ML20052C548
| ML20052C548 | |
| Person / Time | |
|---|---|
| Issue date: | 04/06/1982 |
| From: | Palladino N NRC COMMISSION (OCM) |
| To: | Udall M HOUSE OF REP., INTERIOR & INSULAR AFFAIRS |
| Shared Package | |
| ML20051T417 | List: |
| References | |
| REF-GTECI-A-49, REF-GTECI-RV, TASK-A-49, TASK-OR NUDOCS 8205050135 | |
| Download: ML20052C548 (7) | |
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cwainbaN April 6, 1982 The Honorable Morris K. Udall, Chairman Comittee on Interior and Insular Affairs United States House of Representatives Washington, DC 20515
Dear Mr. Chairman:
In response to your letter dated February 9,1982 we are providing the information requested pertaining to the pressurized thermal shock problem.
Sincerely.
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Enclosure:
Responses to PTS Questions cc: Rep. Manuel Lujan EN
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OUESTION 1.
Please provida a statement of the Coc::ission's position concerning the staff coments on the twelve points
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raised by Mr. Basdekas during your meeting on September 17, 1981.
ANSWER.
The Comission supports the staff coments on the twelve points raised by Mr. Basdekas during the September 17, 1981 meeting.
The NRC staff coments -
were issued on October 8, 1981.
(Enclosure 1) Results from the ongoing extens;ve effort on the pressurized thennal shock' issue since that date have confinned the staff conclusions in the October 8 responses and the Comission continues to support them.
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QUESTION 2.
Please provide the criteria Osed in selecting those control systems and sub-systems thereof that are to be taken into account for the purposes of investigating accident sequences that could lead to a pressurized thermal shock incident, ANSWER.
The sole selection criterion for control systems and sub-systems is whether the systems could initiate or exacerbate a pressurized thermal shock (PTS) incident.
Specifically, one subtask of the NP.C program for resolution of the safety issue related to the PTS problem will screen safety and control system functions to determine which systems are potential contributers to PTS incidents. The NRC, through a contract with Dak Ridge National Laboratory, will generate PTS event trees.' The causes of the event tree branches which could lead to PTS will be investigated so that probabilities can be associated with the most significant branches. This procedure will highlight system functions which have the largest probability of contributing to PTS events. Once the mort significant sequences have been identified, the objective is to determine whether, in light of other information en the susceptibility of a given plant to failure from PTS events, correcti.ve action to prevent PTS is necessary.
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OUESTION 3.
Please provide a description of the status of the review of plant specific information relating to the pressurized thermal shock issue.
(Please include discussion of whether the NRC staff have sufficiently detailed control system design information to permit an adequate assessment to be made of the potential for a pressurized thermal shock incident in the plants under consideration.)
ANSWER.
On August 21, 1981 the NRC sent letters to e.ight pressurized water reactor (PWR) licensees requesting plant specific information related to the pressurized thermal shock (PTS) problem.
Some readily available information was to be sub-mitted in 60 days; each licensee was to submit analyses of PTS events and their consequences showing whether or not continued operation is justified. Further, by letter dated December 18, 1981 the NRC ' requested aeditional infonnation related to the licensees' 60 day responses to be submitted with the 150 day responses. The December 18 flRC letter also amplified what was expected to be submitted in the 150 day responses.
Seven of the eight licensees (Calvert Cliffs, Ft. Calhoun, Maine Yankee, Oconee-1, H. B. Robinson-2, -San Onofre and Turkey Point-4) submitted 150 ' day responses in January 1982.
One (Three Mile Island-1) has comitted to submitting.the 150 day response by March 31, 1982.
In addition, the Combustion Engineering and Westinghouse PTS Owners Groups.
submitted generic reports on the issue in December 1981. Review of the reports is under way by the NRC staff. The initial reviews and discussion of additional ir. formation needed by the NRC staff to complete the reviews were the subjects of meetings with the Owners' Groups and licensees held en February 24 (with Westingh'ouse representatives) and March 17 (with Babcock and Wilcox representa-tives). The NRC staff has not yet completed its assessment of the. technical meri.t of the responses. The NRC program calls for ~prepara' tion' of' a' safety evaluation report on the plant-specific responses and the generic reports by the end of June 1932.
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r 0'JESTION 4.
Please provide a description of steps taken with regard to the plants most threatened by pressurized thermal shock incidents.
ANSWER.
The NRC staff completed an inter-divisional technical review of the pressurized water reactor (PWR) vessel thermal shock issue as reported in a memorandum from D. G. Eisenhut to H. R. Denton and E. G. Case dated April 28, 1981. (Enclosure 2)
It was concluded that no immediate action was required for operating reactors.
Subsequent studies and evaluations have reinforced that conclusion. The analyses provided 'in submittals from PWR Owners Groups and seven licensees (see response to Item 3 above) all led to the same conclusion, i.e., that the most vulnerable plants will not be in jeopardy for at least a few years. Therefore, no corrective actions have been taken except for operator training and education at some vulnerable plants.
The NRC staff has underway a systematic analysis, with appropriate experimental The NRC program which addresses the pressurized thermal shock (PTS) posit support, as the most efficient way to reach an effective regulatory unresolved safety issue (Task A-49) is designed to formulate -a regulatoty. requi,rement. to ensure that the risk of pressure vessel failure from PTS events is sufficiently low through each vessel's design end-of-life.,
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