ML20028H132
| ML20028H132 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 10/01/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20028H131 | List: |
| References | |
| NUDOCS 9010090243 | |
| Download: ML20028H132 (5) | |
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UNITED STATES
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WASHINGTON. D. C. 20666 v..
NUCLEAR REGULATORY COMMISSION s
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ENCLOSURE 2 SAFETY EVALUATICN BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORT 1t$ APENDMENT NO.128TO FACILITY OPERATING LICENSE NO. DPR-79 TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT. UNIT 2 DOCKET NO. 50-328
1.0 INTRODUCTION
By letter dated December 6,1989 (Ref 1), the Tennes5ce Valley Authority (TP orthelicensee)proposedchangestotheTechnicalSpecifications(TSs)for Sequoyah Nuclear plant, Units 1 and 2, to delete Surveillance Requirement (SR) 4.5.2.d.1.
This SR r Nuires verification of the automatic isolation of the residual heat renoval (RHR) system from the reactor coolant system (RCS) when the RCS pressure is above 700 pounds per square inch gauge. The SR 4.5.2.d.1 is proposed to be deleted because the autoclosure interlock (ACl) function of the RHR system is being removed during the Cycle 4 refueling outage for each unit. The ACI function for Unit I was removed in the Unit 1 Cycle 4 refueling outage which ended in May 1990, and for Unit 2 will be rereved during the current Unit 2 Cycle 4 refueling outage.
Removal of the ACI function is expected to reduce the risk to Sequoyah from events involving loss of RHR cooling capabilities during nonpower operations. Additional information was requtisted and was supplied in the letter dated March 15,1990(Reference 2).
The letter dated itarch 15, 1990 provided the Westinghouse Electric Corpora-tion's resort documenting the qualitative probabilistic risk assessnent evalua-tion of tie Sequoyah design for ACI deletion. The Sequoyah design is different from the design reviewed by the staff when it e nluated WCAp-11736-A for the removal of ACI on a generic plant basis. The information provided by the licensee in this letter did not change the substance of the proposed action published in the Federal Register (55 FR 2446) on January 24, 1990 for the proposed amendments and does not affect the staff's initial determination of no significant hazards consideration in that notice.
The proposed changes to the Unit 1 TSs were issued as Amendment 139 to these TSs in the staff's letter dated May 9, 1990.
2.0 EVALUATION ThelicenseereferencedtheapprovedWestinghouseOwnersGroup(WOG) report WCAP-11736-A, " Residual Heat Removal System Autoclosure Interlock Removal Report for the Westinghouse Owners Group."
In this report, the Sequoyah plant is shown to be similar to plants in Group 1 for which the reference plant is Salem Unit 1.
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The licensee presented the results from WCAP-11736-A and applicable Sequoyah itformation from a series of plant-specific analyses. These results take into eccount the impact of the removal cf the ACI function on the RPR inlet isolatict valves, The licensee concluded that implementation cf the proposed design, prcposed technical specifications, and procedure changes will reduce the frequency of an RHR overpressurization event and increase the RHR system availability at Sequoyah.
The staff position taken in its evaluation of WCAP-11736-A and the removal of the ACI function is in Reference 3 and consisted of hardware changes and procedural enhanccments along with ACI removal which the staff believes will produce e net safety benefit correred to the current plant arrangement with the ACI function. The hardware changes at Sequcyah will ccrsist of the addition of an alarm to each RHR suction valve. The alarm will actuate if r
(1) one RRR valve is open and the other is closed or (2) the RPR systen pres-sure exceeds e specified linit below 700 psi gauge.
The open permissive circtitry which prevents these valves from being opened will not be affected by tbt addition of the alarm and the removal of the ACI circuitry. The alarm and valve position indication in the control roer are still available fc110 wing pcwcr lockout of the RFP suction valves.
2.1 P,lant Specific PEA _
i The staff discussed with the licenset the need for a plant-specific probabilis-tic rist assessment (FRA) for Seoucyah and the diversity of the RHR isolation valve pcsition indication. The plant-specific PRA was to account for differ-ences between the desi 15,1990 (gn for Sequoyah as presented in the licensee's letter dated MarcP Reference ?) ar.d the desigt for Salem as presented in PCAp-11736-A. These are the designs for ACI removal. The basic differences between the Selem design and the Sequoyab design arc the followirg:
(1)the pressure sensors for Salta are nn the PCS side and the pressure sensors for Sequoyah are on the RPR side of the suction valves and (2) the alam for Salem is on valve position and pressure ("and" logic) and the alarn for Sequoyah is on valve position or pressure ("or" logic).
The licensce's letter of March 15,)1990 (Ref. P) provided an update to tFeir 1
letter of December 8 1989(Ref.1 and included a Westinghouse report that documents a qualitative PRA evaluation comparing the $61em and Sequoyah designs taking into account the design differences with regard to ACI removal.
Based on Sequoyah's proposed alarm configuration, the estimated failure prob-abilities from the effect of ACI removal were detemined for (1) interfacing system loss of coolant accident potential, (2) RHR availability, and (3) low-temperature over-pressurization protection.
In each one, the failure probability for Sequoyah, with ACI removed and the main control room alarm installed, was estimated to be approximately the same or less than the failure prcbability with ACI remaining, l
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2.2 Diversity of RHR Isolation Valve Position Indication i
In regards to diversity of the RHR isolation valve position indication, the staff was informed in a telecon with the licensee on February 5,1990, that the signal to the local panel, the control room, and the alarm are from the same position i
switch on the valve.
Therefore However, assurance, the indication of valve position is not independent.
is provided that the valves will be closed by the following: the position switch is tested in two ways to relate the signal from the position switch to the proper valve position by (1) the MOYATS program for each valve and (2) a leak rate test of each closed valve (Technical Specification 4.4.6.2.2).
The MOV1.TS program correlates valve position by the-
"signatre" of the valve thrust force and the valves are tested every 18 months as a minimum. The leak rate test is required at every refueling outage and when coming out of a cold shutdown condition which lasts more than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> (if the valves have not been tested within the last 9 months). Redundant pressure sensors to the alarm are a diverse method for valve position indica-tion to assure that at least one valve is fully closed. The pressure sensors l
are calibrated at 22 1/2 month intervals. The combination of the above two
)osition switch tests (M0 VATS program and leak rate) provide assurance that soth valves are closed. The staff concludes that the Sequoyah design is acceptable.
l The licensee also stated that there is a procedure to close and depower the RHR l
valves in the General Oper? ting Instruction (G01)-1 for plant startup from cold shutdown (Mode 5) to hot.tandby (Mode 3). A double sign off will exist in t
G01-1 for acknowledging areaker lockout with a padlock.
2.3 MIProcedureEnhancements The ACI procedure enhancements at Sequoyah are as follows:
1.
An alarm for the RHR suction valves is to be added. The alarm response procedure used during plant startup will be modified to reflect the alarm recognition responses for the added alarm. The procedure will be revised to direct the operator to take the necessary actions to close the open RHR suction valve (s), if they are found open following alarm actuation. The operator will be instructed to not pressurize further and to return to a 1
non-alarm condition.
1 2.
A surveillance procedure for the alarm will be added before entry into Mode 4 to verify that the alarm remains operable.
L 3.
Operating and test procedures will be in place to ensure that these valves areclosedwhenthepowerislockedout(seeSection2.2abovefor discussion on MOVATS, leak rate tests, and pressure sensors).
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l The licensee has stated that the procedural enhancements will be completed before Unit 2 is restarted from its Cycle 4 refueling outage without ACl.
Unit 2 is currently in its Cycle 4 refueling outage and the ACI function will be removed from the Unit 2 RHR system during this outage.
3.0
SUMMARY
The staff has evaluated the Sequoyah submittals (References 1 and 2) and has concluded that the hardware and procedural modificathns proposed by the licensee meet the staff's requirements for ACI removal and are, therefore, acceptablo for removing the ACI function. This is discussed above. Based on this, the proposed TS changes to delete ACI from the TSs are acceptable.
4.0 ENVIRONMENTAL CONSIDERATION
This amendnent involves a change to a requirement with respect to the installa-tion or use of a facility component within the restricted area as defined in 10 CFR Part 20 and changes to the surveillance requirements. The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any e.*fluents that may be released offsite, and that there is no si nificant increase in individual or cumulative C
occupational radiation exposure. The Comission had previously issued a proposed finding that this amendment involves no significant hazards censidera-tion and there has been no public coment on such finding.
Accordingly, this amendment meets the eligibility criteria for categorical exclusion set forth in 10CFR51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statcnent nor environmental assessment need be prepared in connection with the issuance of this encoc' rent.
5.0 CONCl.USION The Connission made a proposed determination that the amendment involves no significant hazards censideration which was published in the Federal Register (55 FR 2446) on January 24, 1990 and consulted with the State of Tennessee.~
No public comments were received and the State of Tennessee did not have any CoDUents.
The staff has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the will not be endangered by operation in the pro >osed manner, and (2) public such activities will be conducted in compliance wit1 the Comission's regulations, and the issuance of the amendment will not be inimical to the common defense and security nor to the health and safety of the public.
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6.0 REFERENCES
j 1.
Letter, M. J. Ray, Tennessee Valley Authority to USNRC,
Subject:
Technical j
specification Chan9e 8918, dated December 8,1989, 2.
Letter, E. J. Wallace Tennessee Valley Authority to USNRC,
Subject:
Technical Specification Change 8918, Additional Information, dated 4
tiarch 15,1990.
3.
Letter, Harry Rood (USNRC) to J. D. Shiffer (Pacific Gas and Electric),
dated February 17, 1988.
Principal Contributor:
H. Balukjian Dated: October 1, 1990 P
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