ML20063E885
| ML20063E885 | |
| Person / Time | |
|---|---|
| Site: | 05000142 |
| Issue date: | 07/08/1982 |
| From: | Wegst W CALIFORNIA, UNIV. OF, LOS ANGELES, CA |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8207130663 | |
| Download: ML20063E885 (1) | |
Text
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UNIVERSI'IT OF CALIFORNIA, LOS ANGELES UCLA
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COMMUNITY SAFETY DEPARTMENT OFFICE OF RESEARCil er OCCUPATIONAL SAFETY IDS ANGELES, CALIFORNIA 90094 8 July 1982 Director Division of Operating Reactors USNRC Washington, D.C. 20555 Docket 50-142 On June 30 during an initial approach to critical, the reactor operator was unable to take the reactor critical due to the constant engagement of the auto controller. The problem was traced to a failed diode in the inhibit surveillance circuit which is normally enabled only by the auto control switch.
The problem was reported to Region V by telephone on July 1 as a possible reportable event under Technical Specification VIII.L.3.b. The effect of the failure was to lor.k the reactor in auto control, The problem and corrective measures are more completely summarized in the attached minutes of the Radiation Use Committee, that was convened in accordance "
with Technical Specification VIII.H.4. Additional technical information is on file at the Nuclear Energy Laboratory.
Sincerely, Rdu C.0c%4n.
-fn Walter F. Wegst, Director Office of Research and Occupational Safety WFW/jb cc: Director, Region V USNRC 0
8207130663 820708 PDR ADOCK 05000142 S PDR i
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Minutes of the Radiation Use Committee July 2, 1982 The Committee was convened to review the circumstances of an occur-rence reported to the Commission on July 1,1982. A quorum consisting of Prof essor Catton, Dr. Wegst, and Mr. Zane was present. Mr. Ostrander was also present.
The occurrence, an unanticipated reactivity change, was manif ested as a malfunction of the " drive reg rod down" circuit which activated the automatic controller circuit whenever the " auto permit" condition arose, regardless of the " auto demand" condition. The anomolous behavior was ob-served during start-up and prior to attainment of criticality.
The probics was traced to a failed decoupling diode, a past problem in other rod drive circuits, corrected by adding a voltage-limiting (Zener) diode across the relay coil to suppress excessive transients induce;d by de-energizing the coil.
The same corrective action was proposed for the present problem.
The Committee questioned the system behavior upon f ailure of the Zener diode. The Committee was advised tint an open-circuit failure of the Zener diode would return the circuit to the state that has operated suc-cessfully for over a year, and timt the failure would be unobserved unless or until the decoupling diode failed. That failure would be evidenced by an inhibit, non-clearable by the operator. The Committee recommended that a heavier duty (current and voltage) diode be used to replace the f ailed decoupling diode.
The Committee was informed that a short circuit failure of the Zener diode with the reactor operating would automatically initiate the " drive-reg-rod-down" response and sound the audible alarm. The operator would be unable to prevent t he shat-down. Failure of the diode when the reactor was shut down would be evidenced at the next a t t empt to start up by an inability to withdraw the reg rod.
The Committee noted the apparently successful application of Zener diodes to the other control blade relays, and that the addition of a Zener diode across this particular relay would yield either f ail-saf e responses or responses ttat did not decrease the system saf ety. The Committee ap-proved the change.
1 A. Zane / _
.v Secretary, RUC