ML19290B867

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Responds to IE Bulletin 79-24, Frozen Lines. Dec 1975 Review of All Freeze Protection for safety-related Piping & Instrumentation Led to Freeze Protection Improvements
ML19290B867
Person / Time
Site: Millstone Dominion icon.png
Issue date: 10/31/1979
From: Counsil W
NORTHEAST NUCLEAR ENERGY CO.
To: Grier B
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
IEB-79-24, NUDOCS 7912140287
Download: ML19290B867 (2)


Text

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":::::::=l?l:::~~~ aan w eu L L J ::::::=""%l%"lll October 31, 1979 Docket No. 50-336 fir. Boyce H. Grier Director, Region I Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pennsylvania 19406

References:

(1) B. H. Grier letter to W. G. Counsil, dated September 27, 1979 - Bulletin 79-24 Frozen Lines (2) Reportable Occurrence R0-50-336/75-37

Dear Mr. Grier:

This letter responds to IE Bulletin 79-24 on the subject of the possibility of safety related process, instrument and sampling lines freezing during extremely cold weather.

In December 1975, as a result of the malfunction of two channels of level indication for the Refueling Water Storage Tank (RWST) due to partial freezing of the instrument lines, a review of all freeze protection for safety related piping and instrumentation lines was undertaken. The results of this review and the corrective action taken is presented below. Also, the final report (submitted on January 29,1979) for Licensee Event Report 50-336/75-37 discussed corrective actions taken specifically as a result of the freeze-up of the RWST level sensing lines mentioned above.

Based on the results of the inspection of freeze protection for safety related equipment, it was detennined that improvements in freeze protection were warranted. Insulated enclosures were built around the RWST and Condensate Surge Tank (CST) level transmitters and instrument tubing.

These enclosures were provided with space heaters, and in the case of the RWST enclosures, they were powered from redundant vital power sources.

Due to service conditions, it was not required that the space heater for the CST enclosure be powered from vital sources. Further, the heat tracing circuits for the RWST suction lines, engineered safety features pumps minimum flow recirculation line to the RWST and the RWST level sensing lines were modified to provide power from split facility vital power sources.

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U. S. Nuclear Regulatory Commission Page 2 The heat tracing circuits for the CST suction line was not modified, since the tank would be in use in the event of a loss of normal site power; hence flow in the line would prevent freezing. Finally, all the heat traced lines discussed were provided with low temperature alams.

Very truly yours, Northeast Nuclear Energy Company v'i ,/ MO+

. G. ounsil Vice President 1579 146