ML17252A183

Report of Abnormal Occurrence Per Section 6.6.A of the Technical Specifications Failure of Intermediate Range Monitors to Respond

ML17252A183
Person / Time
Site:	Dresden
Issue date:	09/16/1975
From:	Stephenson B Commonwealth Edison Co
To:	James Keppler NRC/RGN-III
References
BBS Ltr. #611-75 50-249/75-41
Download: ML17252A183 (3)

Text

.. Commonwealt.ison One Fi'rst National P

, Chicago, Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 1R1egula!ory Doc~_et.fili

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BBS Ltr. #61J'.'."'75 __..

Mr. James G. Keppler, Regional Director Directorate of Regulatory Operation-Region III

u. s. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 6o137 SUBJJOCT:

REPORT OF ABNORMAL OCCURRENCE PER SECTION 6.6.A OF THE TECHNICAL SPECIFICATIONS FAILURE OF INTERMEDIATE RANGE MONITORS TO RESPOND

References:

1!~1 Regulatory Guide 1.16 Rev. 1 Appendix A

2) Notification of Region III of U. s. Nuclear* Regulatory Commission Telephone: P. Johnson:, 1430 hours0.0166 days <br />0.397 hours <br />0.00236 weeks <br />5.44115e-4 months <br /> on September 8, Telegram: J. Keppler, 1550 hours0.0179 days <br />0.431 hours <br />0.00256 weeks <br />5.89775e-4 months <br /> on September~-~

Report Number:

50-249/75-41 Report Datei Sept~ber 16, 1975 Occurrence Date:

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• -Sl September Q~' 1975.

Facility: Dresden Nuclear.Power Station, Morris, Iilinois IDENTIFICATION OF OCCURRENCE llockJ:t.....

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Intennediate range monitors (!RM' s) 11, 1*2, "14~ 16, and 18 failed to respond during

• p'lant start-up. This occurrence represents a failure to* meet* lilni ting conditions for operation as defined in section 3 *. 1 of the Technical Specifications.

CONDITIONS PRIOR TO OCCURRENCE Unit-3 was in the start-up mode at a power level of <100 MWt.

Control rod withdrawal was in progress.

DESCRIPrION OF OCCURRENCE I

At approximately 0500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br /> on September 8, 1975, the Unit-3 r.eactOr was brought critical for plant start-up.

As reactor power was increased it was noted tha.t five of the eight !RM' s did not appear to be responding.

An immediate investigation 10148

.Septeinber 16, 1975 indicated that the problem was intrinsic to the IRM's themselv~s rather than the

- -local-=--ms~rumenta~ion, and a reactor shutdow-was comnenced.

Control rod insertion

• began at 0510 hours0.0059 days <br />0.142 hours <br />8.43254e-4 weeks <br />1.94055e-4 months <br />, with.all rods "in" by 0559 hours0.00647 days <br />0.155 hours <br />9.242725e-4 weeks <br />2.126995e-4 months <br />.

DESIGNATION OF APPARENT CAUSE OF OCCURRENCE (Unusual* Se~ce Conditions) <

The IRM cables appeared.to have* been inadvertently*pulled "open" by personnel working underneath the reactor vessel in cramped quarters. 'in addition, water was found in some of the cable connectors, which undoubtedly contributed to the IRM response problems. The water prob8.biy entered the cable connectors during the initial vessel "hydro" when control rod drive flanges were discovered leaking.

ANALYSIS OF OCCURRENCE Although the IRM's would have been incapable of providing scram protection, the 15%

average power range monitor (APRM) scram logic was in effect throughout the start-up mode.

Furthennore, the rod worth minimizer *was operable, :preventing any deviation from the established rod withdrawal sequence. Consequently, plant personnel *and the public were not.endangered by this occurrence.

CORR&;TIVE ACTION The faulty IRM cables were replaced from the junction :bt>xes in the drywall to the IRM connectors. In order to prevent a similar recurrence, the master start-up

• checklist will*be revised to include a resistance check on Source Range Monitors (SRM' s) and IRM' s when major work has been performed under the reactor vessel." This final check will*be.performed prior to start-up, after all work under the v~ssel has been completed *.

• RAILURE DATA There have been no previous IRM failures of thi~ nature at Dresden.

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~-B* B. Stephenson Superintendent BBSiCES:smp File/.NRC

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