ML20043A883
| ML20043A883 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 05/09/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20043A879 | List: |
| References | |
| NUDOCS 9005230237 | |
| Download: ML20043A883 (5) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION s
WASHING TON. D. C. 20566 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO.139 TO FACILITY OPERATING LICENSE NO. OPR-77 TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT, UNIT 1 DOCKET NOS. 50-327
1.0 INTRODUCTION
By letter dated December 8, 1989 (Ref. 1), the Tennessee Valley Authorit or the licensee) proposed changes to the Technical Specifications (TSs) y (TVA for Sequoyah Nuclear Plant Units 1 and 2 to delete Surveillance Requirement (SR) 4.5.2.d.1.
This SR requires verification of the automatic isolation of the.
. residual heat removal (P.HR) system from the reactor coolant system (RCS) when the RCS pressure is above 700 pounds per square inch gage.
The SR 4.5.2.d.1 is proposed to be deleted because the autoclosure interlock (ACI) function of the RHR system is being removed during the Cycle 4 refueling outage for each unit. The ACI function for Unit 1 has been removed in the current Unit 1 Cycle 4 refueling outage and for Unit 2 will be removed during the upcening Unit 2 Cycle 4_ refueling outage scheduled to begin in October 1990.
Removal of the ACI function is expected to reduce the risk to Sequoyah from events involv-ing loss of RHR cooling capabilities during nonpower oper;tions.
Additional information was requested and was supplied in the letter dated March 15, 1990 (Reference 2).
The letter dated March 15, 1990 provided the Westinghouse Electric Corpora-tion's report documenting the qualitative probabilistic risk assessment evalua-tion of the Sequoyah design for ACI deletion.
The Sequoyah' design is different from the design reviewed by the staff when it evaluated 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 Notice (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.
2.0 EVALUATION The licensee referenced the approved Westinghouse Owners Group (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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2-The licensee presented the results from WCAP-11736-A and applicable Sequoyah information from a series of plant-specific analyses.
These results take into account the impact of the removal of the ACI function on the RHR inlet isolation valves. The licensee concluded that implementation of the proposed design, proposed technical-specifications, and procedure changes will reduce I
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
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of the ACI function is in Reference 3 and consisted of hardware changes and procedural enhancements along with ACI removal which the staff believes will produce a not safety benefit compared to the current plant arrangement with the ACI function. The hardware changes at Sequoyah will consist of the addition of an alam to each RHR suction valve.
The alarm will actuate if (1) one RHR valve is open and the other is closed or (2) the RHR system pressure exceeds a specified limit below 700 psi gauge.
The oper, permissive circuitry which prevents these valves from being opened will not be affected by the addition of the alann and the removal of the ACI circuitry.
The alarm and valve position indication in the control room are still available following power lockout of the RHR suction valves.
2.1 Plant Specific PRA
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The staff discussed with the licensee the need for a plant-specific probalistic risk assessment (PRA) for Sequoyah and the diversity of the RHR isolation valve position indication. The plant-specific PRA was to account for differences March 15, 1990 (gn for Sequoyah as presented in the licensee's letter dated between the desi Reference 2) and the design for Salem as presented in
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WCAP-11736-A. These are the designs for ACI removal. The basic differences l
between the Salem design and the Sequoyah design are the following:
(1)the pressure sensors for Salem are on the RCS side and the pressure sensors for Sequoyah are on the RHR side of the suction valves and (2) the alarm for Salem is on valve position and pressure ("and" logic) and the alarm for Sequoyah is on valve position or pressure ("or" logic).
The licensee's letter of March 15,1990 (Ref. 2) provided an update to their letter of December 8, 1989 (Ref. 1) and included a Westinghouse report that documents a qualitative PRA evaluation comparing the Salem 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 determined 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 probability with ACI remaining.
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l 2.2 Diversity of RHR Isolation Valve Position Indication 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 switch on the valve.
Therefore, the indication of valve position is not independent. However, assurance 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 MOVATS program for each valve and (2) a leak rate test of each closed valve (Technical Specification 4.4.6.2.2).
The M0 VATS program correlates valve position by the
" signature" 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 lasted more than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> (if the vcives have not been tested within the last 9 months).
Redundant pressure sensors to the alam are a diverse method for valve position indica-tion to assure that at least one valve is fully closed. The pressure sensors are calibrated at 221/2 month intervals.
The combination of the above two position switch tests (M0 VATS program and leak rate) provide assurance that both valves are closed. The staff concludes that the Sequoyah design is acceptable.
The licensee also stated that there is a procedure to close and depower the RHR valves in the General Operating Instruction (GOI)-1 for plant startup from cold shutdown (Mode 5) to hot standby (Mode 3). A double sign off in G01-1 for breaker lockout with a padlock will be added after ACI removal before entry of the units into Mode 4, 2.3 ACI Procedure Enhancements 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 non-alam condition.
2.
A surveillance procedure for the alarm will be added before entry into Mode 4 to verify that the alarm remains operable.
3.
Operating and test procedures will be in place to ensure that these valves dre Closed when the power is locked out (see Section 2.2 above for discussion on M0 VATS, leak rate tests and pressure sensors).
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The licensee has stated that the procedural enhancements will be done before either unit is restarted from its Cycle 4 refueling outage without ACI.
Unit 1 is currently in its Cycle 4 refueling outage and the ACI function has been removed. Unit 2 will be in its Cycle 4 refueling outage in the fall and the ACI function will be removed from the Unit 2 RHR systou at that time.
3.0
SUMMARY
The staff has evaluated the Sequoyah submittals (References 1 and 2) and has concluded the.t the hardware and procedural modifications proposed by the licensee meet the staff requirements for ACI removal and are, therefore, acceptable 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 REFERENCES
1.
Letter, M. J. Ray, Tennessee Valley Authority to USNRC,
Subject:
Technical Specification Change 89-18, dated December 8,1989.
2.
Letter, E. J. Wallace, Tennessee Valley Authority to USNRC,
Subject:
Technical Specification Change 89-18, Additional Information, dated March 15, 1990.
3.
Letter Harry Rood (USNRC) to J. D. Shiffer (Pacific Gas and Electric),
dated February 17, 1988.
5.0 ENVIRONMENTAL CONSIDERATION
This amendment 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 effluents that may be released offsite, and that there is no significant increase in individual or cummulative occupational radiation exposure. The Comission had previously issued a proposed finding that this amendment involves no significant hazards considera-tion and there has been no public comment 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 statement nor environmental assessment need be prepared in connection with the issuance of this amendment.
6.0 CONCLUSION
The Comission made a proposed determination that the cmendment involves no significant hazards consideration which was published in'the Federal Register (55FR2446)onJanuary 24, 1990 and consulted with the State of Tennessee.
No public comments were received and the State of Tennessee did not have any Congnents.
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5 The staff 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, and (') such c
activities will be conducted in compliance with the Commission's regulations, i
and the issuance of the amendments will not be inimical to the common defense and security nor to the health and safety of the public.
Principal Contributor:
H. Balukjian Dated: May 9, 1990 1
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