ML18100A436

LER 93-007-00:on 930528,all Four Rods of Control Rod Bank C, Group 1 Unexpectedly Dropped Fully Into Reactor Core.Caused by Degraded Signal from Regulation Board.Card Replaced & Firing Circuit Satisfactorily tested.W/930625 Ltr

ML18100A436
Person / Time
Site:	Salem
Issue date:	06/25/1993
From:	Pastva M, Vondra C Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-007-01, LER-93-7-1, NUDOCS 9307010285
Download: ML18100A436 (5)

Text

PS~G*

Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge, New Jersey 08038 Salem Generating Station June 25, 1993 U. S. Nuclear Regulatory Commission Document Control Desk*

Washington, DC 20555

Dear Sir:

SALEM GENERATING STATION LICENSE NO. DPR-75 DOCKET NO. 50-311 UNIT NO. 2 LICENSEE EVENT REPORT 93-007-00 This Licensee Event Report is being submitted pursuant to the requirements of the Code of Federal Regulations 10CFR 50.73(a) (2) (iv). This report is required to be issued within thirty (30) days of event discovery.

Sincerely yours,

c. A Vondra General Manager -

Salem Operations MJPJ:pc Distribution 010034 Ths t:ne:*gy People ~fJJ' \

9307010285 930625 PDR ADOCK 05000311

~189 (lOM) 12-89 S PDR

NRC FORM :f66 U.S. NUCLEAR REGULATORY COMMISSION f~-81!)

APPROVED OMB NO. 3150-0104 EXPIRES: 4/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD LICENSEE EVENT REPORT (LER) COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS' AND REPORTS MANAGEMENT BRANCH IP-530), U.S. NUCLEAR REGULATORY COMMISSION. WASHINGTON, DC 20555. AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) I PAGE 131 Salem Generating Station - Unit 2 o 15 Io Io Io 13 11 f 1 1 ioF 014 TM~b'~al Reactor Protection System Actuation Following Dropped Rods of Control Rod Bank C C::rmm 1 '

EVENT DATE (51 LER NUMBER (6) REPORT DATE (71 OTHER FACILITIES INVOLVED (81 MONTH DAY YEAR YEAR ttt SE~~~~~~AL [:) ~~~~~~ MONTH DAY YEAR FACILITY NAMES DOCKET NUMBERISI aI 'i zl s 9 l3 9 b - ~ aI1 - aIa aI 6 2 I s 9 13 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE R~CUIREMENTS CF 10 CFR §: (Check one or more of the following) (111 t---M_o_D_E.,..<e_J_

POWER LEVEL I __._....._':\~

20.402lbl 20.405(1)(1 )(j) 20.405(c) 50.38(cll1l

,L . 50.73(1)(2)(iv) 50.7311l12JM 73.71(b) 73.71(c)

~........ Ol~0-1~0~~ 20.40511l11 lliil

<1..,.0.,.1......,+...- ..__ 50.38(cll2l

-- 50.73(1)(2)(vli)

OTHER (SP11cify in Abstract bolow and in Text. NRC Form ill~i11il,ll= : : : : :;:

50.73(1)(2)(i) 50.73(1)(2)(viii)(A) 366AI 60.73(1l12llii) 50.73(1) (2) (viii) (Bl 50.73(1)(2)(iii) 50.73(1l12llxl LICENSEE CONTACT FOR THIS LER 112)

NAME TELEPHONE NUMBER AREA CODE ih h la I ~ la i..: I? I? I 1 I c; COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 113)

CAUSE SYSTEM COMPONENT MANUFAC- MANUFAC*

TURER TUR ER X Al A F. I r. I R In lAT 11 I ? I O y I I I I I I I I I I I I I I I I I I I I I SUPPLEMENTAL REPORT EXPECTED (141 MONTH DAY YEAR EXPECTED SUBMISSION 11 YES (If yes. comp/ore EXPECTED SUBMISSION DATE!

DATE 1151 I I I ABSTRACT (Limit to 1400 SPBCBS, i.tJ., approximately fiftetm single-space typewritton lines} (16)

On 5/28/93, at approximately 1812 hours0.021 days <br />0.503 hours <br />0.003 weeks <br />6.89466e-4 months <br />, during startup activities following completion of the unit's seventh refueling/maintenance outage, all four rods of Control Rod Bank C Group 1 unexpectedly dropped fully into the reactor core. At approximately 1814 hours0.021 days <br />0.504 hours <br />0.003 weeks <br />6.90227e-4 months <br />, the reactor was manually tripped and the emergency operating procedure entered. The unit remained in MODE 3 (HOT STANDBY) during the entire event. This event did not affect the health and safety of the public. The rod~. dropped due to a degraded signal from the regulation board which caused'**discontinuation of firing orders to the Cl control rod group. This resulted from intermittent component failure of the Rod Control System (RCS) stationary "B" control group firing circuitry regulation card in the RCS 21AC Power Cabinet. The card was replaced restoring RCS operability for Control Rod Bank C Group 1 rods. In addition, all cards in the power cabinets have been removed, visually inspected, satisfactorily tested, and reinstalled. Following NRC concurrence, Unit 2 post refueling/maintenance outage startup testing will continue. An event involving a potential RCS single failure concern (common to Units 1 and 2), identified on June 4, 1993, is being reported in a separate LER.

NRC Form 366 (6-89)

• LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 2 5000311 93-007-00 2 of 4 PLANT AND SYSTEM IDENTIFICATION:

Westinghouse - Pressurized Water Reactor Energy Industry Identification System (EIIS) codes and component function identifiers are identified in the text as {xx/xx}

IDENTIFICATION OF OCCURRENCE:

Manual Reactor Protection System Actuation Following Dropped Rods Of Control Rod Bank C Group 1 Event Date: 5/28/93 Report Date: 6/25/93 This report was initiated by Incident Report No.93-261.

CONDITIONS PRIOR TO OCCURRENCE:

Mode 3 Reactor Power 0% - Unit Load -o- MWe Reactor startup activities were in progress following completion of the unit's seventh refueling outage. Shutdown Banks A, B, c, and D and Control Banks A, B, and C were fully withdrawn and Control Bank D was withdrawn to 160 steps.

DESCRIPTION OF OCCURRENCE:

On May 28, 1993, at approximately 1812 hours0.021 days <br />0.503 hours <br />0.003 weeks <br />6.89466e-4 months <br />, all four rods in Control Rod Bank c Group 1 {AA/ROD} unexpectedly dropped fully into the reactor core. At approximately 1814 hours0.021 days <br />0.504 hours <br />0.003 weeks <br />6.90227e-4 months <br /> the Reactor was manually tripped and the emergency operating procedure entered. The Unit remained in MODE 3 (HOT STANDBY) during the entire event. The NRC was notified of the manual actuation of the Reactor Protection System

{JC}, at 1835 hours0.0212 days <br />0.51 hours <br />0.00303 weeks <br />6.982175e-4 months <br />, in accordance with the requirements of 10 CFR5 0

• 7 2 ( b) ( 2 ) ( ii) .

ANALYSIS OF OCCURRENCE:

The Rod Control System (RCS) is used to withdraw control rods for Reactor startup and to control Reactor power during power operation.

It consists of one Logic Cabinet, five Power Cabinets, and one Direct Current (DC) Hold Cabinet:

The Logic Cabinet translates manually-initiated or automatic commands into signals required by the Power Cabinets to step the banks of Shutdown and Control rod assemblies. This cabinet contains power supply assemblies and processes logic commands required for rod movements.

The Power Cabinets provide DC power pulses to drive the Control

• LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 2 5000311 93-007-00 3 of 4 ANALYSIS OF OCCURRENCE: (cont'd)

Rod Drive Mechanisms (CRDMs) by converting three-phase alternating current {AC) power to DC power and applying it to the CRDM magnetic coils.

On May 28, 1993 at 1512 hours0.0175 days <br />0.42 hours <br />0.0025 weeks <br />5.75316e-4 months <br />, Reactor start-up commenced following satisfactory completion of procedure S2.0P-ST.RCS-0001, "Reactivity Control Systems - Rod Control Assemblies". Shortly before 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br /> on May 28, 1993, Control Rod Bank D was withdrawn to 160 steps during preparation for reactor startup. At approximately 1810 hours0.0209 days <br />0.503 hours <br />0.00299 weeks <br />6.88705e-4 months <br />, dilution to criticality began from a Reactor C.oolant boron concentration of approximately 2060 ppm. At approximately 1812 hours0.021 days <br />0.503 hours <br />0.003 weeks <br />6.89466e-4 months <br />, all four (4) rods in Control Rod Bank c Group 1 dropped fully into the core. Boron dilution was stopped and in accordance with procedure S2.0P-AB.ROD-0002(Q), "DROPPED ROD," the Reactor was manually tripped.

Emergency Operating Procedure, 2-EOP-TRIP-1, "REACTOR TRIP OR SAFETY INJECTION", was entered. All rods were confirmed fully inserted following the trip and the unit remained in MODE 3 (HOT STANDBY) during the entire event. This event is reportable in accordance with 10CFR50. 73 (a) (2) (iv).

Troubleshooting revealed the control rods dropped as the result of defective firing orders on an RCS firing circuitry card due to an intermittent component failure.

Subsequent to this occurrence, an event involving a potential single failure concern (common to Units 1 and 2), identified on June 4, 1993, is being reported in a separate LER.

APPARENT CAUSE OF OCCURRENCE:

The root cause of this event is equipment failure. The Control Rod Bank c Group 1 rods unexpectedly dropped into the core due to intermittent component failure of the stationary "B" control group firing circuitry regulation card in the RCS 21AC Power Cabinet. A degraded signal from the card resulted in the discontinuation of firing orders to the Cl control rod group, which caused the rods to drop. The card failure is attributed to degradation of a solder trace on the printed circuit board.

PRIOR OCCURRENCES:

Prior Control Rod Drop events have been reported in LERs 311/85-009-00 and 311/88-009-00. Review of these occurrences did not reveal similarities in root or contributing cause(s), which are relevant to the May 28, 1993 event.

The 1985 event was a Unit 2 Reactor trip from 100% power due to high negative flux rate trip signals resulting from dropped rod 2C4. A high resistance connection in the rod gripper coil circuitry caused by the rod control rod drive mechanism cable connector pins making poor

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 2 5000311 93-007-00 4 of 4 PRIOR OCCURRENCES: (cont'd) contact, had prevented the stationary grippers from energizing and resulted in the dropped rod. The 1988 event was a Unit 2 Reactor trip from 97% power due to*a power range negative flux trip resulting from dropped rod 103. Testing to determine why rod 1D3 dropped was inconclusive.

SAFETY SIGNIFICANCE:

This event did not affect the health and safety of the public. It occurred with the reactor subcritical and is b.ounded by the at-power analyses, described in Chapter 15 of the Updated Final Safety Analysis Report. For all cases of dropped rod groups, the reactor is tripped by the power range negative neutron flux rate trip and consequently, dropped rod banks do not cause core damage.

CORRECTIVE ACTION:

The RCS 21AC Power Cabinet stationary "B" control group firing circuitry regulation card, Westinghouse Part No. 6050D12G01, was replaceq. As a precautionary measure, the remaining cards in the firing circuitry were replaced: Regulation Circuitry Gripper (Westinghouse Part No. 6050D16G01), Phase Control Card (Westinghouse Part No. 6050D11G01), and the Input/Output AC Amplifier (Westinghouse Part No. 3359C65G01). The firing circuit was then satisfactorily retested.

Following NRC concurrence, Unit 2 post-refueling/maintenance outage startup testing will continue.

General Manager -

Salem Operations MJPJ:pc SORC Mtg.93-058