05000354/LER-2001-010
| Hope Creek Generating Station | |
| Event date: | 12-12-2001 |
|---|---|
| Report date: | 02-28-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3542001000R00 - NRC Website | |
Hope Creek Generating Station 05000354
PLANT AND SYSTEM IDENTIFICATION
General Electric — Boiling Water Reactor (BWR/4) Rod Block Monitor System {IG}* * Energy Industry Identification System {EIIS} codes and component function identifier codes appear as {SS/CCC}
IDENTIFICATION OF OCCURRENCE
Event Date: December 12, 2001 Discovery Date: December 20, 2001
CONDITIONS PRIOR TO OCCURRENCE
The plant was in OPERATIONAL CONDITION 1 (POWER OPERATION). No other structures, systems or components were inoperable at the start of this event that contributed to the event.
DESCRIPTION OF OCCURRENCE
Local power range monitor (LPRM) {IG/MON} 48-41A was identified to have failed low on 12/12/01 and was bypassed in accordance with plant procedures. On 12/20/01, during troubleshooting for an unrelated problem, it was noted that LPRM 48-41A was providing an upscale input to the rod block monitoring (RBM) system despite being bypassed. The cause of the erroneous input to the RBM was a failed LPRM card in the 10-C-608, Power Range Monitoring Panel. The LPRM card was pulled to eliminate the erroneous signal.
The effect of the erroneous upscale output from LPRM 48-41A was to cause the RBM channel "A" gain change circuit to produce a lower than required gain, so that RBM channel "A" may not have been capable of imposing a rod block when required for 15 control rods in the vicinity of LPRM 48- 41A. Technical Specification (TS) 3.1.4.3 requires that an inoperable RBM channel be restored to OPERABLE status within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Otherwise, the inoperable RBM channel is required to be placed in the tripped condition within the next hour.
Since this condition existed for longer than the time permitted by TS 3.1.4.3, it is reportable as a condition prohibited by plant Technical Specifications in accordance with 10 CFR 50.73(a)(2)(i)(B).
CAUSE OF OCCURRENCE
This event was caused by the failure of the bypass circuit on the LPRM flux amplifier card for LPRM 48-41A. For a selected control rod, each RBM channel averages up to eight LPRM inputs and applies the resultant voltage to a trip circuit for comparison with a flow bias voltage generated in the flow FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) CAUSE OF OCCURRENCE (continued) control trip reference unit. If the LPRM average exceeds the flow bias voltage, the trip circuit trips and a rod withdrawal block is generated. RBM "A" receives signals from LPRM flux amplifier cards associated with "A" and "C" level detectors and RBM "B" receives signals from "B" and "D" level LPRM detectors surrounding the selected rod. When the LPRM averaging amplifier output is less than the core average power as determined by comparison to one of the Average Power Range Monitor (APRM) outputs, the gain of the averaging amplifier is increased until its output is at least equal to the APRM output. The effect of the erroneous upscale input to RBM "A" was to cause the gain change circuit to produce a lower than required gain. In addition, because the input from LPRM 48-41A was constant, the increase in output from the LPRM averaging circuit in response to a control rod withdrawal was lower than it would have been if LPRM 48-41A was properly bypassed. The procedure for bypassing LPRMs did not require verification that the input to the RBM is removed.
PREVIOUS OCCURRENCES
A review of reportable events within the last two years identified no similar occurrences of LPRM component failure resulting in RBM channel inoperability.
SAFETY CONSEQUENCES AND IMPLICATIONS
There were no safety consequences associated with this event. The LPRM card failure did not affect the associated APRM channel or the RBM channel "B" which remained capable of performing its function for the control rods associated with LPRM 48-41A. During the period covered by this report, the reactor was not operated on a LIMITING CONTROL ROD PATTERN. There was no impact to the public health and safety.
This event does not constitute a Safety System Functional Failure (SSFF) as defined in NEI 99-02.
CORRECTIVE ACTIONS
1. Removed LPRM card 48-41A to eliminate the erroneous signal to the RBM.
2. The applicable operating procedure will be revised to add a step requiring that the four rod display be checked when bypassing an LPRM to confirm that the output for the bypassed LPRM is zero.
COMMITMENTS
The corrective actions cited in this LER are voluntary commitments.
enhancements and do not constitute