ML20205S127

Safety Evaluation Supporting Amend 93 to License DPR-6

ML20205S127
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	10/14/1988
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20205S119	List: ML20205S117 ML20205S124 ML20205S127 ML20206C184
References
NUDOCS 8811100258
Download: ML20205S127 (4)

Text

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l \ UNITED STATES

[ NUCLEAR REGULATORY COMMISSION I.  : WASHINGTON, o, C. 20655 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENvMENT NO 93 TO FACILITY OPERATING LICENSE NO. OPR-6 CONSUMERS POWER COMPANY BIG ROCK POINT PLANT DOCKET NO. 50-155

1.0 INTRODUCTION

By letter dated July 5, 1988, Consumers Power Company (CPC or the 'icensee) requested changes to the Technical Specifications (TS) for Big Rock Point Plant.

Two of the proposed changes are related to the inservice testing (IST) for valves.

One of those two would eliminate cold shutdown or quarterly partial stroke testing of the Reactor Depressurization Syststr. (ROS) depressurizing valves. The second of those two deals with the post-maintenance testing requirement following RDS depressurizing valve pilot valve assembly and installation. Recognizing that those two proposed TS changes deviate from certain ASME Code Section XI requirements, the licensee also submitted two relief requests for HRC review and approval. Those relief requests are addressed in separate correspondence.

Of the two other proposed changes, one would relocate the existing surveillance requirement for the RDS containment penetration assemblies from the RDS section of the TS to the containment leakage section, and the other would reformat the entire RDS section of the TS to the Standard Technical Specification format.

1he NRC staff completed a preliminary review of the July 5, 1988 submittal and had comments on the wording and format of the proposed TS changes. The staff conveyed these comments orally to the licensee on October 4, 1988. Based on the staff's comments, the licensee submitted revised TS changes in a letter dated October 10, 1988. An evaluation of the licensee's submittals dated July 5 and October 10, 1988, is presented below.

On October 14, 1988, the Commission, by oral authorization, approved the requested TS changes and granted this licensee amendment. This Safety Evaluation had been completed. Big Rock Point Plant faced a circumstance which exhibited a strong potential for requiring the plant to enter a cold shutdown. Had that condition been coached on or after October 14, 1988, the existing TS would have required a set of the deleterious partial stroke tests of the RDS depressurizing valves. As described later, those tests provide a net safety reduction for the plant, and their requirement was eliminated by this amendment.

2.0 EVALUATION The Code of Federal Regulations, 10 CFR 50.55a, requires, in part, that certain safety-related power operated valves (POVs) be tested in accordance with the ASME Code Section XI requirements.Section XI in turn requires that these POVs be full stroke tested every three months, or each cold shutdown if quarterly testing is not practical, and after each repair and maintenance.

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The current TS for Big Rock Point Plant require that the RDS depressurizing valves be tested during each cold shutdown, but in no case need these valves be exercised more ofter, than once every three months. While the associated pilot valves are full atroke exercised, the RDS depressurizing valves are only partial stroke exercised because full stroke exercising of the main depressurizing valves is not possible during power operation or without removing them from the system.

At present, these RDS valves are partial stroke exercised using compressed gas trapped in the spool between the system isolation valve and the depressurizing valve. Evidence is available to show that this test is not adequate to demonstrate the operability of the RDS depressurizing valves and also that the test is a significant contributor to chronic pilot valve leakage.

Since the RDS valves for Dig Rock Point Plant discharge directly into containment,

, pilot valve leakage can cause a plant shutdown for repair of the leaking pilot valve. After repair, the current post-maintenance testing practices as discussed above would likely result in pilot valve leakage. Consequently, the plant would be placed in a cycle of frequent cooldowns and heatups adding additional stress to all plant systems and equipment. Based on the licensee's experience, it is concluded that, by eliminating partial stroke exercising of the ROS depressurizing valves, the probability of pilot valve leakage can be significantly reduced.

During the 1988 refueling outage at Big Rock Point Plant, the RDS depressurizing valve tops were modified and now have removable pilot valve assemblies. The modification consisted of installation of two isolation valves and a bolting flange between the dep essurizing valve top and the pilot valve inlet, and another bolting flange between the depressurizing valve top and the pilot valve outlet. This modification provides physical separation and isolation of the pilot valve assembly from the RDS depressurizing valve and therefore allows removal of the pilot valve assembly for repair while the plant is in power operation.

Based on the design mo$ification to the RDS depressurizing valves, the licensee proposed to add surveillance requirement 11.4.1.5.d to the Big Rock Point Plant TS as follows: "Should a pilot valve be isolated from service and removed, the replacement pilot valve shall be functionally tested prior to installation and return to service." Since the pilot valve assembly is a separate entity from the RDS depressurizing main valve, any repair work performed on the pilot valve should not affect the operation and integrity of the main valve. As such, post-maintenance testing of the pilot valve need only be done on the pilot valve and not necessarily on the main valve. However, after installation, (1) the pilot valve solenoid electrical continuity should be rechecked, (2) the isolation valves between the pilot valve and main valve should be verified open, and (3) the pilot valve inlet bolting flange leakage should be checked by using system operating pressure.

Based on the evidence that the current partial stroke testing of main RDS depressurizing valves may not be a valid test and likely causes chronic pilot valve leakage, the licensee proposed to change RDS surveillance requirement 11.4.1.5.c.1 from a partial stroke test of the RDS depressurizing valves during each cold shutdown, not to exceed once every 90 days, to a full stroke test each refueling outage. The four RDS valves will be sent off site for a full stroke, full pressure test using live steam. The cold shutdown tests are a higher frequency than the refueling outage tests; however, the current partial stroke

3 test has been shown to be ineffective and may likely result in undesirable pilot valve leakage. The staff, therefore, finds that proposed surveillance requirement 11.4.1.5.c.1 is an acceptable alternative to the existing one, especially when additional measures of disassembly and visual inspection are taken into consideration.

However, the Code requires that the full stroke test be performed either '

quarterly or during cold shutdown. Justification, as well as relief from the ,

l Code requirement, are prerequisites under 10 CFR 50.55a for extending the test

• interval to refueling outages. Based on the licensee's submittals, the staff

has concluded (1) that a full stroke test using system pressure could not be performed during any mode of operation because the RDS valves for Big Rock Point  !

l Plant discharge directly to containment, and (2) that there is no practical method available to perform the full stroke test on-site. Additionally, during a regular cold shutdown, it is impractical to remove the valves for off-site l* testing. To offset the impact of the longer test interval, the iicensee intends L J

to disassemble and visually inspect one depressurizing valve each refualing outage as a preventive measure. If results of the inspection indicate corrective 1 repairs to the valve are required, the licensee will disassemble and visually l inspect additional valves to ensure the concern is not generic. -

The staff also reviewed the two requests for TS changes not pertaining to RDS valve testing. The existing RDS containment penetration assemblies surveillance i requirement is not pertinent to RDS operability and should be placed together with all other requirements pertaining to containment leakage. The reformatting I of the RDS section of TS into Standard Technical Specification format is  !

appropriate for improving the cla^ity and readability of the operability 4

requirecents for the R05. .

Based on our review, we find:

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) A. That proposed surveillance requirement 11.4.1.5.c.1, c ecarning full stroke

testing all four RDS depressurizing valves at each refueling outage, is '

acceptable provided that the proposed additional measures of disassembly and t

]

visual inspection are taken to offset the impact of less frequent testing, '

B. That proposed surveillance requirement 11.4.1.5.d, concerning post-

maintenence testing requirements following an RDS cepressurizing valve  !

pilot valve assembly and installation, is acceptable provided that proper t

reinstallation of the pilot valve assembly is ensured by appropriate plant procedures, C. That the proposed move of surveillance requirements for the RDS containment [

penetration assemblies from TS 11.4.1.5.G to new TS 3.7(h) is acceptable, and D. That reformatting the RDS section of the TS is acceptable.  :

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3.0 ENVIRONMENTAL CONSIDERATION

An Environmental Assessment and Finding of No Significant Impact has been issued (

i for the amendment.

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4.0 CONCLUSION

We have concluded, based on the considerations discussed above, that (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations, and the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

Date: October 14, 1988/ Revised Principal Contributors: J. Huang i

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