ML19263A852

LER 78-033/01T-0 on 781214:reactor Scram Occurred in Range 1 of Intermediate Range Monitor Sys.Caused by Failure of Emergency Rod in Switch Due to Bent Switch Stop

ML19263A852
Person / Time
Site:	Oyster Creek
Issue date:	12/28/1978
From:	Ross D JERSEY CENTRAL POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19263A841	List: ML19263A852 ML19267A266
References
LER-78-033-01T, LER-78-33-1T, NUDOCS 7901030155
Download: ML19263A852 (1)

Text

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. LICENSEE EVENT REPORT

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• 8 9 LICENSEE CODE 14 15 LICENSE NUMBER 25 26 LICENSE (PE 40 CON'T 3 Q 60L.j@l015l0l0l0

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[g 1 2 I l 19 l@l 1 1211 141718 l@l112 l2181718 l@ 80 7 6 61 DOCKET NUVSER 68 69 EVENT DATE 74 75 REPORT DATE EVENT DESCRIPTION AND PROBABLE CONsr 'UENCES h o 2 l During routine startup, a reactor scram occurred in range one nf the IPM

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LO l 3 l system. At the time of the scram, rods were beina withdrawn for acoroach  !

o 4 l to critical. Because of high xenon concentrations. the coerator was 1 0 s) l making the approach using information from the SRM. Since the SRM count l 0 s l rate had chanced very little, rods were beina withdrawn in the notch over. l 0 7 l Tide mode. An attempt to insert the rod using the emergency rod in switch I o e i failed and the reactor scram followed. _

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44 47 CAUSE DESCRIPT!ON AND CORRECTIVE ACTIONS 27 i Ol The failure of the emergency rod in switch is attributed to a bent switch I i i i stop. The stop would not allow contact to be maintained in the fullv 1 stroked position of the switch. The mechanical stop plate on the switch l 1 7 lil3l was replaced and the two dogs on the switch shaft were positionally inter- l 3 4 l changed tc, reduce the tendency to bend the tab in the stroked position. I 80 7 8 9 ST S  % POWER OTH ER STATUS DISCO RY DISCOVERY DESCRIPTION 1 5 l C lh l0 0l0l@l NA l l A l@l NA l A TIVITY CONTENT OF RELE ASE AMOUNT OF ACTIVITY LOCATION OF RELEASE 1 6 lZ RELEASE @D lZ l@l NA 44 l l 45 NA 80 l

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Madison Avenue at Punch Bowl Road Mornstown, New Jersey 07960 (201)455-8200 OYSTER CREEK NUCLEAR GENERATING STATION Forked River, New Jersey 08731 Licensee Event Report Reportable Occurrence'No. 50-219/78-33/IT-0 Report Date ,

December 28, 1978 Occurrence Date December 14, 1978 Identification of Occurrence While performing a routine reactor startup following a scram from full power, a reactor period less than Tive seconds occurred resulting in a scram in range one of the IRM's. This event is considered to be a reportable occurrence as defined in the Technical Specifications, paragraph 6.9 2.a.4.

Conditions Prior to Occurrence The plant was in a routine startup.

Moderator temperature - 380*F.

Reactor pressure - 190 psig Recirculation flow - 5.2 x lo" gpm Source range monitor count rate - 450 cps Reactor at peak xenon.

Rod worth minimizer in service withdrawal sequence Vill A-1.

Description of Occurrence On December 14, 1978, at 0415 hours0.0048 days <br />0.115 hours <br />6.861772e-4 weeks <br />1.579075e-4 months <br />, a reactor scram occurred in range one of the IRH's. At the time of the scram, control rods were being withdrswn for approach to critical as part of recovery operations following a scrab from full power at approximately 1900 hours0.022 days <br />0.528 hours <br />0.00314 weeks <br />7.2295e-4 months <br /> on December 13 Because of the high xenon concentrations, an accurate estimated critical position was not-possible. The operator at the controis was using SRM count rate information as the guide for approach to critical. Since the SRM count rate had changed only slightly (425 to 450 cps) from the start of the rod withdrawal process, it was thought that the reactor was still strongly subcritical; hence, rods were being withdrawn in the " notch override mode." When control rod 10-43 (first rod in Group 9) was withdrawn to notch position (10), the reactor became critical on an estimated 2.8 second period. The operator attempted to in-sert the rod using the " emergency rod in" control switch to no avail. The neutron flux excursion was terminated by a reactor scram in range one of the IRM's.

Jersey CenW Power & Lght Com;:any is a Member cf the Genera' Pubhc Ut.!r.es System

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Reportable Occurrence No. 50-219/78-33/IT-0 Page 2

• December 28, 1978 Apparent Cause of Occurrence The operator at the controls did not expect criticality to occur at this time considering the low SRM count rate. Furthermore, the approach to critical procedure does not provide specific guidance for startup under hot / peak xenon conditions. The reason that the rod did not respond to the

" emergency rod in" switch was a failure of the switch to maintain contact in the fully stroked position due to a bent mechanical switch stop.

Analysis of Occurrence There is no safety significance to the fast positive period since it occurred very low in power and did not cause any observed heating of the moderator or changes in reactor pressure. In addition, because of the time constant between neutron flux and heat flux, the fuel cladding integrity safety limit was not violated. It is highly likely that, had the " emergency rod in" switch functioned properly, the short period would have been terminated by manual control.

Corrective Action The mechanical stop plate on the switch was replaced and the two dogs on the switch shaft that contact the tab on the stop plate were positionally inter-changed to reduce the tendency to bend the tab when the switch is full stroked to the " emergency in" position.

Failure Data Type: SRM Control Switch Part replaced: Front plate, Catalog No. 127A6753P1

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