ML19269B841

LER 78-033/01T-1 on 781214:attempt to Insert Rod Using Emergency Rod in Switch Failed & Reactor Scram Followed. Caused by Bent Switch Stop Which Would Not Allow Contact to Be Maintained in Fully Stroked Position of Switch

ML19269B841
Person / Time
Site:	Oyster Creek
Issue date:	01/10/1979
From:	Ross D JERSEY CENTRAL POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19269B837	List: ML19269B836 ML19269B841
References
LER-78-033-01T, LER-78-33-1T, NUDOCS 7901170254
Download: ML19269B841 (3)

Text

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LICENSEE EVENT REPORT 122878 CONTROL BLOCK:

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DATE EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h ITTTl I During routine startup, a reactor scram occurred in range one of the IRM l 0 3 l system. At the time of the scram, rods were being withdrawn for approach l 0 4 l to critical. Because of high xenon concentrations, the operator was l

[TTin l making the approach using information from the SRM. Since the SRM count l 0 6 l rate had changed very little, rods were being withdrawn in the notch over-

[TTT] l ride mode. An attempt to insert the rod using the emergency rod in switch l 0 a i failed and the reactor scram followed. l 80 7 8 9 DE CODE 5 BCO E COMPONENT CODE SU8 COD'E S E lTITl 7 8 l1 l B10 l@ l E l@

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35 36 31 40 41 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h i O l The failure of the emergency rod in switch is attributed to a bent switch l i i l stop which would not allow contact to be maintained in the fully stroked I position of the switch. The mechanical stop plate on the switch was re- l U

lil2l 1 (TT p placed. In addition, the appropriate procedures will be revised to re- l gl quire rods to be notched out after the sixth group on startups. I 7 8 9 80 ST S  % POWER OTHER STATUS DlS O RY DISCOVERY DESCRIPTION s (_C_j@ l 0 l 0 0l@l NA l lA l@l NA ACTIVITY CO TENT RELEASED OF RELEASE AMOUNT OF ACTIVITY LOCATION OF RELEASE Q (_Z_] @ (Z_jZ @ l NA NA l

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PUBLICITY NRC USE ONL /

2 O l k@l Weekly news release - January 3, 1979 IIllllllll'l }

7 8 9 to 68 69 80 5 NAPAE OF PREPARER PHONE: 201-455-8784 {

Jersey Central Power & Ught Company j

., Madison Avenue at Punch Bowl Road l Morristown, 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/lT-1 Report Date January 10, 1979 (Previous report dated 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 five 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 104 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 IRM's. At the time of the scram, control rods were being withdrawn for approach to critical as part of recovery operations following a scram 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 con-centrations, an accurate estimated critical position was not possible. The operator at the controls 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 with-drawn 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 insert 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 Central Power & Light Company is a Member of the General Pubhc Utihties System

8 Reportable Occurrence No. 50-219/78-33/IT-1 Page 2 January 10, 1979 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 moderato.-

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.

The appropriate procedure (s) will be revised to require non-peripheral control (I rods to be notched out when greater than group six (6) on startups.

Reportable Occurrence Report No. 78-33/lT will be placed on the required (I reading list.

The significance of the reportable occurrence will be incorporated into the (1 plant's training program. Emphasis will be placed on hot operation /startup xenon transients.

Failure Data .

Type: SRM Control Switch Part Replaced: Front Plate, Catalog No. 127A6753P1