ML20084C595

AO 251-74-3:on 740812,counting of Daily Composite Steam Generator Secondary Sys Water Sample Revealed Significant Increase in Radiation Level.Caused by Plugged Sample Line to 4-R-19 Detector.Sampling Sys Being Evaluated

ML20084C595
Person / Time
Site:	Turkey Point
Issue date:	08/22/1974
From:	Schmidt A FLORIDA POWER & LIGHT CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
AO-251-74-3, NUDOCS 8304080112
Download: ML20084C595 (2)

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FteqlDA POWLR ?. UGHT CC'. PANY August 22, 1974 Mr. John F. O' Leary, Director g~ NJ A Directorate of Licensing Office of Regulation k

U. S. Atomic Energy Commission f/p k - I 1 h'ashington , D. C. 20545 ---

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Dear Mr. O' Leary:

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ABNORMAL OCCURRENCE NO. 251-74-3 'U s d AUGUST 22, 1974 @N.P '

OCCURRENCE DATE: AUGUST 12, 1974 "~'

TURKEY POINT UNIT NO. 4 FAILURE OF 4-R-19 RADIATION DETECTION SYSTEM t .,

A. CONDITION PRIOR TO OCCURRENCE ,

The reactor was in routine operation at 99% power.

B. DESCRIPTION OF OCCURRENCE At 11:15 a.m. on August 12, 1974, counting of the daily com-posite steam generator secondary system water sample revealed a significant increase in radiation level. The gross concen-tration was 2.4x10- pCi/ml as compared to <1x10-7 pCi/ml on the previous day (AO-251-74-2). This increase in concentra-tion should have been detected by the 4-R-19 radiation detector which would have secured steam generator blowdown to the cool-ing canals, opened blowdown to the waste holdup tank, closed the sample isolation valves and sounde_d an alarm in the control room. None of these events occurred.

The daily counting of the secondary sample, while not required by Technical Specifications, serves as a backup to the R-19 N radiation detector.

C. CAUSE OF OCCURRENCE Investigation has revealed that the occurrence was caused by a plugged sampic line to the 4-R-19 detector.

The sample water from each steam generator passes through a heat exchanger and is mixed before reaching the 4-R-19 radia-tion detector. To-prevent the detector from overheating, the sampic flow rate was reduced by throttling the flow downstream of the heat exchangers. It is believed plugged due to corrosion product buildup,.that thethrottled at the line'became valves.

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/ 's Mr. John F. O' Leary, Director Page 2 August 22, 1974 D. ANALYSIS OF THE OCCURRENCE The maximum activity which could have been discharged to the cooling canals was calculated to be 10.4 mci. This represents ,

s0.2% of the quarterly limit allowed by the Technical Specifi-cations. Thus, the health and safety of the public was not jeopardized by this occurrence.

E. CORRECTIVE ACTION The immediate corrective action consisted of manually securing the blowdown from each of the Unit No. 4 steam generators.

To verify that the 4-R-19 detector would have responded properly if flow had been established, the sample flow was initiated j by opening the throttled valves. The detector responded immediately and at 1200 cpm, the required automatic functions were obtained.

As part of the permanent corrective action, the steam generator sampling system is being evaluated to correct the existing deficiencies. Proposed modifications include: 1) Installation of larger heat exchangers to lower the sample temperature, and

2) Installation of a flowmeter to indicate adequate flow.

Since the detector responded properly once~ flow to the detector was established,.the daily test of the setpoint trip function of the detector and the monthly functional check are considered adequate. However, as an interim measure, the sample flow through the throttled valves will be verified periodically during steam generator blowdown.

F. FAILURE DATA This is the first occurrence of this type at either Turkey Point Nuclear Unit.

Very truly yours, sd ,

-E/IL $1.[. Y wtnu~ -

D..S'chmidt Irc t'or of Power Resources DNR/cpc /

cc: Mr. Norman C. Moseley Jack R. Newman, Esquire l

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