ML16138A817
| ML16138A817 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 08/19/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML16138A816 | List: |
| References | |
| NUDOCS 9608220197 | |
| Download: ML16138A817 (5) | |
Text
00 UNITED STATES 0
NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 217 TO FACILITY OPERATING LICENSE NO. DPR-38 AMENDMENT NO. 217 TO FACILITY OPERATING LICENSE NO. DPR-47 AND AMENDMENT NO. 214 TO FACILITY OPERATING LICENSE NO. DPR-55 DUKE POWER COMPANY OCONEE NUCLEAR STATION, UNITS 1, 2, AND 3 DOCKET NOS. 50-269, 50-270, AND 50-287
1.0 INTRODUCTION
By application dated June 6, 1996, as supplemented by letter dated August 1, 1996, Duke Power Company (the licensee) proposed amendments to the Technical, Specifications (TS) for the Oconee Nuclear Station (ONS) Units 1, 2, and 3.
The requested changes would revise the Technical Specification surveillance requirements related to testing of the Low Pressure Service Water (LPSW) pumps and valves to reflect a design change to remove the Engineered Safeguards (ES) signal from the valves. The proposal would change the low pressure injection system refueling outage test from verification of-the operability of the LPSW system that supplies cooling water to the low pressure coolers, to verification of the operability of the LPSW pumps and manual alignment of valves LPSW-4 and LPSW-5. The August 1, 1996, letter provided clarifying information that did not change the scope of the June 6, 1996, application and the initial proposed no signficant hazards consideration determination.
2.0 BACKGROUND
The licensee is upgrading the Emergency Condenser Circulating Water system to resolve several service water issues. One of these issues, Violation 93-25 03, Example A, "Inadequate Net Positive Suction Head for LPSW Pumps," found that the net positive suction head available (NPSHa) for the LPSW pumps would be less than the NPSH required (NPSHr) under certain design basis conditions.
These conditions involve the loss-of-coolant accident (LOCA) concurrent with a loss of offsite power (LOOP), a single failure of one of the LPSW pumps, and a loss of instrument air. The loss of instrument air would cause the LPSW flow control valves that normally control flow to the low pressure injection (LPI) coolers to fail open, resulting in the potential for inadequate NPSH. The concurrent flow demand by non-essential LPSW loads would also impact the ability to maintain adequate NPSH, which would continue to exist until operator actions could be taken to isolate non-essential loads and reduce flow to the coolers.
9608220197 960819 PDR ADOCK 05000269 P
-2 3.0 SYSTEM DESCRIPTION The LPSW system provides cooling water for normal and emergency services throughout the station. Safety-related functions served are the reactor building cooling units, decay heat removal coolers, high pressure injection pump motor bearing coolers, motor-driven emergency feedwater pump motor coolers, and turbine-driven emergency feedwater pump cooling water jacket.
Oconee Units 1 and 2 have a shared LPSW system that includes three pumps and Unit 3 has its own LPSW system that includes.two pumps.
The present design requires Engineered Safeguards Channels 3 and 4 to actuate at either 550 psig reactor coolant system (RCS) pressure or 3 psig reactor building (RB) pressure. Actuation of these channels, which would occur several seconds after a LOCA, automatically opens valves LPSW-4 and LPSW-5 on the affected Oconee unit to:admit LPSW flow through the A and B LPI coolers respectively. Initially, following actuation of the ES signals, the LPI System would be operating in the injection mode, taking suction from the borated water storage tank (BWST).
When a specified minimum level is reached in the BWST, operators would establish the recirculation mode for injection into the RCS by aligning LPI pump suction to the Reactor Building Emergency Sump (RBES). Because the water in the BWST is at low (ambient) temperature and the water in the RBES would be elevated due to the LOCA, LPSW cooling water flow through the LPI coolers is only necessary for removing heat from the LPI while in the RBES recirculation mode. The BWST contains enough water inventory to support LPI injection for at least 30 minutes after a large break LOCA.
To provide adequate NPSH during all design basis conditions, the LPSW flow demand after a LOCA/LOOP would be reduced to decrease NPSHr by isolating LPSW flow from any unnecessary loads early in the LOCA/LOOP. However, flow to the LPSW non-essential header cannot be isolated too early without significant equipment damage to turbine-generator equipment that is normally cooled by the LPSW non-essential header.
To resolve the NPSH issue, the licensee has proposed to remove the ES signal that automatically opens valves LPSW-4 and LPSW-5. After establishing RBES recirculation, operators would then isolate flow to the LPSW non-essential header and throttle open LPSW-4 and LPSW-5 from the control room. This will maintain LPSW flow demand low enough so that the NPSHa remains greater than NPSHr.
Removal of the ES signal requires a change to the surveillance test specified in TS 4.5.1.1.2.a.(2). This TS requires a functional verification of the ES function of LPSW-4 and LPSW-5 on a refueling outage frequency. Under the proposed change, the reference to ES would be changed so that the test applies to the LPSW pumps, but not to the valves. A further TS change would verify the capability of the operators to open the valves from the control room during the refueling outage test.
-3 4.0 EVALUATION TS 4.5.1.1.2.a.(2) requires verification of the ES features function of the LPSW system that supplies cooling water to the low pressure coolers in order to verify operability of the coolers. The associated Bases state that the purpose of the surveillance test is to verify that the LPSW pumps and valves LPSW-4 and LPSW-5 respond to actuation of ES Channels 3 and 4.
Presently, automatic opening of LPSW-4 and LPSW-5 upon actuation of ES Channels 3 and 4 simplifies operator action by pre-staging the necessary LPSW cooling flow to the LPI coolers in preparation for operator alignment from the LPI injection mode to the LPI RBES recirculation mode. However, the licensee has determined that removal of the automatic signal from the valves would not significantly affect the burden on the operators during a LOCA. During the first 30 minutes after a LOCA/LOOP, actions performed by the operators would not be affected by the proposed change. During this time, operators would verify proper operation of ES,equipment, monitor BWST level, begin switchover to RBES recirculation at the appropriate RBES level, and isolate the LPSW non essential header after completion of switchover to the recirculation mode.
Isolation of the non-essential header would require closing one valve in each header, controls for which will be located in the control room upon completion of the same modification that removes the ES signal from the LPSW valves.
Should instrument air be lost during a LOCA, the air-operated valves that normally control flow through the LPI coolers would fail to their full-open position. With the modification installed, motor-operated valves LPSW-4 and LPSW-5 could be used to throttle LPSW flow through the LPI coolers. The existing design basis takes credit for throttling these valves from the full open position withi-n 30 minutes after a LOCA/LOOP to reduce NPSHr.
The licensee has analyzed the consequences of changing the timing of the opening of the LPSW-4 and LPSW-5 valves from immediately after receipt of the ES signal (which would, therefore, occur prior to establishing recirculation flow from the RBES) to manually opening the cooler outlet valves after RBES flow of hot water through the cooler has been established. The operator actions that would be necessary to establish LPSW cooling water flow to the LPI coolers can be taken within 5 to 10 minutes after switchover to RBES recirculation. Analysis was performed for a 30-minute delay. The licensee determined that this condition will have no significant impact on the reactor building heat removal or environmental qualification requirements, peak containment pressure, potential for thermal effects on the LPI coolers, maintenance of adequate core cooling, and LPI and Building Spray NPSH requirements.
A single failure analysis of the LPSW system performed by the licensee has concluded that no single failure could cause a simultaneous failure of a single LPSW pump and one of the valves required to isolate the LPSW non essential header, a condition that would result in inadequate NPSH if it occurred. Each valve that is required to close to isolate the LPSW non essential header is powered from separate power supplies from the power supply for the LPSW pumps.
Each of these valves is or will be powered from Class 1E power supplies.
4I
-4 The licensee's probabilistic risk assessment for replacing the automatic actuation of LPSW-4 and LPSW-5 with operator actions determined that the change has a negligible impact on the projected core melt frequency.
By reducing the LPSW flow to the LPI coolers during the initial phase of a design basis accident, the potential exists for the LPSW pumps to be operated below the recommended minimum continuous flow rate of 4250 gpm per pump, or for a stronger pump to deadhead a weaker pump during low flow conditions. To avoid pump damage due to low flow conditions, the licensee will install a minimum flow line for each LPSW pump.
The system modifications, including removal of the ES signals, are presently planned to be implemented during the refueling outages starting in October 1996 for Unit 3, May 1997 for Unit 1, and August 1997 for Unit 2. To reflect the time-dependence of the modification, the licensee has proposed a footnote that will indicate that the present TS requirements will remain in effect for each unit until the modification has been completed for the unit.
The licensee also proposed changes to TS 4.5.1.1.2.b to differentiate between the test acceptance criteria for ES actuated and non-ES actuated components since LPSW-4 and LPSW-5 will become non-ES actuated components. These valves will no longer receive an ES actuation signal; however, the test acceptance criterion will be to ensure that they have completed their travel.
An.additional change has been proposed to the Bases to reflect the proposed changes to the TS surveillance requirements.
The staff has evaluated the changes to the TS and the plant modification to remove the automatic operation of the LPSW-4 and LPSW-5 valves and replace it with operator actions to control cooling water flow through the LPI coolers.
These actions are within the capability of the operator to perform during an accident condition. In addition, adequate controls and indications will be provided in the control room to operate these valves. There appears to be no adverse safety consequences to the modification to the LPSW system and valves.
The licensee will perform tests to demonstrate acceptable LPSW pump operation under minimum flow conditions following completion of the modification. The staff, therefore, has determined that the proposed changes to the TS are appropriate to support the modification. They also provide the necessary surveillance test requirements to ensure operability of the LPSW pumps and valves on a refueling outage frequency. Therefore, the proposed change is acceptable.
5.0 STATE CONSULTATION
In accordance with the Commission's regulations, the South Carolina official was notified of the proposed issuance of the amendment. The State official had no comments.
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6.0 ENVIRONMENTAL CONSIDERATION
The amendments change surveillance requirements. 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 is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (61 FR 37298). Accordingly, the amendments 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 statement or environmental assessment need be prepared in connection with the issuance of the amendments.
7.0 CONCLUSION
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 Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
David E. LaBarge Dated:
August 19, 1996