05000266/LER-2001-001
| Docket Number | |
| Event date: | 01-12-2001 |
|---|---|
| Report date: | 02-13-2001 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2662001001R00 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Point Beach Nuclear Plant Unit 1 05000266
Event Description:
The Point Beach Nuclear Plant (PBNP) Technical Specification Table 15.4.1-1, "Minimum Frequencies for Checks, Calibrations and Test of Instrument Channels," Item No. 44, "Reactor Protection System and Emergency Safety Feature Actuation System Logic," requires monthly testing of those logic trains except during periods of refueling shutdown. Among the reactor protection system (RPS)[ JE ] features tested under this specification are the logics for the nuclear instrumentation [ IG ] power range low power trip (PR-LOW), which actuates at approximately 20% of full power, and the intermediate range nuclear instrumentation high flux trip (IR HIGH), which actuates at the equivalent of approximately 25% power. These trips provide protection against reactivity excursions during subcritical to low power operation to prevent Departure of Nucleate Boiling (DNB) in the core. When two out of four power range channels are above approximately 10% power, a permissive bistable, known as the P-10 permissive, deenergizes so that both the PR-LOW and IR-HIGH trips may be manually blocked. When three out of four of the power range channels are below the 10% P-10 permissive setpoint, those trips are automatically reinstated.
Prior to reactor startups, the RPS permissives and trip logic, including the P-10 permissive and the PR-HIGH and IR- LOW, are tested using ICP 2.15, "Reactor Protection System Permissives and Trip Logic Pre-startup Test," and ICP 2.17, "Reactor Protection System Trip Logic Post Refueling Test." TS Table 15.3.5-2, items 2a. and 3. allows continuous operation once the unit is operating at above 10% power and the PR-LOW and IR-HIGH trips have been blocked. Therefore when this permissible bypass condition has been met, the PR-LOW and IR-HIGH logic does not have to be operable. Under those conditions, the monthly surveillance test for these logics has not been conducted.
When shutting down the unit after having operated at greater than 10% full power (the P-10 permissive block point) for more then 38 days, (based on 1.25 times that specified monthly surveillance frequency), at the point in the shutdown when the reactor power goes below 10% and the P-10 bistables have energized, the monthly surveillance test for the PR-LOW and IR-HIGH trip logic is technically over due since the surveillance test for these logics have not been completed within the past month. TS 15.4.0.3 specifies that when a surveillance was not performed within its specified frequency, the requirement to declare the system or component inoperable may be delayed up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to allow for performance of the surveillance. It has been our position that since the unit is in the process of shutting down, and this action is consistent with the required operator action if the minimum number of channels for TS Table 15.3.5-2 items 2a and 3. has not been met, it is not necessary to perform the overdue surveillance at that time. The decision to not perform this TS surveillance has been acceptable because the unit has been proceeding to hot shutdown; however, the missed surveillance has not been formally declared or logged. During the subsequent unit start ups, the RPS logic, including the PR-LOW and IR-HIGH trip logic, has been tested and verified using appropriate plant procedures. That testing is used to confirm the operability of these trips prior to taking the reactor critical, at which point it is necessary to have the RPS in service.
We are hereby conservatively reporting that during shutdowns from operations at power for greater than 38 days, our past practice had resulted in a condition prohibited by the Technical Specification, that is, a missed surveillance; and should have been reported in the past, under 10 CFR 50.73(a)(2)(i)(B). Note that under the guidance of NUREG 1022, Revision 2, and the revised reporting requirements of 10 CFR 50.73(a)(2)(i)(B)(2), which became effective on January 23, 2001, a late surveillance would not be reportable under the revised reportability rules, provided the equipment is shown to be operable once the surveillance is accomplished,.
Cause:
This condition was identified on January 12, 2001, during a review of procedural changes necessary for implementation of the Improved Technical Specifications (ITS). (The NRC is presently reviewing our ITS submittal. We are anticipating implementation of the ITS later this year.) That review identified that although the testing of the logic for the PR-LOW and IR-HIGH trips can be conducted at power, the monthly testing was not being done when power levels were above 10% full power and those trips were blocked. A condition report (CR 01-0118) was initiated to document FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) Point Beach Nuclear Plant Unit 1 05000266 that concern. The cause of this condition was a conservative change in interpretation of the existing TS requirement concerning monthly testing of the PR-LOW and IR-HIGH trip logic. That interpretation now recognizes that when the PR-LOW and IR-HIGH trip logic testing has not been completed within the past 38 days, then once reactor power is taken below 10% of full power, a missed surveillance should be declared. However, since we have recognized that the PR-LOW and IR-HIGH trip logic can be tested at power, we intend to perform this logic testing on a monthly basis so that the potential for missed surveillance of these logics will be avoided.
Corrective Actions:
The logic testing for the PR-LOW and 1R-HIGH trip logic will be tested on a monthly basis. Procedures 1(2) ICP 2.3 A and B and 2.23 A and B, "Reactor Protection System Logic Monthly Surveillance Test," are being revised to assure this logic testing is done.
Safety Assessment:
The function of the PR-LOW and IR-HIGH trip logic is to protect against reactivity excursions during subcritical to low power operations. When the reactor thermal power is below the 10% of full power setpoint, the nuclear instrumentation intermediate range high flux trip and the low setting for the power range nuclear instrumentation high flux trips are active. Although the failure to perform a surveillance for a system or component within the specified frequency, including the provisions of TS 15.4.0.3, results in the declaration of that system or component being inoperable; if the subsequent performance of that surveillance determines that the system or component is capable of performing its specified safety function, the actual safety impact of that missed surveillance becomes negligible. In the specific conditions which resulted in missed surveillances as discussed in this report, subsequent testing of the logic for the PR- LOW and IR-HIGH trips was conducted prior to the next unit startup. That testing confirmed that the safety function of those devices would be satisfied and the equipment remained operable. Accordingly, we have concluded that the health and safety of the public and the plant staff was not impacted by this event. We have further concluded that the missed surveillances did not result in a loss of the capability of these trips to perform their safety function and; therefore, this event did not result in a safety system functional failure.
Similar Occurrences:
A review of recent LERs (past two years) identified the following events which involved missed or incomplete technical specification surveillances.
LER NUMBER Title 266/1999-003-00 Technical Specification Surveillance Requirement for ECCS and Containment Spray Not Fully Implemented 301/1999-003-00 Missed Technical Specification Surveillance Test of Emergency DC Lighting 266/2000-002-00 Technical Specification Surveillance Requirement to Verify ECCS Valve Position Not Fully Implemented