ML20128E002
| ML20128E002 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 04/03/1974 |
| From: | James Shea US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Ziemann D US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9212070444 | |
| Download: ML20128E002 (2) | |
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UNITED STATES i
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ATOMIC ENERGY COMMISSION w Asmuovow, o c. roso
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' %,.i' kk 3 $74 Files (Docket No. 50-263) q. g Ziemann, Chief, ORB #2, L TilRU D
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REVIEW 0F CONT.ROL CIRCUITS OF SAFETY RELATED EQUIPMENT - MONTICELLO (NORTHERN STATES POWER COMPANY)
By letter dated December 22, 1972, we notified Northern States Power Company of two incidents that had occurred at nucicar power plants indicating a deficiency in the control circuit design that warranted a review of the control circuits to assure that similar deficiencies
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do not exist or are corrected if they do exist. Both incidents involved the inadvertent disabling of a component by racking out the circuit breaker for different components. In one case, this caused the loss of capability to isolate secondary containment and in the second case a redundant pump, in addition to the disabled pump, was removed from service. Both of these occurrences resulted from the use of auxiliary contacts on the movable portion of the circuit breakers in the control circuits of other components.
By letter dated February 20, 1973, NSP reported the results of their revicw of control circuits of safety related equipment and acknowledged that a similar deficiency, which has been known to NSP, existed for the standby liquid control system pumps.
Operating orders were issued to assure that neither standby liquid control pump starter could be racked out of the operating position without the operator electrically defeating the interlock.
Item 4, page IV-2, included in Monticello Six-Month Operating Report No. 6, July 1,1973, to December 31, 1973, transmitted by letter dated February 28, 1974, described the modification of the standby liquid control pump circuit to permanently correct the deficiency.
It is now impossible to make both pumps inoperable when the source breaker to either pump is removed f rom the operate position.
The original control circuit contained an interlock that disabled the local test and control room starting switches for one pump whenever the breaker for the other 9212070444 740403 PDR ADOCK 05000263 PDR g
o Files &n 31974 pump was closed or removed irom the operate position.
The change bypassed the interlocks contacts associated with the control room switch Th objectives of our December 22, 1972 1ctter have been satisfied.
'o further effort in this regard is expected.
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Jimes J. Shea
\\ perating Reactors Branch #2 irectorate of Licensing cc: Northern States Power Company AEC PDR Local PDR D. J. Skovholt, L:0R T. J. Carter, L 0R D. L. Ziemann, L:0RB #2 J. J. Shea, L 0RB #2 R. M. Diggs, L 0RB #2 T. V. Wambach, L:0RB #1 R0 (3)
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