ML19211D144
| ML19211D144 | |
| Person / Time | |
|---|---|
| Site: | Vallecitos Nuclear Center |
| Issue date: | 01/11/1980 |
| From: | Darmitzel R GENERAL ELECTRIC CO. |
| To: | |
| References | |
| NUDOCS 8001160555 | |
| Download: ML19211D144 (2) | |
Text
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G E N E R A 1. h E 1.E C T R ENGINEERING 1C GENERAL ELECTRIC COMPANY, P.O. BOX 460, PLEASANTON, CALIFORNIA 94566 D1VlSION January 11, 1980 Mr. D. G. Eisenhut, Acting Director Division of Operating Reactors Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Comission Washington, D.C. 20555 Ref: License R-33 Docket 50-73
Dear Mr. Eisenhut:
During routine shutdown maintenance at the General Electric Nuclear Test Reactor (NTR), Vallecitos Nuclear Center, on January 2,1980, the separation switch for Safety Rod #3 did not open as required. This occurrence is con-sidered reportable pursuant to Section 11(1) of the Technical Specifications for License R-33.
During normal operation the safety rod separation switch is depressed by an activation plunger. Upon receiving a scram signal the safety rod separates from its electromagnet, and the switch opens. If one safety rod were to drop (not initiated by a scram signal) the opening of that safety rod switch would energize a visual alarm and cause current to all safety rod electro-magnets to be interrupted.
As the result of the malfunction the current to the other rod magnets would not have shut off. However, at the time of the malfunction all of the other safety rods were fully inserted and maintenance was being performed only on Safety Rod #3. The safety rod did insert normally, and the insertion of a single safety rod is sufficient to make the NTR subcritical. Had the reactor been operating, malfunction of the switch would not have interfered with the capability to scram the other safety rods as a scram signal simultaneously interrupts the current to all of the safety rod magnets. Therefore, the switch failure had no adverse safety effect.
An investigation revealed that the malfunction was due to misalignment of the switch with the activation plunger. In addition, it was determined that two separation switches (including the Safety Rod #3 switch) were slightly different from the other two separation switches, and this contributed to the misalignment. Both of these switches were replaced.
po/o s
175f 150 do 8001160 5 3 3
GENER AL h ELECTRIC Mr. D. G. Eisenhut January 11, 1980 Page 2 In addition, lock washers were added to the switch brackets to help maintain alignment, and the maintenance procedure will be modified prior to the next scheduled quarterly maintenance (April 1, 1980) to include a check of switch alignment.
Sincerely,
$lhW R. W. Darmitzel, Manager Irradiation Processing Operation Nuclear Engineering Division RWD:sl cc: USNRC-Region V 175(151