ML20082Q770
| ML20082Q770 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 08/30/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20082Q759 | List: |
| References | |
| NUDOCS 9109130058 | |
| Download: ML20082Q770 (4) | |
Text
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.173 TO FACILITY OPERATING LICENSE DPR-57 AND AMENDMENT NO. 113 TO FACILITY OPERATING LICENSE NPF-5
, GEORGIA POWER COMPANY, ET AL.
EDWIN 1. HATCH NUCLEAR PLANT, UNITS 1 AND 2 DOCKET N05. 50-321 AND 50-366
1.0 INTRODUCTION
By letter dated October 9, 1990, Georgia Power Company, et al. (the licensee) submitted a request for changes to the Edwin I. Hatch Nuclear Plant, Units 1 and2,TechnicalSpecifications(TS). The requested changes would reduce the scram water level setpoint (Level 3) approximately 10 inches below the current setpoint. Specifically, the setpoints associated with fuel cladding integrity, reactor protection system instrumentation, primary containment isolation instrumentation, and the emergency core cooling system actuation instrumentation will be changed.
There is no change to system or component maintenance or testing. The safety-related systems and components whose operation may be initiated by a Level 3 low water level signa? will still operate in the same manrzer as they do currently.
2.0 EVALUATION Lov water level in the reactor vessel indicates that the reactor is in danger of being inadequately cooled. Should the water level decrease too far, fuel damage could occur. The purpose of the low water level (Level 3) scram is to prevent fuel damage following events involving a loss of inventory or loss-of-coolant accidents (LOCA) that result in a decreasing reactor vessel water level. The setting of the scram signal is chosen far enough below normal operational levels to avoid spurious scrans but high enough above the top of active fuel to assure that enough water is d ailable to account for evaporation losses and displacements of coolant following the most severe abnormal operational transient involving a level decrease.
A decrease in the reactor vessel water level to Level 3 will generate:
(1) a reactor scram; (2) a permissive signal for the Automatic Depressurization System (ADS) to verify that the reactor vessel water level is, in fact, low; (3) a i
causes the Residual Heat Removal (RHP.) pump to slow speed; (4) a signal which signal which shift the recirculation l
System shutdown cooling isolation valves to close (during shutdown cooling operation only); (5) a signal which causes RHR valvestoclose;and(6)jection(LPCI)linevalvesandRHRvesselheadsprayline low pressure coolant in a signal which isolates certain containment isolation 9109130000 910830 ADOCKOSOOg1 DR
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valves. Except for the initiation of a reactor scram, the other Level 3 water level instrumentation isolation functions are anticipatory, and credit for the actual setpoint is not explicitly assumed in safety aralyses.
The licensee proposed to lower the current scram setpoint for the 'ow reactor water level scram and isolation function from its current value of greater than 10 inches above instrument zero to greater than 0 inches. Reducing the scram water level setpoint will provide several additional seconds for operator actions 4
in the event of a feedwater transient and may avert an unnecessary reactor scram.
The proposed reduction of the reactor vessel water level (Level 3) scram setpoint potentially affects the system response to transient and accident conditions.
Specifically, the reduction of the setpoint will impact the analyses for loss of Offsite Power (LOOPS), Appendix R Event, High Energy Line Bresk (HELB), and the design basis accident event for the LOCA analyses. The licensee stated that analyses have been completed which support a 17-inch reduction in the Level 3 setpoint (the proposed 0-inches above instrur,ent zero setpcint was selected for convenience and is bounded by the supporting analyses). The licensee ststed that the Reactor Core Isolation Cooling (RCIC) is capable of preventing reactor water level from reaching Level 1 following system initiation at level 2.
- Also, LOCA analyses were performed with the water level setpoints Level 3 reduced by 12.5 inches. The results demonstrated that there is no effect on the calculated peak clad temperature for the design basis accident event.
The modified Level 3 low water level signal will still generate signals to initiate systems / components in the same manner as they currently are. Tho following discusses the influence of the reduced level satpoint on the signals that are generated by the level 3 signal.
The Reactor Core Isolation Cooling (RCIC) system is Q ned to prov adequate 3
makeup inventory to prevent the reactor water level from reacni,,3 1-aw-low (Level 1) following system initiation at low-low (Level 2) regardles of the scram function generated by the Level 3 scram setpoint.
Furthermore, the licensee has performed analyses that demonstrate that RCIC has the capability to prevent the reactor water level from reaching Level 1 for events in which there is a loss of normal feedwater.
The RHR Shutdown Cooling valves also receive automatic closure signals upon receipt of a low reactor water level (Level 3) signal. Lowering the Level 3 signal 10 inches will have an insignificant impact on this isolation function.
The modified Level 3 setpoint will still be approximately.4 feet above the top of active fuel, and sufficient water inventory will be av; :able to assure the fuel is covered.
_ The ADS logic requires a Level 3 signal, in addition to Level I signal and high drywell signal, to start the 2-minute ADS timer. A Level 3 signal and a sustained Level 1 signal can initiate a timer which will bypass the high drywell signal in approximately 13 minutes and stort a 2-minute timer.
If the 2-minute timer expires and a signal is present indicating a low-pressure ECCS pump is running, ADS will actuate. Since the Level 3 input would occur prior to the Level 1 input, lowering the setroint to 0 inches will have no impact on ADS operation.
The LPCI injection valves are designed to close on a 1.-s i 'er level signal (Level 3) to prevent inadvertent flow from the reactor vessel to the suppression pool. A continued lowering 01' vessel water level would result in an LPCI initiation signal on Level 1 (low-low-low water level).
The LPCI isolation signal is only reaningful when the injection valves are open and thus, would only have an impact during the shutdown mode. No change in system operation will result from the proposed change in the Level 3 setpoint.
Lowering the low water icvel setpoint from 10 inches to 0 inches will not significantly decrease the m ety margin.
i Certain containment isolation valves (CIVs) receive closure signals generated by the Level 3 signal. There are CIVs in the purge and inerting system, sampling system, process radiation monitoring system, drywell equipinent and floor drain i
sump discharge lines, traversing in-core probe (TIP) guide tubes and nitrogen purge lines, drywell pneumatic ccmpressor's suction liae, torus dreinage and purification line, RHR-to-radwaste line, and the RHR heat exchanger sample line. These isolations are anticipatory and credit for the actual setpoint is not explicitly assured in the safety analysis.
Lowering the trip setpoint as proposed will not have a significant impact on the safety analysis.
Furthermoie, the modified Level 3 signal may avert an unnecessary scram since the reduced setpoint will provide a few additional seconds for operator action in the event of a feedwater transient.
l Pased on the discussion above, the NRC staff concludes that the proposed change in reduction of the Level 3 scram setpoint to greater than or equal to 0 above the instrument zero is acceptable.
l l
The staff has reviewed the Edwin 1. Hatch Nuclear Plant, Units 1 & 2 submittal and has found that the proposed changes to the TS to reduce the Level 3 scram I
setpoint approximately 10 inches below the current Level 3 setting is acceptable.
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3.0 STATE CONSULTATION
In accordance with the Consnission's regulations, the Georgia State official l
was notified of the proposed issuance of the amendments. The State official l
had no coments, j
a 1
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4.0 ENVIRONMENTAL CONSIDERATION
The amendments change requirements with respect to installation or use of a facility component located within the restricted area as defined in 1
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 u no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that the
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amendments involve no significant hazards consideration, and there ha-been no public comment on such finding (56 FR 27045). Accordingly, the ameadments 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 stat ment or environmental assessment need be prepired in connection with the issuance of the amendments.
5.0 CONCLUSION
i The Commission has concluded, based on the considerations discusst a 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, j
and (3) the issuance of the amendments will not be inimical to the common l
defense and security or to the health and safety of the public.
Principal Contributor:
L. Tran, SRyB/ DST Date:
August 30, 1991 i
.m.