ML20072Q703

RO 50-336/83-07:nonconservative Assumptions Discovered in Steam Generator Tube Rupture analysis.C-E Failed to Utilize Conservative Secondary Side Steam Pressure Values in Analysis.Addl Info Will Be Provided

ML20072Q703
Person / Time
Site:	Millstone
Issue date:	03/18/1983
From:	Mroczka E NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	Haynes R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
MP-4801, RO-50-336-83-07, RO-50-336-83-7, TAC-49798, NUDOCS 8304050287
Download: ML20072Q703 (2)

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March 18, 1983 MP-4801 Mr. Ronald C. Haynes Regional Administrator, Region I U.S. Nuclear Regulatory Commission Regional Office 631 Park Avenue King of Prussia, PA 19406

Reference:

Facility Operating License No. DPR-65 Docket No. 50-336 Reportable Occurrence R0 50-336/83-07

Dear Mr. Haynes:

This letter provides notification of Reportable Occurrence 83-07, pursuant to the requirements of Millstone Unit 2 Appendix A Technical Specifications, Section 6.9.1.8.h.

This letter describes an error discovered in the transient analyses that could have permitted reactor operation in a manner less conservative than assumed in the safety analysis.

This report documents the discovery of non-conservative assumptions in our Steam Generator Tube Rupture Analysis.

Millstone 2's Steam Generator Tube Rupture Analysis was performed by Combustion Engineering.

The error was discovered by Northeast Utilities while performing an in-house Steam Generator Tube Rupture Analysis with the RETRAN 02 MOD 2 computer code.

Combustion Engineering failed to utilize conservative secondary side steam pressure values in the analysis.

Combustion Engineering used the minimum secondary side pressure to maximize flow thru the ruptured tube.

This maximizes break flow but fails to account for the opening of the atmospheric dump valves.

With RETRAN, Northeast Utilities using the maximum secondary steam pressure as a precondition for the tube rupture, found that the secondary side atmospheric steam dump valves would open and increase radiological consequences.

The bounding case using a maximum secondary side pressure resulted in a 0.25 REM dose to the thyroid at the site boundary.

The Combustion Engineering case showed a.006 Rem dose to the thyroid at the site boundary.

Both of these dose valces are significantly below the 300 REM dose to the thyroid at the site boundary which is allowed by 10CFR100 limits.

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.Mr. Ronald C. Haynes Page 2 Combustion Engineering therefore ' erred in not performing a parametric analysis on secondary side steam pressure to determine which pressure provided worse case radiological consequences for. the Steam Generator tube rupture transient.

l Further information will be provided in the two week report.

Yours truly, NORTHEAST NUCLEAR ENERGY COMPANY h

E. J. Mroczka Station Superintendent Millstone Nuclear Power Station EJM/JP:jlc cc:

Director, Office of Management and Program Control, Washington, D.C. (3)

U.S. Nuclear Regulatory Commission,fc/o Document Management Branch, Washington, D.C. 20555' s

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