ML19247A093
| ML19247A093 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 05/29/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19247A087 | List: |
| References | |
| NUDOCS 7907300011 | |
| Download: ML19247A093 (7) | |
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SAFETY EVALUATION Introduction In their submittal of July 21, 1978, Florida Power Corporation (FPC) proposed a permanent solution to the Babcock & Wilcox ECCS Small Break Analysis problem at Crystal River, Unit No. 3 (CR-3).
Additional infonnation was provided by letters dated July 28 and November 17, 1978 and January 12, February 28 and April 5,1979.
The existing High Pressure Injection (HPI) system is designed to have two make-up and purification pumps (MVP's) provide HPI flow with a third pump as a standby.
All three pumps are automatically started when the Emergency Safeguards (ES) signal is actuated.
The discharge of these pumps is directed through four injection lines to the primary loops to maintain core cooling following a loss of coolant accident (LOCA) (See Figure 1).
To mitigate the accident resulting from a small break at the reactor coolant pump discharge, which initiates the HPI system but not the low pressure injection system (LPI), the licensee has determined that the HPI system should achieve at least the equivalent of 70% of the flow of one pump to the reactor.
It was also determined that the following injection line pump configuration will result in at least the required flow:
4 lines with 2 HPI pumps 4 lines with 1 HPI pump 3 lines with 2 HPI pumps 2 lines with 2 HPI pumps
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. The proposed modif t:ation of the HPI system is intended to assure one of these configurations with the worst case single failure for the small break LOCA (assuming the loss of offsite power).
For certain single failures (i.e. loss of a diesel generator, a dc battery or an ES actuation signal), this will require operator action by 10 minutes into the accident.
The licensee has stated that the modifications proposed are evnsistent with the staff positions regarding allowable operator actions for which credit may be taken following a small break LOCA.
4 Evaluation The proposed modification consists of keeping the HPI pump cross-connect valves normally open and providing means of supplying electrical power to the motor operators of the HPI valves (MUV-23, 24, 25 and 26) from the Engineering Safeguards electrical buses for both channels through appropriate transfer switches and circuit breakers (See Figure 2).
The present electrical distribution system has MUV 23 and MUV 24 supplied from ES-Al-MCC and MUV 25 and MUV 26 supplied from ES-B1-MCC.
The proposed modification will provide new motor control center sections with motor-operated molded case circuit breakers or contactors and electrical transfer switches arranged such that MUV-23, MUV-24, MUV-25 and MUV-26 each can be supplied power from ES-Al-MCC and ES-B1-MCC.
Selector switches are provided in the main control room to enable the operator to select the MCC to which each train of motor-operated valves can be connected.
FPC has stated that the equipment required for the proposed modification will be designed, manufactured and qualified in conformance to the applicable standards end codes that apply to the present HPI system (as documented in Crystal River, Unit No. 3 FSAR Section 6.1 and 8).
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! The proposed modification, by providing manual selector switches to initiate transfer of MOV loads between redundant power supplies, assures that no automatic connection is provided between redundant load groups.
Thus, this design conforms to the requirements of Regulatory Guide 1.6
" Independence Between Redundant Standby (Onsite) Power Sources and Between Their Distribution Systems." The licensee has stated that the design is in conformance with Regulatory Guide 1.75 " Physical Independence of Electrical System." Our review of the control schematics of the transfer switches has shown no single failure in the transfer circuits will compronise redundant load groups of the plant.
In the exemation issued to FPC on Septencer 1,1978, we concluded that the small break LOCA analysis for the facility are acceptably conser-vative and wholly in conformance with 10 CFR 50.46 and Appendix K to Part 50. We did not, however, consider the need to assume prompt operator action (valve operation starting within 5 minutes after the LOCA) outside the control room to be in compliance with 10 CFR 50.46.
By letter dated September 26, 1978, we informed the licensee of the staff's position regarding operator actions for which credit could be taken while remaining in compliance with 10 CFR 50.46.
This position states credit may be taken for " simple" operator actions ten minutes or later after the accident and defines the type of actions which can be characterized as " simple.'
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. In the event of a LOCA at CR-3 the operators must check indications for ficw in both HPI trains.
If flow does not exist in either train the operator must turn the associated transfer switch and go to "open" on the associawed HPI isolation valves.
This action must be taken by 10 minutes after the LOCA.
This action is taken in the control room and meets our definition of " simple" and therefore we find it acceptable to assume the operator will take this action by 10 minutes after the LOCA.
FPC has shown by single failure analysis, that the operator action described above will provide a minimum of four injection lines and one HPI pump assuming loss of offsite power and the worst single failure.
Therefore, the minimum flow path requirements will be met.
FPC has performed an analysis which indicates that four injection lines and one pump provides at least 70% of the flow of one pump to the reactor.
In addition FPC will verify by measurement the HPI flow rate of all combinations of the one pump-four line case, prior to reactor operation with the modification installed.
Conclusion Based on our review, we find that:
(1) The proposed modification will assure that for all postulated single failure conditions the HPI system will be capable of supplying sufficient flow to the reactor to mitigate the small break LOCA.
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. (2) The equipment required to implement the proposed modification will be designed, manufactured, qualified and tested to the codes and standards that apply to the facility's ECCS system.
(3) The proposed modification will not affect the performance of other systens important to safety.
(4) Operator action associated with the proposed modification qualifies as " simple" operator action between 10 and 20 minutes after the LOCA and therefore is in conformance with the requirements of 10 CFR 50.46.
Accordingly, we conclude that the proposed modification is consistent with the small break LOCA analysis and is acceptable as a permanent solution to the small break LOCA issue.
Dated: May 29, 1979
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