ML20033E199
| ML20033E199 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 02/21/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20033E198 | List: |
| References | |
| GL-88-17, NUDOCS 9003090338 | |
| Download: ML20033E199 (4) | |
Text
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j UNITED STATES g
e NUCLEAR REGULATORY COMMISSION W A6HING TON, D. C. 20666 t
j SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 35 TO FACILITY OPERATING LICENSE NO. NPF-42 WOLF CREEK NUCLEAR OPERATING CORPORATION WOLF CREEK GENERATING STATION DOCKET NO. 50-482 INTRODUCTION j
The NRC issued 3eneric Letter 88-17, " Loss of Decay Heat Removal," on October 17, 1988 because of the potential serious consequence of loss of shutdown cooling concurrent with significant core decay heat.
Included in the Programmed i
Enhancements section of the generic letter was Item 5 that statec:
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" Technical Specifications (TSs) that restrict or limit the safety benefit of the actions identified in this letter should be identified and appropriate changes should be submitted."
In their February 2, 1989 response to the abcve item of the generic letter, the licensee stated:
"WCNOC is evaluating a Technical Specification arendment request to reduce RHR minimum flow rate in Mode 6, while maintaining decay heat removal requirements. This reduction in minimum flow rate would avoid potential prcblems due to vortexing and subsequent loss of the RHR system.
In addition WCNOC is revieving a possible amendrent request to eliminate the 1
requirement for tagging the Safety Injection Pump breaker and handswitch out of service of cold overpressure protection in Modes 5 and 6 and elimination of the autoclosure interlock function.
WCh0C will sutrit applicable Technical Specification amendment requests by November 30, 1989."
I By letter dated November 30, 1989, the licensee submitted proposed Technical Specificationchangesthatincluded(a)areductioninRHRminimumflowrate in Mode 6; (b) an additional requirement to maintain reactor vessel water level above the vessel flange before deenergizing the final operable RHR pump while in Mode 5; (c) an additional requirement to maintain reactor vessel water level above the vessel flange before deerergizing the safety injection pumps while in hodes 5 and 6; and (d) revisions to the supporting Bases.
In their letter, the licensee deferred action on tagging out the safety injection pump breaker ard handswitch.
EVALUATION The Technical Specification changes proposed by the licensee are intended to enhance the overall decey heat removal capabilities during plant operations in Modes 5 and 6.
9003090338 900221 PDR ADOCK 050004B2 P
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2 EductioninRequiredRHRFlowrate Technical Specifications (TS) 4.9.8.1 and 4.9.8.2 refers to operation of the i
resioual heat removal (RHR) system during refueling operations with high and icw reactor coolant water levels respectively.
The current TS requires that et least one train of RHR be operable with a minimum flew rate of 2800 gpm. The licensee has proposed revising the surveillance requirements of TS 4.9.8.1 and 4.9.E.2 by (a) reducing the required flow rate of the running RHR pump from greater than or equal to 2800 gpm to greater than or equal to 1000 gpm and (b) introducing a new requirement that the RHR flow be sufficient to maintain the reactor coolant system (RCS) temperature at less than or equal to 140'F.
Operation with the RCS partially drained in Modes 5 and 6 is necessary for required inspection and maintenance of RCS components such as reactor coolant punps and steam generators. As indicated in NUREG-1269, " Loss of Residual Heat Rereval at Diablo Canyon Unit 2," reduced RHR flowrote would provide a greater margin against vertexing and preclude an inadvertent loss of decay heat removal capability due to air entrairment and cavitaticn of the RHR purps.
As the time after plant shutdown increases, decay heat removal requiren.ents from the RHR suction flow are reduced since decay heat decreases as a function of time after initial reactor shutdown. The change proposed by the licensee will provide sufficient flowrate to maintain RCS less than or equal to 140*F.
In addition, a minimum RHR flowrate is required to prevent boron stratification to minimize the potential for 1ccalized variation in beren concentration in the RCS. For Wolf Creek, Westinghouse has recomended a minimum flowrate of 1000 ppm.
Since the proposed Technical Specification will require that the RHR flowrate is raintained at least greater than 1000 gpm and sufficient to maintain RCS temperature less than 140'F, the staff finds the proposed Technical Specification modifications to be acceptable.
Deenernizing RHR Pumps TS 3.4.1.4.2 requires that while in Mode 5 with the reactor coolant 1 cops partially drained, two pHR purps remain operable with at least one RHR loop in operatiori. A footnote to the TS permits deenergizing the single operating RHR loop for up to one hour provided that (a) no cperations are wculd cause dilution of the RCS boron concentration and (b) permitted that core outlet temperature is maintained at least 10*F below saturation temperature. The licensee has proposed a modification to this footnote that would also require the reactor vessel water level to be above the vessel flange before deenergizing the final cperable RHR loop.
The additional requirement to the footnote prevents intentional deenergizing l
of the remaining cperable RHR loop when the RCS level is low.
Requiring the RCS water it:yel to be above the flange increases the RCS inventory before i
i allowing the remaining RHR loop to be deenergized. The increased inventory l
would delay the enset of core boiling if difficulties were encountered in j
restartirt the RHR system. Since the proposed modification is conservative l
with respect to loss of decay heat removal, we find it acceptable.
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t A110 wino Safety injection Fumps to be Energized in Modes 5 c'.d 6 TS 3.5.4 currently requires that when in Modes 5 or 6 with the reactor vessel head on, all safety injection pumps must be deenergized with the motor circuit breakers secured in the open position. This provides low temperature over-pressure protection to the primary coolant system e.nd helps to assure that a mass addition transient (via a charging pump) can be relieved by the operation of a single PORY or RHR suction relief. valve.
The licensee has pointed out that should RHR cooling be lost while in this configuration, it would require 15 to 20 minutes for alent operators to restoreasafetyinjection(SI) pump.
In addition, tie licensee stated that with the reactor coolant water level below the vessel flange, there would be a minimum empty volume of 17.000 gallons in the primary system.
Accordingly, the licensee has proposed a redification to TS 3.5.4 that will permit operability of the SI pumps provided the level of the reactor coolant water is below the vessel flange. Due to this minimum empty space, this will permit the reactor operators to either (3) recover from an inadvertent actuation of the Si pumps without going solid or (2) immediately inject water into the primary system via the SI purps upon loss of RHR.
This nodification was proposed by the staff in Generic Letter 88-17 and is acceptable.
Modifications to the TS Bases The licensee has proposed modifications to TS Bases "3/4.5.2, 3/4.5.3, 3/4.5.4 ECCS Subsystems" and "3/4.9.8 Resioual Heat Removal and Coolant Circulation."
These modifications simply reflect the previously discussed TS changes and are acceptable.
ENVIRONMENTAL CONSIDERATION l
The amendment involves a change in a requirement with respect to the installe-tien or use of a facility component located within the restricted area as I
defined in 10 CFR Part 20 and changes in surveillence requirements. The staff has determined that the arendrent involves no significant increase in the amounts, and ro 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 exposures. The Commission has previously issued a proposed finding that the amendment involves no sienificant hazards consideration and there has been no public comment on such finding. Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forthin10CFRSection51.22(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 amendment.
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4 CONCLUSION, The staff has concluded, based on the considerations discussed above, that:
(1) there is reascoable assurance that the health and safety of the will net be endangered by operation in the proposed manner, and (2) public such ectivities will be conducted in compliance with the Comr.ission's regulations, and the issuance of the amendr.ent will not be inimical to the common defense and security or to the health and safety of the public.
Date:
February 21, 1990 Principal Contributor:
D. Pickett
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