ML20086U049
| ML20086U049 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 07/21/1995 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20086U036 | List: |
| References | |
| NUDOCS 9508030251 | |
| Download: ML20086U049 (4) | |
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+'a UNITED STATES j
j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20656 4 001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0.196 TO FACILITY OPERATING LICENSE DPR-57 AND AMENDMENT NO.136 TO FACILITY OPERATING LICENSE NPF-5 GEORGIA POWER COMPANY. ET AL.
EDWIN I. HATCH NUCLEAR PLANT. UNITS 1 AND 2 DOCKET NOS. 50-321 AND 50-366
1.0 INTRODUCTION
By letter dated October 13, 1994, as supplemented by letter dated January 13 and May 4, 1995, Georgia Power Company, et al. (the licensee or GPC), proposed license amendments to change the Technical Specifications (TS) for the Edwin I. Hatch Nuclear Plant, Units 1 and 2.
The proposed changes would revise the TS to lower the anticipated transient without scram-recirculation pump trip (ATWS-RPT) setpoint by approximately 2 feet 2 inches to minimize the potential for RPTs following reactor scram, and allow restarting the recirculation pump following an RPT when the temperature differential between the coolant at the reactor bottom head and the reactor steam dome cannot be obtained, provided certain conditions are met.
If a thermally stratified condition were to develop in the reactor vessel following an unplanned reactor trip and RPT, and a depressurization to atmospheric conditions was required, a delay in restart of at least 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> could occur.
Such events have occurred at Hatch twice before. The January 13 and May 4, 1995, letters provided clarifying information that did not change the scope of the October 13, 1994, application and the initial proposed no significant hazards consideration determination.
2.0 EVALUATION Boiling Water Reactor operating experience indicates that the bottom head region of the reactor pressure vessel (RPV) experiences a rapid cooldown following a reactor scram coincident with RPT. The reduction in metal temperature in the bottom head region, while the steam dome remains near rated temperature and pressure, causes an approach toward the TS pressure -
temperature limits.
This reduction in the bottom head coolant temperature prevents restart of the reactor coolant pumps if the temperature difference between the steam dome and the bottom head exceeds 145 degrees F.
The 145 degrees F(requirement is specified to avoid thermal fatigue on the control rod drive (CRD) penetration nozzle stub tubes in the bottom head due to a thermal shock by the reactor hot water on the cold stub tubes during the start of the recirculation pumps.
9508030251 950721 PDR ADOCK 05000321 P
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l For TS purposes, the bottom head drain line temperature is used as a representation of coolant temperature in the bottom head region.
The temperature in the drain line would not be meaningful if the Reactor Clean-up System is secured and would result in no flow through the drain line.
If the drain line temperature cannot be determined or it exceeds 145 degrees F limit, RPV is depressurized as required by the TS. This scenario happened at Hatch in August 1992 and October 1993.
To alleviate the thermal stratification problem, two approaches were proposed by the licensee:
(1) Reduce the probability of an RPT, and (2) Provide alternatives to the drain line temperature measurement, if the recirculation pumps trip.
The licensee with the assistance of their consultants from General Electric Company (GE) evaluated the proposed changes.
2.1 Lowerina of RPV Water level Setooint for ATWS-RPT To reduce the probability of RPTs, GPC proposed to reduce the low-water level ATWS-RPT setpoint from -47 inches (level 2 setpoint) to -73 inches (level 3 scram setpoint is 0).
GE evaluated the plant ATWS response that could i
potentially be affected by the proposed changes, and determined that the most limiting event is the loss-of-feedwater (LOFW) ATWS event. The LOFW was selected, since the low level RPT setpoint is reached during an ATWS event.
The staff approved the REDY model that was used for the analysis.
Level 2 was reached and the high pressure coolant injection (HPCI) and the reactor core isolation coolant (RCIC) were initiated and the RPV level was stabilized.
Since the reactor pressure and the heat flux do not increase above their initial value and no safety / relief valve opens, there is no increase in peak fuel cladding temperature or in suppression pool temperature.
The ATWS analysis acceptance guidelines of RPV discussed in NUREG-0460,
" Anticipated Transients Without Scram For Light Water Reactors," dated April 1978, (less than 1500 psig) and the suppression pool temperature.(less than 200 degrees F) are satisfied.
i It should be noted that the RPT on reactor high pressure set at 1095 psig, during an ATWS event, will mitigate the rapid pressurization transients.
Therefore, the setpoint will not impact these ATWS scenarios.
The ATWS-RPT is supplied by the analog transmitter trip system (ATTS).
Reducing the setpoint may require installation of new slave trip units in ATTS.
According to the licensee, the new trip units are functionally identical to the trip units being used at Hatch and within the design capabilities of the ATTS.
The plant ' transient analysis takes credit only for the reactor high pressure ATWS-RPT which remain unchanged from the current design.
Since plant ATWS response-will not be significantly impacted, the staff finds the proposed change of lowering the RPV water level setpoint for ATWS-RPT acceptable.
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- 2.2 Restart of the Reactor Recirculation Pumo Within 30 Minutes of RPT When the differential temperature cannot be confirmed, the proposed alternative to the current criteria is to start the recirculation pump within 30 minutes of the RPT, if the drive flow in either loop is above 40% of rated prior to the pump trip. This alternative will be used only when the differential temperature cannot be determined and in situations where neither HPCI nor RCIC injection occurs and feedwater temperature does not decrease below 300 degrees F.
The licensee with the assistance of its consultants from GE evaluated the proposed change.
The staff agrees with the licensee (based on GE's review of other operating BWR startup test data) that stratification up to the 145-degree F level does not develop until one hour following the RPT.
Restarting the pumps within 29 minutes in situations where neither HPCI nor RCIC injection occurs and the feedwater temperature does not decrease below 300 degrees F, assures sufficient mixing in the lower plenum to avoid thermal stratification and maintain the differential temperature between the steam dome and the bottom head within 145 degrees F.
Allowing the early restart is acceptable because the conditions for restart assure that a stratified condition has not yet developed.
Therefore, the structures at the vessel bottom will not experience a severe thermal shock resulting from the injection of het water following the pump restart. The proposed change should reduce the number of RPV blowdowns, reducing thermal cycles on the RPV.
It may be noted that the restriction on pump start specified in TS 3.6.D that states "The pump in an idle recirculation loop shall not be started unless the temperatures of the coolant within the idle and operating recirculation loops are within 50 degrees F of each other" is not changed.
l GE's review of plant transient and accident analyses identified no adverse affect due to this change. Therefore, GPC's proposal to restart the recirculation pumps within 30 minutes is acceptable.
The low level RPT setpoint change is justified at both Hatch units based on j
the GE LOFW ATWS analyses performed. The restart cf the pumps after 30 minutes is acceptable under the special conditions based on the BWR operating experience.
Based on its review, the staff finds that the above changes have no adverse J
impact on safety and does not pose an undue risk to public health and safety.
Therefore, the proposed changes to TS 3.3.4.2 and associated Bases for Unit 1 and TS 3.3.4.2 and associated Bases for Unit 2 are acceptable.
3.0 STATE CONSULTATION
1 In accordance with the Commission's regulations, the Georgia State official was notified of the proposed issuance of the amendments.
The State official had no comments.
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4.0 ENVIRONMENTAL CONSIDERATION
The amendments change a requirement with respect to the installation or use of facility components located within the restricted area as defined in 10 CFR Part 20 and change surveillance requirements.
The NRC staff has determined that the amendments involve 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 amendments involve no significant hazards consideration, and there has been no public comment on such finding (59 FR 65813 dated December 21,1994). 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.
5.0 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, 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 Contributors:
G. Thomas K. Jabbour Date: July 21,1995
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