ML20053A644
| ML20053A644 | |
| Person / Time | |
|---|---|
| Issue date: | 04/06/1982 |
| From: | Palladino N NRC COMMISSION (OCM) |
| To: | Udall M HOUSE OF REP., INTERIOR & INSULAR AFFAIRS |
| Shared Package | |
| ML20053A645 | List: |
| References | |
| REF-GTECI-A-49, REF-GTECI-RV, TASK-A-49, TASK-OR NUDOCS 8205270061 | |
| Download: ML20053A644 (5) | |
Text
e p2 n tog'o,y
,b-8 UNITED STATES 9
[
p, NUCLEAR REGULATORY COMMISSION I
WASHINGTON, D. C. 20655 5
j
\\"
/
l April 6, 1982 CHAM AN i
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.
Sincere'y, l
}-
p Nunzio.'
ladino
Enclosure:
Responses to PTS Questions cc:
Rep. Manuel Lujan 8205270DM
c ~-
l f-QUESTION 1.
Please provide a statement of the Commission's position concerning the staff comments on the twelve points raised by Mr. Basdekas during your meeting on September 17, 1981.
ANSWER.
The Commission supports the staff comments on the twelve points' raised by Mr. Basdekas during the September 17, 1981 meeting. The NRC staff comments-were issued on October 8, 1981.
(Enclosure 1) Results from the ongoing extensive effort on the pressurized thermal shock ~ issue since that date have confirmed the staff conclusions in the October 8 responses and the Commission continues to support them.
4
e d
QUESTION 2.
Please provide the criteria used in selecting those control sys. ems 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 NRC 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 Oak 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 most significant sequences have been identified, the objective is to determine whether, in light of other information on the susceptibility of a given plant to failure from PTS events, corrective action to prevent PTS is necessary.
l l
f
n QUESTION 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 eight 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 additional information related to the licensees' 60 day responses to be submitted with the 150 day t
responses. The December 18 NRC : 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 committed 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 l
information needed by the NRC staff to complete the reviews were the subjects j
of meetings with the Owners' Groups and licensees held on February 24 (with Westinghouse representatives) and March 17 (with~ Babcock and Wilcox representa-tives). The NRC staff has not yet completed its assessment of the technical merit of the responses.
The NRC program calls for' preparation of a' safety evaluation report on the plant-specific responses and the generic reports by the end of June 1982.
l l
l l
t
~
t QUESTION 4.
Please provide a description of steps takea with regard to l
the plants most threatened by pressurized thermal shock incidents.
1 ANSWER.
l The NRC staff completed an inter-divisional technical review of the pressurized j
water reactor (PWR) vessel thermal shock issue as reported in a memorandum from i
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 l
support, as the most efficient way to reach an effective regulatory position.
The NRC program which addresses the pressurized thermal shock (PTS) unresolved l
safety issue (Task A-49) is designed to formulate a regulatory. 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.
t
{
i f
l
-