05000321/LER-2009-006
| Docket Numbersequential Revmonth Day Year Year Month Day Year Edwin 1. Hatch Nuclear Plant Unit 2 05000 366Number No. | |
| Event date: | 12-15-2009 |
|---|---|
| Report date: | 01-18-2011 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3212009006R01 - NRC Website | |
(This revision adds the failure of isolation valve 1P41-F123B, provides additional discussion regarding the safety assessment of the as found condition and contains editorial changes.)
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EllS Code XX).
DESCRIPTION OF EVENT
On December 10, 2009 a condition was identified reporting the fact that the cooling water isolation valves were not being tested for a non-safety related air conditioner that is outside the MCR boundary, but the function of the valves was not discussed in the condition report (CR). Additional information was placed in the CR following the initial review of that CR by Operations, that included a review of the work history for valve 1P41-F123A. This information also described the previous unreliable operation of the valve and better defined the function of the valves. This information was directly communicated to the shift Operations personnel who after gaining this information from Engineering, isolated the affected cooling water line to the air conditioner early on December 12, 2009. On December 15, 2009 Unit 1 was operating at 2792 CMWTh 99.6 percent rated thermal power, Unit 2 was operating at 2792 CMWTh, 99.6 percent rated thermal power. On that date it was identified that the plant had been operating in a condition prohibited by the Technical Specifications in that the cooling for the main control room air conditioning was no longer single failure proof.
Further investigation revealed that on January 6, 2006, valve 1P41-F123A was identified as not having any stem travel while the valve is required to automatically close. This valve is in the Plant Service Water (PSW, El IS Code BI) cooling line for the air conditioner for the Operations Shift Manager's office. This air conditioner is outside the MCR boundary and outside of the area serviced by the main control room air conditioners (EllS Code VI). This additional air conditioner was added in 1982 as part of a design modification which added office space adjacent to the main control room in order to allow the space in the main control room to be better utilized. Cooling water isolation valve (1 P41-F I23A) is one of two valves that is designed to automatically isolate in the event of a failure of the non-safety related portion of the PSW line during a design basis seismic event. This portion of the PSW line is not seismic class IE by design. The isolation of this section of piping ensures that adequate flow is maintained for main control room air conditiorier(s) cooled by Division 1 PSW. Since valve 1P41-F123A would not isolate, this portion of the line would no longer be considered single failure proof. This condition required entry into a Technical Specification required action statement (RAS) for the loss of redundancy for the cooling water for the MCR Air Conditioner Units, which are aligned to Division I PSW. During the subsequent investigation and repair of 1P41 -F l 23A valve, the second isolation valve, I P4 I -F123B, was found to also be inoperable on December 17, 2009. The result of the second valve being inoperable is the same as for the initial condition of the first valve being inoperable. There was no previous condition identified that indicated a problem existed with the isolation capability of this second valve. The cooling for the Main Control Room Air Conditioner Units is described in the Technical Specifications Bases, but not to the component detail that would make it obvious that the presence or role of these cooling water isolation valves were critical to the cooling system for the MCR air conditioners to remain single failure proof. Since the PSW valve that failed provides cooling to a non-safety related air conditioner unit, the operating shift team did not recognize the significance of the failure of these isolation valves.
When the initial repair of isolation valve 1P41-F 123A was completed, the affected cooling water line was- reopened on December 25, 2009. However, since isolation valve 1P41-F123B was still inoperable, the line was required to remain isolated and was reclosed when this condition was recognized on December 28, �NRC FORM 366A (9-2007) PRINTED ON RECYCLED PAPER NRC
- FORM 366A U.S. NUCLEAR REGULATORY COMMISSIONLICENSEE EVENT REPORT (LER)(0-2007)
CONTINUATION SHEET
05000366 2009 - 006 - 1 2009. On December 25, 2009 and periodically between that time and June 7, 2010, the isolation boundary was inadvertently shifted from a safety related manual isolation valve to a different manual isolation valve that was not safety-related. During those time frames that a non-safety related manual isolation valve was used as a boundary, credit could not be taken for the system being isolated. This was recognized by Operations who put the necessary administrative controls in place such that from June 7, 2010 forward the safety related isolation valve serving as the isolation boundary remains in place to ensure this configuration is maintained. The permanent modification will leave this portion of PSW piping isolated and will involve a different cooling water source for the non-safety air conditioner.
CAUSE OF EVENT
This event was caused by less than adequate design implementation of a design change implemented in 1982. Currently a design change that results in a change to the Technical Specifications or Bases results in the relevant design and licensing information being provided to licensed operators in licensed training. This was needed in order for licensed operators to be able to recognize the significance of the failure of the isolation valves 1P4 I -F123A and 1P41-F123B. The design change process has changed significantly since 1982 and is currently set up to more comprehensively address the full implications of a design change in licensed operator training. The current design change process would preclude the implementation of a design change affecting a licensing document without first ensuring that the needed level of detail was provided to licensed personnel so that operability and Technical Specification compliance was clearly understood.
Though unknown to the operating crews at the time of discovery, failure of these valves resulted in the cooling system for the main control room air conditioner units cooled by Division I PSW to no longer meet single failure criteria for a time frame greater than the Technical Specifications required action statement (RAS). As a result the required Technical Specification Required Action Statement for inoperable main control room air conditioner unit was not entered on December 12, 2009 when the condition was most recently identified and its significance recognized. There was a missed opportunity to strengthen the Technical Specifications and Bases as well as to establish the periodic testing of the isolation valves when preparing the historical design change package that installed the additional air conditioner in 1982. At the time this design change was implemented the details provided by the custom Technical Specifications and Bases in place at that time nor the design change process served to provide the needed information to licensed Operations personnel regarding the function of the affected isolation valves.
The periodic use of the incorrect valve to isolate the cooling water line for the Shift Manager's office air conditioner resulted from putting less than adequate administrative controls in place to ensure the valve used for isolation was safety related.
REPORTABELITY ANALYSIS AND SAFETY ASSESSMENT
This event is reportable under 10 CFR 20.73(a)(2)(i)(B), Any operation or condition which was prohibited by the planes Technical Specifications. Since valves I P41-F123A and I P41-F123B would not isolate, this portion of the line was no longer considered to be single failure proof. This condition should have resulted in entry into the Condition required by the Technical Specifications for the loss of Main Control Room Air Conditioner Units, which are aligned to the Division I of PSW, but did not. The cooling line was isolated within the completion time of the Tech Spec required action statement (RAS) of Tech Spec 3.7.5 based on the time of discovery on December 12, 2009, but the cause deterrriination concluded that this was a pre existing condition for a time longer than the required completion time.
The Control Room AC portion of the Main Control Room Environmental Control System (hereafter referred to as the Control Room AC System) provides temperature control for the control room following isolation of the control room. The Control Room AC System consists of three 50 percent capacity subsystems containing the 'A', 'B' and 'C' coolers, respectively and that provide cooling and heating of control room supply air. Each subsystem consists of an air handling unit (AHU) (i.e., cooling coils and fan), water cooled condensing units, refrigerant compressors, ductwork, dampers, and instrumentation and controls to provide for control room temperature control. The condensing units receive cooling water from the Plant Service Water System. One condensing unit receives cooling from Division I PSW, one unit is capable of receiving cooling from both Divisions I and II PSW, the other condensing unit receives cooling from Division II PSW.
The Control Room AC System is designed to provide a controlled environment under both normal and accident conditions. Two subsystems provide the required temperature control to maintain a suitable control room environment for a sustained occupancy of 14 persons. The design conditions for the control room environment are 72-79°F and less than 75 percent relative humidity.
In the event the loss of the non-seismic piping was to occur, the valves in the seismic portion of the cooling water lines for the MCR AC AHU would not automatically provide isolation from the Division I PSW cooling for the MCR air conditioners served by this division. It should be noted that the main control room air conditioning system is manually placed into service. As long as the alignment and operation of the system can be manually accomplished, operability of the system is maintained. The "as found" condition resulted in a portion of the system no longer meeting "single failure" criteria, requiring entry into a Tech Spec RAS in accordance with Tech Spec 3.7.5. Since loss of cooling water does not result in the design limits being exceeded immediately and the area is continuously inhabited, it is reasonable to expect the operating crews to identify and compensate for the loss of cooling in a reasonable period of time.
A Main Control Room Air Conditioning PSW Flow Evaluation was performed to evaluate the as found" PSW flow issues associated with the 'loss of ability' to isolate the Shift Manager's office cooling unit due to the failure of isolation valves 1P4I-F123 A/B. The as found" piping condition for the 'B' and 'C' coolers with the 'A' cooler turned off allowed flows of 63.9 gpm and 78.9 gpm for 'B' and 'C' coolers, respectively, with a simulated break in the piping to the shift manager's cooling unit. The cooling capacity of the main control room air conditioning unit is 40 tons or 480,000 BTUH. The calculated heat load of the main control room is 328,125 BTUH. Design of the main control room air conditioning unit established, the minimum flow for the rated capacity at 95°F inlet water condition as 100 gpm. The design water supply flow, from plant service water was specified to be 120 gpm to maintain a flow margin. On reducing the cooler capacity to the calculated heat load value, the minimum PSW flow to the main control room air conditioning unit was established as 81 gpm at 95°F. Through a more detailed evaluation, given the degraded PSW flow of 63.9 gpm to the main control room air conditioning unit, a maximum river temperature of 91.8°F was established in order for the cooler to satisfy the calculated control room heat load. When additional margin is removed from the evaluation, given the degraded PSW flow of 63.9 gpm to the main control room air conditioning unit, and a maximum river temperature of 95.0°F was used, the main control room air conditioning unit was shown by analysis to remain capable of removing the calculated heat load of the main control room in its "as found" condition. There are high pressure cut-off switches provided on each air conditioning unit for the protection of the unit from a catastrophic failure. The high pressure switches are set at 265 psig (with a ± 5 psig uncertainty) which is higher than the expected operating refrigerant pressure of 258.3 psig for the air conditioning unit. This methodology was also reviewed with the vendor for the air conditioning unit in question who confirmed the soundness of the assumptions made for this evaluation. This being the case, even if the cooling water lines to the Shift Manager's air conditioner failed and were not isolated, the cooling function would continue to be satisfied, but with a much reduced margin. For this reason there were no adverse safety implications that resulted from the failure of the isolation valves or in periodically using the Based on this analysis, it is concluded that this event had no adverse impact on nuclear safety.
CORRECTIVE ACTIONS
The cooling line to the shift manager's office air conditioner was isolated from the Division I cooling water that supplies cooling to the MCR air conditioners. Appropriate administrative controls are in place to ensure that this line remains isolated until permanent resolution of this condition is in place. The current plans are to provide cooling to MCR Annex A/C unit using non-safety related cooling water.
The development of training for licensed personnel for modifications implemented was reviewed and the Lessons Learned from this event and the operability implications were included in licensed re-qualification segments for licensed personnel.
The current SNC Design Change procedure requires a review to determine if a proposed design change warrants a change to licensing documents along with impact reviews by the affected department(s) at the site including Operations. These impact reviews ensure that adequate information is contained in the Technical Specifications and/or Bases to ensure the operating shift teams have adequate guidance to recognize the significance of the modification and how it can impact the operability of the system with which it interfaces.
Operations administrative controls were changed to include additional guidance regarding the management of tagouts, cautions, and boundaries associated with components affecting the operability of components required by the Technical Specifications.
ADDITIONAL INFORMATION
Other Systems Affected: None Failed Components Information:
Master Parts List Number: 1P4I-F123A, IP4 1 -F123B EIIS System Code: BI Manufacturer: Valcor Reportable to EPIX: Yes Model Number: V526-5631-17 Root Cause Code: A Type: Valve, Valve, Shutoff EIIS Component Code: SHV Manufacturer Code: V030 Commitment Information: This report does not create any new permanent licensing commitments.
Previous Similar Events: This is considered to be an isolated event of this nature.
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