05000321/LER-2009-001
| Docket Number | |
| Event date: | 03-09-2009 |
|---|---|
| Report date: | 05-04-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3212009001R00 - NRC Website | |
CONTINUATION SHEET
Edwin I. Hatch Nuclear Plant Unit 1 05000321 2009 - 001�0
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EIIS Code XX).
DESCRIPTION OF EVENT
On March 9 at 1200 EDT, Unit 1 was in Mode 1 at 2798 CMWT, 99.8 percent power. Based on instrument elevation survey data taken on March 6, 2009, and the evaluation of that data on March 9, 2009, a determination was made that the level switch (1E41-N003) for High Pressure Coolant Injection (HPCI) (EIIS Code BJ) suction swap from the Condensate Storage Tank (CST) (EIIS Code KA) to the suppression pool had an actual setpoint that was less conservative than that specified in the Technical Specifications. Loss of this instrument requires HPCI to be declared inoperable within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> from discovery of loss of HPCI initiation capability. Operations personnel entered the applicable Technical Specifications Required Action Statement (RAS) for an inoperable HPCI system and realigned HPCI to the suppression pool in accordance with Tech Specs. At that point, HPCI was returned to an operable status. A similar review was performed for instrumentation associated with the Reactor Core Isolation Cooling (RCIC) system (EIIS Code BN). That evaluation determined that level switch (1E51-N060) for RCIC suction swap from the CST to the suppression pool also had an actual setpoint that was less conservative than that specified in the Technical Specifications. Loss of this instrument requires RCIC to be declared inoperable within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> from discovery of loss of RCIC initiation capability. Operations personnel entered the applicable Technical Specifications RAS for an inoperable RCIC system and realigned RCIC to the suppression pool in accordance with Tech Specs.
At that point RCIC was returned to an operable status. The redundant instruments 1E41-N002 and 1E51-N061 remained operable and both HPCI and RCIC would have continued to perform their respective functions but with the automatic suction swap capability degraded due to a reduction in redundancy.
During continued review of the setpoint criteria on March 17, 2009 it was determined that the setpoint for the CST level suction swap to the suppression pool was based on a switchover time of 164 seconds (82 seconds each for valves 1E41-F041 and 1E41-F042) to open and for the CST suction valve (1E41- F001) to close. Current valve stroke times are assessed at post-accident reduced battery (DC) voltages associated with post-accident assumptions that the battery chargers are not available. Taking into account the reduced voltage assumption, and other conservatisms for valve friction, effectively increases the assumed switchover time, based on the limiting valve stroke times in the current torque switch setting guide. This additional time requires the CST low level setpoint for suction swap to the torus to be higher in order to minimize vortex ing at the suction from the CST. Based on HPCI / RCIC flow after throttling HPCI to 3,000 gpm, including flow instrument uncertainty, this would add about 3" to the existing setpoint. This would make the current minimum setpoint requirement non conservative based on current assumptions of instrument uncertainty. Initially the only HPCI switch setpoint that was assumed to be affected was 1E41-N003. Based on the additional discovery regarding reduced battery voltages, the redundant switch 1E41-N002 was also affected. However, since Unit 1 HPCI remained aligned to the suppression pool at the time of this discovery, HPCI would have continued to perform its function.
� PRINTED ON RECYCLED PAPERNRC FORM 366A (9-2007) Based on instrument elevation survey data taken as part of an "extent of condition" review from the issue identified with the RCIC suction swap from the CST to the suppression pool, a determination was made on March 30,2009 that the level switch for the suppression pool high level suction swap for RCIC pump suction has an actual setpoint that was less conservative than that specified in the Technical Specifications. Loss of this instrument (1E51-N062B) requires RCIC to be declared inoperable within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> from discovery of loss of RCIC initiation capability. The corresponding Tech Spec Bases further defines this time to be from discovery of loss of automatic component initiation capability for the RCIC system. At the time of discovery, RCIC suction was aligned to the suppression pool in accordance with the Tech Specs as a result of the previous instrument setpoint condition. The redundant instrument, (1E51-N062A), remained operable. Additionally, RCIC would continue to perform its function but with the automatic suction swap capability degraded due to a reduction in redundancy.
CAUSE OF EVENT
This event was caused by calculation, design and configuration control weaknesses related to HPCI / RCIC CST and Suppression Pool level switches and inadequate verification of elevation during installation.
REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT
The loss of the above instruments would not prevent HPCI / RCIC from performing their respective functions. However, the conditions described above do result in non-conservative setpoints, which is a condition prohibited by the technical specifications as recognized by 10CFR50.73(a)(2)(i)(B).
The HPCI system consists of a steam turbine driven pump and the necessary piping and valves to transfer water from the suppression pool or the condensate storage tank to the reactor vessel. The system is designed to inject water to the reactor vessel over a range of reactor pressures from approximately 160 psig through full-rated pressure. The HPCI system starts and injects automatically whenever low reactor water level or high drywell pressure indicates the possibility of an abnormal loss of coolant inventory. The HPCI system is designed to replace lost reactor coolant inventory in cases where a small line break occurs which does not result in full depressurization of the reactor vessel.
The Reactor Core Isolation Cooling system is a steam turbine driven system similar to the HPCI system.
RCIC is designed to provide core cooling to the reactor pressure vessel upon a loss of the feedwater/condensate supply. The RCIC system is not a credited accident mitigation system and is a much lower volume system (approximately 400 gpm vs. 4000 gpm for HPCI). However in the event of a loss of feedwater event, both the HPCI and RCIC systems are designed to automatically initiate.
The backup for the HPCI / RCIC systems is the Automatic Depressurization System (ADS, EIIS Code JE) together with two low pressure injection systems: The Low Pressure Coolant Injection (LPCI, EIIS Code BO) system and the Core Spray (CS, EIIS Code BM) system. The CS system is composed of two independent, redundant, 100 percent capacity subsystems. Each subsystem consists of a motor-driven pump, its own dedicated spray sparger located above the core, and piping and valves to transfer water from the suppression pool to the sparger. Upon receipt of an initiation signal, the CS pumps in both subsystems start. Once ADS has reduced reactor pressure sufficiently, CS system flow begins.
PRINTED ON RECYCLED PAPERNRC FORM 366A (9-2007) 4 independent, redundant, 100 percent capacity LPCI subsystems, each consisting of two motor driven pumps and piping and valves to transfer water from the suppression pool to the reactor vessel. Upon receipt of an initiation signal, all four LPCI pumps automatically start. Once ADS has reduced reactor pressure sufficiently, the LPCI flow to the reactor vessel begins.
The ADS system consists of 7 of the 11 Safety Relief Valves (SRV). It is designed to provide depressurization of the Reactor Coolant System during a small break Loss of Coolant Accident (LOCA), if HPCI / RCIC fails or is unable to maintain required water level in the Reactor Pressure Vessel (RPV). ADS operation reduces the RPV pressure to within the operating pressure range of the low pressure Emergency Core Cooling System (ECCS) subsystems (CS and LPCI), so that these subsystems can provide coolant inventory makeup.
Based on this analysis, it is concluded that this event had no adverse impact on nuclear safety. This analysis is applicable to all power levels and operating modes in which a LOCA is postulated to occur.
CORRECTIVE ACTIONS
A Design Change has been implemented to raise the elevation and change the setpoint of 1E41-N002, 1E41-N003, and 1E51-N060.
A Work Order has been implemented to lower the installation height of 1E51-N062B to its design setpoint.
ADDITIONAL INFORMATION
Other Systems Affected: None Failed Components Information: None Commitment Information: This report does not create any new permanent licensing commitments.
Previous Similar Events:
There are no similar events within the past two years in which an instrument design and installation resulted in a less conservative setpoint than what is specified in the Technical Specifications.
�