ML20138H960
| ML20138H960 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 05/05/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20138H953 | List: |
| References | |
| NUDOCS 9705070343 | |
| Download: ML20138H960 (4) | |
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- w s * *,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0. 94 TO FACILITY OPERATING LICENSE NO. NPF-47 ENTERGY OPERATIONS. INC.
RIVER BEND STATION. UNIT 1 DOCKET NO. 50-458
1.0 INTRODUCTION
By application dated November 15, 1996, Entergy Operations, Inc. (the licensee) requested changes to the Technical Specifications (TSs) (Appendix A l
to Facility Operating License No. NPF-47) for the River Bend Station, Unit 1 (RBS). The proposed changes would revise the TSs to allow the performance of the 24-hour emergency diesel generator (EDG) maintenance run while the unit is in either Mode 1 or Mode 2.
2.0 BACKGROUND
The Class IE AC distribution system supplies power to three divisional engineered safety features (ESF) load groups (i.e., Divisions I, II, and III),
with each division powered by an independent Class IE 4.16-Kv ESF bus.
Each i
ESF bus receives power from either offsite sources or a dedicated onsite EDG.
During normal operation, the Division I & II ESF buses are aligned to their preferred offsite sources with the Division III ESF bus powered from the normal 4.16-Kv switchgear, which can be powered from either preferred station service transformer.
In the event that the preferred offsite source is lost or degrades, the affected ESF bus is automatically transferred to an alternate standby onsite source.
The onsite standby power source for each 4.16-Kv ESF bus is a dedicated EDG.
These EDGs (i.e., Division I, II, and III) automatically start following generation of either a loss-of-coolant accident (LOCA) signal (i.e., low reactor Mater level or high drywell pressure), ESF bus degraded voltage, or undervoltage signal. Any..one of the standby diesel generators on Division I or II has the capacity to power the loads required to safely shutdown the plant during a design-basis accident.
3.0 EVALUATION Currently, RBS's TSs require that the operability of each EDG be demonstrated every 18 months by operating an EDG for 24 hou s in parallel with an offsite source.
Because of staff concerns related to the performance of this test during power operation, the current RBS TSs prevent the 24-hour test from being performed during Modes 1 and 2.
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Specifically, the staff concerns are related to fault conditions or grid disturbances that may exist while an EDG is connected in parallel with the offsite system. These types of events could affect the availability of the EDGs for subsequent emergency operations.
4 However, the Nuclear Regulatory Commission (NRC) staff has recently approved other requests for eliminating the restrictions for performing the 24-hour test in Modes 1 and 2.
This approval has been based on the existence of unique EDG design features and special provisions that ensure paralleled operation of the EDG with the offsite system will not prevent it from performing it assumed safety functions. The special design features and provisions are as follows:
1.
On an accident signal, the EDG being tested will be separated from the offsite source by tripping of its output breaker and will be switched from the droop mode to the isochronous mode.
If offsite power is available, the EDG continues to run in standby mode.
Ii~ offsite power is not available, the EDG continues to run, but its corresponding bus is deenergized when the offsite feeder breakers open on undervoltage. The isolated bus then allows the EDG's output breaker to reclose, energizing the bus and carrying the accident loads for that load group.
2.
During the 24-hour test of the an EDG, no other EDG is operated in parallel with the offsite power grid, and the remaining redundant divisions are supplied from a separate offsite sourec. This configuration ensures that only one EDG is susceptible to grid perturbations and independent safe shutdown capability is maintained.
3.
Assuming a single failure of an EDG, adequate capacity is available from the remaining EDGs to power the remaining divisions, and the remaining divisions will have the required equipment operable to mitigate the consequences of DBA or loss of offsite power (LOOP).
4.
The EDGs will not be paralleled to the offsite systems during severe weather or unstable grid conditions.
5.
There is current surveillance testing that demonstrates on an 18-month frequency the capability of the EDG to revert to the ready-to-load status following a LOCA signal while operating in the parallel test mode.
Demonstration of thii capability ensures that the EDG availability under accident conditions is not compromised as result of testing.
At RBS Unit 1, similar design features and provisions exist. The EDG is equipped with a design feature that enables the EDG, upon detection of an accident signal (i.e., LOCA), to automatically terminate parallel operation with the offsite system and return to a standby mode of operation. This design feature prevents offsite system disturbances from affecting the availability of the EDG.
Additionally, current surveillance requirements at RBS demonstrate every 18 months that the EDG has the capability to revert from the test mode (i.e., paralleled to the offsite system) to the standby mode following detection of a LOCA signal.
. Upon detection of a LOOP, without a LOCA, the loss of power instrumentation would actuate, which would result in an automatic start signal from the associated EDG.
For Division I and II, prior to connecting the EDG to its appropriate bus, all loads are shed except for the feeder to the 480-volt load centers. The RBS electrical system also has the capability to recognize a grid undervoltage condition.
Should the grid go to an undervoltage condition while the EDG is being paralleled to the offsite system, the incoming offsite breakers will open and the EDG will switch from parallel operation to isochronous mode, picking up the loads on the bus sequentially.
E01 is taking special administrative provisions related to the performance of the 24-hour test during Modes 1 and 2. In accordance with SR 3.8.1.13 at RBS, only one EDG will be paralleled to the offsite system at any one time. This restriction will prevent the possibility of a common-mode failure, which could result in more than one EDG being unavailable. Additionally, administrative controls will maintain all required safety features supported by the remaining EDGs.
Specifically, no maintenance or testing will be planned for these features for the duration of the test. This will help ensure that there is adequate safe shutdown capability if the EDG under test should become unavailable.
Finally, administrative controls at RBS will caution against conducting the 24-hour test during periods of severe weather or other events that could impact EDG availability.
Although performance of the 24-hour EDG functional test during Modes 1 and 2 is contrary to the standard TSs, performance of the test has been found acceptable due to the unique EDG design features and special provisions.
Based on the above review, the staff concludes that the licensee has satisfactorily met the required conditions for conducting the EDG 24-hour test at power, and the proposed TS change and bases change are acceptable.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Louisiana State Official was notified of the proposed issuance of the amendment.
The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a r,d within the restricted area as defined in 10 CFRequirement w facility component locate Part 20. The NRC staff has determined that the amendment involves no significant 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 amendment involves no significant hazards consideration, and there has been no public comment on such finding (62 FR 127). Accordingly, the amendment meets 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 amendment.
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6.0 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, I
and (3) the issuance of the amendment will not be inimical to the common i
defense and security or to the health and safety of the public.
1 Principal Contributor:
M. Pratt Date:
May 5, 1997 M
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