ML20207H445

Safety Evaluation Supporting Amends 218 & 199 to Licenses NPF-4 & NPF-7,respectively

ML20207H445
Person / Time
Site:	North Anna
Issue date:	03/02/1999
From:	NRC (Affiliation Not Assigned)
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ML20207H442	List: ML20207H438 ML20207H445
References
NUDOCS 9903120329
Download: ML20207H445 (4)

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UNITED STATES j

j NUCLEAR REGULATORY COMMISSION o

WASHINGTON, D.C. 20555-0001

-SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION

- RELATED TO AMENDMENT NOS. 218 AND 199 TO FACILITY OPERATING LICENSE NOS. NPF-4 AND NPF-7 VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION. UNITS NO.1 AND NO. 2

1.0 INTRODUCTION

. By letter dated October 25,1995, as supplemented February 5,1999, Virginia Electric and Power Company.(VEPCO, the licensee) submitted a request to change the Technical Specifications (TS) for North Anna Power Station, Units 1 and 2. Specifically the proposed change is to TS 3.4.3.2 to include an allowed outage time of 14 days for inoperable backup 3-i nitrogen supply for the pressurizer power-operated relief valves (PORVs) and to separate the

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ACTION statements for the PORV based on inoperability. The February 5,1999, letter l

contained clarifying information only and did not expand the scope of the original Federal 1

Reaister Notice or change the initial no significant hazard consideration determination.

l TS 3.A.3.2 requires that both PORVs and their associated block valves be operable in MODES 1,2, and 3 when the average reactor coolant temperature is greater than or equal to 350*F.

l Each PORV may be operable by its normal motive force, the non-safety-related instrument air, or by the backup motive force, nitrogen. The North Anna nitrogen supply is a redundant, j

. seismically supported safety grade motive force and the PORVs are considered inoperable when the nitrogen supply is not available.

~ 2.0 EVALUATION

' Initially, the PORV power sources were addressed by the staff as part of NUREG-0737, item II.G.1, Emergency Power for Pressurizer Equipment to Enhance PORV Reliability. VEPCO responded by indicating that in the event of loss of offsite power, emergency motive power would be provided by seismically suppoited high pressure nitrogen tanks. As the safety role of the PORV increased, the staff issued GL-90-06, which required operating pressurized-water reactor plants to modify the limiting conditions for operation of the PORVs and block valves for MODES 1,2, and 3.

Consequently, a surveillance requirement was added that required testing the emergency power

- sources for the PORVs and block valves by manually transferring the motive and control power from the normal to the emergency power and operating the valves through a complete cycle of -

travel. Also~ plant operation in Modes 1,2, and 3 with PORVs and block valves inoperable for reasons other than seat leakage was not permitted beyond 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.

j in addition, current North Anna TS ACTION statements provide requirements for configurations involving inoperable PORVs. These action statements take into consideration the ability to

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- manually cycle the PORVs. However, operability of the backup nitrogen accumulators is not

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a a t f addressed and there are no surveillance requirements associated with the PORV nitrogen

_ accumulators.

The licensee proposes to provide separate ACTION statements for PORVs which are -

inoperable due to seat leakage, an inoperable backup nitrogen supply, an inoperable automatic pressure control system, and other causes. The licensee indicates that this change will allow more specific and appropriate actions for each inoperable case.' The licensee also proposes to include surveillance requirements on the backup nitrogen supply accumulator pressure.

j 2.1 Deterministic Evaluation

_In ts case of a PORV inoperable due to seat leakage, the block ' alve must be clot,ed in order v

- to reestablish the reactor coolant system (RCS) presstce boundary integrity. The licensee indicated that the pressure conti al capability could be restored by opening the block valves and therefore power should be maintained to the block valves. This would enable the PORVs to continue to provide the safety-related function of manual RCS depressurization in the event of a steam generator tube rupture - the only North Anna, MODE 1, 2, or 3 event that the PORVs are relied on to mitigate, j

in the case where one or both PORVs are inoperable due to the malfunction of the PORV automatic control system, the licensee proposes that_the PORV be placed in manual control to

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limit the potential for spurious opening of the PORV. The licensee concluded that closure of the i

block valves is not required in this case, and the manual control function remains available.-

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The two cases discussed above are a more specific application of the ACTION statement

TS 3.4.3.2.a in the current TS, which allows the power to be maintained to the block valves; e

therefore, the staff agrees with the licensee's proposed TS change.

For the case with one or both of the PORVs inoperable due to an inoperable backup nitrogen supply, the licensee proposes continued operation of 14 days provided the normal motive force

. for the PORVs (instrument air) remains available. The licensee is requesting to extend the allowed outage time (AOT) in the case where one or both PORVs are capable of manual operation,' but the safety grade backup nitrogen supply is inoperable. This change has no impact on the current safety analysis, but instead,~ is an extension of the current AOTs.

Therefore, the current safety analysis' remains valid. Since the safety analysis remains valid, it is concluded that there is no difference in the deterministic safety significance of the extension of the AOT for the safety grade motive force. The difference in the current TS versus the proposed extension lies in the added risk due to the extension of the AOT, which is reviewed in Section L 2.2, " Risk Evaluation,". of this evaluation.

For the case when one or both PORVs are ineperable due to a failure not involving seat leakage, the backup nitrogen supply, or the automatic control system, the ACTION statement remains the same as the current TS.

2.2 Risk Evaluation

- North Anna proposed a TS change that allows an AOT of 14 days, instead of the current 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />; for one or both inoperable pressurizer PORV backup nitrogen supplies (backup motive power). The licensee stated that the extended AOT would provide additional time to correct

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"o l problems associated with the backup motive power, which require entry to containment. The licensee's submittal concludes that the 14-day AOT would result in a negligible increase in the risk of loss of the functional capability of the PORVs at power.

The backup motive power is used to ensure that the PORVs can perform their safety function in the event of loss of non-safety-related instrument air. The licensee indicates that there has not been a loss of instrument air event nor a loss of offsite power event at the North Anna site during the period between 1985 to 1996 (note that loss of offsite power results in loss of instrument air).

The current AOT has not been used since early 1995. The licensee does not expect an unavailability increase for the related system given the extended AOT, since it would be used primarily for rare corrective maintenance activities. Based on this, the staff finds that the AOT extension would be insensitive to the probability of loss of PORVs to perform their safety function, and the increase in the PORV failure probability due to the proposed change would be insignificant. Experience has also shown that mechanical failure of PORVs is the dominant failure mechanism, not loss of normal and backup motive power. A study by the licensee shows that the core damage frequency (CDF) and large early release frequency (LERF) are insensitive to the variations in AOT. The study also shows that even a significant unavailability increase for the backup motive power would have a small risk impact in terms of CDF and LERF. The result is summarized as fol!ows:

Unavailability of CDF (/yr)

ACDF LERF (/yr)

ALERF Accumulators 0 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> 4.049E-5 5.492E-6 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> 4.052E-5 3E-8 5.540E-6 SE-8 7 days 4.060E-5 1 E-7 5.594E-6 1 E-7 14 days 4.071 E-5 2E-7 5.696E-6 2E-7 The licensee indicates that pressurizer PORVs and backup motive power are within the scope of the maintenance rule, and their performance is monitored consistent with the maintenance rule.

The current unavailability performance criterion for the backup motive power is 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> per accumulator per year, which is much less than a single 14-day AOT.

The VEPCO risk configuration evaluation is governed by an administrative procedure that requires the use of an online maintenance matrix to evaluate the removal of risk significant equipment from service. The licensee indicates that the accumulators would not be removed from service during power operation without performing a risk evaluation. In addition, a Configuration Risk Management Program (CRMP) description has been add to the Administrative Control section of the licensee's TS. The staff believes that the licensee's CRMP is sufficient for an appropriate control of plant ectivities to avoid potential risk significant configurations during the proposed AOT.

3.0 STATE CONSULTATION

in accordance with the Commission's regulations, the Virginia State official was notified of the proposed issuance of the amendments. The State official had no comment.

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L 4.0 ENVIRONMENTAL CONSIDERATIO_N These amendments change a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and change

. surveillance requirements. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluent that

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may be released offsite, and that there is no significant increase in individual or cumulative l'

occupational radiation exposure. The Commission has previously issued a proposed finding that these amendments involve no significant hazards consideration and there has been no public.

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. comment on such finding (61 FR 28620). Accordingly, these amendments meet the eligibility

l criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no.

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. environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amenoments.-

5.0 CONCLUSION

. The staff reviewed the licensee-proposed changes to TS 3.4.3.2 and the associated surveillance.

The licensee is requesting a more specific application of the current TS by redefining the ACTION statements based on the type of inoperability, and the staff finds this change acceptable. The licensee is proposing to add a surveillance requirement to verify that the i

pressure in the nitrogen wcumulators is greater than the surveillance limit. This surveillance ensures that there is adequate motive power for the PORVs to mitigate the consequences of a

.j steam generator tube rupture coincident with a loss of the containment instrument air. The l

proposed surveillance imposes greater operating requirements on the licensee and ensures an adequate level of safety and is, therefore, acceptable to the staff.

' The staff concludes that the proposed AOT extension of the' backup motive power would result in an insignificant plant risk, and the licensee's risk analysis and experience strongly support such a finding. The licensee has sufficient control of the performance of the PORVs and backup motive

. power by implementing the maintenance rule and by using ilk CRMP, which has been added to its TS.~ Therefore, the staff concludes that the risk evaluation supports the proposed AOT

- extension for PORV backup motive power.

Based on the preceding discussions, the staff finds that the proposed changes to the TS to provide an AOT of 14 days for the PORV nitrogen accumulators, as well as to provide separate statements for the PORV depending on the reason for the PORV inoperability,are acceptable.

The Commission has 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, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.

T Principal Contributors: Sarita Brewer and Ian Jung Date:

March 2,1999 L

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