ML20011E098
| ML20011E098 | |
| Person / Time | |
|---|---|
| Issue date: | 01/18/1990 |
| From: | Michelson C Advisory Committee on Reactor Safeguards |
| To: | Taylor J NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| References | |
| ACRS-R-1384, NUDOCS 9002070368 | |
| Download: ML20011E098 (2) | |
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i ADVISORY COnselTTEE ON REACTOR SAFEOUARDS w Amuwatow c.c. sones January 18, 1990 Mr. James M. Taylor-Executive Director for Operations i
U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Dear Mr. Taylor
SUBJECT:
RESOLUTION OF THE INTERFACING SYSTEMS IDCA ISSUE During the 357th meeting of the Advisory Cosomittee on Reactor t
Safeguards, January 11-12, 1990, we discussed the subject topic with. members of the NRC staff.
This issue was also discussed during our 356th meeting, December 14-15, 1989.- Our Subcommittee on Thermal Hydraulic Phenomena considered this issue during its meeting on December 7, 1989.
The interfacing systems loss of coolant accident (ISIOCA) has been identified by the NRC staff as a problem of sufficient risk potential that a special program for its resolution is warranted.
Cuch an event creates the potential for loss of two of.the three barriers to fission product release, and if it occurs, is likely to lead to early fission product release outside of containment.
Although earlier studies, including those reported in NUREG-1150,
" Severe Accident Rirts:
An Assessment-for Five U.S. Nuclear Power.
Plants," indicate tbt such an event has a low probability, the statf members who have undertaken the special program do not believe the previous studies have accurately represented human error contributions to the likelihood that such an event occurs.
The NRC ISIOCA program includes. evaluation of aval.lable PRA analyses of accident sequences that may lead to such an event.
Special emphasis is to be given to the human reliability contribu-tion to initiation of such a sequence, and to ways in which its consequences may be mitigated.
Engineering analysis of the low pressure piping systems will be carried out to determine where leaks or breaks could occur.
A program of selected PWR plant audits is also under way.
The results of these studies will be of value to the IPE effort in general, as well as to the ISIDCA issue, and the studies'are encouraged.
Special attention should be given to the environmental ef fects and flow-induced mechanical impact on equipment in the vicinity of the leak if the results are to be meaningful.
Efforts should be made to ensure that the study results are broad enough to be applicable to BWRs.
Our concern lies in how the results of these studies will be used.
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Mr. James M. Taylor January 18, 1990 Information provided by the staff leads us to conclude that causes of and optimal mitigation strategies for ISLOCA events are likely to be highly plant specific.
In addition, important ISIhCA sequences apparently involve complex human actions that are not well modeled even in state-of-the-art PRAs.
While the plant-specific nature of ISIhCA would seem to make it a logical candidate for the IPE process, the statf expressed concern that the PRAs that are likely to be used by licensees in performing their IPEs will not adequately deal with ISIOCA.
Three approaches to resolving this issue were discussed (1)
Information developed by the staff in its ISIACA program could be used to modify PRAs used in IPEs no that ISIhCA is adequately analyzed. This is probably not practical and could undesirably delay completion of IPE programs.
(2)
Information developed by the staff in its ISIDCA program could be used to develop a resolution and set of licensee require-ments entirely separate from the IPE program. We believe this would tend to unnecessarily burden licensees with demands on their engineering and other resources and interfere with efforts to efficiently manage their IPE programs.
We would not favor this option unless the staff program indicates ISIDCA might be an unexpectedly high contributor to plant risk.
(3)
Information developed by the staff in its ISI4CA program might be furnished to licensees for incorporation into their IPE programs without the expectation that it would be comprehen-sively included in PRAs.
We believe that PRAs should be regarded only as one, albeit important, tool and source of information to be used by licensees in their IPE programs.
As a general premise, information from the ISLOCA program, resolution of GSIs and USIs, and many ot'it r sources can and should be used in IPEn, whether or not formally included in PRAs.
We recommend option number three as making the most efficient and effective use of staff and licensee resources.
Sincerely, car yle Michelson Chairman