ML19350F133

RO 50-336/81-20:Dresser Industries Model 31739A Safety Valves Found to Have Less than Min Upstream Inside Diameter. Caused by Facility Design.Significant Impact Unlikely

ML19350F133
Person / Time
Site:	Millstone
Issue date:	06/17/1981
From:	Mroczka E NORTHEAST NUCLEAR ENERGY CO.
To:	Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
MP-2-4817, RO-50-336-81-20, NUDOCS 8106240254
Download: ML19350F133 (2)

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C' FN s Mr. Boyce H. Grier b Director, Region I l Office of Inspection and Enforcement U. S. Nuclear Regulatory Ccmmission k-,%.

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Reference:

Facility Operating License No. DPR-65 QSs ) ~

Occket No. 50-336 Reportable Occurrence R0-50-336/81-20

Dear Mr. Grier:

This letter provides notification of Reportable Occurrence 81-20 pursuad to the requirements of Millstone Unit 2 Appendix A Technical Specifications, Section 6.9.1.8.h. Based on information provided by Combustion Engineering, the following is forwarded concerning Millstone Unit.2's pressurizer safety valves.

Millstone Unit 2 was designed and constructed with 2-1/2 inch fittings immediately upstream of our Dresser Industries Model 31739A safety valves.

These fittings nominally have an inside diameter of 2-1/8 inches or less. The l Dresser interface requirement for this model valve is a minimum upstream I

inside diameter of 2-1/2 inches although this was not explicityly stated on their 1970 interface drawings.

The reduced inlet pipe diameter for these valves will reduce the valva discharge capability and invalidate the as:,umptions in plant overpressure protection reports and any safety analysis which result in actuation of the pressurizer safety valves. The degree to which pressures exceed those calculated will depend upon the exter.t of valve performance degradation.

While it is not pocsible to precisely predict the change in discharge l

capacity, it is believed to be small since the actual bore diameter of the Model 31739A valve is only about 1-7/8 inches. Since the valve bore is the limiting flow area, the only effect a short length upstream restriction will have is to modestly reduce the pressure upstream of the flow nozzle, thereby modestly reducing the critical flow rate.

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.- q Mr. Boyce H. Grier Page 2 Based on the licensing method for Millstone, the calculated required safety valve capacity is more than an order of magnitude be:ow that specified for the pl .,n t. It is unlikely that the reduced valve capacity resulting from the smaller inlet piping could have a significant impact in light of the large design margin.

Yours truly, NORTHEAST NUCLEAR ENERGY COMPANY f/ks< i:w E? J. Mroczka Station Superintendent Milistone Nuclear Power Station EJM/ RAP:ws cc: Director, Office of Management and Program Control, Washington, D. C. (2)

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

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