ML18107A395

LER 99-004-00:on 990520,reactor Tripped from 100% Power,Due to Negative Flux Trip Signal from Nuclear Instrumentation. Cause Has Not Been Determined.Discoloration Was Identified on One of Penetrations.With 990617 Ltr

ML18107A395
Person / Time
Site:	Salem
Issue date:	06/17/1999
From:	Garchow D, Nagle J Public Service Enterprise Group
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
LER-99-004-02, LER-99-4-2, LR-N990291, NUDOCS 9906290019
Download: ML18107A395 (5)

Text

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OPS~cf Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge, New Jersey 08038-0236 Nuclear Business Unit JUNl 71999 LR-N990291 Regional Administrator U.S. Nuclear Regulatory Commission Region 1 475 Allendale Road King of Prussia, PA 19406-1415 Gentlemen:

LICENSEE EVENT REPORT 99-004-00 SALEM GENERATING STATION - UNIT 1 FACILITY OPERATING LICENSE NO DPR 70 DOCKET NO. 50-272 This Licensee Event Report entitled " UNPLANNED REACTOR TRIP DUE TO NEGATIVE FLUX RATE TRIP." is being submitted in accordance with the requirements of 10CFR50.73(a)(2)(iv) Licensees shall report "any event or condition that resulted in a manual or automatic actuation of any Engineered Safety Feature (ESF), including the Reactor Protection System (RPS)"

Sincerely,

.2L)~

cr*~r David F. Garchow 7 .II General Manager-Salem Operations Attachment C U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555

/JCN Distribution:

LER File 3.7

.: 0 9906290019 990617 \

PDR ADOCK 05000272 S PDR The power is in your hands.

95-2168 REV. 6194

II NRC FORM 366

• (6*1998)

U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150*0104 EXPIRES 06/30/2001 I Estimated burden per response to comply with this mandatory information collection request: 50 hrs. Reported lessons learned are incorporated into the LICENSEE EVENT REPORT (LER) licensing process and fed back to industry. Forward comments regarding burden estimate to the Records Management Branch (T-6 F33), U.S. Nuclear Regulatory Commission, Washington. DC 20555-0001, and to the Paperwork (See reverse for required number of Reduction Project (3150.0104), Office of Management and Budget, Washington, DC 20503. If an information collection does not display a currently digits/characters for each block)

- valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

FACILITY NAME l1l DOCKET NUMBER 121 PAGE 131 SALEM GENERATING STATION UNIT 1 05000272 1 OF 4 TITLE (41 UNPLANNED REACTOR TRIP DUE TO NEGATIVE FLUX RATE TRIP.

EVENT DATE 151 LER NUMBER 161 REPORT DATE 171 OTHER FACILITIES INVOLVED 181 MONTH DAY YEAR YEAR I SEQUENTIAL NUMBER I REVISION NUMBER MONTH DAY YEAR FACILITY NAME DOCKET NUMBER 05000 FACILITY NAME DOCKET NUMBER 05 20 99 99 4 00 06 17 99 05000 OPERATING

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NAME TELEPHONE NUMBER !Include Area Code)

John C. Nagle Senior LicensinQ EnQineer 856-339-3171 r-nlUIDI CTC niuc I ..... cnD ..... ,.u - ,..JCIUT .... ., llDC llU ,.,,,. D .. DnDT 1 .. ,

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ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) 116)

On 5/20/99, at approximately 2137 hours0.0247 days <br />0.594 hours <br />0.00353 weeks <br />8.131285e-4 months <br />, the reactor tripped from 100% power due to a negative flux trip signal from the nuclear instrumentation. The negative flux rate resulted from a dropped control rod which was caused by a loss of power to the stationery gripper coil. The loss of power was determined to be the result of a blown fuse. Investigation identified a low insulation resistance pathway on the control cable at the containment penetration seal. The junction box for this seal was found to have an accumulation of rust on the lower panel area with some warpage of the side plates, possibly resulting from a previous service water leak which may have impinged on the junction box. The cable in question was rerouted through a spare cable "feedthrough" in the penetration assembly and returned to service. The penetration seal continues to serve the mechanical sealing function without degradation. All systems functioned as designed in response to the trip. The fuse functioned properly to protect the penetration. The root cause of the cable failure has not been determined.

A report was made to the NRC as required by the plant's Emergency Classification Guide and 10CFRSO. 72 (b) (2) (ii). This report is being made in accordance with 10CFRS0.73(a) (2) (iv) Licensees shall report "any event or condition that resulted in a manual or automatic actuation of any Engineered Safety Feature (ESF), including the Reactor Protection System (RPS)".

NRC FORM 366 (6-1998)

' U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER) i TEXT CONTINUATION .I DOCKET 121 FACILITY NAME 111 NUMBER 121 LER NUMBER 161 PAGE 13)

YEAR I SEQUENTIAL NUMBER IREVISION NUMBER l

.erating Station Unit 1 05000272 99 - 04 00 2 OF 4 *I

.nore space is required, use additional copies of NRC Form 366AJ 117)

.~T AND SYSTEM IDENTIFICATION Westinghouse - Pressurized Water Reactor Control Rod Drive System/Cable {AA/CAB}*

• Energy Industry Identification System (EIIS) codes and component function identifier codes appear as {SS/CCC} in the text.

CONDITIONS PRIOR TO OCCURRENCE The unit was operating at 100% power at the time of the event.

DESCRIPTION OF OCC~CE At 2137 on 05/20/99, Unit 1 reactor automatically tripped from 100% power due to a nuclear instrumentation negative rate trip signal. The negative rate trip signal was due to the loss of the stationary gripper coil voltage for control rod #1A3, due to a blown fuse, permitting the control rod to drop into the core. This dropped rod caused a negative rate trip signal on nuclear instrument channels 2 and 4. The trip signal on two channels occurred because of the relative position of the rod with regard to the detectors. No testing was being conducted at the time of the trip. All control rods inserted completely. The auxiliary feed-water system actuated due to the low-low steam generator levels reached during the trip, as expected.* No safety or relief valves lifted following the trip.

CAUSE OF OCCURRENCE The cause of the loss of power to the stationery gripper coil was a blown fuse protecting the penetration and control cable to the coil. Investigation determined that there was low insulation resistance on cable feedthrough 18-1 at the Conax containmept penetration .seal assembly 1-11. The junction box housing the seal assembly was found to have an accumulation of rust on the lower panel area and some warping of the side plates. Inspection of the penetration seal assembly showed evidence of a deposition of indeterminate nature at the cable feedthrough. It is believed that the rust was the result of previous events where the junction box may have been inadvertently sprayed with service water from a leaking Containment Fan Cooler *unit. The physical condition of the junction box may have allowed water entry resulting in the deposit thus causing the low resistance pathway. The root cause of the failure has not been determined. It is believe.d that this failure was random pnd may have resulted from a cable insulation defect which, when NRC FORM 366A (6-1998)

t. NRC FORM 366A (6-199B)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION DOCKET (2)

FACILITY NAME (1) NUMBER (2) LER NUMBER (6) PAGE 131 YEAR ISEQ~tNTI I NUMBER REVISION NUMBER SALEM GENERATING STATION UNIT 1 05000272 99 04 00 3 OF 4 TEXT (If more space is required, use additional copies of NRC Form 366AJ (17) combined with the environmental conditions, ultimately resulted in the failure. The cause of the insulation defect is not known, however physical inspections of the penetrations in the 1995-1996 time frame may have moved the penetration feedthrough cable excessively thus initiating the defect.

The feedthrough cable part of the Conax penetration assembly is No. 6 solid copper conductor coated with polysulfone insulation material approximately 30 mils in thickness. Polysulfone is a very durable material with excellent resistance to environmental conditions. The use of polysulfone as an insulator is limited to Unit 1 Type B, C, and D feedthroughs of the l/C 750 MCM, 3/C 2 AWG, and 9/C 6 AWG sizes.

PRIOR SIMILAR OCCURRENCES The Salem ~nd Hope Creek electronic correspondence databases have been reviewed to identify any Licensee Event Reports, Inspection Reports or other relevant correspondence which may have identified similar occurrences. No similar occurrences of cables failing at the containment penetration have been identified.

Industry data was also reviewed in attempt to identify similar events. No information was identified which aides in the understanding of this event* or which indicates that there is a potential generic concern.

SAFETY CONSEQUENCES AND IMPLICATIONS All systems performed as designed in response to the reactor trip. The fuse operated as designed and protected the penetration from damage. The design integrity of the penetration seal was maintained by the fuse protection and the penetration seal continues to perform the mechanical sealing role successfully. The sealing capability is demonstrated by the fact that the nitrogen pressure in the seal cavity is being maintained. All of the conductors utilizing this penetration seal are associated with the rod control system (RCS). The RCS electrical penetration circuits are non Class lE.

The failure appears to be random in nature. This event was the only incidence of a cable failure at the penetration identified during a review of the Salem and Hope Creek correspondence database performed in support of the root cause investigation.

Rod control system maintenance activities routinely include checking of the insulation resistance of the cables.

NRC FORM 366A 16-199Bl

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I ' NRC FORIVI 366A U.S. NUCLEAR REGULATORY COMMISSION

'f' (6-1998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION DOCKET 121 FACILITY NAME 11) NUMBER (21 LER NUMBER (6) PAGE 131 YEAR I SEQUENTIAL NUMBER IREVISION NUMBER SALEM GENERATING STATION UNIT 1 05000272 99 04 00 4 OF 4 TEXT (If more space is required, use additional copies of NRC Form 366AJ 1171 CORRECTIVE ACTIONS

1) Inspection determined that one additional conductor feedthrough (18-8) on the penetration assembly also had a low resistance reading on the cable insulation. Both the cable to the gripper coil and the additional low resistance cable ~ere rerouted through spare conductor feedthrough leads in the penetration assembly.

2) Three additional Unit 1 penetration junction boxes were opened and inspected. A discoloration was identified on one of these penetrations but the associated cable insulation resistance was found to be acceptable.

3) An inspection has been completed on similar junction box installations on Unit 2. Corrective Maintenance type Action Requests have been generated to open and inspect two Unit 2 penetration junction boxes identified as having some limited external rust noted. This activity will be completed as resources and plant conditions permit but in no case later than the completion of the next refueling outage (1Rl3).

NRC FORM 366A (6-1998)