[Federal Register Volume 70, Number 191 (Tuesday, October 4, 2005)]
[Notices]
[Pages 57901-57903]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-19790]
-----------------------------------------------------------------------
NUCLEAR REGULATORY COMMISSION
Notice of Availability of Draft Report for Comment: ``Estimating
Loss-of-Coolant Accident (LOCA) Frequencies Through the Elicitation
Process,'' NUREG-1829
AGENCY: Nuclear Regulatory Commission.
ACTION: Notice of availability and request for comments.
-----------------------------------------------------------------------
DATES: Written comments must be provided by November 30, 2005.
Background: In support of an effort to develop a risk-informed
revision of the emergency core cooling system (ECCS) requirements for
commercial nuclear power plants, estimates of loss-of-coolant accident
(LOCA) frequencies have been developed which will enable redefinition
of the design-basis break size for these requirements. These LOCA
frequency estimates have been developed using an expert elicitation
process by consolidating service history data and insights from
probabilistic fracture mechanics (PFM) studies with knowledge of plant
design, operation, and material performance. This expert elicitation to
develop LOCA frequency estimates is described in draft NUREG-1829,
``Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the
Elicitation Process'' (June 2005).
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
[[Page 57902]]
instantaneous break with a flow rate equivalent to a double-ended
guillotine break (DEGB) of the largest primary piping system in 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.
Solicitation of Comments: 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
disadvantages?
Comment Period: The NRC will consider all written comments received
before November 30, 2005. To facilitate the comment process the NRC
will conduct a workshop on October 31, 2005, to be held in room O4B6 at
NRC Headquarters, 11545 Rockville Pike, Rockville, Maryland. 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. A separate notice will be published in the Federal
Register announcing the public workshop. Comments received after
November 30, 2005, will be considered if time permits. Comments should
be addressed to the contact listed below.
Availability: 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-1829 ML051580341 Microsoft Excel Worksheet.
BWR Piping Raw Data for NUREG-1829.... ML051580344 Microsoft Excel Worksheet.
PWR Non-piping Raw Data for NUREG-1829 ML051580346 Microsoft Excel Worksheet.
PWR Piping Raw Data for NUREG-1829.... ML051580347 Microsoft Excel Worksheet.
----------------------------------------------------------------------------------------------------------------
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.
FOR FURTHER INFORMATION CONTACT: Dr. Charles A. Greene, Mail Stop
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 19th day of September 2005.
For the Nuclear Regulatory Commission.
Andrea Lee,
Acting Branch 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,''
NUREG-1829
October 31, 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
[[Page 57903]]
9:45 a.m.-10:15 a.m.--Discussion of 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
[FR Doc. 05-19790 Filed 10-3-05; 8:45 am]
BILLING CODE 7590-01-P