ML20084R479

AO 50-249/75-17:on 750318,main Steam Line High Radiation Monitor 1705-2A Setpoint Above Tech Spec Limit.Caused by Lack of Conservatism in Setpoint Valve.Monitor Trip Point a & B Reset

ML20084R479
Person / Time
Site:	Dresden
Issue date:	03/27/1975
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20084R481	List: ML20084R479 ML20084R485
References
198-75, 198075, AO-50-249-75-17, RO-50-249-75-17, NUDOCS 8306150131
Download: ML20084R479 (2)

Text

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i Mr. James C. K:ppler rea 27, 1975 i

DESIGNATION OF APPARETP CAUSE OP OCCURRDEE 1

The scale for the MSL radiation monitors is logrithmic from o to 106 eps. This I allows for errors to be easily made in interpreting the 1500 ops setpoint.

The investigation also revealed that an error in the non-conservative direction can be made due to the characteristic of the monitor to continue j going upscale after the trip occurra. This could cause a trip cotting to j

' appear high. It was also noted that during additional investigation on 3-26-75, that Monitor 1705-2A scale was not zeroed. This condition when corrected caused the trip point to decrease. The scale for monitor 1705-2B was also clightly above zero which would have provided a higher than actual indicated ,

reading. The single most significant cause of the occurrence is probably '

the lack of conservatism in the setpoint valve. The n:onitors are calibrated for 1500 eps which does not allow for any error in interpretation or electronto reliability.

ANALYSIS OF OCCURREEE On the date of the occurrenco, monitors 1705-2C and 2D were found within the 1500 cps limit. The NSL monitors are connected in t. "one-out-of-two-twico" -

logic which will provido a ceram and icolation when the "A" or 'C" monitor and "B" or "D" monitor trip. Therefore, the systctn would have operated within specifications. It in therefore concluded that the safety of plant personnel or the general public was not jeopardized as a result of this occurrence.

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Con 3H:TIVE ACTION The innediato corrective action was to reset the A & B monitor trip point to 1500 op3. Additional action will bo to lower the trip point of all IGL radiation monitors on both Dresden Unita 2 and 3 to 1300 f,100 cps.

PAILURE DATA The MSL Radiation Monitors aro General Electric Log Rad Monitors vendor part no. 194x629G7. A review of the abnorcal occurrenco records reveal that no similiar occurrences have bacn reported for tho instrtunents in question.

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1. . BB. Stephenson

I Superintendant BBS

smp File /MRC 8306150131 750327 PDR S

ADOCK 05000249 PDR

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.g Com wIllth Edis:n y >' Oce Fi ational Ptiza, Chicago, Ilknois j l@ 2ddr:ss Reply to: Post Chicago, Illinois 60690 Office Box 767 BBS LTR. #198-75 Dresden Nuclear Power Station R. R. #1 Norris, Illinois 60450 March 27, 1975 / / .,

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Mr. James G..Keppler, Regional Director

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Directorate of Regulatory Operation-Region III -B) 'l s

U. S. Nuclear Regulatory Comnission '#'N g' ' ]

799 Roosevelt Road '~

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Glen Ellyn, Illinois 60137

SUBJECT:

REPORT OF APNOPRAL OCCURRENCE PER SECTION 6.6.A OF THE TECHNICAL SPECIPICATIONS EXCEEDING SETFOINT ON MAIN STEAM LINE HI HI RAD

References:

1) Regulatory Guide 1.16 Rev. 1 Appendix A

2) Notification of Region III of U. S. Nuclear Regulatory Comnission Telephone: P. Johncon, 1015 hours0.0117 days <br />0.282 hours <br />0.00168 weeks <br />3.862075e-4 months <br /> on March 19, 1975 Telegram: J. Keppler, 1105 hours0.0128 days <br />0.307 hours <br />0.00183 weeks <br />4.204525e-4 months <br /> on March 19, 1975

3) Drawing thanber 12E2503 Report Nu:nber: 50-249/1975-17 Report Dates March 27, 1975 Occurrence Date: March 18. 1975 Pacility: Dresden Nuclear Power Station, Morris, Illinois ,

IDD?TIFICATION OP OCCURRFNCE Dresden Unit 3 Main Steam Line high radiation monitor setpoint above the technical specification limits.

CONDITION PRIOR TO OCCURRE1CE Dresden Unit 3 was operating at a steady 390 MWe with weekly instrument surveillance in progress.

DESCRIPPION OF OCCURRENCE

. During the weekly trip check of the Main Steam Line Radiation Monitors, Monitor 1705-2A was fcund to trip at 1600 cps and r::onitor 1705-2B at 1550 cps. This is above the technical specification of equal to or less than three times the 100% power bachground. (500 ops = 100%)

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