ML081270079

Safety Evaluation for License Amendment Request, Change in Refueling Water Tank Level Requirement

ML081270079
Person / Time
Site:	Palo Verde
Issue date:	05/06/2008
From:	Cranston G V NRC/NRR/ADES/DSS/SBWB
To:	Hiltz T G NRC/NRR/ADRO/DORL/LPLIV
Miranda S, NRR/DSS/SPWB, 415-2303
References
TAC MD8496
Download: ML081270079 (6)

Text

May 6, 2008 MEMORANDUM TO: Thomas G. Hiltz, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing

FROM: Gregory Cranston, Chief /RA/ for Samuel Miranda Reactor Systems Branch Division of Systems Safety

SUBJECT:

SAFETY EVALUATION FOR LICENSE AMENDMENT REQUEST, CHANGE IN REFUELING WATER TANK LEVEL REQUIREMENT Plant Name: Palo Verde Nuclear Generating Station (PVNGS) Utility: Arizona Public Service Company (APS) TAC Nos: MD8496 Docket Nos: 50-529 License Nos: NPF-51 Plant Licensing Branch: IV Project Manager: Michael T. Markley Review Branch: DSS/SRXB Review Status: Complete

By application dated April 10, 2008, the licensee, Arizona Public Service Company, requested changes to the Facility Operating Licenses and Technical Specifications (TSs) for the Palo Verde Nuclear Generating Station, Unit 2, that would modify TS 3.5.5 to increase the minimum required Refueling Water Tank (RWT) water volumes, in TS Figure 3.5.5-1, by 3%. The additional water volume, available in the RWT and subsequently in the containment sumps, would provide assurance that the engineered safety feature pumps and the containment recirculation sump strainers will meet their intended design functions during loss of coolant accidents (LOCAs).

The SRXB staff has reviewed the information submitted on April 10, 2008, and found that it is sufficient to justify the proposed changes to the PVNGS2 TSs. The details of the review, and results are discussed in the attached safety evaluation.

Enclosure:

As stated CONTACT: Samuel Miranda, SXRB/DSS (301) 415-2303

May 6, 2008 MEMORANDUM TO: Thomas G. Hiltz, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing

FROM: Gregory Cranston, Chief /RA/ for Samuel Miranda Reactor Systems Branch Division of Systems Safety

SUBJECT:

SAFETY EVALUATION FOR LICENSE AMENDMENT REQUEST, CHANGE IN REFUELING WATER TANK LEVEL REQUIREMENT Plant Name: Palo Verde Nuclear Generating Station (PVNGS) Utility: Arizona Public Service Company (APS) TAC Nos: MD8496 Docket Nos: 50-529 License Nos: NPF-51 Plant Licensing Branch: IV Project Manager: Michael T. Markley Review Branch: DSS/SRXB Review Status: Complete

By application dated April 10, 2008, the licensee, Arizona Public Service Company, requested changes to the Facility Operating Licenses and Technical Specifications (TSs) for the Palo Verde Nuclear Generating Station, Unit 2, that would modify TS 3.5.5 to increase the minimum required Refueling Water Tank (RWT) water volumes, in TS Figure 3.5.5-1, by 3%. The additional water volume, available in the RWT and subsequently in the containment sumps, would provide assurance that the engineered safety feature pumps and the containment recirculation sump strainers will meet their intended design functions during loss of coolant accidents (LOCAs).

The SRXB staff has reviewed the information submitted on April 10, 2008, and found that it is sufficient to justify the proposed changes to the PVNGS2 TSs. The details of the review, and results are discussed in the attached safety evaluation.

Enclosure:

As stated CONTACT: Samuel Miranda, SXRB/DSS (301) 415-2303 DISTRIBUTION: NRR/DSS

ADAMS: ML081270066 OFFICE SXRB/DSS SXRB/DSS NAME S Miranda G Cranston /RA/ for Samuel Miranda DATE 5/6/08 5/6/08 OFFICIAL RECORD COPY ENCLOSURE SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO FACILITY OPERATING LICENSE No. NPF-51 ARIZONA PUBLIC SERVICE COMPANY PALO VERDE NUCLEAR GENERATING STATION, UNIT 2 CHANGE IN REFUELING WATER TANK LEVEL REQUIREMENT DOCKET NO. 50-529

1.0 INTRODUCTION

By application dated April 10, 2008 [1], the licensee, Arizona Public Service Company (APS),

requested changes to the Facility Operating Licenses and Technical Specifications (TSs) for the Palo Verde Nuclear Generating Station, Unit 2 (PVNGS2), that would modify TS 3.5.5 to increase the minimum required Refueling Water Tank (RWT) water volumes, in TS Figure 3.5.5-1, by 3%. The additional water volume, available in the RWT and subsequently in the containment sumps, would provide assurance that the engineered safety feature (ESF) pumps and the containment recirculation sump strainers will meet their intended design functions during loss of coolant accidents (LOCAs).

The proposed change stems from APS' reevaluation of PVNGS2's containment flooding calculations, which were performed to respond to a generic letter [2] from the NRC staff. APS identified a more limiting LOCA scenario that was not considered when the current TS minimum RWT levels, depicted in TS Figure 3.5.5-1, were determined. In this LOCA scenario, the strainers would not necessarily be fully submerged, post-LOCA, at the time the recirculation actuation signal (RAS) is generated. Therefore, APS has proposed to raise the RWT minimum level, in PVNGS2, to 3% above the current TS Figure 3.5.5-1 levels.

2.0 REGULATORY EVALUATION

The TS minimum RWT levels, depicted in TS Figure 3.5.5-1, the ESF pumps, and the containment recirculation sump strainers, operating in accordance with the RAS, deliver to the reactor vessel, in order to cool the core, in postulated LOCA scenarios. They act as, "a structure, system, or component that is part of the primary success path and which functions or actuates to mitigate a design basis accident or transient that either assumes the failure of or presents a challenge to the integrity of a fission product barrier." Thus, they satisfy Criterion 3 of 10 CFR 50.36(c)(2)(ii)(C).

3.0 TECHNICAL EVALUATION

APS' containment flooding calculation validation efforts, conducted in response to Generic Letter 2004-02 [2], revealed a LOCA break scenario that requires more water, in the RWT, than that shown in the current TS minimum RWT levels of TS Figure 3.5.5-1, to assure that the strainers become fully submerged, post-LOCA, at the time the RAS is generated. This LOCA scenario postulates a small break at the top of the pressurizer. This break size and location results in less spillage to the containment floor, since the reactor coolant system (RCS) pressure does not drop to a level that permits water from the safety injection tanks (SITs) to enter the RCS. In this LOCA scenario, water from the SITs does not flow into the RCS, and eventually into the containment sump. Water from the SITs cannot help to flood the strainers. According to the PVNGS UFSAR [3], about 7,656 ft 3 (or 57,300 gallons) of water would remain in the SITs. The licensee has determined that the minimum flood level requires the transfer of 543,200 gallons of water from the RWT to the RCS (and eventually to the containment sump) prior to receipt of the RAS. The licensee has also that, in order to make this amount of water available, the RWT level would have to indicate 83% of scale, an increase of 3% ove rthe current value. The proposed increase amounts to about 24,000 gallons of water, a significant portion of the SIT inventory that does not become available during a small break LOCA.

The SRXB staff concludes that the licensee has demonstrated that their proposal, to increase the minimum required RWT water volumes, in TS Figure 3.5.5-1, by 3%, would continue to satisfy the analysis acceptance criteria for the affected licensing basis events (e.g., the LOCA events). Therefore, the licensee's proposal is consistent with their "no significant hazards consideration", and in accordance with the terms of 10 CFR 50.92 (c).

4.0 STATE CONSULTATION

The PM is responsible for contacting the state official and verifying that this statement is correct. In accordance with the Commission's regulations, the [Name of State] State official was notified of the proposed issuance of the amendment. The State official had [no] comments. [If comments were provided, they should be addressed here].

5.0 ENVIRONMENTAL CONSIDERATION

Caution: The environmental consideration discussed below is written for a categorical exclusion based on 10 CFR 51.22(c)(9). The PM/LA are responsible to ensure that this is accurate for the specific amendment being issued.

The 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. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (XX FR XXXX). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.

6.0 CONCLUSION

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.

Principal Contributor: S. Miranda Date: May 5, 2008

7.0 REFERENCES

[1] 102-05844-DCM/GAM, "Request for Amendment to Technical Specification 3.5.5, Refueling Water Tank (RWT), to Increase the RWT Minimum Water Level for Unit 2 Under Exigent Circumstances", Arizona Public service Company, April 10, 2008

[2] NRC Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents At Pressurized-Water Reactors,"

September 13, 2004 and Palo Verde Nuclear Generating Station letter to NRC, Response to NRC Request for Additional Information Related to Generic Letter 2004 -02 , Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors, dated February 29, 2008 (ADAMS Accession No. ML080710546)

[3] Table 6.2.1-6A, Updated Final Safety Analysis Report for Palo Verde Nuclear Generating Station, Rev 14

Principal Contributor: S. Miranda, Date: May 8, 2008