ML20137F270
| ML20137F270 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 03/22/1997 |
| From: | Sorensen J NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9704010041 | |
| Download: ML20137F270 (4) | |
Text
N Northern States Power Company Prairic Island Nuclear Generating Plant 1
1717 Wakonade Dr. East Welch. Minnesota 55089 l
March 22,1997 U S Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Resolution of issues Related to Auxiliary Feedwater Pump Discharae Pressure Trio Setooints The purpose of this letter is to provide, for the information of the NRC Staff, a summary of the actions being taken to resolve the issues related to the setpoints for the Prairie Island Unit 2 auxiliary feedwater (AFW) pump discharge pressure trips.
Prior to Prairie Island Unit 2 leaving MODE 4 the following actions, related to the 21 motor-driven and 22 turbine-driven AFW pump control circuit modifications, will be completed:
21 Motor-Driven AFW Pump The setpoint for the 21 motor-driven AFW pump discharge pressure switch setpoint will be changed to 800 psig. This action was completed on March 20,1997.
The low suction pressure trip circuit will be separated from the low discharge i
pressure trip circuit by installing a second time delay relay. The 4 in Hg low suction pressure trip time delay relay will not be changed. The low discharge pressure trip time delay relay will be set to an appropriate value. Preoperational testing will then be performed to verify the installation. The Modification Process will ensure the proper design documentation, procedures and training are in place prior to turnover to operations and declaration of 21 motor-driven /FW pump to be operable.
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< USNRC NORTHERN STATES POWER COMPANY March 22,1997 Page 2 22 Turbine-Driven AFW Pump e
The setpoint for the 22 turbine-driven AFW pump low discharge pressure switch setpoint will be changed to 800 psig. This action was completed on March 20, 1997.
The low suction pressure trip circuit for the 22 turbine-driven AFW pump will not be separated from the low discharge pressure trip circuit prior to Unit 2 leaving MODE
- 4. The 4 in Hg low suction pressure trip and the low discharge pressure trip time delay relay will not be changed. The 22 turbine-driven AFW pump, in this configuration, will be operable for MODE 3 operation.
The above actions are currently scheduled for completion on March 23,1997.
Following their completion, the MODE 4 hold on Unit 2 will be released and the unit will be taken to MODE 3 for completion of the remaining 22 turbine-driven AFW pump testing and control circuit modifications.
This mode change is acceptable because with the new setpoints for the pump discharge pressure switches in place, the Auxiliary Feedwater System is capable of mitigating all accident and abnormal events as described in the Safety Analysis with the exception of the complete loss of feedwater ATWS. With respect to the mitigation of the complete loss of feedwater ATWS event, the auxiliary feedwater system is not required for mitigation of an ATWS in MODE 3 because the reactor is not allowed to be critical in that mode. The new setpoints for the pump discharge pressure switches are consistent with those previously reviewed and approved by the NRC. As described in the USAR, the pump discharge pressure switches will trip the pumps to protect them from potential damage due to runout and the operator will then take action to restart the pump (s). All of these functions can be satisfied by the configuration of the auxiliary feedwater system following the modifications described above.
Once in MODE 3, the following actions related to the 22 turbine-driven AFW pump testing and control circuit modifications will be completed:
When the appropriate plant conditions are achieved, the plant heatup will be suspended, and 22 turbine-driven AFW pump will be run to gather data that is necessary for setting the discharge pressure switch time delay. The 22 turbine-driven pump will be inoperable during this testing. Following completion of the testing, the pump will be returned to operable and the piant heatup to 547 F will be completed.
Upon completion of the plant heatup,22 turbine-driven AFW pump will be removed from service for completion of the control circuit modifications and testing. The low suction pressure trip circuit will be separated from the low discharge pressure trip I
'a USNRC NORTHERN STATES POWER COMPANY Niarch 22,1997 Page 3 circuit by installing a second time delay relay. The 4 in Hg low suction pressure trip time delay relay will not be changed. The low discharge pressure trip time delay relay will be set to an appropriate value. The setpoint will be based on data obtained from the pump runs conducted during the plant heatup.
The 22 turbine-driven AFW pump low discharge pressure trip circuitry will be modified to incorporate monitoring of reactor trip breaker position and pump control selector switch position to ensure the pump does not trip during an ATWS condition.
Preoperational testing will then be performed to verify the installation.
The modification process will ensure the proper design documentation, procedures and training are in place prior to turnover to operations and declaration of the pump to be operable. The modifications to the 22 turbine-driven pump are currently scheduled for completion on March 25,1997.
The modifications to the Prairie Island Unit 2 auxiliary feedwater system described above will not be performed until it has been determined that the modifications do not involve an unreviewed safety question as defined by 10 CFR 50.50.
A portion of the modifications to the 22 turbine-driven AFW pump to be performed in MODE 3 are inten: led to ensure that the ATWS mitigating system actuating circuitry (AMSAC) system will perform its intended safety function as described in the plant USAR. The AMSAC system is only required for mitigation of an ATWS event at power levels greater than 40% power. Below 40% power, operator manual action is utilized to mitigate the effects of an ATWS. The current configuration of the auxiliary feedwater i
system is adequate to support manual mitigation of an ATWS event at less than 40%
power. In addition, the planned modifications to the auxiliary feedwater system control circuitry will not impact the operators ability to manua!!y operate the auxiliary feedwater system to mitigate an ATWS at less than 40% power. Therefore, the auxiliary feedwater pumps can be considered operable up to 40% power. Even though the auxiliary feedwater system, with the new low discharge pressure setpoints in place, can be considered operable up to 40% power, Prairie Island Unit 2 will not be taken to MODE 2 until all of the modifications and testing described above are complete.
In addition to the actions described above, an evaluation is being performed to determine if the response of the Unit 1 and 2 auxiliary feedwater systems, in their current configuration, to a complete loss of feedwater ATWS is in accordance with the Prairie Island current licensing basis.
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USNRC NORTHERN STATES POWER COMPANY March 22,1997 Page 4 l
In this letter we have made new Nuclear Regulatory Commission commitments, identified above in italics. NSP will inform the NRC Staff of any changes to the planned actions described in this letter. Please contact Gene Eckholt (612-388-1121) if you have any questions related to this letter.
Joel P Sorensen Plant Manager Prairie Island Nuclear Generating Plant 4
c: Regional Administrator - Region lil, NRC Senior Resident inspector, NRC NRR Project Manager, NRC J E Silberg 1