ML20212D084
| ML20212D084 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 09/17/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20212D081 | List: |
| References | |
| NUDOCS 9909220278 | |
| Download: ML20212D084 (5) | |
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NUCLEAR REGULATORY COMMISSION 4"
WASHINGTON, D.C. 20555-0001
- ...+l SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 62 TO FACILITY OPERATING LICENSE NO. NPF-86 NORTH ATLANTIC ENERGY SERVICE CORPORATION SEABROOK STATION. UNIT NO.1 DOCKET NO. 50-443
1.0 INTRODUCTION
By letter dated June 23,1999, the North Atlantic Energy Service Corporation (North Atlantic) submitted License Amendment Request (LAR) 99-19 which requests changes to the Seabrook Station Technical Specifications (TSs). Currently, TS Limiting Condition for Operation (LCO) 3.7.6.2 requires "Two independent Control Room Air Conditioning Subsystems (CRACS) shall be operable" during all modes of operation. If one subsystem becomes inoperable, it must be restored within 30 days or further operational restrictions are invoked, depending on the operational mode of the plant. LAR 99-19 requests a one-time extension to the allowable outage time (AOT) from 30 days to 60 days. North Atlantic plans to use the extended AOT to replace the existing safety-related refrigerant subsyst'ms with safety-related chilled water subsystems. In addition, LAR 99-19 requests an exception to the requirements of TS 3.0.4 and TS 4.0.4 during implementation of the proposed modification to the CRACS.
2.0 BACKGROUND
Per section 9.4.1.2 of Seabrook's Updated Final Safety Analysis Report (UFSAR), CRACS is a subsystem of the control room complex heating, ventilation, and air conditioning system (HVAC) and consists of an electric motor-driven refrigerant compressor, an air-cooled refrigeration condensing coil with an electric motor-driven centrifugal fan, and a direct-expansion evaporator with an electric motor-driven centrifugal fan. Section 9.4.1.1 of the UFSAR states that the cooling system is designed to maintain the control room temperature at or below design maximum temperatures when the outside air temperature is 88 *F or lower.
This section also states that the control room complex air conditioning system is physically and operationally independent of the filtering, heating, and ventilating of the remainder of the control
. building. Per section 9.4.1.2 of the UFSAR, the other subsystems that make up the control room complex HVAC system are: the computer room air conditioning system, the control room normal makeup air subsystem, the control room emergency air makeup and filtration subsystem, and the control room exhaust and static pressure control subsystem. Therefore, the scope of the proposed change is limited to the cooling function only since all other functions are performed by other subsystems.
9909220278 990917 ENCLOSURE PDR ADOCK 05000443 P
PDR D
. Seabrook's CRACS provides cooling of the control room complex in accordance with General Design Criteria (GDC) 4 and 19 of Title 10 of the Code of FederalRegulations (10 CFR) Part 50, Appendix A, General Design Criteria for Nuclear Power Plants.
GDC 4 requires that " Structures, systems, and components important to safety shall be designed to accommodate the effects of and to be compatible with the environmental conditions associated with normal operation, maintenance, testing, and postulated accidents, including loss-of-coolant accidents." With regard to this criterion, Seabrook's CRACS is designed to provide the upper temperature limit for the operability of equipment within the control room complex.
GDC 19 states that "A control room shall be provided from which actions can be taken to operate the nuclear power unit safety under normal conditions and to maintain it in a safe condition under accident conditions, including loss-of-coolant accidents." With regard to this criteria, Seabrook's CRACS is designed to provide the upper temperature limit inside the control room complex to ensure the comfort of the plant operators.
Seabrook's CRACS consists of two independent safety-related air conditioning subsystems (trains) that provide cooling of recirculated control room air. Each train of CRACS is designed to handle 100 percent of the heat load postulated for a design basis accident and is expected to run on demand for a period of 30 days following an accident. Availability of the CRACS is necessary on a continuous 24-hour per day basis during all modes of plant operation in order to comply with the requirements of TS 3.7.6.2.
However, this system has required a' substantial amount of maintenance and had been the cause of two unplanned plant shutdowns. Therefore, in order to reduce the operationalload on the safety-related refrigerant trains and to improve overall CRACS reliability, a non-safety-related chilled water subsystem was installed. The non-safety-related chilled water system includes two chiller units, two chilled water pumps, two air cooling coils, an expansion tank, valves and associated controls and instrumentation. Piping and valves located within the Control Building are designed and installed in accordance American National Standards Institute (ANSI) standard B31.1 with Regulatory Guide 1.29 seismic supports (Seismic Category NNS-1). Piping and valves located on the Non-Essential Switchgear Building roof, and in the Administration Building and the Administration Building's Mechanical Equipment Room 18 are classified as non-seismic and are designed and installed in accordance with ANSI B31.1.
Expansion and air separator tanks are designed and fabricated to ASME Section Vill.
According to the application, the temperature of the control room is normally maintained between 70 to 72 *F, at the discretion of the Unit Shift Supervisor, utilizing the non-safety-related train of the CRACS with the two safety-related refrigerant trains on standby. In the event that the contre! room temperature b~;omes greater than 75 'F, plant procedures require starting other equipment in the non-safety-related subsystem or starting one of the safety-related trains of CRACS to restore the control room ten;puta.a to iu nunnat operating band.
There are no TSs associated with the operation of the non-safety-related chilled water subsystem.
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. 3.0 ' EVALUATION The proposed change would replace the existing safety-celated refrigerant subsystem with a safety-related chilled water subsystem. The existing direct expansion refrigerant evaporators, refrigerant compressors, and condensers will be removed and the direct expansion coils in the fan units will be replaced with safety-related chilled water coils. Each independent train will be supplied with chilled water from its own safety-related refrigerant chiller and pump.
The proposed installation of the new safety-related chilled water system will be performed on each train individually during separate AOT periods. In order to permit installation of the revised design in each train, it is necessary that the associated safety-related train of CRACS be declared inoperable which requires entry into the applicable action statement of TS 3.7.6.2.
TS 3.7.6.2 requires that two independent Control Room Air Conditioning Subsystems be operable during all modes of operation. For operational modes 1,2,3, and 4, the TS states the following:
"With one Control Room Air Conditioning Subsystem inoperable, restore the inoperable system to operable status within 30 days or be in at least Hot Standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Cold Shutdown whhin the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />."
For operational modes 5 and 6, the TS states:
"With one Control Room Air Conditioning Subsystem inoperable, restoro the inoperable system to operable status within 30 days or initiate and maintain operation of the remaining Operable Control Room Air Conditioning Subsystem or immediately suspend all operations involving Core Alterations or positive reactivity changes."
or "With both Control Room Air Conditioning Subsystems inoperable, or with the Operable Control Room Air Conditioning Subsystem unable to maintain temperature below the limiting equipment qualification temperature in the control room area, suspend all operations involving Core Alterations or positive reactivity changes."
The proposed TS change is to temporarily increase the AOT by adding Me note:
"For cycle 7, the allowable outage time may be extended to 60 days, on a one-time basis, for each train, to implement modifications to the Control Room Air Conditioning Subsystems. The provisions of specifications 3.0.4 and 4.0.4 are not applicable during the implementation of modifications to the Air Conditioning Subsystems."
The proposed change is a one-time only change to TS 3.7.6.2 in order to facilitate the installation of the design change to the CRACS during the present operating cycle. This j
change will not affect the existing 30-day AOT period presently in place in TS 3.7.6.2.
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. which requires specific actions in the event that the CRACS is determined to be f
inoperable for any other reason. Therefore, no changes to the Bases section B 3/4.7.6
" Control Room Subsystems" are necessary.
The proposed change also requests an exception to the requirements of TS 3.0.4 and TS 4.0.4 during implementation of the proposed modification to the CRACS. TS 3.0.4 prohibits entry into a mode when the conditions for the LCO are not met and the associated action (s) requires a shutdown if they are not met within a specified time interval. TS 4.0.4 prohibits entry into a mode unless the associated surveillance l
requirement (s) has been performed within the stated interval.
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i During the implementation of the modification, when one safety-related train of CRACS f
is inoperable, the requirements of TS 3.0.4 and TS 4.0.4 would unnecessarily prevent a 1
restart of the plant in the event of an unplanned plant shutdown. The conditions established by the note are necessary to allow the plant to restart without meeting the surveillance and LCO requirements of TS 3.7.6.2, in the event of a plant shutdown while f
the design change is being implemented. During implementation of the design change, there will still be two other trains to cool the control room area, one safety-related train of CRACS, and the non-safety-related chilled water subsystem.
North Atlantic has committed that they will not enter the subject action statements to initiate installation of the design changos to CRACS unless the non-safety-related chilled water subsystem is functional. In addition, North Atlantic has stated that they will not exercise the exceptions to TS 3.0.4 and SR 4.0.4 during implementation of the modification unless the non-safety-related chilled water subsystem is functional.
Therefore, it is not necessary to impose the requirements of TS 3.0.4 and 4.0.4 during implementation of the modifications to the CRACS.
The CRACS is excluded from modeling in the Seabrook Station Probabilistic Risk Assessment (PRA) due to its extremely low risk significance. The safety-related CRACS are support subsystems which control the temperature in the control room area to assist in maintaining a habitable environment for personnel and to protect the equipment qualification of safety-related components in the control room area. CRACS does not perform actions required to mitigate the consequences of an accident.
The risk significance involved with removing a safety-related train of the CRACS is extremely low based on the short period (60 days per train) and the consequences of losing this function. North Atlantic performed a risk evaluation of the simultaneous failure of the non-safety-related chilled water subsystem and the operable safety-related train of CRACS during the total 120-day period. This evaluation concluded that while the losc of equipment in the ion-safetv-rd;ited chilled water subsystem is not unlikely over the 120-day total penoc, based on generic component failure rates, the likelihood
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of the loss of both the non-safety-related chilled water subsystem and the operable d
safety-related train of CRACS is low (7.4E ). If this occurs, the TS requires operator actions to shut down the plant, during which there would be a slow gradual rise of temperature in the control room area. Therefore, there would be no impact to the core damage frequency because the plant would be shut down before control room area temperatures reached the point where equipment operation would be affected.
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. In summary, the plant design originally included only two trains to cool the control room area and Seabrook currently has three trains. During the plant modification, one of the l
two safety-related trains will be declared inoperable, which will still leave two trains to cool the control room area.
If the non-safety-related train becomes inoperable, the safety-related train will be placed in service. In the unlikely event that the non-safety-related train and the operable safety-related train of CRACS both become inoperable during the proposed 60-day AOT period, TS 3.7.6.2 would require that actions be taken to shut down the plant.
Lastly, the risk significance is low, the proposed modifications are intended to increase the reliability of the CRACS, which has already caused two forced outages, and the l
proposed change is consistent with the regulatory criteria. Therefore, based on the j
information contained in the application and in the UFSAR, the staff finds that the i
proposed one-time increase of the AOT from 30 to 60 days for TS 3.7.6.2 is acceptable 1
and the proposed change to exclude the requirements of TS 3.0.4 and 4.0.4 during implementation of the modifications to the CRACS is also acceptable.
4.0 STATE CONSOLTATION c
in accordance with the Commission's regulations, the New Hampshire and Massachusetts State officials were notified of the proposed issuance of the amendment.
The State officials had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes surveillmce requirements. The NRC staff has determined that the amendment involves no signnicant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendrnent involves no significant hazerds consideration, and there has been no public comment on such finding (64 FR 98032). Accordingly, the amendment meets the eligibility criteria for categorical l
exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmentalimpact statement or environmental assessment need be prepared in connection with the issuance of th6 amendment.
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6.0 CONCLUSION
l The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: Jo' hn Harrison l'
Date:
September-17, 1999 i: