ML20073L423
| ML20073L423 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 10/05/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20073L416 | List: |
| References | |
| NUDOCS 9410130088 | |
| Download: ML20073L423 (7) | |
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.172 TO FACILITY OPERATING LICENSE NO. DPR-71 AND AMENDMENT NO.203 TO FACILITY OPERATING LICENSE NO. DPR-62 CAROLINA POWER & LIGHT COMPANY l
BRUNSWICK STEAM ELECTRIC PLANT. UNITS 1 AND 2 DOCKET NOS. 50-325 AND 50-324
1.0 INTRODUCTION
By letter dated September 9, 1994, Carolina Power & Light Company (the licensee) submitted a request for changes to the Brunswick Steam Electric Plant (BSEP), Units 1 and 2, Technical Specifications (TS). The requested changes would revise TS Section 3.6.4.1 to change the frequency for verifying the position of the drywell-suppression chamber vacuum breakers when the position indication is inoperable from at least once every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to at least once every 14 days.
i 2.0 EVALUATION On September 3, 1994, the licensee found that the closed position indicator for the BSEP, Unit 1, "C" drywell-suppression chamber vacuum breaker was inoperable.
Thus, Action Statement c. for TS 3.6.4.1 required, as a compensatory measure, that a surveillance test be performed within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> and at least once per 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> thereafter to verify that the vacuum breaker was in the closed position while the position indicator is inoperable. The surveillance test confirms that the vacuum breaker is closed by verifying that the test differential pressure placed between the drywell and suppression chamber is maintained at greater than one-half the initial differential pressure for one hour without nitrogen makeup. The licensee stated that the position indication could not be repaired without an unscheduled unit shutdown.
By letter dated September 9,1994, the licensee requested the U.S. Nuclear Regulatory Commission (NRC) to change the BSEP TS Section 3.6.4.1, Drywell -
Suppression Chamber Vacuum Breakers, to revise the test frequency for verifying that the vacuum breakers are closed. The licensee specifically proposed that TS 3.6.4.1, Action Statement c, be revised to change the test frequency to at least once every 14 days. The licensee has also proposed the addition of a new surveillance requirement that requires each vacuum breaker be verified closed, as indicated by the position indicating system, at least once per 14 days and within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after any discharge of steam to the suppression chamber from any source. As a result of adding this new surveillance requirement, the remaining surveillance requirements are being renumbered. This renumbering of the surveillance requirements also 9410130088 941005 PDR ADOCK 05000324 P
, necessitates changes to the TS 3.6.4.1 action statements to reflect the correct referencing of surveillance requirements.
Since the renumbering does 1
l not change the content of the remaining surveillance requirements, the proposed renumbering is administrative.
The drywell-suppression chamber vacuum relief function is accomplished by 10 vacuum breakers located on the torus ring header in 5 groups of 2 valves each.
The vacuum breakers are designed to prevent primary contcinment external overpressure, to permit the flow of non-condensible gases from the suppression chamber to the drywell and to minimize water level oscillations in the downcomers. The licensee's analysis has shown that 8 of the 10 vacuum breakers will limit the drywell-suppression chamber differential pressure to 2 psi. Following drywell spray actuation, the analysis shows that in about 2 seconds the drywell-suppression chamber differential pressure would equalize.
If a vacuum breaker should be partially open during a loss-of-coolant accident, a suppression pool bypass flow path would be created. This would allow some steam to pass directly to the suppression chamber without being fully condensed in the pool, thereby causing a higher than expected peak containment pressure during the accident.
However, the vacuum breakers are designed with magnetic latches that assure positive closing, making it less likely for a valve to be in a partially open position.
Each vacuum breaker is also provided with separate open and closed limit switches that provide position indication to the control room personnel. Thus, the loss of the closed position indicator light would alert the operators that the valve disk may be in an intermediate position. The TS would then require operator action to verify that the valve is closed.
After verification testing to confirm that the disk is in the closed position, there is a very low likelihood that the disk will be moved from the closed position during normal operation. A magnetic latch provides a holding force which could only be overcome by (1) intentional stroking using the test actuator, or (2) a suppression chamber to drywell differential pressure near the opening set point.
Potential differential pressure saurm that could unseat the disk, and thus present a need for reverificatic, of the closed position, include: steam additions to the suppression chamber (e.g., high pressure coolant injection system and reactor core isolation cooling system turbine operation, safety relief valve discharge), makeup nitrogen additions to the primary containment via the suppressian chamber connections, and venting the drywell for pressure reduction.
To account for rotential disk unseating due to steam admission to the suppression chamber, the licensee has proposed an additional surveillance test, as further compensation, that reverifies the closed position of the vacuum breakers following each steam admission to the suppression chamber.
If the position indication is out of service, this would then require the surveillance test to be performed to verify the vacuum breaker is closed. This action provides cdequate assurance that the vacuum breaker is closed, since no conditions exist during normal operation that would open this vacuum breaker. On September 24, 1994, during a telephone conversation with licensee representatives, the NRC staff discussed the potential for the vacuum breakers to open due to other
. differential pressure causing sources.
Based on these discussions, the NRC staff has concluded that the plant operating procedures for venting and inerting the primary containment will not result in the vacuum breakers becoming opened from these evolutions.
Additionally, the licensee stated that the change in test frequency is consistent with the at least once per 14 days frequency specified in the Improved Standard Technical Specifications for Boiling Water Reactors (BWR/4).
After reviewing the licensee's basis for the proposed changes, the NRC staff finds that the proposed revision to the test frequency with the addition of a surveillance test requirement to be acceptable. The change in the test frequency does not increase the probability that a vacuum breaker may be partially open during a period when the position indicator is not in service.
The test frequency of at least once every 14 days and the surveillance requirement for verification of valve position after any discharge of steam to the suppression pool provide adequate assurance of valve position. The change will also reduce the risk of an inadvertent plant transient when raising the drywell pressure for the verification tests by reducing the number of times l
that a these tests must be conducted when the position indication is inoperable. The proposed change in test frequency is also consistent with the frequency specified in the Improved Standard Technical Specifications for Boiling Water Reactors (BWR/4) (NUREG-1433).
3.0 EXIGENT CIRCUMSTANCES
The Commission's regulations,10 CFR 50.91, contain provisions for issuance of amendments when the usual 30-day public notice period cannot be met. One type of special exception is an exigency. An exigency is a case where the staff and the licensee need to act promptly and time does not permit the Commission to publish a Federal Register notice allowing 30 days for prior public comment, and determines that the amendment involves no significant hazards consideration.
The staff has determined that exigent circumstances exist in that each time the survaillance test is performed the operational margin between the actual drywell pressure and the high drywell pressure trip setpoint is reduced, raising the possibility for an inadvertent plant transient. The licensee stated the closed position indication was found inoperable on one vacuum breaker on September 3, 1994, and that they have been performing the required testing to verify that the vacuum breaker is closed. Since the plant is in operation and the primary containment suppression chamber is inerted with nitrogen, the suppression chamber is not accessible to repair the vacuum breaker position indication without an unscheduled plant shutdown. To conduct the vacuum breaker test, the nitrogen pressure is increased inside the drywell to establish the test pressure. This test reduces the cperational margin between the actual drywell pressure and the high drywell pressure trip
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setpoint.
If this setpoint is reached or exceeded, a reactor scram and Group 1 isolation will occur. Therefore, the changes to the test frequency will reduce the potei.;ial for incurring an unnecessary plant transient.
Based on the above, the NRC staff has determined the licensee has used its best efforts to make a timely application and that exigent circumstances are present which warrant processing the requested amendment pursuant to 10 CFR 50.91(a)(6).
4.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION
DETERMINATION The amendments change TS to revise the frequency for verifying the position of the drywell-suppression chamber vacuum breakers when the position indication is inoperable from at least once every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to at least once every 14 days.
The Commission's regulations in 10 CFR 50.92 state that the Commission may make a final determination that a license amendment involves no significant hazards consideration if operation of the facility in accordance with the amendment would not:
(1) Involve a significant increase in the probability or consequences of any accident previously evaluated; or I
(2) Create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) Involve a significant reduction in a margin of safety.
The licensee has provided the following analysis regarding no significant hazards consideration using the Commission's standards.
(1) The proposed amendment does not involve a significant increase in the probability or consequences of an a.cident previously evaluated.
The proposed change revises the surveillance requirements 4
associated with inoperable position indication for drywell-suppression chamber vacuum breakers.
No safety-related equipment, safety function or plant operations will be altered as a result of the proposed change. The change does not affect the design, j
materials, or construction standards applicable to the vacuum breakers or their position indication instrumentation.
Relaxation of the frequency for verifying the position of the drywell-suppression chamber vacuum breakers from at least once every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to at least once every 14 days, as stated in the existing Technical Specification 3.6.4.1, ACTION c, will not affect the ability of the drywell-suppression chamber vacuum breakers to perform their intended safety function. The extended frequency provides adequate assurance that the vacuum breakers will perform their intended safety function.
Each drywell-suppression chamber e
. vacuum breaker will continue to be demonstrated OPERABLE and closed at least once per 31 days and after any discharge of steam to the suppression chamber in accordance with Technical Specification 4.6.4.1.a.
In addition, the new surveillance requirement provided in the proposed Technical Specification 4.6.4.1.a will require that each vacuum breaker be verified to be closed at least once every 14 days. The new surveillance provides further assurance that the vacuum breakers are capable of performing their design function under accident conditions of allowing the venting of non-condensible gases from the suppression chamber to the drywell while not allowing bypass flow from the drywell to the suppression chamber.
Based on the above, the proposed change does not create a significant increase in the probability or consequences of an accident previously evaluated.
(2) The proposed change would not create the possibility of a new or different kind of accident from any accident previously evaluated.
As stated above, no safety-related equipment, safety function or plant operations will be altered as a result of the proposed change. The change does not affect the design, materials, or construction standards applicable to the vacuum breakers or their position indication instrumentation.
Relaxation of the frequency for verifying the position of the drywell-suppression chamber vacuum breakers of the existing Technical Specification 3.6.4.1, ACTION c from at least once every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to at least once every 14 days will not affect the ability of the drywell-suppression chamber vacuum breakers to perform theie intended safety function.
In addition, the new surveillance requirement provided in proposed Technical Specification 4.6.4.1.a will require that each vacuum breaker be verified to be closed at least once every 14 days. The new surveillance will provide further assurance that the vacuum breakers are capable of performing their design function under accident conditions without altering plant operations in a manner that would create a new or different kind of accident.
As such, the proposed license amendment cannot create the possibility of a new or different kind of accident from any accident previously evaluated.
(3) The proposed amendment does not involve a significant reduction in a margin of safety.
The proposed change does not involve any changes to the plant design or operation. Therefore, no margins of safety, as defined by the plant's accident analyses, are impacted. Relaxation of the frequency for verifying the position of the drywell-suppression
. chamber vacuum breakers of the existing Technical Specification 3.6.4.1, ACTION c from at least once every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to at least once every 14 days will not affect the ability of the drywell-suppression chamber vacuum breakers to perform their intended safety function. The extended frequency provides adequate assurance that the vacuum breakers will perform their intended i
safety function.
Each drywell-suppression chamber vacuum breaker will continue to be demonstrated OPERABLE and closed at least once per 31 days and after any discharge of steam to the suppression chamber in accordance with Technical Specification 4.6.4.1.a.
In addition, performance of Technical Specification 4.6.4.1.b requires pressurization of the drywell to approximately 1.0 psig and then verifying that us differential drywell to suppression chamber pressure is maintained greater than one-half the initial differential pressure for one hour without nitrogen makeup. During this evolution actual pressure will increase as high as 1.1 psig before stabilizing. The Drywell Pressure - High setpoint, which initiates a reactor scram and a Group 1 isolation, is less than or equal to 2.0 psig (the actual setpoint is 1.8 psig). As such, performance of this evolution once per 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> unnecessarily risks a plant transient without providing a significant increase in the level of safety gained by performing the verification on a 14 day frequency.
The new surveillance requirement provided in proposed Technical Specification 4.6.4.1.a will require that each vacuum breaker be verified to be closed at least once every 14 days. The new surveillance provides further assurance that the vacuum breakers are capable of performing their design function under accident conditions of allowing the venting of non-condensible gases from the suppression chamber to the drywell while not allowing bypass flow from the drywell to the suppression chamber.
l Based on the above reasoning, the proposed license amendment does not involve a significant reduction in the margin of safety.
Based on the preceding analysis, the licensee determined that the proposed change to the TS would not involve a significant increase in the probability or consequences of an accident previously evaluated, create the possibility of a new or different kind of accident from any previously evaluated or involve a significar.t reduction in the margin of safety.
The NRC staff ho reviewed the licensee's no significant hazards consideration determination and agrees with the licensee's analysis. Accordingly, the staff finds that the requested amendments do not involve a significant hazards consideration.
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5.0 STATE CONSULTATION
In accordance with the Commission's regulations, the State of North Carolina official was notified of the proposed issuance of the amendments. The State official had no comments.
6.0 ENVIRONMENTAL CONSIDERATION
The amendments change 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 the Surveillance Requirements. The NRC staff has determined that the amendments involve no significant increase in the amounts, nd 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 amendments involve no significant hazards consideration, and there has been no public comment on such finding (59 FR 47648). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
7.0 CONCLUSION
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, l
and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
P. Milano W. Long Date: October 5, 1994 I
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