ML20247P303
| ML20247P303 | |
| Person / Time | |
|---|---|
| Issue date: | 05/21/1998 |
| From: | Rossi C NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | Lochbaum D UNION OF CONCERNED SCIENTISTS |
| References | |
| NUDOCS 9805270397 | |
| Download: ML20247P303 (2) | |
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4 UNITED STATES g
j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 2066M001
- ,o May 21, 1998 Mr. David A. Lochbaum Nuclear Safety Engineer Union of Concerned Scientists 1616 P Street NW, Suite 310 Washington, DC 20036-1495
Dear Mr. Lochbaum:
SUBJECT:
REQUEST FOR REVIEW OF SPECIAL REPORT - RATES OF INITIATING EVENTS AT U.S. COMMERCIAL NUCLEAR POWER PLANTS, 1987-1995 i
(DRAFT) l l
Enclosed is a copy of a draft report, " Rates of initiating Events at U.S. Commercial Nuclear Power Plants," INEElJEXT-98-00401. The objective of this study was to update the initiating j
event frequency estimates based on operating experience from licensee event reports during the time period 1987 through 1995. For loss-of-coolant accident (LOCA) initiators whose frequency is low enough that no events would be expected in the 1987-1995 time period, additional operating experience and information from other sources were used. These inc!ude operating experience from U.S. and foreign reactors, as well as evaluation of causal factors affecting potential medium and large break LOCAs. The report also includes a comparison with initiating event frequency estimates published in probabilistic risk assessments and individual plant examinations (IPEs), an evaluation of the most significant trends, and an evaluation of dominant contributors to risk-significant initiators.
This is the first major analysis of initiating event frequency estimates for non-LOCA events since NUREG/CR-3862, " Development of Transients initiating Event Frequencies for Use in Probabilistic Risk Assessments," was published in 1985. Also, this report is the first significant effort to update LOCA pipe break frequencies since 1975 when WASH-1400," Reactor Safety Study," was issued.
Major findings from this study are the following:
The combined initiating event frequency for all initiators is lower than the frequencies e
used in NUREG-1150," Severe Accident Risks: An Assessmet for Five U.S. Nuclea.
-/
l Power Plants," and IPEs by a factor of two and four, respectively.
/D General transients contribute 76 percent of all initiating events. Events tha,t pose a more e
severe challenge to the plant's mitigation systems contribute the remaining 24 percent.
All initiating events displayed either a decreasing or constant time trend. The overall initiating event frequency decreased over the period by a factor of three. Most risk-significant initiators (such as loss of offsite power, total loss of feedwater flow, and loss of condenser heat sink for boiling-water reactors) were decreasing at a faster rate than the overall initiating event frequency.
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LOCA frequencies are lower than those used in NUREG-1150 and industry-wide IPEs.
e In accordance with our peer review process prior to the finalization and distribution of this report, we want to provide you with the opportunity to review and comment on the draft report.
To meet our planned publication schedule, we would appreciate receiving your comments within 45 days from receipt of this letter.
As you may know, the Office for Analysis and Evaluation of Operational Data studies do not i
represent an official U.S. Nuclear Regulatory Commission position or the position of the l
responsible NRC program office. Our reports are one input to an ongoing review and evaluation process.
A copy of this draft report and letter are being placed in the Public Document Room at 2120 L Street NW, Washington, DC 20555.
If you have any questions related to this report, please feel free to contact Mr. Don Marksberry (301-415-6378) (e-mail: dgm2@nrc. gov) of my staff.
I Sincerely, original signed by j
Charles E. Rossi, Director Safety Programs Division I
Office for Analysis and Evaluation of Operational Data l
Enclosure:
As stated Distribution' w/o enclosure:
RRAB RF File Center DHickman TTMartin AThadani SPD RF Publi JRosenthal JMitchell DOCUMENT NAME: H:\\ DON \\lE_ PEER 3.WPD l
l To receive a copy of this document, Ind6cate in the box: "C" = Copy wolattach/encls *E" = Copy Wattach/encle "N" = No copy OFFICE RRAS/RRAB C
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NAME DMarksberrf SMays b PBaranowsh CERopsF4 DATE 5 /Zo /98 5 /W /98 6 /M/58 r/ hv /98 OFFICIAL RECORD COPY