ML20039A242

Provides Info Re Pressurized Thermal Shock,In Response to Question Raised at ACRS Cessar Subcommittee 811119 Meeting. Main Steam Line Isolation Break Transient Analysis Shows No Potential for Shock for Design Life of 40 Yrs

ML20039A242
Person / Time
Site:	05000470
Issue date:	12/08/1981
From:	Scherer A ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
To:	Charemagne Grimes Office of Nuclear Reactor Regulation
References
LD-81-092, LD-81-92, NUDOCS 8112160405
Download: ML20039A242 (2)

Text

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o C E Power Systems Tel. 203/688-1911 Comhustion Engineenng, Inc. Telex: 99297 1000 Prospect Hill Road Windsor, Connecticut 06095 POWER H SYSTEMS Docket No: STN-50-470F December 8, 1981 LD-81-092 Mr. Christopher I. Grimes *

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Standardization & Special Projects Branch S Division of Licensing Q *,){"// d U. S. Nuclear Regulatory Comission ,

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Subject:

CESSAR Pressurized Thermal Shock /, s "e

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Dear Mr. Grimes:

The followlag response is provided to address the outstanding questica raised by Mr. Bender on Pressurized Thermal Shock at the November 19, 1981 CESSAR ACRS Subcommittee Meeting.

The plate materials used in the System 80 reactor vessel beitline and the as-deposited welds used to join plates are controlled to contain residual elements not to exceed the following percentages: copper - 0.10%, phosphorous - 0.012%,

sulfur - 0.015%, and vanadium - 0.03%. It is known that such control of residual elements in the SA-533B materials used in the System 80 vessels result in the lowest sensitivity to changes in mechanical properties due to irradiathn.

The predicted end-of-life fluence value stated in CESSAR is 3.15 x 10 91 n/cm2 (Section 4.3.2.8). It is recognized that this value is a calculated prediction, and that actual experience may vary somewhat due to such factors as plant operating conditions, as-built dimensions different than nominal, and other uncertainties.

For this reason, a surveillance program is employed by each operating plant to establish the actual fluence history at regular intervals during the life of each vessel. Assuming, for the sake of this discussion, that the end-of-life fluence is found to be even as much as a factor of 2 higher than the preoperational prediction, (i. e., 6.3 x 1019 n/cm2), the maximum end-of-life RTNDT value at the inner surface of the System 80 vessel would still be less than 2500F. Obviously, because of attenuation of the fluence through the wall of the vessel, the material properties of the vessel would be better nearer the outer surface than the inner surface.

The Main Steam Line Break (MSLB) design basis accident has, in the past, been found to represent the most challenging pressurized thermal shock transient for a C-E NSSS. Evaluation of a typical MSLB transient for a CESSAR reactor vessel, even assuming twice the predicted end-of-11fe fluence, shows no susceptability to pressurized thermal shock for a full plant design life of 40 years. It is expected 6003

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Mrs Christ:ph:r I.- Grimes . . that additional evaluations in compliance with the still developing requirements

      . for evaluation of pressurized thermal shock will continue'to demonstrate the relative insensitivity of the System 80 vessels in this' regard.

If I can be of additional assistance in this matter, please contact me or Mr. G. A. Davis of my staff at (203)688-1911, Extension 2803. Very truly yours, COMBUSTION ENGINEERING, INC. 2-L ( S"cherer

.                                                Director.

i Nuclear Licensing AES:ctk 4 i 4 k A i e i e

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