ML20127K873

Ao:On 730929,SGBT Sys B Low Heat Alarm Received & Low Differential Pressure Observed.Caused by Failure of 30 Amp 600 Volt Fuse Block Assembly in Heater Circuit.Fuse Block Assembly Replaced & Operability Test Performed

ML20127K873
Person / Time
Site:	Monticello
Issue date:	10/08/1973
From:	Mayer L NORTHERN STATES POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9211230301
Download: ML20127K873 (1)

Text

.,

ttery %4 N r NORTHERN STATES POWER COMPANY MIN N E A f*0M s. MIN N E SOTA 59400 October 8, 1973 @

S D '

Dog N Mr. J P 0' Leary, Director 9 ~~._ -

Directorate of Licensing T OCT U jap 3 7 , & '

Office of Regulation 9 ptG3pAh .q(/ ,

U S Atomic Energy Commission hit Cuf1 V '

Washington, D C 20545 g

Dear Mr. O' Leary:

MTh -

MONTICELLO NUCLEAR GENERATING p1 ANT '.

' _ . /

Docket No. 50-263 License No. DPR-22 Malfunction of the "B" SBGT System 11 cater A condition occurred at the Monticello Nuclear Generating Plant which we are reporting to your office in accordance with Section 6.7.B.1, Abnormal Occurrence Reports, of Appendix A, Technical Specifications, of Provisional Operating License DPR-22.

On September 29, 1973, while deinerting the primary containment during a scheduled reactor shutdown, the "B" Standby Gas Treatment (SBGT) System LOW llEAT alarm was received and indication of low differential temperature was observed. The redun-dant SBrr train was immediately placed in operation.

Subsequent investigation revealed failure of the 30 amp-600 volt fuse block assembly in the heater circuit. It was determined that a loose fuse clip on the fuse block had created a high resistance path resulting in overheating of the assembly to the point of failure. '1he fuse block assembly was replaced.

Physical inspection and electrical testing of the heater revealed it to be undam-aged. An operability test of the "B" SBGT System was satisfactorily performed on October 2, 1973, prior to reactor startup.

'Ihis occurrence did not affect safe operation since the redundant train was fully operabic and within minutes the plant conditions were stch that SBGT operability was not required.

No similar failures have occurred at Monticello. An inspection of the redundant SBGT train heater circuit was performed and no abnormal conditions noted. It is felt that the measures taken were sufficient to prevent repetition.

Yours very truly,

, , o fu N L 0 Mayer, PE Director of Nuclear Support Services 9211230301 731008 3 cc: J G Keppler ADOCK 0500 gDR G Charnoff I Minnesota Pollution Control Agency 'y y ]

Attn. Ken Dzugan