ML20138E166

Safety Evaluation Re 850809 Inservice Insp of Components Relief Requests 29 & 66.Alternative Acceptable & Relief Should Be Granted

ML20138E166
Person / Time
Site:	Prairie Island
Issue date:	10/11/1985
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20138E154	List: ML20138E151 ML20138E166
References
TAC-59523, NUDOCS 8510240601
Download: ML20138E166 (4)

Text

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION NORTHERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNIT N0. 2 DOCKET NO. 50-306 INSERVICE INSPECTION OF COMPONENTS -

I5I RELIEF REQUEST NOS. 29 AND 66 Introduction By letter dated August 9, 1985, Northern States Power Company (the licensee) requested relief from two requirements of Section XI of the ASME Boiler and Pressure Vessel Code for the Prairie Island Nuclear Generating Plant Unit 2.

The licensee's relief requests pertain to the first 10-year interval which is due to expire at the start of cycle 11 (October 1985) for Unit 2.

During the first 10-year interval, the requirements cf the 1974 edition through Sumer of 1975 Addenda of Section XI of the ASME Boiler and Pressure Vessel Code apply.

The licensee, pursuant to 10 CFR 50.55a(g)(5)(iii), submitted by letter dated August 9, 1985, information to support the determination that examinations imposed by the ASME Code are impractical for Prairie Island Unit 2 request.

Evaluation This evaluation addresses two relief requests related to the inservice in-spection of components identified in the licensee's letter dated August 9, 1985. These relief requests are identified as Relief Request No. 29 dealing with hydrostatic testing and Relief Request No. 66 dealing with examination of the internal pressure boundary surface of one valve.

1.

Relief Request No. 29 A.

Component Description The affected component is a Class 2 charging line pipe section down-stream of valves'2 VC-7-10 and 2 VC-7-11. This line includes 35 feet of 2" diameter pipe located outside containment and 4 feet of 3/4" diameter pipe located inside containment. This piping is considered part of the charging system.

B.

Code Requirement Pursuant to IWC 5220, Pressure piping systems shall be hydrostatically pressure tested to at least 1.25 times the system design pressure (2485 psig) at a test temperature not less than 100*F.

Licensee's Basis for Requesting Relief C.

The piping system described above is not isolable from the Class 1 piping unless a freeze plug is installed in the charging line to the cold leg downstream of the 3/4" bypass line and in the charging line to auxiliary 8510240601 8510113j6 DR ADOCK O

.. spray on the regenerative heat exchanger outlet. Although a freeze plug has been used in the past, the licensee is reluctant to utilize this technique because of the hazards associated with installing and maintaining the plug in the pipe system during the test period.

D.

Licensee's Proposed Alternative This.section of pipe will be visually inspected in accordance with the rules of IWC 2000 and pressure tested to approximately 2600 psig following each refueling outage as an alternative.

E.

Evaluation Because of the design, the charging line downstream of valves 2 VC-7-10 and 2 VC-7-11 cannot be pressurized to the proper test pressure without the utilization of a freeze plug. We agree with the licensee regarding the potential hazards associated with the use of a freeze plug in that, if the freeze plug should break loose during the pressure test, it could damage the downstream piping.

It is therefore impractical to meet the code requirements for pressure testing the pipe section described above because of the risk associated with the use of a freeze plug. The 2600 psig test pressure is approx-imately 400 psig below the prescribed test pressure in IWC 5000 and approximately 350 psig above the normal operating pressure.

F.

Conclusion Based on the above evaluation, the staff concludes that, for the section of pipe discussed above, the code requirement regarding hydrostatic testing is impractical.

It is further concluded that the alternative discussed above will provide adequate assurance of structural integrity of the pipe section described above. Therefore, relief from IWC 5000 of Section XI of the ASME Boiler and Pressure Vessel Code should be granted for the section of pipe described above provided that, following each refueling cycle, the pipe section is hydrostatically tested to approximately 2600 psig and welds are visually inspected in accordance with IWC 2000 of Section XI of g.

the ASME code.

2.

Relief Request No. 66 A.

Component Description The component concerned with this relief request is a 10-inch motor operated gate valve. The manufacturer is Darling Company and the valve is located in the Unit 2 residual heat removal B return line (valveNo.MV32169).

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B.

Code Requirement IWB 2412 and Table IWB 2500, B-M-2 of Section XI of the ASME Boiler and Pressure Vessel Code, require visual inspection of the internal pressure boundary of valves of the same constructural design, e.g.,

globe or check valves, manufacturing method and manufacturer, that perform similar functions in the system.

C.

Licensee's Basis for Requesting Relief The licensee's bases for requesting relief from the Code requirement are as follows:

1.

The disassembly of the valve will require breaking a seal weld and replacing it after the examination of internal pressure boundary is completed. The remaking of the seal weld presents the potential of damaging the valve internals.

2.

Valve No. MV-32169 is the only gate valve existing in Unit 2 that s

was supplied by Darling Company. Therefore, this valve does not represent a population of valves existing in Unit 2 other than MV-32169 itself.

3.

A hazardous condition will exist during the examination of the valve since there will be a single check valve isolating the water in the refueling canal which is flooded during this period.

The check valve is designed to seal at a much higher pressure and temperature than will exist during the examination period of the valve.

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The later edition of the ASME Code does not require the extent of the examination to include the manufacturer.

5.

The examination of the same valve in Unit No. I performed in January 1985 showed no evidence of wear, erosion, corrosion or other anomalies.

In this case the seal weld between the body and bonnet was not remade because of difficulty and potential damage to the valve internals.

D.

Licensee's Proposed Alternative As an alternative, the licensee proposes to examine a motor operated valve from a different manufacturer during the Unit 2 refueling and if the residual heat removal system shows evidence of possible valve degradation during hydrostatic testing, to disassemble and examine the subject valve.

E.

Evaluation Access to perform an internal surface examination on valve MV-32169 is restricted due to the valve design and the potential hazardous conditions that exist during the examination. The result of the examination of the same valve in Unit 1 gives reasonable assurance

. that the internal surface of the valve in Unit 2 has not degraded to the point where its intended safety function would be affected. As a matter of fact, the examination showed no signs of degradation after 10 years of service.

In addition it is unlikely that it will be possible to remake the seal weld after the examination based on the experience gained from the examination of the Unit i valve.

F.

Conclusion Based on the above evaluation, the staff finds that it is impractical to meet the code requirement by the examination of this valve. As an alternative, the licensee has committed to examine a motor operated valve from a different manufacturer during the Unit 2 refueling outage.

In addition, if during hydrostatic testing the residual heat removal system shows evidence of possible valve degradation, then the subject valve would be disassembled and examined.

In conclusion, the staff finds this alternative acceptable and there-fore the relief should be granted.

Date: October 11, 1985 Principal Contributor:

D.C. Di Ianni l

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