ML18065A084

LER 95-011-00:on 950817,CR 40 Withdrawal Occurred When Given Insertion Signal Due to skill-based Error in Crimping & Removing Foreign Matl from CRDM Motor Connection Box.Crd Package replaced.W/950918 Ltr

ML18065A084
Person / Time
Site:	Palisades
Issue date:	09/18/1995
From:	Roberts W, Smedley R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-95-011, LER-95-11, NUDOCS 9509210276
Download: ML18065A084 (8)

Text

{{#Wiki_filter:consumers Power POWERING MICHIGAN'S PROGRESS Palisades Nuclear Plant 27780 Blue Star Memorial Highway, Covert, Ml 49043 September 18, 1995 US Nuclear Regulatory Commission* Document Control Desk Washington, DC 20555 DOCKET 50-255 - LICENSE DPR PALISADES PLANT INFORMATIONAL LICENSEE EVENT REPORT 95-011 - CONTROL ROD 40 WITHDRAWAL WHEN GIVEN AN INSERTION SIGNAL Informational Licensee Event Report (LER) 95-011 is attached: This event is being reported because of its potential to result in an inadvertent reactivity adjustment and its general interest to the industry.

SUMMARY

OF COMMITMENTS This letter contains 3 new commitments and no revisions to existing commitments. I. The circumstances of this event and the industry experience on control rod drive grounds will be reviewed during electrical maintenance continuing training.

2. The Periodic Preventative Maintenance Control for th.e inspection, cleaning, testing, and repair of Control Rod Drive Mechanisms (CRDMs},

(PPAC CRD005}, will be revised to include inspection of the CROM drive motor connection boxes for the presence of foreign debris and properly crimped electrical connection lugs.

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3. A method for testing for shorts and grounds in the CROM control circuitry will be developed for use during refueling outages~

r Richard W. Smedley Manager, Licensing 1 tc Administrator, Region III, USNRC Project ~anager, NRR, USNRC I NRC Resident Inspector - Palisades I I I ' Il

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NRC Form 388 U.S. NUCLEAR REGULATORY COMMISSION (11-83) APPROVED OMB NO. 3160-0104 EXPIRES: 8/31/86 LICENSEE EVENT REPORT (LERI FACILITY NAME (1) DOCKET NUMBER (2) PAGE (31 Palisades Plant 0 5 0 0 0 2 5 5. 1 OF 0 6 TITLE t41 INFORMATIONAL LICENSEE EVENT REPORT 95-011 - CONTROL ROD 40 WITHDRAWAL WHEN GIVEN AN INSERTION SIGNAL EVENT DATE (6) REPORT DATE 181 OTHER FACILITIES INVOLVED (81 REVISION FACILITY NAMES MONTH DAY YEAR YEAR NUMBER MONTH DAY YEAR N/A 0 6 0 0 0 08179595-01 -00091895 N/A 0 ~ 0 0 0 THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR I: (Ch<<Jr °"" OI' more of tM following/ (11 I OPERATING Nt--..-2-0.-40_2_{b)-----------..---.-2-0-.4-06-{c-)----'------....-....--50-.7-3(-1)-{2-){lv-l--------....,....-.--7-3.-71-{b-)-------------I MODE (8) 20.406{1lt°1Hil So.38tcH11 60.7311H21M 73.71(cl 20.406(1)(1 ){iii 60.38{c){2) .X OTHER {Specify in At>.tr1ct 20.406(1)(1 ){iii) 50.73{1){2)(i) 60.7311H2HvliiHAI below and in Text, 20.406{1){1)(iv) 60.73(1){2){ii)

• 60.73(1){2)(viiiHBI NRC Form 386Al 20.406(1)(1 ){vi 60.7 3{1){2)(iii) 60.7311){2)(x)

LICENSEE CONTACT FOR THIS LER (121 NAME. TELEPHONE NUM.BER William L Roberts, Staff Licensing Engineer AREA CODE 6 6 7 6 4 8 9 3 MANUFAC* REPORTABLE MANUFAC* REPORTABLE CAUSE SYSTEM COMPONENT TURER TO NPRDS CAUSE SYSTEM COMPONENT TUR ER TO NPRDS SUPPLEMENTAL REPORT EXPECTED 1141 MONTH DAY YEAR EXPECTED

                                                                                                                                                 *suBMISSION YES flf ,,... comp#te EXPECTED SUBMISSION DA TEI                                                                                           . DATE (161 ABSTRACT UJm/t to 1400 ~ /.e., _..,,imately              rtftffn ain'11o-'PflC9  typewritten lineal (18)

On August 17, 1995 at approximately 0730 hours, the reactor was critical with the primary coolant system in the hot standby condition. Low power physics testing was in progress following plant refueling. Control room operators were moving the Group 4 Control Rods (38,39,40 and 41) to ensure that the resultant reactivity change was being sensed by test equipment. *A Rod Deviation Alarm- was received while attempting to reinsert the Group 4 Rods in the Manual Sequential mode. The rods were checked and control rod 40 was determined to be greater than 4 inches higher than the other Group 4 rods and appeared to have traveled in the opposite direction (withdrawn rather than inserted). A second attempt to insert control ro.d 40 was made in the Manual Individual Mode and the control rod still would only withdraw. Control rod 40 was declared inoperable and the reactor borated to a shutd9wn condition. Troubleshooting determined that Up and Down drive motor switches in the control rod drive motor were shorted such that an up or down signal would result in the motor driving in either direction, dependent on which drive switch happened to energize fir.st. The control rod drive package was replaced. Additional testing was completed to assure that no other electrical problems existed with the entire control rod drive system. During the testing a slight ground on control rod drive package #15 was identified and this rod drive was also replaced. During future refueling outages, planned enhancements to the control rod drive checkout

• procedures will test for system shorts or grounds.

NRC Form 388A U.S. NUCLEAR REGULATORY COMMISSION (9-831 APPROYED OMB NO. 3160-0104 EXPIRES: 8/31 /86 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION FACILITY NAME 111 DOCKET NUMBER 121 LER NUMBER 131 PAGE 141 SEQUENTIAL REVISION YEAR NUMBER NUMBER I Palisades Plant 0 I5 I0 I0 I0 I2 I5 I5 9 I5 - 0 I1I1 - 0. I0 0 I2 OF 0 I6 i. EVENT DESCRIPTION On August 17, 1995 at approximately 0730 hours, the reactor was critical with the primary coolant system in the hot standby condition. Low power physics testing was in progress following plant refueling. Control room operators were moving the Group 4 Control Rods (38,39,40 and 41) to ensure that the resultant reactivity change was being sensed by test equipment. A Rod Deviation Alarm was received while attempting to reinsert the Group 4 Rods in the Manual Sequential mode. The rods were checked and control rods 40 and 41 were determined to be greater than 4 inches higher than the other Group 4 rods and appeared to have traveled in the . opposite direction (withdrawn rather than insertion). A second attempt to insert control rod 40 was made in the Manual Individual Mode .and the control rod still would only withdraw. A second attempt was made to insert control rod 41 in the Manual Individual Mode arid it responded properly. A conceptual troubleshooting plan was prepared to lift leads for the uup" and the UDOWN" Control Rod Drive Mechanism (CROM) contactors; and to install a recorder to monitor the voltage signal to CRDMs 38 through 41 in various control m()des (i.e. manual individual, manual sequential, and manual group). It was believed that voltage may have been simultaneously applied to both the Up and Down drive contactors and that a race was occurring between the Up and Down relay's on CRDM-40, with th.e uUP" relay contactor being picked up first. The Palisades CRDMs consist of a rack and pinion gear assembly that is coupled to a motor-clutch drive package. The CRDMs are used for reactor startup, power level changes and temperature control maneuvers, but normal plant power operation is conducted with the control i rods fully withdrawn. With the control rods withdrawn, when the clutch is tripped, the control r! rods will always drop into *the core. At 0727 hours it was determined that although control rod 40 could not be successfully manually controlled, it could be tripped and would drop to its appropriate position in the core. The CROM for control rod 40 was however declared inoperable because the drive mechanism would not respond as expected. It was also decided to shut down the reactor prior to performing any troubleshooting. At 1120 hours, the reactor was borated to critical boron plus 100 ppm. The Reactor was sub-critical (less than 10-4% power), at 1133 hours. At 1212 hours maintenance began troubleshooting CROM 40. During troubleshooting it would be necessary to test all of the Group 4 rods and take various readings. Still unsure as to how the Group 4 control rods would react to the insert or withdraw signals, it was decided to declare all four Group 4 rods inoperable while the testing was being completed. The plant technical

NRC Form 388A U.S. NUCLEAR REGULATORY COMMISSION 19-83) APPROVED OMB NO. 3160-0104 EXPIRES: 8/31/86 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION FACILITY NAME (11 DOCKET NUMBER 121 LER NUMBER 131 PAGE 141 SEQUENTIAL REVISION YEAR NUMBER NUMBER Palisades Plant 0 5 Q 0 Q 2 5 5 9 5 - Q 1 1 - Q Q Q 3 OF Q 6 specifications require that with more than one control rod inoperable, the rod in-operability must be resolved or the plant be put in hot shutdown within 12 hours. As a prerequisite to the testing, the 12 hour Technical Specification action statement was entered to fix CRDM-40 or to proceed to hot shutdown mode. Troubleshooting identified that in either the Manual Group or Manual Sequential modes all contactors, (UP and DOWN) for the entire Group 4 CRDMs were receiving a 120 VAC s*ignal in both direction, (Raise or Lower) simultaneously. Troubleshooting also identified that in the Manual Individual mode only CRDM-40 .exhibited a simultaneous *120 VAC signal on both contactors (UP and DOWN) while attempting to drive in either direction, raise or lower.* CRDMs 38, 39, and 41 did experience a 45 VAC signal on the de-energized contactor (ie.,Down contactor if going to the Raise position) indicating a slight ground, however, this was not enough voltage to pick up the contactor. Further troubfeshoofing on CRDM-40 identified a short to exist between the Up and Down drive motor contactors (LS-1 and LS-2). At this point, it yvas decided to move the control rods to the* bottom of the core in preparation for replacement of the CROM 40 package. The reactor was manually tripped at 1615 hours which put the controls rods at the bottom of the core. The CROM package for control rod 40 was replaced with a $pare and the defective CROM package inspected for possible shorts. Upon a visual inspection of the CROM 40 motor junction box, an unattached wire lug, absent of wire, was found lodged between a terminal strip for the Up and Down drive motor contactors (Ls.:1 and LS-2). Further inspection identified the lug to be crimped, however, not broken off from any wire lead. The inspection also revealed that none of the wires .internal to the motor junction box were broken or defective~ It appears that the wire lug causing the shorted condition became a foreign material during some previous maintenance activity. A plan was developed to perform additional ground detection testing to determine whether or not CRDM-40 was masking an additional problem. A slight ground was found in CROM for control rod 15, which correlated to what was seen on the de-energized contactors when testing CROM 38 through 41. The drive package for control rod #15 was replaced. Following replacement and successful testing both CROM drive packages were declared operable. No recurrence of this event or any other similar event has been observed. This event does not fall under the formal reportability requirements of 10 CFR 50. 73. This event is being reported as an Informational Licensee Event Report because of its potential to result in an inadvertent reactivity adjustment and as a general interest to the industry.

NAC Form 388A u:s. NUCLEAR REGULATORY COMMISSION (9-831 APPROVED OMB NO. 3160-0104 EXPIRES: 8/31 /86 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION FACILITY NAME !11 DOCKET NUMBER (21 LEA NUMBER !31 PAGE 141 SEQUENTIAL REVISION YEAR NUMBER NUMBER Palisades Plant Q 5 Q Q 0 2* 5 5 9 5 - Q 1. 1 - Q Q Q 4 OF Q 6 1-CAUSE OF THE EVENT The Root Cause for this event is a skill-based error in crimping and removing foreign material from the CROM Motor Connection Box which left an unsecured wire lug within the CROM motor housing. The lug may be an original construction lug. The lug appears to have been inside the motor connection box since at least 1988 when we last performed significant electrical work on the CRD drive packages.* * . l t f ANALYSIS OF THE EVENT I The Palisades CRDMs consist of a rack and pinion gear assembly that is coupled by a motor-clutch drive package. The CRDMs are used for reactor startup, power level changes and I ' temperature control maneuvers, but normal operation is conducted with the. rods fully withdrawn. With a control rod withdrawn and it's clutch is de-energized, the control rod will always drop into the core by gravity. Work Order history was reviewed from 1985 through 1995 to determine possible maintenance activities that could have contributed to this event. Four (4) activities occurred that could be contributors: . f I

1. .Work was performed in the 1995 Refueling Outage to replace the brake coil. The wires for the brake coil are located inside the motor junction box in question.* An interview with the I electrical repair worker concludes that the wire was cut at the motor junction box penetration and pl:Jlled back both ways during the removal process. The extra lug had a ~

crimp mark on it, therefore, the likelihood of an new unused lug falling into the motor connection box is not considered to be a contributor to this Root Cause. However, opportunity did exist to perform additional visual inspections to look for any foreign debris. i I' I

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2. The drive package was removed during the 1992 Outage. However, no physical work was performed. The package was only tested on the CROM portable test stand. This is not considered to be a contributor to this Root Cause.

3. During the 1988 Outage the limit switches were replaced. This is considered to be the activity that most. likely contributed to this event.

4. During the 1985 Outage the limit switches were adjusted and tested with no physical replacement of components. This is not considered to be a contributor.

I During a switch or brake replacement, the electrical repair workers would attach a new lug to r. each wire to be connected. The lug found causing the short appears to be an old style and the . t j. t' i I

NRC Form 3SSA U.S. NUCLEAR REGULATORY COMMISSION 19*831 APPROVED .OMB NO. 3160-0104 EXPIRES: 8/31 /86 LICENSEE EVENT REPORT (LERI TEXT CONTINUATION

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• FACILITY NAME 111 DOCKET NUMBER 121 LER )ljUMBER 131 PAGE 141 SEQUENTIAL REVISION YEAR NUMBER NUMBER Palisades Plant Q 5 Q Q Q 2 5 5. 9 5 - Q 1 1 - Q Q Q 5 OF Q 6 crimp indentor is IlQl consistent with the crimper used at Palisades for many years. This suggests that the loose lug has been in the motor junction box for years, and happened to jar loose during this outage.
• The lug may be an original construction lug. The lug appears to have been inside the motor connection box since at least 1988. Since the entire cir~uitry was tested for grounds, the other packages worked on during the 1995 outage were not in question since the circuitry was free of all shorts or grounds once the drive packages for CRD-15 and 40 were replaced.

The most control rods could be affected with the drive controls in the Manual Sequential Mode of rod operation. By design when the Manual Sequential Mode is selected, a group of CRDMs are simultaneously energized for movement. Because of the way that the system is designed a short between the two drive switches in one CROM would automatically energize both sets of drive switches in all the other CRDMs in the rod group selected. What would then occur is similar to what we saw with the Palisades Group 4 control rods. When a control rod movement signal was given, both drive switches in each of the selected CRDMs would be energized. The control rod would move however in the direction of that switch which energized fastest. Once a limit switch is energized, it also has a feedback circuit to the other limit switch prohibiting it from closing. In the Manual Individual mode only one CROM would be affected as CROM 40 was during this event. In the Manual Group mode only those cont_rol rods in the selected group would be affected. In this case it was the group 4 control rods, 38 through 41. However, the Manual Sequential Mode has the capability of driving two control rod groups at once. As an example, in the Manual Sequential mode the Group 4 control rods would be moved until they were almost

• fully inserted and then the Group 3 control rods would be automatically selected and energized for movement. With both Group 3 and 4 rods energized, a total of nine (9) *rods could be subject to this same scenario. Again, Rod Deviation and Rod Sequencing alarms would annunciate adverse rod positions.

A comprehensive program is* in place to assure the CRDM's are functioning properly. Maintenanc testing is performed under CRD-E"'"27, "CROM Drive Package Component Checkout On Test Stand" and Technical Specification Surveillance Tests R0-21, "Control Rod Drive System Interlocks", and R0-22, "Control Rod Drop Times". The overal.1 circuitry can be tested to assure there are no shorts or grounds present prior to leaving a refueling outage to enhance the overall assurance that the circuitry will not cause a malfunction of this nature. SAFETY SIGNIFICANCE

  *In the event of an unsafe condition, the reactor trips and the rods are gravity inserted, independent of the electrical circuitry used for normal rod motion. FSAR Chapter 14 events assume the failure of a single rod to insert. This condition would not have affected control rod 40's.ability to trip.

.,' NRC Form 388A U.S. NUCLEAR REGULATORY COMMISSION (9-83) APPROVED OMB NO. 3160-0104 EXPIRES: B/31/86 LICENSEE EVF;NT REPORT (LERI TEXT CONTINUATION FACILITY NAME 111 DOCKET NUMBER 121 LER NUMBER 131 PAGE (4J* SEQUENTIAL REVISION YEAR NUMBER NUMBER Palisades Plant 0 5 0 0 0 2 5 5 9 5 0 1 0 0 0 6 OF 0 6 The control rod position deviation alarms are provided to alert the operators that one or more of the control rods are out of position. As noted by this occurrence, the control rod deviation alarms worked as designed to alert the operators of a potential unsafe condition. CORRECTIVE ACTION

1. The circumstances of this event and the industry experience on control rod drive grounds will be reviewed during electrical maintenance continuing training.

2. The Periodic Preventative Maintenance Control for the inspection, cleaning, testing, and repair of CRDMs (PPAC CRD005), will be revised to include inspection of the CROM drive motor connection boxes for the presence of foreign debris and properly crimped electrical connection lugs.

3.. A method for testing for shorts and grounds in the CROM control circuitry will be developed for use during a refueling outage. ADDITIONAL INFORMATION There have been no instances of events similar to this.  ! I. i r

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