ML20056A006
| ML20056A006 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 07/30/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20056A004 | List: |
| References | |
| NUDOCS 9008030058 | |
| Download: ML20056A006 (6) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 44 TO FACILITY OPERATING LICENSE NO. NPF-47 GULF STATES UTILITIES COMPANY RIVER BEND STATION, UNIT 1 DOCKET NO. 50-458
1.0 INTRODUCTION
By letter dated May 14, 1990, and supplemented June 26, 1990, Gulf States Utilities Company (GSU) (the licensee) requested an amendment to Facility Operating License No. NPF-47 for the River Bend Station, Unit 1.
The proposed amendment would raise the 95'F Limiting Condition for Operation (LCO) on suppression pool temperature to 100'F.
Seasonal high ambient temperatures increase the service water temperature and other heat sources discharged to the suppression pool, This causes the suppression pool temperature to approach the technical specification v
(TS) action limit.
Since the problem is recurrent, the licensee has proposed a permanent TS change to-increase the suppression pool TS LCO limit. The 105'F limit on allowable suppression pool temperature during safety system testing, the suppression pool limit of 110'F, which requires immediate plant shutdown and the 120*F suppression pool limit which requires vessel depressuri-zation remain unchanged.
2.0 EVALUATION The suppression pool temperature LC0 for normal operation currently is 95'F.
This value was chosen by River Bend Station (RBS) based on the maximum expected service water temperature.
The service water system provides cooling to the suppression pool and with service water temperatures near or approaching 95'F, an insufficient differential temperature exists to maintain the suppression pool temperature below the 95'F LCO.
The suppression pool is designed, in the event of a Design Basis Accident (DBA), to absorb the energy released from the Reactor Coolant ~ System (RCS) with the reactor initially at 100 percent power.
The 95*F LCO temperature limit ensures that the suppression pool temperature during and subsequent to a DBA (e.g., Loss of Coolant Accident) would remain suf ficiently subcooled to condense all of the RCS blowdown steam.
The licensee referenced General Electric (GE) document NEDO-31695, "BWR Suppression Pool Temperature Technical Specification Limits," May 1989, as supporting the suppression pool temperature limit incroase.
NEDO-31695 provides a review of the bases and key applications of the current suppression pool temperature limits.
In this document, an updated basis was established which was used by the licensee to justify the proposed changes.
Specifically, the updated basis was used to justify a generic suppression pool temperature LCO of 100*F.
The NRC staff, however, has not yet completed its review of NEDO-31695. Therefore, by letter dated June 11, 1990, the staff requested additional information from 9009030058 900730 PDR ADOCK 05000Q8 l
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By letter dated June 26, 1990, the licensee responded to the staff's request for additional information.
The lia nsea referred to the containment' dynamic loading assessment contained in Appendix 6A of the RBS Updated Safety Analysis Report (USAR) and determined, after further review of the original RBS accident analyses, that the temperatures used for the suppression pool initial conditions were, in all cases, 100'F or greater.
Therefore, the original analyses remain valid.
The proposed change takes operational advantage of the already evaluated 100'F suppression pool temperature.
The events which involve the suppression pool can be divided into two general categories:
safety-relief valve (SRV) discharge to the pool.via the SRV discharge lines and X quenchers, and discharges to the pool via the drywell to wetwell vent pipes during design basis loss of coolant accidents (LOCA).
These are addressed in Section 2.1 and 2.2 below.
Three additional plant specific issues were also addressed and are discussed in Sections 2.3, 2.4 and 2.5.
2.1 LOCA-Related Containment Loads The licensee's USAR for the suppression pool temperature limit for RBS discussed the ranges for operational temperature limits for suppression pool water under LOCA conditions to ensure that containment pressures and temperatures and hydro-dynamic loads under such conditions do not exceed the design values.
The licensee's evaluation concludes that a normal operating suppression pool temperature up to 100*F-for RBS will not affect the design loads since all loads affected by this change (95*F to 100'F) were initially analyzed at 100*F for suppression pool water temperature.
The following paragraphs (a) through (d) summarize these evaluations.
(a) Containment Pressure and Temperature Design Limits The licensee calculated a peak suppression pool temperature of 167.5'F and peak containment pressure of 6.31 psig as a result of a circulation line break.
The design differential pressure and temperature of the containment are 15 psig and 185*F; they provide margins of 138 percent above the peak calculated pressure and about 17.5'F above the peak calculated temperature.
The staff has reviewed the licensee's analysis and found it acceptable in the River Bend SSER 2.
Since the design limits are very high for such containments, there is a large margin between the predicted values under LOCA conditions and the design values that would support a large increase in the normal operational pool temperature.
Therefore, the licensee concludes that an increase in the operational pool temperature limit' to 100'F will not impact the existing analytical results.
(b) Steam Condensation With regard to the ability of the suppression pool to ensure complete steam condensation following a LOCA, the licensee stated in the USAR that a normal operational pool temperature within 185*F would ensure 4
, et,mplete steam condensation.
The staff has previously reviewed the licensee's analysis and found it acceptable as stated in the River Bend SER.
(c) Condensation Oscillation Loads The condensation oscillation (CO) loads are primarily affected by two hydrodynamic parameters, i.e., pool temperature and the enthalpy flux through the downcomer vents.
The staff has previously reviewed GE's pool dynamic load definitions and has arrived at a definitive set of hydrodynamic load definitions that can be used by all Mark III containment applicants for operating licenses. The r6sults of this generic review are documented in NUREG-0978, " Mark III LOCA Related Hydrodynamic Load Definition." They are applicable to RBS.
Based on the above, the RBS bounding hydrodynamic parameter would result in a LCO load that is less than that assumed in the containment load evaluation even with a normal operational pool temperature of 110'F (the shutdown limit).
(d) Chugging Loads.
The licensee's USAR stated that chugging occurs only with small-break LOCAs and relatively low pool temperatures (less than 135'F).
Therefore, the proposed increase in the normal operational pool temperature limit will have no impact on chugging loads.
On the' basis of the information provided in the licensee's USAR, the staff concludes that the LOCA related containment loads resulting from the proposed increase in normal operational pool temperature limit will be within containment design loads, 2.2 SRV Operational Loads The SRV operational loads can be divided into two categories.
The SRV air clearing loads and SRV condensation loads.
(a) SRV Air Clearing Loads The SRV air clearing loads result from the expulsion of air out of the SRV discharge line into the' suppression pool.
These loads are defined in NUREG-0802, "SRV Quencher Loads Evaluation for BWR Mark II and Mark III containments." The expansion and contraction of the air bubble creates an oscillatory load on the containment wall and submerged structures.
The SRV air clearing load will increase with a higher initial pool temperature based on a review of test data (NEDE-210iB P).
however, the staff notes that the Mark III containment program requires that the limiting SRV air clearing load to be considered in containment structural evaluations be determined on the basis of the first actuation of an SRV at the maximum pool temperature permitted by the Mark III plant TS (120'F) with the l
'4-reactor depressurized.
Therefore, the staff concludes that the SRV air clearing load resulting from the proposed increase of normal operational pool temperature from 95'F to 100'F will be bounded by the limiting SRV air clearing load for the River Bend Station, (b)- SRV Steam Condensation Loads l
t The licensee refers to GE Topical Report NE00-30832, " Elimination of Limit on BWR Suppression Pool Temperature for SRV Discharge with Qucncher" submitted to the NRC by the BWR Owner's Group in March 1985.
This report had concluded that the local pool temperature limits for the suppression pool to ensure steam condensation under stable conditions during SRV ster 1 discharge ir.to the pool specified in NUREG-0783, " Suppression Pool Temperature Limits for BWR Containments" dated November 1981, could be eliminated for BWRs that utilize T or X quencher devices.
River Bund Station uses X quencher devices.
GE concluded the above, based on their findings (tabulated in the NEDO-30832 report) that the SRV condensation 1
loads with the above quencher devices were low in comparison with other loads (e.g., SRV air clearing loads) considered in containment s'.ructural j
evaluations. The staff has not yet completed its evaluation of the above report.
Therefore, for this safety evaluation, the staff has used the criteria for local pool temperature limit during SRV steam discharge into the pool that is identified in NUREG-0783 to assess whether the peak local' pool temperature resulting from the proposed initial pool temperature of 100'F will meet the criteria given in the NUREG.
By providing credit for quencher submergence as allowed by the NUREG, the staff reevaluated tha local pool temperature limit for River Bend Station, and concluded that a limit of 209'F is appropriate (River Bend has 13 feet quencher subme.gency; steam flux through quencher perforation is less than 40 lbs.m/f ta.sec,_ when the peak local pool temperature is reached).
The staff determined that the proposed increase of operational 1
pool-temperature by 5*F will not result in a peak pool local temperature higher than the estimated allowable limit of 209*F. Therefore, the staff concludes that there is reasonable assurance that the proposed normal operational pool temperature limit of 100*F will not compromise the ability of the suppression pool to condense steam under stable conditions during SRV. discharge of steam into the pool and, therefore, meets the criteria of NUREG-0783.
Furthermore, the staff notes that the proposed TS changes will not alter the existing requirements for (1) pool cooling whenever the temperature exceeds 100*F, (2) scramming the reactor whenever the pool temperature exceeds 110'F, and (3) depressurizing the reactor whenever
'the pool temperature exceeds 120'F.
2.2 Net Positive Suction Haad (NPSH) for ECCS Pumps RSB was.'equired to assess the impact of increased peak suppression pool temperatura with respect to available NPSH for the ECCS pumps.
At the RBS, the ECCS co'1sists of high pressure core spray (HPCS), low pressure core spray (LPCS) and low pressure coolant injection (LPCI).
At all points in the suction lines for tiese ECCS systems, adequate NPSH is required to preclude local flashing and/or ECCS pump cavitation.
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, Section 6.3.2.2 of the RBS USAR states that the ECCS NPSH calculations are based on a suppression pool temperature greater than 208'F.
The staff reviewed the calculations and their bases documented in Section 6.3.2.2 of the RBS USAR and
= finds them to be acceptable.
Therefore, the suppression pool temperature increase from 95'F to 100'F does not impact the existing NPSH calculations since the calculations were performed using higher pool temperatures and higher temperatures than the maximum containment design temperature of 185'F.
The staff also notes that although the calculations performed by the licensee for the non-ECCS reactor core isolation cooling system (RCIC) were not provided in their May 14, 1990 submittal, the results for the RBS RCIC pump NPSH were stated as exceeding the design value and are, therefore, acceptable.
2.4 ECCS Pump Seal Integrity ECCS pump seal integrity is discussed in Section (2) of the licensee's May 14, 1990, submittal.
The licensee states that an evaluation must be performed to determine the impact of increased suppression pool temperature on the ECCS pump seals.
Previously existing, evaluations of the ECCS pump seals were done for RBS to determine whether or not degradable ECCS pump materials (including the seals) are environmentally qualified to withstand the temperatures which arise from an accident.
The licensee referenced GE documents NEDO-30717, 30718, and 30719 as the evaluations performed by GE for the RBS ECCS pumps environmental qualification.
The staff reviewed these GE NE00 documents and finds that an increased LCO for suppression pool temperature from 95'F to 100*F does not adversely affect the environmental qualification of the ECCS pumps.
The qualification temperatures remain above the expected local temperatures for the ECCS pumps, including the pump seals.
Therefore, the staff concludes that all of the ECCS pump seals are environmentally qualified to withstand temperatures which exceed those arising from the consequences of the proposed TS change.
2.5 Impact on the EPGs or E0ps
-In review of the impact-on Emergency Procedure Guidelines (EPGs) and Emergency Operating Procedures (EOPs) for the RBS, the licensee determined that, although an entry condition of suppression pool temperature, as suggested by GE NEDO-31695, was possible, the RBS has not taken credit for entry into either an EPG or E0P on the suppression pool LCO-proposed to be changed by this TS amendment.-
The staff reviewed the licensee's submittal and their conclusions regarding the potentially affected EPG and E0P entry conditions and agrees with the licensee's determination.
3.0 ENVIRONMENTAL CONSIDERATION
Pursuant to 10 CFR 51.21, 51.32 and 51.35, an environmental assessment and finding of no'significant impact was published in the Federal Register on J"ly 12. 1990 (55 FR 28851).
Accordingly, based upon the environmental assessment, the Commission has determined that issuance of this amendment will not have a significant effect on the quality of the human environment.
4.0 CONCLUSION
The staff has concluded, based on the considerations discussed above, that:
(-) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations, and the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
The staff therefore concludes that the proposed changes are acceptable.
Dated:
July 30, 1990 Principal Contributors:
R. Anand, SPLB T. Rotella, SRXB 1
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