[Federal Register Volume 70, Number 209 (Monday, October 31, 2005)]
[Pages 62352-62353]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-21650]

[[Page 62352]]



Notice of Public Workshop on Draft Report for Comment: 
``Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the 
Elicitation Process,'' NUREG-1829

AGENCY: Nuclear Regulatory Commission.

ACTION: Announcement of public workshop. Revision of workshop date.


DATES: Workshop date, November 9, 2005.
    Background: The Nuclear Regulatory Commission (NRC) issued draft 
NUREG-1829, ``Estimating Loss-of-Coolant Accident (LOCA) Frequencies 
Through the Elicitation Process,'' for public comment in June 2005. The 
report is available under ADAMS Accession Number ML051520574 and on the 
NRC Web site at http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1829/. A separate notice was published in the Federal Register 
on October 4, 2005, announcing the availability of this report (70 FR 
57901). This report describes LOCA frequency estimates developed using 
an expert elicitation process in support of an effort to develop a 
risk-informed revision of the emergency core cooling system (ECCS) 
requirements for commercial nuclear power plants by redefinition of the 
design-basis break size. The expert elicitation process consolidates 
service history data and insights from probabilistic fracture mechanics 
(PFM) studies with knowledge of plant design, operation, and material 
performance to arrive at the LOCA frequency estimates.
    The ECCS requirements in the United States are contained in 10 CFR 
50.46, Appendix K to part 50, and General Design Criterion (GDC) 35. 
Specifically, ECCS design, reliability, and operating requirements 
exist to ensure that the system can successfully mitigate postulated 
LOCAs. Consideration of an instantaneous break with a flow rate 
equivalent to a double-ended guillotine break (DEGB) of the largest 
pipe in the primary piping system of the plant generally provides the 
limiting condition in the required 10 CFR part 50, Appendix K analysis. 
However, the DEGB is widely recognized as an extremely unlikely event, 
so NRC staff is performing a risk-informed revision of the design-basis 
break size requirements.
    A central consideration in selecting a risk-informed design basis 
break size is an evaluation of the LOCA frequency as a function of 
break size. The most recent NRC-sponsored study of pipe break failure 
frequencies is contained in NUREG/CR-5750 (Poloski, 1999). 
Unfortunately, these estimates are not sufficient for design basis 
break size selection because they do not address all current passive-
system degradation concerns (e.g., primary water stress corrosion 
cracking) and they do not discriminate among breaks having effective 
diameters greater than 6 inches.
    There have been two approaches traditionally used to estimate LOCA 
frequencies and their relationship to pipe size: (i) Estimates based on 
statistical analysis of service experience data, and (ii) PFM analysis 
of specific postulated failure mechanisms. Neither approach is fully 
suitable for evaluating LOCA event frequencies due to the rarity of 
these events and the modeling complexity. This study used an expert 
elicitation process, which is well-recognized for quantifying 
phenomenological knowledge when data or modeling approaches are 
insufficient. Elicitation responses from a panel of 12 experts 
determined individual LOCA frequency estimates for the 5th percentile, 
median, mean and 95th percentile of the frequency distribution for each 
of six LOCA categories. Group estimates were determined by aggregating 
the individual estimates using the geometric mean of the individual 
estimates for each frequency parameter (i.e., median, mean, 5th and 
95th percentiles). Group variability was estimated by calculating 95% 
confidence bounds for each of the group frequency parameters. A number 
of sensitivity analyses were conducted to examine the effects on the 
quantitative results from variation of the assumptions, structure and 
techniques of the baseline analysis procedure.
    Public Workshop: The NRC will conduct a public workshop on 
Wednesday, November 9, 2005, to be held in room O6B4 at NRC 
Headquarters, 11545 Rockville Pike, Rockville, Maryland. This is a 
revision to the October 31, 2005, workshop date announced in the 
Federal Register Notice published, October 4, 2005; 70 FR 57901. The 
purpose of the workshop is to facilitate the comment process. In the 
workshop, the staff will provide an overview of the report and address 
clarification of items identified by the public. A preliminary agenda 
is attached. Persons planning to attend this meeting are urged to 
contact the below named individual at least two working days prior to 
the meeting to be advised of any potential changes to the agenda. The 
NRC seeks comments on the report and is especially interested in 
comments on the following questions:
    1. Is the structure of the expert elicitation process appropriate 
for the stated problem and goals of the study?
    2. Are the assumptions and methodology of the analysis framework 
used to process the panel responses appropriate and reasonable? Are 
they consistent with the type of information provided by the expert 
panel and the goals of the study?
    3. Is the geometric mean aggregation methodology appropriate for 
the panel responses and the study goals? Should other aggregation 
methodologies be considered and what are their advantages and 
    As previously published in the Federal Register, October 4, 2005; 
70 FR 57901, the NRC will consider all written comments on draft NUREG-
1829, ``Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through 
the Elicitation Process,'' received before November 30, 2005. Comments 
received after November 30, 2005, will be considered if time permits. 
Comments should be addressed to the contact listed below. An electronic 
version of the report and the accompanying experts' raw data files, are 
available electronically at http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1829/ and through the NRC's Electronic 
Reading Room at http://www.nrc.gov/reading-rm/adams.html. From the 
latter site, you can access the NRC's Agencywide Document Access and 
Management System (ADAMS), which provides text and image files of NRC's 
public documents. The ADAMS accession numbers for the documents related 
to this notice are:

           Document title                   ADAMS Accession No.                       File format
NUREG-1829.........................  ML051520574.....................  Adobe Acrobat Document.
BWR Non-piping Raw Data for NUREG-   ML051580341.....................  Adobe Acrobat Document.
BWR Piping Raw Data for NUREG-1829.  ML051580344.....................  Adobe Acrobat Document.
PWR Non-piping Raw Data for NUREG-   ML051580346.....................  Adobe Acrobat Document.

[[Page 62353]]

PWR Piping Raw Data for NUREG-1829.  ML051580347.....................  Adobe Acrobat Document.

    If you do not have access to ADAMS or if there are problems in 
accessing the documents located in ADAMS, contact the NRC Public 
Document Room (PDR) Reference staff at 1-800-397-4209, 301-415-4737, or 
by e-mail to [email protected].
    These documents may also be viewed electronically on the public 
computers located at the NRC's PDR, O1F21, One White Flint North, 11555 
Rockville Pike, Rockville, MD 20852. The PDR reproduction contractor 
will copy documents for a fee.

T10E10, U.S. Nuclear Regulatory Commission, 11545 Rockville Pike, 
Rockville, MD 20852, telephone (301) 415-6177, facsimile number: (301) 
415-5074, e-mail [email protected].

    Dated at Rockville, Maryland, this 25th day of October 2005.

    For the Nuclear Regulatory Commission.
Jennifer Uhle,
Chief, Materials Engineering Branch, Division of Engineering 
Technology, Office of Nuclear Regulatory Research.

Attachment--Preliminary Agenda

Public Workshop on Draft Report for Comment: ``Estimating Loss-of-
Coolant Accident (LOCA) Frequencies through the Elicitation Process,'' 

November 9, 2005*--9 a.m.-12 p.m., Room O-4B6

Preliminary Agenda
9 a.m.-9:15 a.m.--Introduction
9:15 a.m.-9:45 a.m.--Overview of NUREG-1829
9:45 a.m.-10:15 a.m.--Clarification of items identified by the public
10:15 a.m.-10:30 a.m.--Break
10:30 a.m.-12 noon--Clarification of items identified by the audience
12 noon--Adjourn

    *Revised date
[FR Doc. 05-21650 Filed 10-28-05; 8:45 am]