ML17252A786

Report of Abnormal Occurrence Per Section 6.6.a of the Technical Specification - Exceeding Set-point on Main Stream Line Hi Hi Rad

ML17252A786
Person / Time
Site:	Dresden
Issue date:	03/27/1975
From:	Stephenson B Commonwealth Edison Co
To:	James Keppler NRC/RGN-III
References
BBS 198-75 50-249/75-17
Download: ML17252A786 (2)

Text

Commonwe&Edison One First Nation~za, Chicago, Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690.

• !~atofy Docket Fil'e' BBS LTR. #198-75

• Dresden Nuclear Power Station R* a. #1 Morris, Illinois 6o450 March 27, 1975 Mr. James G. Keppler, Regional Director Directorate of Regulatory Operation-Region llI

u. s. Nuclear Regulatory CODIDission 799 Roosevelt Road Glen Ellyn, Illinois 00137 SUBJEX::Ts REPoRT OF ABNORMAL OCCURRENCE PER smTION 6!6.A OP THE TmHNICAL SPEX:IFICATIONS. . .

EXCEEDING* SE'l'POIN'l' ON MAIN STEAM LINE HI HI ~

References a 1) *Regulato17 Ouide--1.16 Rev. 1 Appendix A

2) Notification of Region III of lJ. s. NuolearRegulatory Commission Telephones P. A~~ _1015 hours on March 19, 1975 Telegrams J. Ke:Piler, 1105 hours0.0128 days <br />0.307 hours <br />0.00183 weeks <br />4.204525e-4 months <br /> on March 19, 1975

3) Drawing Number 12E2503 Report Numbers ~249/1975-17 Report Dates March 27, 1975

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Occurrence Date: March 18, 1975

• Facilitys Dresden Nuclear Power Station, Morris,lllinois mmrIFICATION OF. OCCtJRRBNCE.

Dresden Unit 3 Main Steam Line high radiation moni. tor setpoint a'bave the technical specificati~ limits.

CONDITION PRIOR TO OOCURR!NCE Dresden Unit 3 was operating at a steady 390 MWe with weekly instrument aurveillance in prQgress. . "'~ ': ..

DFS:RIPl'ION OF OCCURRDJCE During the weekly trip eheok of the Main Steam Line Radiation Mot.iitors, .Manitor 1705-2A was found to trip at 1600 ops and monitor 1705-2B at ~550 cps. Tbis is above the technical speoification*of equal.to or less th&ntbree times the 10~ power backgrwn.d. (500 O~S.= 1~)

t.,

.* James G. Keppl~

-"DESIGNATION OP APPARmT CAUSE OF ~E

• March 27' 1975 The scale for the MSL radiation monitors *is logritmnio from O to 106 ops. Thia allows for errors to be easily made in interpreting~ 1500 ops s.etpoint.

The investigation also revealed. that an. error in the non-conservative direction can be made due to the characteristic of the moni.tor to continue going upscale after -the :trip ooc~~~ ;__ '!'his could cause a *trip setting to

• appear high. It-was also noted that miring additional investigation on 3-26-75, that Monitor 1705-2A scale was not zeroed. This coDditian when corrected

• -caused ~the trip point to decrease. _ The scale for moDitor 170~ was also~:ii

- jli,.ghtl.~* above ZeJ' which wOuld have provided & higher than &OtuAl indicated

. _*ri8"1ng. The single most- significant cause of the occurrence is. probably the 'lack of conservatism in the setpoint valve *. The monitors ar~ oalibzt&ted

-for 1500 ops_ which does not allow fQr any error in interpretation or eleo~c reliability. -

ANALYSIS *op OOGURRBNcE.

On the date of the occurrence, moniwrs 1705-2C and_,2D were f~ within-the 1500 cps limit. The MSL moDi.tors_ are C9JU1ected in a~. "one-out-of-two-twice" logic* which will proviti a tlOr&m aDd lllsolatiot).. when °the "A": o~ ~:!* monitor and "B" or "D" monitor trip. Therefore, .the system would-..bave operated within specifications. It is therefore concluded that the sat~ty of pl.ant pers0D11el

_or the general pablic was net Jeopardized. as a resW.t *ot _this occurrence.

The inmeciiate c0rreot1ve action was to reset the A & B*monitor trip point to 1500 ops *. Addi~onal aotion*_Vill .b& to lower the trip poi.Dt of all MSL radiation monitors on both DreSd.en Units 2 .and 3 to 1300 +/- 100 ops. '*

li'AILURE DATA The MSL Radiation Monitors are*oeneral Eleotrio Log Rad Moni.tors vendor-part no. 194X62907. A review.of the abnormal occurrence records reveal that no -

eimi.liar*ocourrences have been reported tor the-instruments in queetion.

Pile,/MlC