ML20127E416
| ML20127E416 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 01/11/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20127E412 | List: |
| References | |
| NUDOCS 9301190292 | |
| Download: ML20127E416 (5) | |
Text
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I SAFETY EVALUATION BY THE Of flCE OF NUCLMB_RMCIOR. REGULATION PEL ATED TO AMENDMENT NQ,9 TO FACILITY OPERATING Li[LNSE NO. NPF-57 PHILADELPHIA ELECTRIC COTA.J{Y LIMERICK _GENEPATING STATION. UNIT 1 DOCKET NO. 50-362
1.0 INTRODUCTION
By letter dated November 6, 1992, the Philadelphia Electric Company (the licensee) submitted a request for changes to the Limerick Generating Station, Unit 1, Technical Specifications (TS). The requested changes would provide a one-time revision to the TS to extend the allowed outage time (A0T) for the Residual Heat Removal Service Water (RHRSW) system and the Suppression Pool-Cooling (SPC) mode of the Residual Heat Removal (RHR) system.
The revision would establish the A0T from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> during the second Unit R refueling outage to allow continued Unit 1 operation while upgrades are made to the 'B' RHR heat exchanger outlet valve on both units.
Unit 2 will comply with the applicable Unit 2 TS allowed outage time.
These changes apply to TS Sections 3.6.2.3, " Suppression Pool Cooling," and 3.7.1.1, " Residual Heat Removal Service Water System - Common System."
2.0 EVALUATID3 The licensee has proposed that TS Sections 3.6.2.3, Action a, and 3.7.1.1, Action a.3, be temporarily amended to allow maintenance to be performed on the RHR heat exchanger service water outlet valves HV-51-lF0688 and HV-51-2F0688 on the 'B' RHR heat exchanger for Units 1 and 2.
This maintenance will upgrade the valves' internals with stainless steel components. These valves are used to isolate and throttle the RHRSW flow through the RHR heat exchangers.
The harsh flow conditions experienced by these valves during the throttling operation have resulted in the degradation of their internals.
Therefore, the proposed maintenance-is considered an upgrade for these valves.
The licensee may also perform maintenance on Units I and 2 'B' RHR heat exchanger RHRSW inlet valves HV-51-lF0148 and HV-51-2F0148, respectively.
Both sets of valves are unisolable.
Therefore, multiple freeze seals and partial system draining are required in order to perform maintenance on these valves.
The change to TS Section 3.7.1.1, Action a.3, would allow one subsystem of the RHRSW to be inoperable for 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br />.
The change to TS Section 3.6.2.3, Action a, would allow the SPC mode of one RHR subsystem to be inoperable for 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> during the second Unit 2 refueling outage.
These one-time TS
.9301190292 930111 PDR ADOCK 05000352-P PDR
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. changes would allow adequate time for the maintenance en the common 'B' RHRSW loop while avoiding a Unit I shutdown.
Unit 2 will be in a refueling outage and will comply with the applicable Unit 2 TS requirements for A0T for the RHRSW system and the SPC mode of the RHR system.
The removal of the 'B' RHRSW loop from service will affect the operability of the heat exchanger af both unitt, which provide decay heat removal and suppression pool /drywell temperature control. Shutdown cooling is required by TS Section 3.4.9.1 for Operational Condition (OPCON) 3 - Hot Shutdown, by TS Section 3.4.9.2 for OPCON 4 - Cold Shutdown, and by TS Section 3.9.11.2 for OPCON S - Refueling. Otherwise, a demonstration of the availability of an alternate method of decay heat removal is required.
The proposed TS requirements have no impact during the Unit 1 power operating condition.
However, if Unit 1 is required to shut down while the 'B' RHRSW loop is inoperabic, alternate decay heat removal methods are available by establishing a shutdown cooling path through the automatic depressurization system (ADS) valves or by using the main condenser as a heat sink if offsite power is available.
These methods will satisfy TS requirements for OPCONs 3 and 4.
For OPCON 5, alternate decay heat removal methods using the Reactor Water Cleanup system can satisfy the shutdown cooling requirements.
The suppression pool /drywell temperature control is an accident mitigation function of the RHR system that is accomplished through the RHR heat exchangers utilizing the suppression pool spray and the suppression pool cooling modes of operation.
TS Section 3.6.2.2 requires t1at two loops of the suppression pool spray mode of the RHR system be operable in OPCONs 1, 2, and
- 3. The A0T for one loop of the suppression pool spray mode is 7 days. The proposed 'B' RHRSW valve loop maintenance will be completed within the A0T.
Therefore, no change is required.
TS Section 3.6.2.3 requires that two loops of the SPC mode of the RHR system be operable in OPCONs 1, 2, and 3.
The A0T for one loop of the SPC mcde being inoperable is 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. The proposed change would allow an extension of Unit 1 A0T to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> during the second Unit 2 refueling outage.
The licensee has addressed the postulated rupture of a recirculation line, which is a bounding event.
The Updated Final Safety Analysis Report (UFSAR),
Section 6.2.2, states that one operable RHR heat exchanger is adequate for the two accident mitigation scenarios:
(1) the operable RHR heat exchanger is utilized in the RHR drywell spray mode while one RHR pump is in Low Pressure Coolant injection (LPCI) mode of operation and one Core Spray loop injects water into the reactor vessel, (2) the operable RHR heat exchanger is used with an associated RHR pump taking suction from the suppression pool and discharging to the reactor vessel while the other RHR pump is in LPCI mode of operation and one Core Spray loop injects water into the reactor vessel.
Both scenarios assume a LOOP, the availability of High Pressure Coolant injection (HPCI) for the duration of the accident, initial suppression 3001 temperature and RHRSW temperature at their maximum allowable limit, all t1e 1
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{k ng:V decay heat from the reactor vessel is rejected through the RHR heat exchanger, and the RHR heat exchanger is operable with the lowest allowable heat transfer capability.
For the postulated rupture of a recirculation line, the peak containment pressure is higher in the second sr.enario, but it is still much less than the containment design pressure.
TS Section 3.7.1.1 requires that two loops of the RHRSW be operable in OPCONs 1, 2, and 3.
The A0T for one loop of the RHRSW system being inoperable, results in the inoperability of the associated RHR heat exchanger for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
The proposed change extends this period to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> for the second Unit 2 refueling outage. The RHRSW system was designed with sufficient capacity so that one loop of the RHRSW with two RHRSW pumps in operation and two spray networks can mitigate a Design Basis Accident (DBA) on one unit and allow the safe shutdown of the other unit, as described in UFSAR Section 9.2.3.
The licensee plans to remove from service the 'B' RHRSW loop at approximately 20 days after the Unit 2 outage.
At this time the decay heat generation for Unit 2 would be reduced from 146 MWt to approximately 3.5 MWt, cold shutdown would be established, decay heat generation would be reduced, the Spent Fuel pool Cooling and Cleanup system wnuld be placed in service, and the recirculation pump or an RHR pump could be placed into service as an alternate source for decay heat removal.
At this point the 'A' RHRSW loop requirement for Unit 2 heat remuval are minimal for maintaining cold shutdown conditions.
Furthermore, draining of the Unit 2 reactor cavity would not be allowed until the 'B' RHRSW loop is returned to service or an alternate decay heat removal method is available.
Therefore, since one loop of the RHRSW system can mitigate a DBA on one unit and support the safe shutdown of the other unit, the potential heat removal requirements with respect to Unit 1, during the period that these prnposed TS changes will be in effect, is within the capacity of the 'A' RHRSW loop.
A single f ailure could render the ' A' RHR heat exchanger or the ' A' RHRSW loop inoperable during the proposed extended A0T.
However, by limiting the time the 'B' RHRSW loop is out of service, and by maintaining the Unit 1 'A' RHR heat exchanger, the 'A' RHRSW loop, and the associated equipment / system operable during that period, the consequences of an accident will remain unchanged.
The staff has reviewed the licensee assessment of the components that can affect the performance of the Unit 1 ' A' RHR heat exchanger or 'A' RHRSW loop.
The information presented on their operation, power supplies, failure rates, testing and maintenance is found acceptable to the staff.
The removal of the 'B' RHRSW loop from service will not affect the capW;ility of any emergency core cooling system (ECCS) from injecting water into the reactor vessel.
The PMSW system is manually operated and is not required during the first 10 minutes of an accident.
Therefore, the short-term emergency core cooling capability of Unit 1 ECCS is unaffected.
The long-term cooling requirements will be met by the Unit 1
'A" RhR heat exchanger and the
'A' RHRSW loon with the RHR system in either the containment spray or the SPC
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. mode of operation.
Further removal of Unit I equipment / systems will be allowed in accordance with existing TS requirements as long as the removal of the equipment / systems from service does not adversely affect the operability of the 'A' RHRSW loop or the operable SPC mode of RHR operation or places the unit outside the analysis described in UFSAR Section 6.2.
The Emergency Service Water (ESW) system will be affected by the removal of the 'B' RHRSW loop from service in that all ESW return flow will be to the 'A' RHRSW loop.
This alignment is within the design capabilities of the ESW system and will be controlled by approved procedures. The licensee has performed a computer analysis of the flow distribution to components cooled by the ESW, which indicates-that sufficient ESW flow is available to support.
operability of essential components.
In addition, the licensee will perform flow measurements on the most limiting components of the ESW system to validate component / system operability.
Furthermore, physical work on the 'B' RHRSW loop will not begin until both loops of the ESW system are verified to be operable.
To ensure adequate heat removal capability for the accident scenario of a LOCA/ LOOP on onc unit and a simultaneous safe shutdown of the other unit, the RHRSW system is designed such that the A0T for operation with less than three RHRSW pumps operable and their associated Emergency Diesel Generators (EDGs) operable, is limited to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
The reduction in margin of safety associated with increasing the A0Ts to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> in a degraded condition of the plant is minimal, since it reflects a small increase-in the probability of a LOCA/ LOOP on Unit I during the three-day period allowed by the TS. The licensee has supported this conclusion with a Probabilistic Risk Assessment evhluation.
The results indicate that the increased risk of extending the A0Ts for Section 3.6.2.3, Action a, and TS Section 3.7.1.1, Action a.3 to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> is minimal.
The staff has evaluated the proposed one-time extension in A0T for the RHRSW system and the SPC mode of the RHR system from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br />, while upgrades are made to the 'B' RHR heat exchanger outlet valve of both units.
The staff concludes that the proposed TS change is acceptable.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations,-the Pennsylvania State official was notified of the proposed issuance of the amendment.
The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or u;e of a facility component located within the restricted area as defined in 10 CFR Part 20.
The NRC 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 cumulative occupational radiation a.
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. exposure.
The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (57 FR 55585). Accordingly, the amendment meets 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 amendment.
5.0 CONCLUS10B 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 Comniission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
F. Rinaldi Date: January 11, 1993
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