ML19329B152
| ML19329B152 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 04/30/1973 |
| From: | Schwencer A US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Sampson G TOLEDO EDISON CO. |
| Shared Package | |
| ML19329B145 | List: |
| References | |
| NUDOCS 8001300725 | |
| Download: ML19329B152 (2) | |
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'rsin e Apg 3 g ig73 Docket No. 50-346 The Toledo Edison Company ATTN:
Mr. Glenn J. Sampson Vice President, Power 300 Edison Plaza Toledo, Ohio 43652 Centlemen:
Two incidents have occurred at a nuclear power plant that indicate a deficiency in the control circuit design that warrants a review of the control circuits of all facilities to assure that these types of defi-ciencies 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 a dif ferent component.
In one case, this caused the loss of capability to isolate secondary containment when this capability
' was required. In the second case, the racking out of a breaker for one n,( 7 -
pump disabled not only the pump being removed from service but also its (d r d redundant counterpart. Both of these occurrences resulted from the use i
G of auxiliary contacts on the movable cortion of the circuit breakers in the control circuits of other components. When the breaker is racked out, the control circuit employing these contacts is opened and may be rendered inoperable. Copies of the licensee's reports on these two occurrences are enclosed for your information. The licensee's corrective measures for both of these cases included redesign of the control circuits so that racking out the breakers would not render the control circuits of other equipment inoperable.
1 As a result of these occurrences, we request that you perform a review of the control circuits of all safety related equipment at the plant to assure that disabling of one component does not, through incorporation in other interlocking or sequencing controls, render other components in-operable. All modes of test, operation, and failure must be considered.
It appears,that in the cases cited above, the racked out position of breakers had not been included in the failure mode analysis of these control circuits.
Also, your procedures should be reviewed to ensure they p.; vide that, whenever part of a redundant system is removed from service, the portion remaining in service is functionally tested i==ediately afcer the dis-abling of the affected portion and, if possible, before disabling of the affected portion.
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