NRC Generic Letter 1981-19

NRC Generic Letter 1981-019: Thermal Shock to Reactor Pressure Vessels

ML031210463
Person / Time
Issue date:	04/20/1981
From:	Eisenhut D Office of Nuclear Reactor Regulation
To:
References
GL-81-019, NUDOCS 8106250094
Download: ML031210463 (2)

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9' h ;UNITED SATE

NUCLEAR REGULATORY COhWISSION

April 20, 1981 TO ALL LICENSEES OF OPERATING PWR HUCMEAR POWER PLANTS

81-19)

SUBJECT: THERMAL SHOCK TO REACTOR PRESSURE VESSELS (GENERIC LETTER

the effects For a number of years the NRC and industry have been studying have focused on of thermal shock to reactor pressure vessels. Efforts repressurization transient the identification and characterization of thermal development of material prop- scenarios and their probabilities and on the vessel integrity.

erties data and improved analytical tools for assessing A number of on-going research programs are supportive actual of this effort and to quantify thennal/vech- continue to provide information intended anical vessel behavior.

in a cooldown In the event of an overcooling system transient resultirfng of the pressure boundary of the reactor vessel, followed by repre',surizationvessel integrity could be above a critical level during the cooling period, jeopardized. The likelihood of a vessel cracking upon experiencing a thermal/repressurlzation transient depends upor. (1) its material properties, which degrade with -increased irradiation; (2) the severity of the thermal of mixing of primary water in the shock which is a function of the degree pressure pumps making system and relatively cold water injected by the high System; and (3) the magnitude of the up part of the Emergency Core Cooling pressure transient occurring during repressurization.

Commission research Earlier this year a number of analyses sponsored by the These program were completed and results became available to the staff. of the severity analyses were directed at providing a better understanding and expected of overcooling transients which combine operational experience frame, as a response reactor vessel material properties. In the same time its review of thermallmechanical to post-THI requirements, the staff initiated reactors intended reports from licensees of Babcock and Wilcox (BW) operating injection on vessel to further evaluate the effect of high-pressure safety accidents (Item II.K.2.13 of integrity for small-break loss-of-coolant 1980).

NUREG-0737, Clarification of THI Action Requirements, Novenber -it that the staff decided was as a result of a review of these on-going efforts to reactor pressure to accelerate its evaluation of possible thermal shock vessels.'

On March 31, 1981, the NRC staff met with the PWR Owners G

UP and repre- sentatives of NSSS vendors to discuss the effects of potential thermal shock transients and.the potential cons to reactor pressure vessels by overcooling low temperature. A

sequences of subsequent repressurization at relatively for your information.

copy of the minutes of that meeting is enclosed

'810625 00ROA

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- 2- This letter isto confirm the intent of the owners groups to perform a study of this concern including developing alternatives to protect the vesrel by aFoiding repressurization with cold water.

As indicated in the enclosed minutes of the meeting, we expect to receive a letter report from each of the owners groups summarizing their efforts not later than May 15, 1981. We expect that you are familiar with the activities of the appropriate owners group, actively participating in their discussions, and will provide a docketed response by May 22, 1981, identifying the specific actions you propose to take for your facility.

Division ofLcensing Office of Nuclear Reactor Regulation Enclosure:

Minutes of PWR Owners Groups.

Meeting With NRC on March 31, 1981 cc w/encl:

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