ML20195E635
| ML20195E635 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 06/07/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20195E640 | List: |
| References | |
| NUDOCS 9906140029 | |
| Download: ML20195E635 (1) | |
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. Although increasing the setpoint may increase the likelihood of a reactor trip on steam generator level, the licensee does not expect the setpoint to be approached during normal plant operation and has stated that an unexpected plant event would be needed to cause the setpoint to be reached. Additionally, the licensee has adjusted the pretrip alarm in the control room to provide the operators with the same advanced notice of a steam generator low level conditioil.
The staff finds the proposed changes acceptable.
FSAR Chapter 10
- The Ncensee has modified FSAR Chapter 10. The modifications include a reference to a new best estimate of LONF analysis. The licensee has stated that the revised analysis now credits the atmospheric dump valves (ADVs) in lieu of the main steam safety valves to remove heat from the generator. Crediting the ADVs results in increased flow to the steam generators because the ADVs can be opened at lower pressure and the AFW system delivers more water to the steam generators at reduced pressure. The staff has determined that crediting the ADVs for the FSAR Chapter 10 analysis is acceptable. With the credit for the ADVs the licensee has stated that the loss of feedwater design basis continues to be met. As a result, the staff finds the proposed changes to be acceptable.
FSAR Chapter 14 The licensee has performed a reanalysis of the FSAR Chapter 14 LONF transient analysis.
The analysis was performed at the new setpoints and reduced AFW, and shows acceptable results.' In addition to the changes to the flow and setpoints, the licensee has made a number of other changes to the transient analysis. The analysis shows that for the most limiting LONF cases analyzed, assuming a single failure, the steam generators do not empty, the pressurizer does not go water solid, and the steam generators do not exceed 110% of the design pressure.
The licensee has stated that another decrease in heat removal from the secondary system event, the loss of electric load or turbine trip event, continues to be more limiting from both the standpoint of minimum departure from nucleate boiling ratio (DNBR) and from a peak reactor coolant system (RCS) standpoint. As a result, these aspects of the LONF event do not need to be evaluated.
In the performance of the new analysis, the licensee has used a different NRC-approved evaluation model. The methodology is contained in the repo;t ANF-89-151(P)(A) ANF-RELAP METHODOLOGY FOR PRESSURIZED WATER REACTORS: ANALYSIS OF NON-LOCA CHAPTER 15 EVENTS, and was approved by the staff in March of 1992. The methodology is appropriate for evaluating the LONF event. The licensee has analyzed five different cases to determine to most limiting conditions. The cases analyzed were chosen to maximize pressurizer water level and minimum steam generator water level and considered different combinations of the limiting single failures and the availability of offsite power. The limiting single failure was either a motor driven or turbina driven AFW pump. The analysis now credits automatic initiation of the motor driven pump and conservatively assumes a minimum total AFW l
flow that includes instrument uncertainties and a 5 percent pump degradation. The initial conditions were also biased to maximize pressurizer water level and minimize steam generator water level. The initial steam generator and reactivity feedback values were conservatively selected in accordance with the approved topical report. The licensee also considered both the availability and unavailability of the normal plant controls and offsite power to be assured the limiting event was considered.
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