05000334/LER-2004-001

LER-2004-001, Control Rod Shutdown Bank Anomaly Causes Entry into Technical Specification 3.0.3

Docket Number
Event date:	08-14-2004
Report date:	10-12-2004
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3342004001R00 - NRC Website

PLANT AND SYSTEM IDENTIFICATION

Westinghouse-Pressurized Water Reactor {PWR} Control Rod Drive System {AA}

CONDITIONS PRIOR TO OCCURRENCE

Unit 1: Mode 1 at 100 percent power There were no systems, structures, or components that were inoperable at the start of the event that contributed to the event other than as described below.

DESCRIPTION OF EVENT

On 8/14/2004, at 0740 hours0.00856 days <br />0.206 hours <br />0.00122 weeks <br />2.8157e-4 months <br />, during performance of the normally scheduled Control Rod Assembly Partial Movement Surveillance Test at Beaver Valley Power Station (BVPS) Unit 1, the operator performing the test observed an unexpected condition during the insertion of control rod Shutdown Bank "A". This test is performed to satisfy BVPS Unit 1 Technical Specification (TS) Surveillance Requirement (SR) 4.1.3.1.1, which requires that each shutdown and control rod not fully inserted in the core to be determined to be OPERABLE by movement of at least 10 steps in any one direction at least once per 31 days. The surveillance first tests Shutdown Bank "A" by inserting the bank 10 steps. Rod positions at the start of the test were at the all-rods-out position for the current cycle, 226 steps withdrawn. Each of the two control rod Groups within Shutdown Bank "A" normally alternates stepping in(out) one step during normal continuous rod motion. The first insertion of the Shutdown Bank "A" rods was 3 1/2 steps, with the group demand counters for Shutdown Bank "A" showing Group I at 222 steps withdrawn and Group II at 223, as expected. In the next rod move, Group I moved in a step instead of the expected Group II, now showing Group I at 221 and Group II at 223 steps withdrawn. This resulted in having a two step difference between the two control rod Groups which was not expected, and, therefore, rod motion was immediately stopped. No rod control alarms were received.

When the expected response to the rod motion was not received, the test was stopped.

Therefore, the TS surveillance exception was no longer applicable. Further rod motion was not attempted due to conservative decision considerations concerning potential adverse control rod consequences, awaiting evaluation by station Instrument and Control technicians.

BVPS Unit 1 TS 3.1.3.5 requires that all shutdown rods meet the insertion limits specified in the Core Operating Limits Report (COLR) in Modes 1 and 2. [The COLR insertion limit is shutdown rods withdrawn at least 225 steps.] TS 3.1.3.5 also requires that with a maximum of one shutdown rod inserted beyond the insertion limit, except for surveillance testing pursuant to SR 4.1.3.1.1, the rod shall be restored to within the limit within one hour or declare the rod inoperable and apply TS 3.1.3.1. The Action requirements of TS 3.1.3.5 allows for only one rod to be inoperable. There are no applicable action requirements for a whole bank not being appropriately withdrawn. Thus, at 0810 hours0.00938 days <br />0.225 hours <br />0.00134 weeks <br />3.08205e-4 months <br />, TS 3.1.3.5 and 3.0.3 were entered, which requires restoration within one hour or place the unit in at least Hot Standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

TS 3.1.3.2 was also entered since the operation of the control rod group demand counters in the control rod position indication system were believed to be potentially inoperable. TS 3.1.3.2 requires control rod group demand counter rod position indication be operable. With one group demand position indicator inoperable, TS 3.1.3.2 Action b.1 requires all rod position indicators for the affected bank be verified operable and that the rods are within 12 steps of each other at least once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.

At 0910 hours0.0105 days <br />0.253 hours <br />0.0015 weeks <br />3.46255e-4 months <br />, Shutdown Bank "A" had not been restored to meet the COLR requirements.

Action was initiated to commence plant shutdown per TS 3.0.3 with the requirement that the plant must be in Hot Standby by 15:10 hours. Power reduction was scheduled to commence at 11:10 hours.

Since no anomaly was identified within the control rod power cabinet and logic cabinet, at 11:07 hours, the Shutdown Bank "A" rods were withdrawn to 225 steps on the Group I demand counter and to 226 steps on the Group II demand counter using the normal rod withdrawal process. With all Control Rods being returned to acceptable Rod Insertion Limit positions, TS 3.0.3 and TS 3.1.3.5 were exited. TS 3.1.3.2 remained in effect as the group demand counter was the initial suspected cause of the event.

On 8/16/2004, the group demand counter was determined to be functioning properly, but the Unit conservatively remained in TS 3.1.3.2 Action b.1.

On 8/17/2004, additional testing indicated a continued rod movement problem, which was determined to be due to a lack of demand signal being continuously generated somewhere within the rod control system. Although subsequently shown not to be required, BVPS Unit 1 conservatively entered TS 3.1.3.1 Action d at 1408 hours0.0163 days <br />0.391 hours <br />0.00233 weeks <br />5.35744e-4 months <br /> due to declaring more than one control rod trippable but inoperable due to the inability to complete the surveillance at that time. TS 3.1.3.1 Action d states: With more than one rod trippable but inoperable, power operation may continue provided that the remainder of the rods in the bank(s) are aligned to within 12 steps while maintaining the rod sequence and insertion limits provided within the COLR and the inoperable rods are restored within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.

On 8/19/04, following replacement of the Slave Cycler logic card, rod control pulse voltage returned to the expected value. At 0425 hours0.00492 days <br />0.118 hours <br />7.027116e-4 weeks <br />1.617125e-4 months <br />, following successful completion of the surveillance test pursuant to SR 4.1.3.1.1, TS 3.1.3.1 and 3.1.3.2 were exited.

REPORTABILITY

Pursuant to NUREG-1022, Rev. 2, page 36: "Entry into STS 3.0.3 is not necessarily reportable under 10 CFR 50.73(a)(2)(i)(B). However, it should be considered reportable under this criterion if the condition is not corrected within an hour, such that it is necessary to initiate actions to shutdown, cooldown, etc." Based upon this NUREG-1022 criteria, any event where Tech Spec 3.0.3 is applied longer than one hour would be reportable under 10 CFR 50.73.

As noted in the description above, BVPS Unit 1 entered TS 3.0.3 and remained in TS 3.0.3 for more than one hour. Therefore, this event is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by plant Technical Specifications because TS 3.0.3 had been entered for longer than one hour, even though actual power level was not decreased from 100 percent.

CAUSE OF EVENT

The cause of the Group II Shutdown Bank "A" control rods to not move as demanded was the result of a degraded Slave Cycler Logic card inside the Rod Control Logic cabinet.

ANALYSIS OF EVENT

The Slave Cycler Logic card was determined to be degraded. The as found pulse voltage to the Slave Cycler Logic card for the associated AC power cabinet was 9 volts or less (6.5 volts to 8.5 volts is a voltage transition region which may deter rod stepping). The correct voltage should be 14 volts. This degraded condition affected the ability of the Group II Shutdown Bank "A" control rods to move under manual or automatic control since movement demand was intermittent due to the degraded voltage. The ability to trip these control rods was not affected.

SAFETY IMPLICATIONS

The control rods associated with Group II Shutdown Bank "A" remained trippable. The degradation caused intermittent Group II movement due to the intermittent logic gate safety analyses in the BVPS Unit 1 Updated Final Safety Analysis Report (UFSAR). The UFSAR only credits the ability of the control rods to trip in the Design Basis Accident safety UFSAR had remained valid.

The plant risk associated with the BVPS Unit 1 Shutdown Bank "A" Group 2 position anomaly that occurred on August 14, 2004 is considered to be low. This is based on the incremental core damage probability for the event when considering manual rod insertion to be unavailable during the time period.

Based on the above, the safety significance of the Shutdown Bank "A" Group 2 position anomaly on August 14, 2004 was low.

CORRECTIVE ACTIONS

1. An initial investigation determined that Shutdown Bank "A" Group I and II control rods had remained trippable.

2. A subsequent investigation identified that a failure in a Slave Cycler Logic card caused intermittent failure to move upon demand of Shutdown Bank "A", Group II. Following replacement of the failed Slave Cycler Logic card and the Master Cycler Selector Card, the surveillance test for SR 4.1.3.1.1 was performed successfully.

3. The Rod Control Preventive Maintenance frequency for both BVPS Units is being evaluated for optimal reliability.

4. Additional actions are being evaluated to address replacing obsolete Rod Control System cards with upgraded cards (as they become available) to help prevent age related card failures.

Completion of the above and other corrective actions are being tracked through the BVPS corrective action program.

PREVIOUS SIMILAR EVENTS

A review found no Beaver Valley Power Station Licensee Event Reports within the last three years involving control rod manual movement or control rod position indication.

COMMITMENTS

There are no new commitment made by FirstEnergy Nuclear Operating Company (FENOC) for BVPS Unit No. 1 in this document.