performance-based

approach is not feasible that formal application

of these guidelines could be largely

unnecessary. Circumstances are also likely in

which the appropriateness of using a

performance-based approach and the

characteristics of that approach are very

obvious and straightforward. Decisions on

these matters are almost always governed by

expert-judgment assessments of margins that

effectively mimic the substance of the process

being spelled out here. In such cases, the staff

may simply choose to use these guidelines as

a check on the performance-based approach

that is being proposed. Similarly, the

guidelines may also be useful to test a

proposed regulatory action that purports to be

performance-based to determine whether the

action, under a formal scrutiny, in fact merits

the label. 

Alternatively, some complex regulatory issues

may require that a far more detailed process

be used than the one described here. If so,

concepts and tools such as decision theory

and objectives hierarchies would likely be

needed. NRC staff in need of, or interested in,

a more systematic and structured process are

directed to Appendix B and the references

therein for decision theory concepts. 

Regardless of the level of effort, some

documentation for case-specific applications

of this process should be maintained for

transparency and efficiency. Individual office

procedures should specify the requirements

for documentation.

What is the relationship between riskinformed and performance-based

approaches to regulation?

Risk-informed and performance-based

approaches to regulation complement one

another. Risk information, when a

probabilistic risk assessment (PRA) is

available, can be useful in finding the most

safety-significant functions and systems. If

a PRA is not available, operational

experience may provide enough

information. Safety would be best served

by demanding the highest (i.e., most

aggregated) levels of performance from

the most safety-significant structures,

systems, and components.

In SECY-01-0218, “Update of the RiskInformed Regulation Implementation Plan”

(December 5, 2001) (Ref. 8), the staff has

stated that, to the extent appropriate,

activities to risk-inform regulations should

also incorporate the performance-based

approach to regulation. The corollary is

also true–performance-based regulations

should be risk-informed when possible.
10

Figure 1 is a schematic representation that

characterizes the most important elements of

the overall process of addressing a regulatory

issue. The guidance presented here is

specifically concerned with the development of

a performance-based regulatory alternative

and corresponds to an entry point at the

“Performance-Based” or “Risk-Informed &

Performance-Based” boxes of Figure 1. The

process contains a number of feedback loops,

which is indicative of the iterative nature of this

process.

The process is intended to determine whether

a given regulatory issue is suited to a

performance-based approach, and if so, to

identify an alternative that most strongly

reflects performance-based attributes. In

addition, other competing objectives must be

considered, such as setting performance and

reliability measures at the highest (i.e., most

aggregated) possible level and, to the extent

practicable, using multiple parameters to

satisfy the defense-in-depth philosophy.

Meeting these objectives may require

application of the methodology in Appendix B.

This process is intended to enable the staff to

identify a preferred performance-based

alternative based on the consideration of all

these objectives. This is accomplished

through an iterative process, similar to that

depicted in Figure 1. Each iteration should

result in more detailed and focused

information that can be used toward improving

the performance-based alternative.

This document has been prepared as

guidance to be used in the context of

rulemaking. However, the resolution of a

regulatory issue may involve changes to any

part of the regulatory framework and may not

result in an actual regulation. For example,

improvements obtained through the revised

reactor oversight process, which is

performance-based in nature, were realized

mainly by changes to the inspection,

assessment, and enforcement aspects of the

regulatory framework. Those improvements

are considered to be highly effective even

though rulemaking was not involved.

3.2 Process Steps

For any given regulatory issue, the design of a

performance-based approach depends on five

basic considerations that are addressed in

detail below. Each of these elements is

treated as a step in a process. The answers to

the questions provide the basis for developing

the required details on a performance-based

alternative, if it is feasible.

Step 1 – Defining the Regulatory Issue and

its Context

Purpose – To define the regulatory issue with

clear objectives that are well-understood.

• What is the arena and sub-arena for the

regulatory issue?

• Which of the NRC’s performance goals

does the regulatory issue address?

• What are the expected outcomes and

results from resolution of the regulatory

issue?

Does a risk-informed and performancebased approach to regulation necessarily

involve rulemaking?

No, any part of the regulatory framework

can be considered for modification.

According to the Strategic Plan (Ref. 6),

the regulatory framework consists of

several interrelated aspects. They are (1)

the NRC's mandate from Congress in the

form of enabling legislation, (2) the NRC's

rules in Title 10 of the Code of Federal

Regulations, (3) the regulatory guides and

review plans that amplify those regulations,

(4) the body of technical information,

obtained from research performed by NRC

or by others and from evaluation of

operational experience, that supports the

positions in the rules and guides and

review plans, (5) the licensing and

inspection procedures utilized by the staff,

and (6) the enforcement guidance.
11

Figure 1: Flow Chart To Address Regulatory Issues

Operating

Experience

Commission

Direction

Stakeholder

Suggestion

Stakeholders

Involvement

NRC Identifies Proposed Modification to

Regulatory Framework

Prioritization Using NRC

Performance Goals

PerformanceBased

Traditional

Approach

Select an Option

Risk-Informed

Selected Option Does

Not Meet Viability

Criteria

Define Proposed

Modification

Develop Regulatory Framework (e.g. Rulemaking Package)

According to Existing Office Procedures

Risk-Informed &

PerformanceBased

Staff

Initiatives

Apply

Appropriate

Principles

Develop Approach and Technical Bases

1 Flow Chart To Address Regulatory Issues
12

Step 2 – Identifying the Safety Functions

Purpose – To identify the safety functions and

systems that affect the regulatory issue

(directly or indirectly).

• What are the safety functions or concepts

that can impact the regulatory issue?

This inquiry should be focused on the nature

of the regulatory issue and the expected

outcomes. For example, if the regulatory issue

is directed at placing appropriate quality

requirements on a set of components, the

safety functions (which are functions that

answer the question, “How is risk mitigated ?”)

served by the components would have to be

considered, along with the sensitivity of the

function to the quality level.

• What equipment/systems/procedures are

necessary to satisfy the safety function?

• What level of safety (based on appropriate

metrics) is required to meet the objectives of

the regulatory issue?

For example, if the objective is to maintain

safety while relaxing the stringency of a

regulatory requirement, an appropriate metric

for monitoring safety should be found and

monitored when the regulatory requirement is

changed.

Step 3 – Identifying Safety Margins

Purpose – To evaluate margins and identify

performance parameters (if any) that satisfy

the regulatory issue objectives.

• How much safety margin is available, and

how robust is it, for performance monitoring

to provide a basis for granting licensee

flexibility?

As mentioned earlier, an effective

performance-based approach to regulation

provides flexibility to the NRC and licensees

provided there is sufficient safety margin.

Safety margin can be divided into two parts,

physical and temporal. Physical margin is the

difference between two physical conditions,

the first of which represents expected

conditions and the second of which represents

a performance-limiting condition. An example

of a performance-limiting condition is the peak

pressure capability of a pressure vessel.

Physical margin in a pressure boundary is the

difference between the pressure-retaining

capability of the vessel and the expected

maximum pressure during an accident

condition. 

A temporal margin represents the time

available to identify a concern and to take

actions, such as restoring a failed safety

function, implementing a corrective action

program, or initiating a regulatory response

that mitigates the concern. A temporal margin

in a spent fuel pool, for example, could be the

difference in time between when the

temperature of the pool water is detected to

be at some elevated level (caused by loss of

cooling) and the time needed to reach the

boiling point of the water.

“Robustness” of a safety margin means that

the margin between two performance levels is

significantly greater than uncertainty and

normal variability in performance. If this

condition is met, a very low probability of the

performance parameter crossing the limit

exists, unless performance changes in a very

significant way. In any case, wherever there is

substantial uncertainty, achieving robustness

requires that nominal performance levels be

set more conservatively than when there is

less uncertainty. Depending on the situation,

uncertainty can be assessed using explicit

models (e.g., PRAs), expert judgment, or

actuarial methods based on operating

experience.

The term “margin” is employed in this

guidance somewhat differently than in its

traditional use for health and safety regulation.

The significance of “margin” is closely

associated with the other factors in the viability

guidelines, namely, performance parameters,

objective criteria, and flexibility. If the

magnitude of the safety margin is sufficient to

support a performance-based approach, it

can, in concept, be subdivided and

apportioned in such a way as to consider the
13

objectives of stakeholders. The NRC and

licensees are the principal stakeholders in

resolving a regulatory issue.

For example, the initiating event indicator in

the reactor oversight process (ROP) for

unplanned scrams ranges from 0–25 per 7000

hours of critical operation. The performance

of a licensee would be declared as

unacceptable from a safety standpoint if such

scrams exceed 25 in number. Thus,

according to the action matrix, green level

performance is limited to 0–3 scrams, white is

characterized by 4–6 scrams, yellow is

characterized by 7–25 scrams, and red

denotes more than 25 scrams. Given the

adverse economic consequences of

unplanned scrams, reactor licensees have a

strong incentive to minimize them and stay in

the green band. Almost all licensees

accomplish this objective in practice. The

licensee will likely view exceeding 3 scrams

as a “serious” concern or condition. In this

way, a proxy objective has been created that

works in NRC’s favor because, although

crossing the green/white threshold has only a

minor adverse safety impact, the licensee has

a strong incentive to correct the underlying

cause expeditiously.

Hence, an evaluation of the available margin

and its robustness should include a search for

appropriate performance parameters that

provide for operational flexibility as well as the

means to fulfill regulatory responsibilities. 

• What observable characteristics,

quantitative and qualitative, exist within the

safety functions identified in Step 2?

Measurable or calculable parameters are

generally associated with quantitative

observable characteristics. Parameters that

are observed directly, such as pressure,

temperature, flow, incurred cost, and radiation

exposure, are called natural measures. Some

natural measures require simple calculation,

such as reliability, percentage, and

concentration. However, qualitative

parameters are also able to support a

performance-based approach under

appropriate conditions and should not be

overlooked.

• Can constructed measures be developed

that provide qualitative expressions

capable of observation with reasonable

objectivity?

Step 4 – Selecting Performance Parameters

and Criteria

Purpose – To select a complement of

performance parameters and objective criteria

(if possible) that both satisfy the viability

guidelines and resolve the regulatory issue.

• Can the identified observable

characteristics, together with objective

criteria, provide measures of safety

performance and the opportunity to take

corrective action if performance is

lacking?

• Can objective criteria be developed that

are indicative of performance and that

permit corrective action?

How can qualitative observations be used?

Qualitative observations present special

challenges, but should not be ignored. For

example, the quality of housekeeping in a

nuclear facility is an important aspect of

preventing fire hazards. Qualitative

observations can be quite effective in

assessing such a characteristic. A

linguistically defined measure that

represents a level of impact or

significance, called a constructed measure,

is a way to represent qualitative

observations. A constructed measure

becomes necessary when natural

measures do not exist or are too difficult to

use. It is used to describe performance

needed to satisfy higher-level objectives.

Examples are (1) impact on public

confidence is high, medium, or low, or

(2) environmental significance is high,

medium, or low.
14

• Is flexibility (for NRC and licensees)

available consistent with level of margin?

The approach recommended by the Advisory

Committee on Reactor Safeguards (ACRS) is

to apply the performance criteria at as high a

level as practicable (Ref. 9). Setting the

criteria at a higher level can allow more

flexibility. However, the need to assure

opportunity to take appropriate corrective

action requires that criteria be set

appropriately for the regulatory issue, in a way

that depends on available margin. In general,

this tradeoff between flexibility and the need

for prompt corrective action will require an

iterative approach. If the complexity of the

regulatory issue increases beyond a certain

point, it may be necessary to apply the

methodology described in Appendix B.

The set of questions in Step 4 may not be

amenable for application exactly in the

sequence shown. They should be viewed as

requiring iteration when questions of margin,

corrective action, and flexibility strongly

interact with one another. Strong linkages can

exist between observable characteristics

chosen as the performance parameters to be

used in a performance-based approach and

the assessment of margin based on criteria

applied to these parameters. For example, in

the area of quality assurance, the quality of

emergency backup power provided by a

diesel generator would not necessarily be

well-reflected just by the criteria that are

applied to each component part of the diesel

generator. Even if very strict quality criteria

are applied to each of the component parts,

the overall diesel generator performance may

not meet regulatory standards. On the other

hand, a diesel generator could adequately

meet performance standards even if the

component parts are only commercial grade.

Step 5 – Formulating a Performance-Based

Alternative

Purpose – To determine the appropriate

implementation of a performance-based

approach within the regulatory framework.

• Does the performance-based regulatory

alternative provide necessary and

sufficient coverage of the regulatory issue

objectives?

One of the important elements of coverage is

consideration of defense-in-depth. The ACRS

recommendations (Ref. 9) included one that

would involve multiple performance

parameters that provide redundant information

to satisfy the defense-in-depth philosophy.

The NRC’s defense-in-depth philosophy also

includes consideration of “prevention” and

“mitigation” strategies which operate in proper

balance. If the regulatory issue involves

complex defense-in-depth issues, the needed

guidance should be drawn from Appendix B.

• Of the performance parameters selected

in Step 4, which of them requires that a

prescriptive approach be used to meet

regulatory needs? Can a combination of

performance-based and prescriptive

measures be implemented such that the

resolution of the regulatory issue is as

performance-based as possible?

• Has the regulatory alternative been

considered for implementation within each

What happens if incentives are excluded

from the regulatory approach?

Experience shows that absence of proper

incentives, or the existence of “perverse”

incentives, can result in such emphasis on

compliance that safety may be adversely

affected. One example of such an

occurrence is when licensees, faced with

the approach of the end of an allowable

outage time for a safety system

maintenance, may feel forced into actions

that may meet compliance standards, but

are not fully supportive of safety. The

Commission’s policy on such matters is

presented in detail in COMSAJ-97-008,

“Discussion on Safety and Compliance”

(Ref. 10).
15

of the levels of the regulatory framework so

that an optimum level is proposed?

For example, a prescribed parameter can be

included in a Technical Specification or other

license condition. It may be possible to

provide flexibility in operation for parameters

that do not have to be strictly controlled. Also,

as mentioned above, staff may consider one

or another type of incentives for licensees to

increase the likelihood of improved safety

outcomes.

• Are licensees’ incentives appropriately

aligned, considering the overall complement

of performance measures, criteria, the

implementation, and the regulatory

framework as a whole?

Licensees’ flexibility can be coupled with

positive and negative incentives. Examples of

positive incentives occur when licensees may

be able to reduce costs of operation if they

meet specified levels of safety or trends in

safety of operation. Examples of negative

incentives occur when NRC’s enforcement

policy causes licensees to experience

undesired consequences when levels of

safety or trends in safety are unfavorable.

Regulation that is based on sampling licensee

performance needs to be designed with care,

in order to avoid incentivizing performance in

one important area at the expense of another,

with a net adverse outcome. As a hypothetical

example, regulation that sought only to

minimize the unavailability of components

might create an incentive to reduce

maintenance to a level at which unreliability

performance would be adversely affected.

When staff considers a change to the

regulatory framework, they must also consider

the incentives created by the new overall

framework.

• Is it worth modifying the regulatory

framework in the manner proposed,

considering the particulars of the regulatory

issue?

Summary

This step-by-step process takes the staff

through a series of questions that should lead

to answers to the following fundamental

questions (1) What is the regulatory issue? (2)

Is it possible to use a performance-based

approach to resolve the issue? (3) Does it

appear worthwhile to pursue a performancebased solution? Although a formal response to

the last question requires application of the

assessment guidelines, management

judgment can be sufficient for considering a

performance-based alternative in a regulatory

analysis or other appropriate process.

17

4 ILLUSTRATIVE EXAMPLES

For illustration purposes, this section presents

actions on three recent regulatory issues are

presented below to exemplify application of

the process steps. By applying this process,

staff can determine whether a regulatory

requirement can be made more performancebased. These examples also demonstrate

how different elements of the regulatory

framework can be targeted for the most

effective and efficient application of the

guidance steps and hence improve the net

benefit from a performance-based proposal.

The first example is a recent proposal to

revise 10 CFR 50.44 concerning combustible

gas control in containment at nuclear power

plants (Ref. 11). The draft regulatory guide

provided with the rulemaking package, DG1117, offers a performance-based approach to

meeting the requirement for hydrogen

monitors to be functional, reliable, and

capable of measuring hydrogen concentration

in the containment after an accident.

The second example is a proposed rule that

addresses geological and seismological

characteristics for siting and design of dry

cask independent spent-fuel storage

installations and monitored retrievable storage

installations (Ref. 12). The regulatory analysis

for this rulemaking recommends a

performance-based approach in order to meet

the safety objectives in a cost-effective

manner.

The third example was originally proposed as

a risk-based performance indicator for

shutdown conditions for use in the ROP. NRC

staff is considering Its essential aspects are

being considered for use in the significance

determination process relative to inspection

findings during shutdown conditions (Ref. 13). 

The process steps are presented below using

specific factors that entered into incorporating

performance-based concepts in each of the

examples. The examples (identified as

Examples 1, 2, and 3) have been employed in

each of the process steps introduced in

Section 3.2 to the extent that they successfully

illustrate the step. In other words, each step

does not employ all examples. Example 3 has

not been incorporated into the ROP; however,

it represents a useful illustration of a way to

look for the most effective performance

parameters. 

Step 1 – Defining the Regulatory Issue and

its Context

• What is the arena and sub-arena for the

regulatory issue?

In the case of Examples 1, 2, and 3, the

issues belong in the reactor and waste

arenas, with the sub-arenas in rulemaking,

spent fuel safety and inspection programs,

respectively.

• Which of the NRC’s performance goals

does the regulatory issue address?

The examples potentially cover all four of the

agency’s performance goals.

• What are the expected outcomes and

results from resolution of the regulatory

issue?

The expected outcome in each example is to

identify the performance-based alternatives

that optimally use the flexibility of the

regulatory framework to obtain a cost-effective

resolution of each regulatory issue.

Step 2 – Identifying the Safety Functions

• What are the safety functions or concepts

that can impact the regulatory issue?

In Example 1, the safety functions are

accident management to maintain

containment integrity and effective emergency

planning. In Example 2, the safety functions

are stability against soil liquifaction during

vibratory motion, and cask sliding and

resulting displacements during an earthquake

event.
18

• What equipment/systems/procedures are

necessary to satisfy the safety function?

The technical evaluation for Example 1

showed that non-safety-related commercial

grade hydrogen monitors that meet lower

category requirements than the existing

safety-related systems would satisfy the safety

function. The evaluation for Example 2

showed that more cost-effective analyses may

be possible to satisfy siting criteria than

existing prescriptive criteria, which essentially

require the same criteria as operation of a

nuclear power plant.

• What level of safety (based on appropriate

metrics) is required to meet the objectives of

the regulatory issue?

For Example 1, the required level of safety is

that which meets the objective of reducing, to

an acceptable level, the risk of early

containment failure from hydrogen

combustion. Hence, the metric in this case is

the conditional containment failure probability.

For Example 3, the required level of safety is

to maintain at an acceptable level the core

damage risk associated with certain

configurations typical of shutdown operations.

Step 3 – Identifying Safety Margins

• How much safety margin is available, and

how robust is it, for performance monitoring

to provide a basis for granting licensee

flexibility?

Example 2 exemplifies an instance for which

the safety margin can be assessed

qualitatively, yet reliably. The casks in

question are designed to safely withstand the

conditions associated with transportation and

handling of spent-fuel operations. The rigors

of such operations, and the associated

regulatory requirements, can reasonably be

expected to envelop, with considerable

margin, the challenges posed by vibratory

motion and sliding displacements during an

earthquake.

A different type of margin can be identified in

Example 3. The technical evaluation identified

four risk-significant categories of

configurations for pressurized-water reactors

(PWRs) and three for boiling-water reactors

(BWRs). For each reactor type, the categories

range from low risk to high risk. Baseline

performance levels were established using

operating history. In the low-risk

configurations, baseline performance is

achieved by exiting a configuration within 20

days in PWRs and 2 days in BWRs. At the

other end of the spectrum, the threshold for

unacceptable performance occurs at 1 day in

a high-risk configuration. Applying the

concepts of the ROP and its action matrix,

under nominal conditions, licensees would

expect to operate within the green band,

which corresponds, for PWRs, to 21 days in a

low-risk configuration and by totally avoiding a

high-risk configuration. One day in a high-risk

configuration would denote unacceptable

performance. Hence, monitoring the time at

risk-significant shutdown configurations

provides the NRC and the licensee with a

performance-based approach for maintaining

safety margins at acceptable levels.

• What observable characteristics,

quantitative and qualitative, exist within

the safety functions identified in Step 2?

For Example 1, the observable characteristics

come from the results of periodic servicing,

testing, and calibration of hydrogen monitors.

The operating margin would come from a

comparison between these results and the

target values established by the licensee

under the maintenance rule. For Example 2,

the observations would likely be based on

verification of design margins by postearthquake inspections, and corrective actions

as necessary over the extended periods of

time over which such sites may be in

operation.

• Can constructed measures be developed

that provide qualitative expressions

capable of observation with reasonable

objectivity?

Among the examples considered, Example 2

may require a constructed measure to
19

characterize the response of the storage

facility to an actual earthquake.

Step 4 – Selecting Performance

Parameters and Criteria

• Can the identified observable

characteristics, together with objective

criteria, provide measures of safety

performance and the opportunity to take

corrective action if performance is lacking?

In Example 1, the recorded results of the

maintenance program provide the observable

characteristics and also provide the

opportunity to take corrective actions if lack of

performance is noted by the NRC or the

licensees themselves.

The performance criterion in Example 3 is the

time period in each of the shutdown

configurations. This exemplifies a focused

application of the recommendation of the

ACRS that the performance parameters

should be identified at as high a level as

practicable. If this recommendation had not

been followed, all systems and sub-systems

involved in risk-significant configurations might

have been targeted for monitoring. The

management of risk in such configurations

could still be accomplished. The

recommendation to search for parameters at a

high level would direct the analyst’s attention

to other, more cost-effective possibilities. In

Example 3, time in risk-significant

configurations fulfills the needed attributes.

The second ACRS recommendation of

providing for defense-in-depth by redundant

observations can also be implemented by

separately monitoring the safety functions of

certain risk-significant components.

• Can objective criteria be developed that are

indicative of performance and that permit

corrective action?

In both Examples 1 and 3, the regulatory

issues are highly amenable to establishment

of objective criteria that are indicative of

performance, as well as permit sufficient time

for corrective action.

• Is flexibility (for NRC and licensees)

available consistent with level of margin?

Example 2 exemplifies how the existence of

substantial margins enables consideration of

higher magnitudes of flexibility. Because of the

robustness of the casks, licensees can

potentially employ simplified analyses to show

that the uncertainties associated with

seismicity and cask response can be reliably

enveloped to demonstrate conformance with

site suitability criteria. Simplified analyses

provide greater cost-effectiveness.

Similarly, in Example 3, a range of flexibility is

considered, consistent with margin available in

each shutdown configuration category. The

least flexibility would be available for the highrisk category, which is appropriate from a

regulatory perspective.

Step 5 – Formulating a Performance-Based

Alternative

• Does the performance-based regulatory

alternative provide necessary and

sufficient coverage of the regulatory issue

objectives?

In both Examples 1 and 2, the staff

determined that sufficient margin is present for

NRC staff to confirm directly that licensee

performance is adequate in key areas, without

requiring compliance with prescriptive

requirements in all areas. Therefore, a lessprescriptive, more performance-based

approach can provide suitable coverage of the

regulatory issue objectives.

• Of the performance parameters selected

in Step 4, which of them requires that a

prescriptive approach be used to meet

regulatory needs? Can a combination of

performance-based and prescriptive

measures be implemented such that the

resolution of the regulatory issue is as

performance-based as possible?

Example 3 offers an illustration of how specific

prescriptive elements can be incorporated into

a less prescriptive regulatory approach. The

regulatory framework permits inclusion of
20

prescriptive elements through Technical

Specification or License Condition provisions. 

• Has the regulatory alternative been

considered for implementation within each of

the levels of the regulatory framework so

that an optimum level is proposed?

In both Examples 1 and 2, various alternative

means for implementing a performance-based

approach within the regulatory framework

were considered. A variety of internal

stakeholder input was explicitly included

before coming up with the recommendations

published in the Federal Register.

• Are licensees’ incentives appropriately

aligned, considering the overall complement

of performance measures, criteria, the

implementation, and the regulatory

framework as a whole?

Inappropriate incentives could potentially

occur in the case of Example 3. In NUREG1753, for the case of PWRs in reduced

inventory operation, the threshold times

corresponding to green/white and white/yellow

threshold are 1 day and 1.08 days,

respectively. Licensees might perceive an

incentive to inappropriately rush through

safety-sensitive operations only to avoid

crossing a threshold. The staff is in a better

position to structure regulatory provisions that

minimize perverse incentives by explicitly

considering the possibilities within the

regulatory framework and the ROP’s action

matrix.

• Is it worth modifying the regulatory

framework in the manner proposed,

considering the particulars of the regulatory

issue?

In both Examples 1 and 2, the proposed

performance-based alternatives have been

published for comment. In both cases,

preliminary indications suggest that the

proposals enjoy considerable stakeholder

support. Hence, the modifications appear

worthwhile.
21

5 REFERENCES

1. Nuclear Regulatory Commission (U.S.) (NRC). “Staff Requirements - SECY-96-218 -

Quarterly Status Update for the Probabilistic Risk Assessment (PRA) Implementation

Plan, Including a Discussion of Four Emerging Policy Issues Associated with RiskInformed Performance-Based Regulation.” NRC: Washington, DC. January 22, 1997.

2. Nuclear Regulatory Commission (U.S.) (NRC). “Staff Requirements - COMSECY-96-061

- Risk-Informed, Performance-Based Regulation (DSI 12).” NRC: Washington, DC. April

15, 1997.

3. Nuclear Regulatory Commission (U.S.) (NRC). “Staff Requirements - SECY-98-144 -

White Paper on Risk-Informed and Performance-Based Regulation.” NRC: Washington,

DC. March 1999.

4. Nuclear Regulatory Commission (U.S.) (NRC). SECY 00-191, “High-Level Guidelines for

Performance-Based Activities.” NRC: Washington, DC. September 2000.

5. Nuclear Regulatory Commission (U.S.), Washington, DC. “Revised High-Level

Guidelines for Performance-Based Activities,” Proposed Rule. Federal Register: Vol. 65,

No. 90. pp. 26772-26776. May 9, 2000.

6. Nuclear Regulatory Commission (U.S.) (NRC). NUREG-1614, Vol. 2, Parts 1 & 2,

“Strategic Plan Fiscal Year 2000 - Fiscal Year 2005.” (Final Report) NRC: Washington,

DC. September 2000.

7. Nuclear Regulatory Commission (U.S.) (NRC). NUREG/BR-0058, Rev. 3, “Regulatory

Analysis Guidelines.” (Final Report) NRC: Washington, DC. June 2000.

8. Nuclear Regulatory Commission (U.S.) (NRC). SECY 01-0218, “Update of the RiskInformed Regulation Implementation Plan.” NRC: Washington, DC. December 5, 2001.

9. Letter, Dana A. Powers (ACRS) to William D. Travers (EDO, NRC), September 8, 2000.

Subject: Proposed High-Level Guidelines for Performance-Based Activities.

10. Nuclear Regulatory Commission (U.S.) (NRC). “Staff Requirements - COMSAJ-97-008 -

Discussion on Safety and Compliance.” NRC: Washington, DC. August 25, 1997.

11. Nuclear Regulatory Commission (U.S.), Washington, DC. “Combustible Gas Control in

Containment,” Proposed Rule. Federal Register: Vol. 67, No. 149. pp. 50374-50383.

August 2, 2002.

12. Nuclear Regulatory Commission (U.S.), Washington, DC. “Geological and Seismological

Characteristics for Siting and Design of Dry Cask Independent Spent Fuel Storage

Installations and Monitored Retrievable Storage Installations,” Proposed Rule. Federal

Register: Vol. 67, No. 140. pp. 47745-47755. July 22, 2002.

13. Nuclear Regulatory Commission (U.S.)(NRC). NUREG-1753, “Risk-Based Performance

Indicators; Results of Phase 1 Development.” NRC: Washington, DC. April 2002.

APPENDIX A

HIGH-LEVEL GUIDELINES FOR PERFORMANCE-BASED ACTIVITIES

A-1

APPENDIX A

HIGH-LEVEL GUIDELINES FOR PERFORMANCE-BASED ACTIVITIES

The U.S. Nuclear Regulatory Commission

(NRC) staff developed, and provided to the

Commission and the public, high-level

guidelines to identify and assess

performance-based activities in SECY-00-191,

dated September 1, 2000 (Ref. A-1). These

guidelines were developed consistent with the

direction in the Staff Requirements

Memorandum (SRM) to SECY-99-176, “Plans

for Pursuing Performance-Based Initiatives”

(Ref. A-2). The staff made presentations on

the guidelines to the Advisory Committee on

Reactor Safeguards (ACRS) and the Advisory

Committee on Nuclear Waste and provided

them for information to the Advisory

Committee on Medical Use of Isotopes. On

September 8, 2000, the ACRS (Ref. A-3)

provided conclusions and recommendations

that included the following:

• The guidelines should explicitly state that

the performance levels and reliability

parameters should be set at the highest

practical level.

• Guidance should be given on the extent to

which multiple performance parameters

that provide redundant information should

be used to satisfy the defense-in-depth

philosophy.

The staff has determined that, in order to meet

these recommendations, the guidelines need

to be modified and the process that is followed

to implement the guidelines must have the

following guidance:

1. A hierarchical structure of goals and

objectives should be developed that

reflects the decisionmaking values of a

regulatory issue so that the term “highest

practical level” can be interpreted

objectively.

2. The development of redundant information

to satisfy the defense-in-depth philosophy

requires that the association of

performance parameters with objectives

should be represented in a formal manner

so that attributes such as “prevention” and

“mitigation” are explicitly treated.

The re-formulated high-level guidelines for

performance-based activities are presented

below in two versions. The first version is the

formal one that maintains similarity and

consistency with the guidelines provided to the

Commission in SECY-00-191 and published in

the Federal Register at 65 FR 26772

(Ref. A-4). The only changes made are those

needed to implement the ACRS

recommendations. The second version is a

plain-English rendition of the high-level

guidelines that relates more directly to the

stepwise process described in Section 3.

Version 1 (Formal)

I. Viability Guidelines

A. A framework exists or can be developed

to show that performance by identified

elements will serve to accomplish desired

goals and objectives. Margins of

performance exist such that if

performance criteria are not met, an

immediate safety concern will not result.

(1) An adequate safety margin exists.

(2) Time is available for taking corrective

action to avoid safety concerns.

(3) The licensee is capable of detecting

and correcting performance

degradation. 

B. Measurable, calculable, or constructable

parameters to monitor acceptable plant

and licensee performance exist or can be

developed.

(1) Directly measured parameters related

to the safety objective are preferred

and will typically satisfy this guideline.
A-2

(2) Calculated or constructed parameters

may also be acceptable if there is a

clear relationship to the safety

objective. 

(3) Parameters that licensees can readily

access, or are currently accessing, in

real time are preferred and will

typically satisfy this guideline.

Parameters monitored periodically to

address postulated, design basis, or

other conditions of regulatory

significance may also be acceptable.

(4) Acceptable parameters will be

consistent with defense-in-depth and

uncertainty considerations.

C. Objective criteria to assess performance

exist or can be developed.

(1) Objective criteria consistent with the

desired outcome are established

based on risk insights, deterministic

analyses, and/or performance history.

D. Licensee flexibility in meeting the

established performance criteria exists or

can be developed.

(1) Programs and processes used to

achieve the established performance

criteria will be at the licensee’s

discretion.

(2) A consideration in incorporating

flexibility to meet established

performance criteria will be to

encourage and reward improved

outcomes, provided inappropriate

incentives can be avoided.

II. Assessment Guidelines

A. Maintain safety and protect the

environment and the common defense

and security.

(1) Safety considerations play a primary

role in assessing any change arising

from the use of performance-based

approaches.

(2) Adequate safety margins are

maintained using realistic safety

analyses, including explicit

consideration of uncertainties.

B. Increase public confidence.

(1) An emphasis on results and objective

criteria (characteristics of a

performance-based approach) can

help NRC to be viewed as an

independent, open, efficient, clear,

and reliable regulator.

(2) A performance-based approach helps

provide the public clear and accurate

information about, and a meaningful

role, in the regulatory programs.

(3) A performance-based approach helps

explain NRC’s roles and

responsibilities and how public

concerns are considered.

C. Increase effectiveness, efficiency, and

realism of the NRC’s activities and

decisionmaking.

(1) The level of conservatism existing in

the currently applicable regulatory

requirements would be assessed,

considering analysis methodology and

the applicable assumptions. Any

proposal to use realistic analysis

would take into account uncertainty

factors and defense-in-depth relative

to the scenario under consideration.

(2) The performance criteria and the level

in the performance hierarchy at which

they have been set would be

assessed. In general, performance

criteria would be set at a level

commensurate with the function being

performed. In most cases,

performance criteria would be

expected to be set at the system level

or higher.
A-3

D. Reduce unnecessary regulatory burden.

(1) A performance-based approach

enables the NRC to impose regulatory

burden that is commensurate with the

safety benefit and that effectively

focuses resources on safety issues.

(2) A performance-based approach will

enable the costs associated with NRC

activities to States, the public,

applicants, and licensees to be

focused on areas of highest safety

priority and avoid burden imposed by

overly prescriptive regulatory

requirements.

E. The expected result of using a

performance-based approach is an overall

net benefit.

(1) A reasonable net benefit test begins

with a qualitative approach to evaluate

whether there is merit in changing the

existing regulatory framework. When

the net benefit test is approached from

the perspective of existing practices,

stakeholder input would be sought.

(2) Unless imposition of a safety

improvement or other societal benefit

is contemplated, expending resources

for a change in regulatory practice

would be justified only if NRC or

licensee operations benefit from such

a change. Licensees themselves will

be the primary source of initial

information and feedback regarding

potential benefits.

(3) For the limited purpose of screening

potential performance-based changes,

consideration of a specific result (such

as net reduction in worker radiation

exposure) may be sufficient for

weighing the immediate implications of

a proposed change.

F. The performance-based approach can be

incorporated into the regulatory

framework.

(1) The regulatory framework may include

regulation in the Code of Federal

Regulations, the associated regulatory

guides, NUREGs, standard review

plans, technical specifications, and

inspection guidance. 

(2) A feasible performance-based

approach would be directed

specifically at changing one, some, or

all of these elements.

(3) The proponent of the change to the

elements of the regulatory framework

would be responsible for providing

sufficient justification for the proposed

change; all stakeholders would have

the opportunity to provide feedback on

the proposal, typically in a public

meeting.

(4) Inspection and enforcement

considerations would be addressed

during the formulation of regulatory

changes rather than afterwards. Such

considerations could include reduced

NRC scrutiny if performance so

warrants.

G. The performance-based approach would

accommodate new technology.

(1) The incentive to consider a

performance-based approach may

arise from the development of new

technologies, as well as difficulty in

finding spare components and parts

for existing technologies.

(2) Advanced proven technologies may

provide more economical solutions to

a regulatory issue without

compromising safety, hence justifying

consideration of a performance-based

approach.

III. Guidelines for Consistency with

Regulatory Principles

A. A proposed change to a more

performance-based approach is

consistent and coherent with other
A-4

overriding goals, principles, and

approaches in the NRC’s regulatory

process.

(1) These principles are provided in the

Principles of Good Regulation (Ref. A5); the Probabilistic Risk Assessment

Policy Statement (Ref. A-6);

Regulatory Guide 1.174, “An Approach

for Using PRA in Risk-Informed

Decisions on Plant-Specific Changes

to the Licensing Basis” (Ref. A-7); and

the NRC’s Strategic Plan (Ref. A-5).

(2) Consistent with the high level at which

the guidelines have been articulated,

specific factors that need to be

addressed in each case (such as

defense in depth and treatment of

uncertainties) would depend on the

particular regulatory issues involved.

Version 2 (Plain English)

I. Viability Guidelines (Can a performancebased approach be developed?)

A. Estimate margin realistically, using

quantitative and/or qualitative factors. Is

the margin robust, or is it sensitive to

unpredictable factors? Is there time to take

corrective action if expectations regarding

the regulatory issue or the licensee are not

borne out? Can the affected licensees

reasonably be expected to react

appropriately if surprises occur?

B. Are there quantitative or qualitative

parameters, using natural or constructed

measures, that can be observed and that

can promptly reveal an unacceptable

reduction in margin? Does the observation

of these parameters support the objectives

of defense in depth and control of

uncertainty?

C. Can objective criteria, consistent with the

desired outcome, be established based on

risk insights, deterministic analyses,

and/or performance history?

D. Is the flexibility afforded to licensees in the

existing regulatory framework consistent

with the realistic margin estimate? Can a

change in the level of flexibility be effected

in a way that would encourage and reward

improved outcomes, while avoiding

inappropriate incentives?

II. Assessment Guidelines (Is it worthwhile to

develop a performance-based change?)

A. Can a performance-based change to the

regulatory framework fulfill the

performance goal of “Maintain safety and

protect the environment and the common

defense and security”?

B. Can a performance-based change to the

regulatory framework fulfill the

performance goal of “Increase public

confidence”?

C. Can a performance-based change to the

regulatory framework fulfill the

performance goal of “Increase

effectiveness, efficiency, and realism of

the NRC activities and decisionmaking”?

D. Can a performance-based change to the

regulatory framework fulfill the

performance goal of “Reduce

unnecessary regulatory burden”?

E. Does implementing a performance-based

approach yield a net benefit?

F. Where does the performance-based

change best fit into the regulatory

framework? What are the effects on

inspection and enforcement functions?

G. Is accommodation made to employ the

best available technology, now and in

future?

III. Guidelines for Consistency with

Regulatory Principles

A. Is any part of a performance-based

approach inconsistent with basic

regulatory principles?
A-5

REFERENCES

A-1 Nuclear Regulatory Commission (U.S.) (NRC). SECY 00-191, “High-Level Guidelines for

Performance-Based Activities.” NRC: Washington, DC. September 2000.

A-2 Nuclear Regulatory Commission (U.S.) (NRC). SECY 99-176, “Plans for Pursuing

Performance-Based Initiatives.” NRC: Washington, DC. July 12, 1999.

A-3 Letter, Dana A. Powers (ACRS) to William D. Travers (EDO, NRC), September 8, 2000.

Subject: Proposed High-Level Guidelines for Performance-Based Activities.

A-4 Nuclear Regulatory Commission (U.S.), Washington, DC. “Revised High-Level

Guidelines for Performance-Based Activities,” Proposed Rule. Federal Register: Vol. 65,

No. 90. pp. 26772-26776. May 9, 2000.

A-5 Nuclear Regulatory Commission (U.S.) (NRC). NUREG-1614, Vol. 2, Parts 1 & 2,

“Strategic Plan Fiscal Year 2000 - Fiscal Year 2005.” (Final Report) NRC: Washington,

DC. September 2000.

A-6 Nuclear Regulatory Commission (U.S.), Washington, DC. “Use of Probabilistic Risk

Assessment Methods in Nuclear Activities: Final Policy Statement.” Federal Register:

Vol. 60, No.158. pp. 42622–42629. August 16, 1995.

A-7 Nuclear Regulatory Commission (U.S.) (NRC). Regulatory Guide 1.174, “An Approach

for Using PRA in Risk-Informed Decisions on Plant-Specific Changes to the Licensing

Basis.” NRC: Washington, DC. July 1998.

APPENDIX B

SUPPLEMENTARY GUIDANCE FOR MORE COMPLEX ISSUES

B-1

What is an “objectives hierarchy?”

An objectives hierarchy is a diagram

representing the relationships and

dependencies between goals, top-level

fundamental objectives, lower-level

fundamental objectives, and means

objectives. Fundamental objectives are

ends in themselves; means objectives are

things that are desirable because they

support fundamental objectives. An

example of a goal is “protection of the

health and safety of the public;” an

example of a fundamental objective is

“protection of the public from excessive

radiological exposures;” and an example of

a means objective is “reliability of safety

systems.” These are examples from the

structure of the Reactor Oversight Process

(ROP), which makes use of an objectives

hierarchy.

APPENDIX B

SUPPLEMENTARY GUIDANCE FOR MORE COMPLEX ISSUES

B.1 Background

In some cases, the general guidance offered

in Section 3 of this document is insufficient,

because the treatment of the regulatory issue

is affected by one or more of the following:

• complexity

• uncertainty

• multiple objectives, especially competing

objectives

• different stakeholder perspectives

When these conditions are present, a more

considered approach, based on decision

analysis, is warranted (Ref. B-1). The

application of this type of analysis to nuclear

technology has recently appeared in the

technical literature (Refs. B-2, B-3, B-4). The

purpose of this appendix is to discuss

selected elements of such an approach. 

As mentioned in Section 3, the purpose of this

document is to support the development of a

performance-based regulatory alternative, if

one is appropriate. Generally, a performancebased regulatory alternative needs to:

1. allocate performance across relevant

functions, systems, or barriers, in order to

assess whether the target safety

objectives are satisfied

2. then implement that allocation of

performance which entails identifying the

steps to be taken by licensees and/or NRC

to make the performance allocation “come

true” in practice

Part of implementation is confirmation of

ongoing performance.

Accordingly, this appendix is aimed at a more

rigorous development of Step 2 in Section 3,

which called for “identifying the safety

functions.” Depending on the individual case,

this level of rigor may vary. For example,

where an issue affects many areas and

different objectives, this added complexity

may justify the explicit development of a more

detailed objectives hierarchy (see text box). 

With an objectives hierarchy in hand, it

becomes easier to assess the levels of

performance needed from each element. And,

in conjunction with the viability guidelines, one

can determine those cases in which

performance can appropriately be monitored

through inspections or performance indicators,

and where it cannot, which would suggest that

a more prescriptive approach is warranted. 

The approach discussed below is intended to

promote adequate coverage of key

performance areas with performance

measures in a way that qualitatively

addresses defense-in-depth considerations.
B-2

What value does an objectives hierarchy

add to the process of formulating a

regulatory alternative?

Formulation of a performance-based

alternative is supported directly by an

objectives hierarchy. First, systematic

consideration of the objectives hierarchy

fosters completeness in the set of

performance areas considered. Second,

the hierarchy structure segments the

objectives that are more suitable for

performance-based and prescriptive

alternatives which typically correspond to

the upper and lower levels of the hierarchy,

respectively. Finally, in the allocation step,

the objectives hierarchy helps to keep track

of the satisfaction of each safety objective

at each level in the objectives hierarchy. 

B.2 Development of the Objectives

Hierarchy

Decisionmaking, and in particular the

development of performance-based

approaches to regulation, conventionally

begins with clarification of the objectives

(Refs. B-1, B-4). This is especially important

when competing objectives are involved as is

often the case in regulatory decisionmaking. A

common instance of competing objectives

occurs when there is a need to weigh safety

benefits against burden (unless the issue is

related to adequate protection

considerations). In the present case, two

reasons exist for emphasizing this

consideration. First, the viability guidelines

focus on parameters in terms of which criteria

can be specified; a clear picture of the desired

functional attributes is necessary in order to

carry out this step properly. Second,

determining these objectives also establishes

the scope of the net benefit test applied under

the assessment guidelines, which constitutes

the second step in a three-step application of

the high-level guidelines. 

Even if an issue is not concerned with a safety

enhancement (that is, the current level of

safety is considered appropriate), regulatory

proposals to resolve the issue must address

safety so as to confirm that it is being

maintained. Alternatively, if an issue initially

involves only safety, regulatory proposals to

resolve it must address burden, public

confidence, and efficiency and effectiveness

(except when the issue is deemed to be one

of adequate protection).

Figures B-1 through B-3, based in part on the

ROP (Ref. B-5), illustrate concepts of an

objectives hierarchy. Figure B-1 shows the

goal, fundamental objectives, and means

objectives of an objectives hierarchy. Figure

B-2 presents more detail of the ROP. The

cornerstone areas identified in Figure B-2 are

intended to be a complete set of key

performance areas affecting safety. The key

attributes identified within each cornerstone

are likewise intended to be a complete set.

Completeness is one of the reasons to pursue

such a systematic development. In Figure B-2,

consideration of the different cornerstone

areas also illustrates how the implicit 

underlying allocation of performance

addresses defense-in-depth at a high level.

Balance between prevention and mitigation is

shown by the presence of cornerstones

addressing initiating events, mitigating

systems, and emergency preparedness; the

additional consideration of barrier integrity

further reinforces defense-in-depth. 

Analogous to logic tree development, each

level of the objectives hierarchy is derived

from the level above by decomposing each

node into constituent elements. Each means

objective relates to an objective above it on

the hierarchy, in that it answers the question,

“How is the higher-level objective to be

accomplished?” (Question: How will safety

function X be accomplished? Answer: By

reliable function of systems A, B, and C.) In

fact, a system reliability model developed

hierarchically and expressed in “success

space” is essentially a partial objectives

hierarchy. It is “partial” because it addresses

only safety performance, and because, even

within safety, a logic model does not usually

address cross-cutting programmatic issues of

the sort that appear at the bottom of

Figure B-3.
B-3

























































Goal Fundamental

Objectives

Means

Objectives

Figure B-1

Overview of Objectives Hierarchy

Key

Attributes

Performance

Elements

Cornerstones

Strategic

Performance

Areas

PUBLIC HEALTH AND SAFETY AS A RESULT OF

CIVILIAN NUCLEAR REACTOR OPERATION

B-1 Overview of Objectives Hierarchy
B-4

PUBLIC HEALTH AND SAFETY

AS A RESULT OF CIVILIAN

NUCLEAR REACTOR

OPERATION

REACTOR

SAFETY

RADIATION

SAFETY SAFEGUARDS

Strategic

Performance

Areas

Cornerstones INITIATING

EVENTS

MITIGATION

SYSTEMS

BARRIER

INTEGRITY

EMERGENCY

PREPAREDNESS PUBLIC OCCUPATIONAL PHYSICAL PROTECTION

HUMAN

PERFORMANCE

SAFETY CONSCIOUS WORK

ENVIRONMENT

PROBLEM

IDENTIFICATION AND

RESOLUTION

           

 Fundamental Objectives

        

 Means Objectives

Figure B-2

Reactor Oversight Process Objectives Hierarchy 

B-2 Reactor Oversight Process Objectives Hierarchy
B-5

Mitigation Systems Performance

Function

System

Trains

Components

Human Actions

Line Supervision

Management

Training / Values Engineering Support Human Factors

Engineering

Procedures Programmatic Activities 

Cornerstone Level

Objectives Hierarchy

Figure B-3

More Detailed Decomposition of Means Objectives

B-3 More Detailed Decomposition of Means Objectives
B-6

Figure B-3 illustrates levels of a hierarchy

applicable to many issues involving safety

assessments. A complete and explicit

development of all hardware and programs

involved in accomplishing high-level safety

functions would be a significant undertaking.

The point of the present guidance is not to

mandate such an explicit, detailed, and

laborious development, but to point out how

the concepts can apply even if the

development exists only in the abstract or in a

qualitative way. The value of this construct will

be clearer in light of the discussion in the

following subsection. 

B.3 Allocation of Performance

Before selecting performance measures, it is

logically necessary to determine what kind of

performance and what level of performance is

needed from each performance area. For

example, in the reactor arena, each of the

cornerstone areas (initiating events, mitigating

systems, barrier integrity, emergency

preparedness) receives attention.

Performance is expected in each cornerstone

area. Strong performance in all areas provides

an important defense-in-depth component,

because to some extent, performance in one

area can compensate for lack of performance

in another. For example, an increase in

initiating events frequency will not typically be

a safety issue, if the mitigating systems’

performance is satisfactory. This approach is

fully consistent with the Commission’s White

Paper definition of defense-in-depth, which

states:

Defense-in-depth is an element of the

NRC’s Safety Philosophy that employs

successive compensatory measures to

prevent accidents or mitigate damage

if a malfunction, accident, or naturally

caused event occurs at a nuclear

facility. The defense-in-depth

philosophy ensures that safety will not

be wholly dependent on any single

element of the design, construction,

maintenance, or operation of a nuclear

facility. The net effect of incorporating

defense-in-depth into design,

construction, maintenance, and

operation is that the facility or system

in question tends to be more tolerant

of failures and external challenges

(Ref. B-6).

Generally, it is desirable to specify and

monitor performance targets as high on the

objectives hierarchy as possible, consistent

with the viability guidelines. Allocating

performance too far down on the hierarchy

reduces licensee flexibility. Arriving at an

implementation that maintains safety, while

appropriately balancing licensee flexibility with

the need for regulatory assurance of ongoing

performance, will require some iteration with

the allocation step.

B.3.1 Example

In order to understand what it means to

allocate performance, and why performance

may need to be allocated, consider the

following example. The quantitative analysis

presented in the Reactor Safety Study (Ref. B7) showed that resources were allocated in an

imbalanced way. Much attention had

previously been focused on plant response

conditional on a design-basis loss-of-coolant

accident, while somewhat less attention had

been focused on decay heat removal in

scenarios initiated by transients or small

breaks. This was addressed in a TMI

requirement (Ref. B-8), as a result of which

auxiliary feedwater systems (AFWS) in

pressurized-water reactors (PWRs) licensed

during the 1980s were expected to

demonstrate low unreliability “in the range of

1E-4 to 1E-5 per demand” (Ref. B-9).

Assuming reasonable initiating event

frequencies, satisfaction of this requirement

would mean that a certain class of accident

sequences was being controlled reasonably

well. 

This is a specific example of an allocation.

Performance in the initiating events area was

tacitly allocated at then-current levels, while

target performance in AFWS reliability was set

at a level somewhat better than was then

being achieved at certain plants. Note that this

was a design and licensing issue, not a

“performance” issue. 
B-7

What do we mean by “allocation?”

Given a top-level safety objective (such as

CDF, or dose limits, or frequency of

overexposure), the “allocation” of

performance among barriers, structures,

systems, and components (SSCs), etc., is

the choice of performance targets set by a

regulatory alternative in order to assure that

the safety objective is met. A choice among

possible allocations must often be made,

because it may be formally possible to

meet a safety objective in more than one

way. However, cost and practicality

significantly restrict the possibilities that

need to be considered.

Does allocation always require setting

explicit numerical targets?

No. But the history of the development of

regulations at NRC suggests that it is

helpful to work with performance targets

that are at least implicitly numerical.

Otherwise, it is difficult to determine how

stringent the performance requirements

need to be, or whether performance

monitoring is a viable option in some areas.

This example serves to illustrate the previous

comments regarding licensee flexibility. Refer

again to Figure B-3. Some flexibility was made

available in the application of this requirement

to AFWS systems, provided that alternative

methods of core cooling were shown to be

available (e.g., feed and bleed). Thus, the real

allocation was pitched at the functional level

(decay heat removal), with alternative

allocations available at the systems level

(allocate all performance to AFWS, or

alternatively, allocate some to AFWS and

some to high-pressure injection and primary

depressurization).

Carried down to lower levels, these

requirements have implications for such areas

as inservice testing and inspection, and

technical specifications.

B.3.2 Process

A thought process analogous to the above

should be carried out, at least implicitly or

qualitatively, whenever regulatory

requirements are being formulated. The

stringency of requirements at a given level

needs to be related to the top-level safety

objectives being addressed.

The starting point is an allocation of

performance at the upper levels of the

hierarchy. This allocation should appropriately

balance prevention and mitigation, while

satisfying agency safety objectives. In the

reactor arena, this top-level allocation step

frequently begins with core damage frequency

(CDF) and large-early-release frequency

(LERF) objectives, and then infers practical

limits on the frequencies of various accident

sequence families from the heuristic guideline

such that no single sequence type dominates

risk. This sort of insight can inform

performance allocation over initiating event

types, mitigating systems performance, and

emergency preparedness. 

At this point, the allocation continues by

segmenting each high-level performance

objective into sub-objectives corresponding to

the performance elements on the adjacent

lower level. The collective satisfaction of these

sub-objectives assures performance at the

higher level. This entails making choices,

because this decomposition is not unique.

This process is continued on down the

objectives hierarchy, until a point is reached at

which it is no longer appropriate to articulate

objectives, because there would be no net

benefit to measuring performance at that level.

The operational character of this guidance

means that meaningful allocation must be

done iteratively with the selection of

performance measures and their

implementation. 

In the reactor arena, because of variations in

plant design, it will be difficult to perform this

kind of allocation generically below the

functional level. As illustrated in the AFWS

example cited above, the requirement was

actually formulated at the functional level, with

the expectation that either the AFWS alone

would meet it, or additional systems would be
B-8

How does defense in depth affect

allocation of performance?

Part of defense in depth is avoiding overreliance on any one performance area in

satisfying the top-level safety objectives.

Therefore, defense-in-depth considerations

favor allocations that spread out

performance over redundant and diverse

barriers and SSCs.

What is the relationship between nominal

performance, performance criteria, and

allocated performance?

The allocated performance level is the level

of performance that is needed in order to

satisfy safety objectives. In general, normal

performance will be significantly better than

this level. In order for a performance-based

approach to be viable, the performance

criterion needs to be set at a level having

significant margin to the allocated level, in

order for problems to be detected and

addressed before a safety issue arises. In

order for this approach to be practical,

there must also be some margin must also

exist between the normal performance

level and the criterion.

credited in a more flexible evaluation. On the

other hand, system-level, train-level, and

component-level requirements clearly derive

from an implicit allocation of performance that

is not numerically precise, but derives from

implicit consideration of safety objectives.

Improving the alignment of regulatory

requirements with real safety objectives is the

essence of “risk-informing” regulatory practice.

Significant progress can be made in this area

without overly detailed developments of

objectives hierarchies or allocations.

B.4 Formulation of an Appropriate

Implementation: Selecting

Performance Measures

Given an allocation, one must still decide on

an implementation, i.e., a suitable combination

of regulatory requirements, inspections, and

performance indicators, collectively aimed at

assuring performance at (or better than) the

stated target levels. These elements then

need to be captured within appropriate parts

of the regulatory framework.

It is useful to illustrate this point by continuing

with the AFWS example introduced above, in

which a target range for unreliability was

given. Once that objective was fixed, very

different implementations could have been

chosen. The implementation actually selected

allowed considerable flexibility in design, and

this flexibility is reflected in the variety of

system topologies to be found among U.S.

nuclear power reactors. However, the

implementation was not fully performancebased. Instead, the implementation followed

the traditional regulatory approach; system

reliability was achieved through numerous

prescriptive American Society of Mechanical

Engineers (ASME) code requirements on

testing and inspection, and Technical

Specifications addressed allowed outage time

in the usual way. Essentially, the effect of the

top-level requirement on unreliability was first

to drive performance to a level better than that

of a typical, active two-train fluid system with

no backup, and second, to provide improved 

guidance on the formulation of the traditional

prescriptive requirements.The aim of the

present guidance is to foster choices in

implementation that are as performancebased as appropriate, in light of the high-level

guidelines. Therefore, given the objectives

hierarchy and the allocation, one uses the

objectives hierarchy once again to select

promising performance areas that are high up

the hierarch as possible. If it is impractical to

determine performance at a particular level,

the next level down is tried. In the case of the

AFWS, it is readily established that it is

impractical to measure unreliability at the

system level, because too few system

demands occur to support a useful

measurement. One must measure or

prescribe at a level lower than that of the

AFWS, and the complement of measures and

prescriptive requirements must collectively
B-9

provide the needed assurance of

performance.

The actual process may have to rely on some

amount of trial and error or iteration, making

repeated use of the viability guidelines. Trying

to work directly at the level of a highly reliable

system will typically fail the test of viability,

because risk-significant changes in the

operation of such a system cannot be

identified and addressed in a timely fashion.

Therefore, the process must seek a level on

the objectives hierarchy at which performance

can be objectively determined through

prescriptive requirements, and/or confirmed

either by inspection or through direct

confirmation of performance (performance in

tests or in actual demands). Once such

performance elements have been identified,

performance parameters and associated

criteria can be determined, and the viability

guidelines can be applied as discussed in

Section 3. Note that the “criteria” discussed in

the viability guidelines are not the target

allocations discussed above, but thresholds

whose violation signals declining performance

well before a significant safety problem has

developed, i.e., the allocated performance

levels are violated.

When moving down the hierarchy, looking for

a level at which an explicit allocation can be

addressed either by monitoring or by

prescriptive requirements, it is important to

recognize that it is possible to underperform at

a higher level, even if redundant elements at

lower levels nominally succeed. To see why

this is true, return once again to the AFWS

example. Even if all trains are highly reliable

and available, performance at the system level

can suffer if (for example) the trains’

unavailabilities are sometimes concurrent, or

the contributors to train unreliability include

shared hardware or common cause

contributions affecting more than one train.

Concurrent unavailability is addressed through

technical specifications, and the possibility of

common cause mechanisms is one reason for

prescriptive requirements on testing and

inspection. This example serves to illustrate

the ineffectiveness of excessively prescriptive

approaches without a disciplined analysis of

the outcomes and results sought to be

achieved.

B.5 Summary

Three major activities have been described: 

1. formulation of an objectives hierarchy

2. allocation of performance

3. selection of an appropriate complement of

prescriptive requirements and

performance measurements

The regulatory alternative developed by this

process is intended to have the following

properties.

1. The top-level safety objectives are

satisfied by the performance levels

targeted by the performance allocation.

2. The performance allocation is consistent

with defense in depth: no single

performance area is relied on excessively.

3. The complement of prescriptive

requirements and performance measures

also reflects defense in depth, in that it

samples performance in enough areas

and in sufficient depth to support a reliable

assessment of safety performance. 

4. Prescriptive requirements are imposed

only when considerations of viability or net

benefit preclude using performance

measures.

5. Performance measures and prescriptive

requirements are implemented as high on

the objectives hierarchy as possible, in

order to maximize licensee flexibility

consistent with the viability guidelines.

B-11

REFERENCES

B-1 Clemen, R. T. Making Hard Decisions. 2nd Edition. Belmont, California: Wadsworth

Publishing Company. 1996.

B-2 Weil, R. and G. E. Apostolakis. “A Methodology for the Prioritization of Operating

Experience in Nuclear Power Plants.” Reliability Engineering and System Safety.

Vol. 74, pp. 23-42. Elsevier. 2001.

B-3 Apostolakis, G. E. and S. E. Pickett. “Deliberation: Integrating Analytical Results into

Environmental Decisions Involving Multiple Stakeholders.” Risk Analysis. Vol. 18, No. 5,

pp. 621-634. Society for Risk Analysis. 1998.

B-4 Keeney, R. L. Value-Focused Thinking. Cambridge, Massachusetts: Harvard University

Press. 1992.

B-5 Nuclear Regulatory Commission (U.S.) (NRC). SECY 99-007, “Recommendations for

Reactor Oversight Process Improvements.” NRC: Washington, DC. January 8, 1999.

B-6 Nuclear Regulatory Commission (U.S.) (NRC). “Staff Requirements - SECY-98-144 -

White Paper on Risk-Informed and Performance-Based Regulation.” NRC: Washington,

DC. March 1999.

B-7 Nuclear Regulatory Commission (U.S.) (NRC). WASH-1400, NUREG-75/014, “Reactor

Safety Study: An Assessment of Accident Risks in U.S. Commercial Nuclear Power

Plants.” NRC: Washington, DC. October 1975.

B-8 Code of Federal Regulations, Title 10, Energy, Part 50.34(f)(1)(ii)(A), “Contents of

Applications; Technical Information.”

B-9 Nuclear Regulatory Commission (U.S.) (NRC). NUREG-0800, “Standard Review Plan,”

Section 10.4.9. NRC: Washington, DC. July 1981.