05000293/LER-2005-002
| Docket Number | |
| Event date: | 04-14-2005 |
|---|---|
| Report date: | 06-13-2005 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2932005002R00 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)
BACKGROUND
The safety objective of the core standby cooling systems (CSCS), in conjunction with other engineered safeguards systems, is to limit the release of radioactive materials to the environs during postulated accident conditions so that resulting radiation exposures are within guideline values in published regulations.
The safety objective of the primary containment system (PCS) is to provide the capability in conjunction with other safety features, to limit the release of fission products in the event of a postulated design basis accident so that offsite doses would not exceed 10 CFR 100 limits. The PCS consists of a drywell, a pressure suppression chamber (torus) which stores a large volume of water, a connecting vent system between the drywell and torus, isolation valves, vacuum relief system, and other service equipment.
The drywell atmosphere pressure is monitored by instrumentation that includes pressure transmitters that are part of the analog trip system (ATS). In addition to the pressure transmitters, the ATS includes master trip units and slave trip units. Each pressure transmitter (e.g. PT-1001-89B) has a master trip unit (e.g.
PIS-1001-89B) and may have one or more associated slave trip units. The transmitter and respective trip unit(s) are part of an instrument channel(s) to the trip and control circuit(s) of a safety system(s). Typically, a master trip unit provides an indication of the monitored parameter (e.g. drywell pressure) and a trip function to the respective trip circuit of a safety system(s). A slave trip unit provides a trip function to the respective trip circuit of a safety system(s) but does not provide an indication of the monitored parameter (e.g. drywell pressure).
The drywell pressure transmitters include PT-1001-89A/B/C/D. Transmitters PT-1001-89A/C (Division 'A') and PT-1001-89B/D (Division 'B') are part of the CSCS (i.e. ECCS) drywell pressure instrument channels.
These channels input to the actuation logic of the automatic depressurization system (ADS), the core spray system (CS), the residual heat removal system (RHR), the emergency diesel generators (EDGs) and related load shedding, the high-pressure coolant injection system (HPCI), and the HPCI turbine steam exhaust vacuum breakers. With the inoperability of a single ECCS Division 'A' or Division 'B' drywell pressure transmitter and/or related instrument channel(s), these systems will still actuate if a high drywell pressure condition occurs.
Technical Specifications (TS) Table 3.2.B governs the instrumentation that functions to initiate and control the core and containment cooling systems. Table 3.2.B specifies limiting conditions for operation for the parameters and functions listed in the table. Table 3.2.B identifies that whenever any CSCS subsystem is required by TS 3.5 to be operable, that there be two operable trip systems, and if the minimum number of operable instrument channels cannot be met for one of the trip systems, that system shall be repaired or the reactor placed in the Cold Shutdown condition within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after that trip system is made or found to be inoperable.
EVENT DESCRIPTION
At 0905 hours0.0105 days <br />0.251 hours <br />0.0015 weeks <br />3.443525e-4 months <br /> on April 14, 2005, drywell pressure transmitter PT-1001-89B was mistakenly valved out of service (isolated) by a utility licensed operator. This action resulted in the inoperability of one of the two Division 'B' high drywell pressure instrument channels.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) At 1944 hours0.0225 days <br />0.54 hours <br />0.00321 weeks <br />7.39692e-4 months <br /> on April 14th, the drywell pressure indication on master trip unit PIS-1001-89B (from PT-1001-89B) was checked in accordance with TS Table 4.2.B as part of a routine tour, by a different licensed operator (tour operator). The indicated pressure was recorded at 1.30 psig.
On the next day, April 15th at 2020 hours0.0234 days <br />0.561 hours <br />0.00334 weeks <br />7.6861e-4 months <br />, the same tour operator checked the drywell pressure indication on PIS-1001-89B and identified that the indication was downscale (i.e. at or near zero psig). The tour operator reported the indication to the shift control room superintendent (CRS). The CRS initiated troubleshooting activities.
As part of the troubleshooting, a calibration of PIS-1001-89B was performed with satisfactory results. The indication on PIS-1001-89B remained downscale after the calibration. Further investigation, at about 0955 hours0.0111 days <br />0.265 hours <br />0.00158 weeks <br />3.633775e-4 months <br /> on April 16th, found the isolation valve of PT-1001-89B to be closed. Immediate action taken was to open the isolation valve of PT-1001-89B, restoring to operable status PT-1001-89B and the related instrument channels. From the time of discovery, at 2020 hours0.0234 days <br />0.561 hours <br />0.00334 weeks <br />7.6861e-4 months <br /> on April 15th, the instrument and related channels were inoperable for about 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> and 35 minutes. This was within the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> time period allowed by the Technical Specifications for the instrument channels to be inoperable, and continued plant operation.
Subsequent investigation identified the incorrect isolation of PT-1001-89B and that the condition had existed since 0905 hours0.0105 days <br />0.251 hours <br />0.0015 weeks <br />3.443525e-4 months <br /> on April 14th. This meant the condition existed for a period of about 49 hours5.671296e-4 days <br />0.0136 hours <br />8.101852e-5 weeks <br />1.86445e-5 months <br />, which was greater than the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> timeframe specified by Table 3.2.B.
The condition existed near the end of the fuel cycle, in coast-down, at about 87 percent reactor power with the reactor mode switch in the RUN position. The reactor vessel pressure was about 1035 psig with the reactor water at the saturation temperature for that pressure.
CAUSE
The direct cause of the condition was the closing of the PT-1001-89B isolation valve, 2-1001-89B. The root cause was a human performance error by a utility licensed operator. The operator mistakenly closed valve 2-1001-89B instead of valve HO-C2206A-1. The error was the direct result of inadequate use of human performance tools, i.e. self-checking and a questioning attitude.
This condition began on April 14th when the operator who mistakenly closed isolation valve 2-1001-89B was supposed to verify that valve HO-C2206A-1 was closed. These valves and check valve CK-2206A-1 are located on instrument rack C2206. Valve HO-C2206-A1 is a hand-operated valve equipped with a T-type handle and is located about four and one-half feet above floor level. The isolation valve, 2-1001-89B, of PT-1001-89B is a hand-operated valve equipped with a round handle and is located about two feet and nine inches above floor level in the same area of the rack. Attached to and hanging below each of these valves is an equipment label that identifies the valve by identification number and functional description. The equipment label of check valve CK-2206A-1 is directly above the handle of isolation valve 2-1001-89B.
Circumstantial evidence indicates the operator misread the labels and closed isolation valve 2-1001-89B instead of the intended valve, HO-C2206A-1.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) I The cause of the operator recording the drywell pressure indication of PIS-1001-89B to be 1.3 psig on April 14th while the plant computer indicates the pressure indication was 0.01 psig could not be determined, although past history indicates the meter on this type of indicator is susceptible to sticking. The cause could be attributed to operator error in reading the indication, a sticking meter needle on PIS-1001-89B, or static.
CORRECTIVE ACTION
Corrective actions taken include the following. Upon discovery, the isolation valve of PT-1001-89B was opened. Walk-downs were conducted to ensure other instrumentation was correctly configured. The licensed operator who mistakenly closed the isolation valve of PT-1001-89B received appropriate disciplinary action. The surveillance procedure that includes daily checks of instrumentation was revised to increase the frequency of required ATS instrumentation checks from once per day to once per shift, and to obtain readings from the plant computer in addition to meter checks.
SAFETY CONSEQUENCES
This condition posed no threat to public health and safety.
The Pilgrim Station analysis required by 10 CFR 50.46 and 10 CFR 50 Appendix K includes several assumptions. The analysis assumes ECCS (i.e. CSCS) initiates on high drywell pressure for all breaks inside containment (i.e. the drywell). The analysis assumes ECCS initiates on low reactor water level for breaks outside containment. The analysis assumes the reactor scrams on low reactor water level at time zero for small breaks inside containment. The condition described in this report did not affect the ability of the ECCS Division 'A' or Division 'B' low reactor water level instrumentation to initiate the safety systems.
The Pilgrim Station LOCA analysis identifies four significant single failures that challenge the capability of ECCS to prevent fuel damage during the postulated LOCA: failure of a single battery, failure of the selected LPCI injection valve, loss of one EDG, or HPCI failure. In all cases, the remaining ECCS resources are sufficient to prevent fuel peak clad temperature from exceeding 2200 degrees Fahrenheit and other criteria in 10 CFR 50.46 and Appendix K. ' The drywell pressure transmitters include PT-1001-89A/B/C/D. Transmitters PT-1001-89A/C (Division 'A') and PT-1001-89B/D (Division 'B') are part of the CSCS (i.e. ECCS) drywell pressure instrument channels.
These channels input to the actuation logic of ADS, CS, RHR, EDGs and related load shedding, HPCI, and .
HPCI turbine steam exhaust vacuum breakers. With the inoperability of a single ECCS Division 'A' or Division 'B' drywell pressure transmitter and/or related instrument channel(s), these systems will actuate if a high drywell pressure condition occurs. Moreover, and except for the HPCI turbine steam exhaust vacuum breakers, a low water level condition inputs to the actuation logic of these systems.
Other activities occurred while PT-1001-89B was isolated and the related high drywell pressure instrument channels were inoperable. These activities were conducted separately and resulted in the inoperability of a single system, train or component and did not in combination with the reported condition result in any loss of safety function. These activities were conducted to support plant operation or planned surveillance or planned maintenance, and were each completed well within the Pilgrim Technical Specifications allowed timeframes.
�FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) I� SEQUENTIAL� I REVISION � NUMBER� NUMBER The condition described in this report involved a reduction in the level of redundancy in the actuation logic for the ECCS (i.e. CSCS) functions described in this report. Previous analyses have been conducted for improvements to surveillance test intervals of ECCS actuation instrumentation. Among other findings, the analyses showed that safety system reliabilities are not dominated by logic system reliabilities, but are dominated by mechanical components (i.e. pumps and valves) that are more frequently tested. The condition described in this report did not involve the reliability of these mechanical components.
REPORTABILITY
This report was submitted in accordance with 10 CFR 50.73(a)(2)(i)(B) because there was less than the minimum number of operable high drywell pressure instrument channels specified in TS Table 3.2.B and the condition existed for greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
SIMILARITY TO PREVIOUS EVENTS
A review for similarity was conducted of Pilgrim Station LERs submitted since 2002. The review focused on a similar event(s) and/or a condition(s) or cause. The review identified a personnel error described in due to Licensed Operator Error During Startup.
ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) CODES The EIIS codes for this report are as follows:
COMPONENTS
�
CODE
Transmitter, Pressure (PT-1001-89B)� PT Valve, isolation (2-1001-89B)� I SV Valve (CK-2206A-1)� V
SYSTEMS
Emergency Onsite Power Supply System (EDG)�EK High Pressure Coolant Injection System (HPCI) BJ Low Pressure Core Spray System (CS)� BM Residual Heat Removal System (LPCI) BO Solid State Control System (ATS)� JG