ML18031A751
| ML18031A751 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 09/02/1986 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML18031A750 | List: |
| References | |
| GL-83-28, NUDOCS 8609050069 | |
| Download: ML18031A751 (3) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 N
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SAFETY EVALUATION E" E I~N 4..2 REACTOR RIP S
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-LIN TESTING BR INTRODUCTION AND
SUMMARY
Generic Letter 83-28 was issued by NRC on July 8, 1983, indicating actions to be taken by applicants and licensees based on the generic implications of the Salem ATWS events.
Item 4.5 indicates a staff position of requiring on-line functional testing of the reactor trip system, including independent testing of the diverse trip features, for all plants.
Item 4.5.2 requires licensees with plants not currently designed to permit periodic on-line testing to justify not making modifications to permit such testing.
By letters dated November 7, 1983, and March 15,
- 1984, TVA committed to and described their program and procedures for on-line surveillance testing.
We find TVA's response to be satisfactory.
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EVALUATION In their March 15, 1984 letter, TVA noted that Browns Ferry does not have a
system defined as a "reactor trip system."
A channel functional test includes full actuation of (I) the associated logic, (2) two output scram contactors in each channel, and (3) two scram valve solenoids.
Each individual channel output contactor is tested at least ll times each month.
Each of the scram valve solenoids associ-ated with a control rod drive is actuated 22 times each month.
The actuation of the scram valve solenoids during the monthly tests do not test the operability
'f the valves.
However, ten percent of the control rods are tested every 16 weeks.
In addition to verifying operation of the scram solenoid valves, the control rod tests check rod insertion times. and operation.,of the hydraulic control units (HCU). scram inlet and outlet valves.
The Browns Ferry reactor protection system has diversity in the sensor channels and relays, the scram contactors, the scram solenoid valves, and the control rod drives.
In addition to the primary scram logic, backup scram logic is provided in the RPS.
The backup scram valves are redundant valves with redundant trip signals from both RPS logic trains A and B.
The logic is diverse from the primary RPS since the backup scram valve solenoids are energized to trip and are dc-powered, whereas the primary scram valve solenoids are ac-powered and deenergized to trip.
The applicant notes that although the logic for the backup scram system, including the scram contactor contacts, is tested periodically during channel functional
- tests, the backup scram valve solenoids themselves are not.
On-line testing of the backup scram solenoid valves is not possible because the only time the backup scram solenoid valves.are actuated is when a complete scram signal is initiated.
The sta
~ has addressed this testing limitation previously (Reference I) and has accepted it based primarily on the fact that the backup scram system provides additional assurance for control rod insertion for single failure of the scram solenoid valves rather than as a diverse trip in the event of any potential common mode failure of the scram solenoid valves.
Moreover, the overall design of the scram system is such that a number of single scram solenoid valve failures could occur without resulting in a shutdown failure, and multiple failures are not likely because of the on-line testing of the scram solenoid valves.
As to common mode failures, it is noted that the same reactor protection logic, which includes on-line testing, is used to actuate both the scram and backup scram valve solenoids.
Thus, the most likely source of common mode failures for the overall scram system is tested on-line.
3 Therefore, we support the previous staff conclusion that sufficient basis exists to justify not requiring modification of the backup scram to provide for on-line testability.
- However, we conclude that the backup scram function should be tested during refueling outages, and such testing should be included in the plant technical specifications.
We have not attempted to evaluated the frequency of the testing (Item 4.5.3) or any required changes in the Technical Specifications
( Item 4.3.T.S MPA-B90) in this review.
Item 4.5.3 and Item 4 '
.T.S.
(HPA-B90) will be separately reviewed.,
CONCLUSION We find that TVA's on-line testing capability of the reactor protection system meets the intent of Item 4.5.2 of Generic Letter 83-28 and is therefore acceptable REFERENCE 1.
NRC memorandum, Gus Lainas to R.
Wayne Houston "Generic Letter 83-28, Item 4.5 On-Line Testing of Backup Scram, GE Plants,"
November 16, 1984
'rincipal Contributor:
AD Toalston Dated:
September 2,
1986