[Federal Register Volume 73, Number 24 (Tuesday, February 5, 2008)]
[Notices]
[Pages 6746-6747]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E8-2082]


=======================================================================
-----------------------------------------------------------------------

NUCLEAR REGULATORY COMMISSION

[NUREG-1855]


``Guidance on the Treatment of Uncertainties Associated with PRAs 
In Risk-Informed Decision Making, Draft Report for Comment''

AGENCY: Nuclear Regulatory Commission.

ACTION: Notice of availability of NUREG-1855, ``Guidance on the 
Treatment of Uncertainties Associated with PRAs in Risk-Informed 
Decision Making, Draft Report for Comment,'' and request for public 
comment.

-----------------------------------------------------------------------

SUMMARY: The Nuclear Regulatory Commission (NRC) is announcing the 
availability of and is seeking comments on NUREG-1855, ``Guidance on 
the Treatment of Uncertainties Associated with PRAs in Risk-Informed 
Decision Making, Draft Report for Comment.''

DATES: Comments on this document should be submitted by March 28, 2008. 
Comments received after that date will be considered to the extent 
practical. To ensure efficient and complete comment resolution, 
comments should include references to the section, page, and line 
numbers of the document to which the comment applies, if possible.

ADDRESSES: Members of the public are invited and encouraged to submit 
written comments to Michael Lesar, Chief, Rulemaking, Directives, and 
Editing Branch, Office of Administration, Mail Stop T6-D59, U.S. 
Nuclear Regulatory Commission, Washington, DC 20555-0001. Hand-deliver 
comments attention to Michael Lesar, 11545 Rockville Pike, Rockville, 
MD, between 7:30 a.m. and 4:15 p.m. on Federal workdays. Comments may 
also be sent electronically to [email protected].
    This document, NUREG-1855, is available at the Agencywide Documents 
Access and Management System (ADAMS) Public Electronic Reading Room on 
the Internet at the NRC Web site at http://www.nrc.gov/reading-rm/adams.html under Accession No. ML072990412 on the NRC Web site http://www.nrc.gov/reading-rm/doc-collections/nuregs/docs4comment.html; and at 
the NRC Public Document Room, 11555 Rockville Pike, Rockville, MD. The 
PDR's mailing address is USNRC PDR, Washington, DC 20555; telephone 
(301) 415-4737 or (800) 397-4205; fax (301) 415-3548; e-mail 
[email protected].

FOR FURTHER INFORMATION, CONTACT: Mary Drouin, Division of Risk 
Assessment, Office of Nuclear

[[Page 6747]]

Regulatory Research, telephone (301) 415-6675, e-mail [email protected].

SUPPLEMENTARY INFORMATION: 

NUREG-1855, ``Guidance on the Treatment of Uncertainties Associated 
With PRAs in Risk-Informed Decision Making, Draft Report for Comment.'' 
December 2007

    This NUREG provides guidance on how to treat uncertainties 
associated with probabilistic risk assessment (PRA) in risk-informed 
decision making. The objectives of this guidance include fostering an 
understanding of (1) the uncertainties associated with PRA, (2) the 
impact of the uncertainties on the results of the PRA, and (3) the 
uncertainties in the context of the decision making. The guidance in 
this document focuses on the use of PRA insights and results and ways 
to address the associated uncertainties. Consequently, the scope of the 
guidance contained in this report is limited to addressing the 
uncertainties associated with the use of the results of risk models.
    In implementing risk-informed decision making, the U.S. Nuclear 
Regulatory Commission expects that appropriate consideration of 
uncertainty will be given in analyses and interpretation of findings. 
Such consideration should include using a program of monitoring, 
feedback, and corrective action to address significant uncertainties. 
To meet this objective, it is necessary to understand the role that PRA 
results play in the context of the decision process. Defining the 
context includes providing an overview of the risk-informed decision 
making process itself.
    With the context defined, the characteristics of a risk model and, 
in particular, a PRA need to be understood. This understanding includes 
a recognition of the different forms of uncertainty which include 
aleatory and epistemic. A PRA, as a probabilistic model already 
characterizes aleatory uncertainty. The focus of this document is 
epistemic uncertainty. Therefore, guidance is given on identifying and 
describing the different types of sources of epistemic uncertainty 
including the different ways that they are treated. The different types 
of epistemic uncertainty include parameter, model, and completeness 
uncertainties.
    The final part of the guidance includes addressing the uncertainty 
in PRA results in the context of risk-informed decision making and, in 
particular, the interpretation of the results of the uncertainty 
analysis when comparing PRA results with the acceptance criteria 
established for a specified application. In addition, guidance is 
provided for addressing the other elements contributing to completeness 
uncertainty in risk-informed decision making (e.g., unknown phenomena 
that have not been recognized or factors that have been identified but 
for which there is no agreed on method for addressing them in PRAs).
    The Electric Power Research Institute (EPRI), in parallel with the 
NRC, has been developing guidance documents on the treatment of 
uncertainties. The activities of the NRC and EPRI are meant to be 
complementary.
    The NRC is seeking public comment in order to receive feedback from 
the widest range of interested parties and to ensure that all 
information relevant to developing this document is available to the 
NRC staff. This document is issued for comment only and is not intended 
for interim use. The NRC will review public comments received on the 
document, incorporate suggested changes as necessary, and issue the 
final NUREG-1855 for use.

    Dated at Rockville, Maryland, this 18th day of January, 2008.

    For the U.S. Nuclear Regulatory Commission.
Christiana H. Lui,
Director, Division of Risk Analysis, Office of Nuclear Regulatory 
Research.
 [FR Doc. E8-2082 Filed 2-4-08; 8:45 am]
BILLING CODE 7590-01-P