ML20140C975
| ML20140C975 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 04/14/1997 |
| From: | Sorensen J NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-91-18, NUDOCS 9704220027 | |
| Download: ML20140C975 (3) | |
Text
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1 Northern states Power Company 1717 Wakonade Dr. E.
1 Welch, MN 55089 Telephone 612-388-1121 April 14,1997 U S Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 4
PRAIRIE ISLAND NUCLEAR GENERATING PLANT j
Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 i
Resolution of issues Related to 4
Auxiliary Feedwater Pump Discharae Pressure Trio Setpoints 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 1 Auxilisry Feedwater (AFW) pump discharge pressure trips.
In Mcy of 1996, a concern was identified that proper runout protection was not provided for the AFW pumps for all possible ranges of secondary side pipe breaks or cracks. A review of the setpoints for the discharge pressure switches indicated that the AFW pump (s) would not trip until they were operating at pressures below the onset of cavitation. For a specific range of postulated secondary side break or crack sizes the AFW pump discharge pressure could remain above the trip setpoint but below the onset of cavitation, and (without operator intervention) pump damage could occur.
A Generic Letter 91-18 evaluation was performed and it was determined, using the Generic Letter 91-18 guidance for manual operator actions in lieu of automatic actions, that the AFW pumps were operable based on the use of corapensatory actions. Specifically, the control room operators were required to throttle AFW pump discharge motor operated valves to maintain pump discharge pressure above a minimum value determined to prevent runout, procedures were revised accordingly and training was conducted. Based on these actions, a 10 CFR 50.59 evaluation was prepared, which determined that the proposed compensatory actions did not involve an unreviewed safety question, and the pumps were returned to an
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i' operable but degraded status. The Generic Letter 91-18 and 10 CFR 50.59 j
evaluations were reviewed by the NRC Staff and the results of that review are documented in Inspection Report 96-07 dated September 13,1996.
Subsequently, an investigation was performed to develop a means which relies on equipment operation in lieu of operator intervention to provide AFW pump runout protection. It was concluded that increasing the AFW pump low discharge pressure j.
switch setpoint would provide adequate pump runout protection. For secondary side faults (main steam line break or feedwater line break) the increased low discharge pressure setpoints would result in the AFW ptmps tripping to protect against pump j.
runout. As indicated in the Updated Safety Analysis Report (USAR), the operator j
j
.would then restart the AFW pump (s).
I l
Modifications'to improve the runout protection for the Unit 2 AFW pumps were i
completed in March 1997 as described in our March 22,1997 letter. In addition to j
increasing the setpoint for the low discharge pressure pump trips, modifications were performed to separate the time delay circuit for the low discharge pressure and low suction pressure pump trips and a new time delay circuit for the low suction
. pressure trip was added. These changes are consistent with the design basis 1
currently contained in the USAR.
l Recently, Northern States Power Company (NSP) re-evaluated the use of manual operator actions to provide runout protection for the AFW pumps in Unit 1. As a result of this re-evaluation, on April 3,1997 NSP determined that an unreviewed safety question may exist on Unit i until the AFW pump discharge pressure switch j
settings are increased and time delay circuit modifications similar toihose implemented on Unit 2 are installed and tested.
NSP proposes to implement AFW pump runout protection modifications on Unit 1 similar to those performed on Unit 2. These' modifications will be evaluated in j
accordance with the plant modification control process. Like the Unit 2 modifications, NSP will assure that the modification design, installation and testing l
do not involve an unreviewed safety question as defined by 10 CFR 50.59. NSP l
i plans to start physical modifications on Unit 1 the week of April 14,1997. These i
AFWpump discharge pressure trip setpoint modifications are scheduled to be
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completed on Unit 1 by April 30,1997. Upon completion of the modifications the i.
unreviewed safety question relating to AFW pump runout protection will be j
resolved.
t in light of the expeditious implementation of physical changes to resolve the I
. unreviewed safety question, NSP proposes not to submit a license amendment request to address the unreviewed safety question. NSP has been preparing a license amendment request in parallel with the design, procurement and scheduling of the physical modifications. However, NSP believes that once the unreviewed
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safety question is resolved through physical modifications, a license amendment request which addresses this issue would not be necessary, 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, if you have any questions related to this letter, please contact myself or Dale Vincent at 612-388-1121.
Joel P, Sorensen Plant Manager, Prairie Island Nuclear Generating Plant i
c:
Regional Administrator-lli, NRC NRR Project Manager, NRC Senior Resident inspector, NRC State of Minnesota Attn: Kris Sanda J E Silberg i
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