ML18025B517
| ML18025B517 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 05/13/1981 |
| From: | Mark J Advisory Committee on Reactor Safeguards |
| To: | Hendrie J NRC COMMISSION (OCM) |
| References | |
| ACRS-R-0931, ACRS-R-931, TAC-08269, TAC-11037, TAC-8269, NUDOCS 8105210208 | |
| Download: ML18025B517 (10) | |
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81'0521 0208, DOC ~ DATE'!'1/05/13 NOTARIZED !
NO Browns Ferry Nuclear Power Stat'ion<'nit3~
AUTHOR AFFILIATION ACRS>> Advisory Committee on Reactor Safeguar ds RECIPIENT AFFILIATIONS Comm,i ss'i oners OOCKE>>T. ¹ 05000296 DISTRIBUTION CODE:
XA018 TITLE ACR6 Letters
SUBJECT:
. Responds to NRC. 801212',
1 tr" re MK Udal l. inquiries concerning, 800628 partial-fa>lure-to-scram at facil,ity',Actions by NRC It.util'ere conducted in~ time/y manners Recommends prompt act.ion to resolve>>
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UNITED STATES NUCLEAR REGULATORY COMMISSION ADVISORYCOMMITTEE ON REACTOR SAFEGUARDS WASHINGTON, D. C. 205S5 May 13, 1981 Honorable Joseph N. Hendrie Chairman U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
RESPONSE
TO IN(UIRIES CONCERNING THE BROWNS FERRY NUCLEAR POWER STATION UNIT 3 PARTIAL-FAILURE-TO-SCRAM
Dear Dr. Hendrie:
In response to Commissioner Ahearne's letter of December 12, 1980, the Ad-visory Committee on Reactor Safeguards has reviewed the issues contained in Congressman I<orris K. Udall's inquiries which were prompted by the June 28, 1980 Browns Ferry Unit 3 partial-failure-to-scram.
There appear to be four specific concerns expressed by Congressman Udall which include:
(1) the level of confidence placed in the Staff's ability to calculate the consequences of an anticipated transient without scram (ATMS);
(2) the level of confidence in the adequacy of actions taken 'subsequent to the Browns Ferry Unit 3 partial-failure-to-scram; (3) the extent to-which emergency procedures at operating plants contain instructions for the operator, given an ATMS; and (4) an assessment of the causes of the Browns Ferry Unit 3 partial-failure-to-scram.
These matters, as related primarily to BMRs, were discussed during Subcom-mittee meetings with the NRC Staff held on March 10 and April 8, 1981 and during the 253rd ACRS meeting, i%ay 7-9, 1981.
The Staff, through its contractor, Brookhaven National Laboratory (BNL), has the ability to calculate consequences of a full ATMS event.
BNL's current capability to calculate consequences of a partial ATMS (where only a fraction of the control rods fail to insert) is not well developed.
However, it is our belief that the consequences of a partial ATMS are bounded by those of a full ATMS..
New, more sophisticated codes are being developed which should more accurately model both full and partial ATMS consequences.
It is expected these codes will be completed by 1982.
By 05210208
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Honorable Joseph M. Hendrie May 13, 1981 Regarding
.the adequacy of actions taken subsequent to the Browns Ferry Unit 3 partial-fai'lure-to-scram, we believe that the NRC Staff and the industry responded in a timely manner.
The initial-Bulletin resulting from this event (Bulletin 80-17) was issued on July 3, 1980 and was aimed at preventing the accumulation of water in the scram discharge volume (SDV), which was the pr obabl.e cause of the Br owns Ferry Unit 3 partial-failure-to-scram.
We also take note of the ongoing effort by the NRC Staff to continue the review of BMR scram systems.
As a result of the Browns Ferry Unit 3 partial-failure-to-scram, the Commis-sion directed the Office of Inspection and Enforcement to conduct a survey to determine the existence of adequate emergency procedures
.for coping with ATWS events at operating power reactors.
Bulletins issued following the Browns Ferry Unit 3 partial-failure-to-scram required checks to assure adequate ATWS procedures were in place at BWRs.
The results of the survey made after the Bulletins were issued, indicated that all util'iti'es which were. operating BWRs then. had procedures for coping with ATMS which were acceptable to the NRC.
In addition, steps have since been taken to ensure that PMRs as well as BMRs now have ATWS procedures acceptable to the NRC.
It is expected that further improvements will be made in ATMS procedures as in-depth examination of the matter continues.
We note that these procedures, of themselves, do not substitute adequately for design improvements to mitigate and reduce the probability of an ATMS.
Although we believe that the Browns Ferry Unit 3 incident was caused by water in the
- SDV, a complete explanation as to why the water was present is not available.
The most plausible explanation is that some type of flow resist-ance existed in the drainage system for the SDV, which prevented adequate drainage.
The cause of the failure to detect this condition was poor hy-draulic coupling between the scram discharge volume and the instrumented volume.
This design deficiency is common to a number of the older BWRs.
Later designs of the BWR have an improved hydraulic coupling which reduces this concern.
Among the long-term fixes for this problem will be a combin-ation of the two volumes as in the newer system design.
It is unclear why the scram discharge system design was changed without older plants having been subjected to a reexamination.
Some mechanism should be formulated or a better system developed to ensure design improvements are reviewed for applicability to existing plants.
It is our opinion that the Commission's previous responses to Congressman Udall reflected the best information available at the time those responses were prepared and that those responses still repr esent a reasonable assess-ment of the situation.
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Honorable Joseph M. Hendrie May 13, 1981 Although the actions taken by the NRC were timely as a direct response to the Browns Ferry Unit 3 incident, we believe that this incident should have inspired a very considerable acceleration of the Commission's efforts to resolve the ATWS issue.
This has not been the case.
We recommend strongly that the Commission act promptly and with high priority to resolve ATWS.
In this regard, we reiter ate the recommendations made in our letter.of April 16, 1980 on ATWS.
Si ncerely, J.
Carson Mark Chairman
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TO:
Chairman Hendrie ACTION CONTROL COMPL DEADLINE ACKNOWLEDGMENT INTERIM REPLY F INALREPLY FILE LOCATION ATES CONTROL NO.
DATE OF DOCUMENT PREPA E
OR SIGNAT OF:
Q CHAIRMAN Q EXECUTIVE DIRE OTHER:
RE TOR DESCRIPTION Q LETTER Q MEMO Q REPORT Q OTHER
Response
to inquiries concerning the Bro~ins Ferry Nuclear Power Station Unit 3 partial-failure-to-scraIII SPECIAL INSTRUCTIONS OR REMARKS PDR Suspense 5/18/81 MAY 3. 9 198)
DOCUIVIENT/COPY NO.
CLASSIFIED DATA CLASSIFICATION NUMBER OF PAGES POSTAL REGISTRY NO.
ASSIGNED TO:
enton DATE CATEGORY Q NSI ORD OFRD INFORMATION ROUTING tHnogue Cornell ge~~l Rehm Nichel son Stello..-
LEGAL REVIEW DATE ASSIGNED TO:
COPY Q FINAL Q
NO LEGAL OBJECTIO S
NOTIFY:
COMMENTS, NOT IFY:
EXT.
NRC F'ORM'23 (7-79 I EXECUTIVE DIRECTOR FOR OPERATIONS PRINCIPAL CORRESPONDENCE CONTROL
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