ML19242A535

Final Rept Re Conduit Junction Box Deficiency.Junction Boxes Insufficiently Sealed.Terminations Will Be Replaced W/Splices Using Heat Shrinking Sleeving Before Fuel Loading

ML19242A535
Person / Time
Site:	Sequoyah
Issue date:	07/12/1979
From:	TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML19242A529	List: ML19242A528 ML19242A535
References
NCR-EEB-79-7, NUDOCS 7908030092
Download: ML19242A535 (1)

Text

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s ENCLOSURE SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 CONDUIT JUNCTION BOXES INSIDE CONTAINMENT NCR EEB 79-7 10 CFR 50.55(e)

FINAL REPORT Description of Condition With the issuance of NRC IE Circular 79-05, we became concerned with the adequacy of the " sealed" junction boxes to withstand pressure that could occur from a loas-of-coolant accident (LOCA) or a main steamline break (MSB).

TVA purchases conduit boxes of coccercial grade quality specified to meet a National Electrical Manufacturers Association (NEMA) type. Sequoyah Nuclear Plant has boxes inside primary containment that are 14 gauge, NEMA 4-type (watertight). These boxes are used as intermediate junction boxes that house terminations for field wiring that interfaces with vendor equipment and components.

TVA has determined that the field installed conduits connected to these intermediate junction boxes have no provision for sealing around the conduit to box interface. Hewever, a room temperature vulcanizing (RTV) sealant is installed around the cables within the conduits where they enter the box or within a rearby condulet. Although this design will restrict noisture incursion within the conduit during normal operation, it will provide a leakage path during LOCA or MSB conditions. Thus, we do not believe these intermediate junction boxes can be adequately sealed without a redesign.

Safety Implications had this condition gone uncorrected, saf ety-related circuits could have been damaged if enough moisture or steam eatered the junction box during a LOCA or MSB. Thus, under LOCA or MSB conditions the safe shutdown of the plant could have been adversely af fected.

Corrective Action Terminations housed in junction boxes will be replaced with splices using Raychem WCSF type N heat shrinkable sleeving as the insulativn replacement material fer the splices. This corrective action applies to Class IE circuits required to achieve and maintain saf e shutdown following a LOCA or main steamliae break. These circuits will be spliced before fuel loading cf the respective unit.

Action Taken to Prevent Recurrence In the future the use of terminal blocks for Class IE circuits will be avoided, unless they can be housed in conduit boxes that are sealed to withstand the primary containment design pressure.

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