ML071770095
| ML071770095 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 05/10/2007 |
| From: | Entergy Operations |
| To: | Office of Nuclear Reactor Regulation |
| Vaidya B, NRR/DORL/LP4, 415-3308 | |
| Shared Package | |
| ML071770088 | List: |
| References | |
| TAC MD3293 | |
| Download: ML071770095 (3) | |
Text
DRAFT Response to Request for Additional Information Related to Proposed Changes to the Analytical Methods Referenced in TS 5.6.5 Question:
With respect to the use of the proposed EXEM BWR-2000 model, please provide:
(1) the detailed explanation why the increase in PCT is beyond 50°F using the proposed EXEM BWR-2000 model. Since the 94°F PCT increase is a significant increase above the 50°F, a more detailed explanation is required;
Response
The change in Peak Clad Temperature (PCT) is the result of the change in methodology as well as more conservative assumptions for two input parameters as stated in Section 4.0 of the RBS License Amendment Request (Reference 1). The input parameters used for both analyses are provided in Tables 1 through 5 of to Reference 1. Processes in place at RBS ensure that the input parameters bound actual plant performance.
The input parameters changed are the number of Automatic Depressurization System (ADS) valves available and the reactor vessel low pressure Emergency Core Cooling System (ECCS) permissive value. Specifically, the new analyses assume operation of only 4 ADS valves; whereas, the current analyses assume operation of 5 ADS valves. The reactor vessel low pressure ECCS permissive was changed from 450 to 350 psia.
The ADS consists of 7 of the 16 Main Steam Safety Relief Valves. The ADS is designed to provide depressurization of the reactor pressure vessel (RPV) during a small break Loss of Coolant Accident (LOCA) if the High Pressure Core Spray (HPCS) fails or is unable to maintain required water level in the RPV. ADS operation reduces the RPV pressure to within the operating pressure range of the low pressure ECCS systems (Low Pressure Core Spray (LPCS) and Low Pressure Coolant Injection (LPCI) systems), so that these systems can provide core cooling. The Technical Specifications require 7 ADS valves to be operable. Assuming that only 4 ADS valves operate is conservative but does not have a significant impact on PCT because the RBS limiting analysis for PCT is a large break LOCA. The RPV depressurization rate during a large break is not significantly affected by whether 4 or 5 ADS valves are assumed to function.
The reactor vessel low pressure permissive signals ensure that, prior to opening the LPCI and LPCS injection valves, the reactor pressure has fallen to a value below these systems' maximum design pressure. The Technical Specifications require the permissive setpoint to be at or above 472 psig. Using a pressure permissive value of less than 472 psig for the analysis is conservative because the ECCS injection is delayed until the reactor vessel pressure falls to the low pressure value.
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DRAFT Both of these changes represent more conservative conditions. As such, the input parameters for the new analyses continue to bound actual plant performance.
With respect to the change in PCT, the impact associated with the operation of one less ADS valve is not significant since the limiting break for RBS is the large break.
Thus, the observed increase in PCT is due primarily to the conservative lower reactor pressure ECCS permissive assumptions.
(2) which parameter such as reactor pressure permissive for operating valves or number of valves available contributes the most increase in PCT of 94 °F due to changing the old EXEM BWR model to EXEM BWR-2000 model in the River Bend LOCA analysis;
Response
As discussed above, the lower reactor pressure permissive signal assumed for the LPCI and LPCS injection valves is the most significant contributor to the increase in PCT.
(3) the results of the calculation based on the same assumptions used for EXEM BWR model
Response
As explained in responses (1) and (2) above, the primary contributor to the increased PCT is the conservative assumption of a lower reactor pressure permissive parameter (from 450 psia to 350 psia). It is expected that without this change to the analysis inputs, the EXEM BWR-2000 methodology would have produced a slightly lower PCT than the current EXEM BWR methodology used. The precise PCT impact for each of the changes has not been quantified because a thorough sensitivity analysis is not practical.
(4) the rationale for not using the lower initial MCPR input value in the EXEM BWR-2000 model
Response
The initial hot assembly MCPR input selected for the new analysis is consistent with the current analysis. The initial MCPR input assumed in the current EXEM BWR analysis was reasonably selected to provide additional margin to the MCPR operating limits and ensure the MCPR associated with the LOCA analyses would remain non-limiting. Since the initial MCPR value of 1.16 remains non-limiting and is conservatively bounding for the current and expected future cycles, the same initial value is used in the EXEM BWR-2000 LOCA analysis.
(5) consistent common assumptions used for the analysis to support APLHGR.
Response
The LOCA analysis to support APLHGR uses the NRC approved EXEM BWR-2000 LOCA methodology and the plant -specific input parameters such as reactor power, core flow, and ECCS parameters. The plant -specific input parameters used in the Formatted: Indent: Left: 0.5" Formatted: Indent: Left: 0.5"
DRAFT LOCA analysis are selected to be bounding for actual plant performance within the RBS licensing basis.
References :
- 1.
Letter RBG-46583, License Amendment Request: Changes to the Analytical Methods Referenced in Technical Specification 5.6.5, Core Operating Limits Report (COLR) dated October 16, 2006