ML20063E832
| ML20063E832 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 02/04/1994 |
| From: | Richard Anderson NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-89-10, NUDOCS 9402100269 | |
| Download: ML20063E832 (5) | |
Text
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Northem States Power Company 414 Nicollet Mall Minneapolis. Minnesota 55401-1927 Telephone (612) 330-5500 February 4, 1994 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 Response to Generic Letter 89-10 Inspection Followup Items NRC Inspection Report Fos. 50-282/93012(DRS) and 50-306/93012(DRS)
Motor-operated Valve (MOV) Testina and Surveillance T
This letter refers to the Generic Letter 89-10 motor operated valve inspection conducted Septen6er 27 through November 15, 1993.
Your letter of December 2, 1993, which transmitted Inspection Report No. 50-282/93012(DRS) and 50-306/93012(DRS), required a response to the Notice of Violation. That response i
was submitted on January 14, 1994.
Your letter also requested that we respond to each of the 3 inspection followup items; our response is given below. We concur'that management attention is essential to strengthen our program in the y
areas of test control and technical evaluation; increased management attention is being exercised.
j In this letter we have made new NRC commitments which are identified as such as the statements which are in italics.
1 Inspection Followup Item 1
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1 The licensee became aware of a manufacturer's technical bulletin, which stated that motor brakes may not release at less than.90% of nameplate-vcitage.
Since degraded motor terminal voltage for most MOV's was
.l calculated to be between 80% and 88% of nameplate, a thorough assessment of the potential effect on MOV operability was appropriate. To address this issue, the licensee performed limited bench testing of three motors and closed the issue without contacting the manufacturer or addressing the j
applicability of the test results to the remaining 34 MOV's with motor brakes.
In response to the inspectors # concerns, the licensee contacted the manufacturer and other utilities and prepared a more complete
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corrective action plan and operability assessment.
The planned actions to j
resolve the motor brake issue and modifications to remove all motor brakes will be evaluated in a future inspection as an inspection followup item i
(50-282/93012-01; 50-306/93012-01(DRS)).
t 9402100269 940204
{DR ADOCK 05000282 PDR f
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Northem States Power. Company
' February 4, 1994 Page 2 b
Response
BACKGROUND In response to an August 26, 1993 INPO operating experience report on motor q
brakes, conversations were held with various utilities, and 3 motor brakes available in our warehouse were tested to determine their pickup and dropout voltages. The 3 tests indicated that the brakes operated at voltages well below any expected reduced voltage value.
It was decided that additional brake testing would be done as motor brakes became available, but based on testing to this point, no immediate operational problem was evident. As a result of the inspectors' concerns, we proceeded with additional research into
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the motor brake concern.
CORRECTIVE ACTIONS Testing of motor brakes continued as they became available. To date, 10 tests of motor brakes have been conducted. All 5 models of motor brakes installed at Prairie Island have been tested.
All the tests indicate proper motor brake operation below expected reduced voltage values,' including instrument uncertainties.
l A plant modification to remove motor brakes is in progress. Several motor t
brakes have already been removed, and at this writing 14 MOV's still have motor brakes installed. Motor brakes will be removed from the remaining MOV's at the next refueling outages, Unit 1 scheduled for May 1994, and Unit 2 scheduled for Spring 1995.
SUHMARY Based on testing to date, all remaining motor operated valves with brakes are considered operable. We will continue to remove all remaining motor brakes to improve reliability.
We will continue to monitor industry information concerning motor brakes.
Inspection Followup Item 2 The preliminary assessment of Limitorque's May 13, 1993, Part 21 report regarding high ambient temperature effects on MOV motor output torque assumed that there would be no net loss of torque and assigned a date of
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March 1994 for completion.
The licensee assumed that torque output losses due to high temperature would be offset by gains due to Limitorque's allowance to use an application factor of 1.0 in certain instances instead i
of the'O.9 originally used.
This assumption was questioned by the
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inspectors and found to be invalid.
In response to the inspectors' concerns, the licensee performed calculations for some'of the most affected MOV's and showed that the worst case torque reduction would;be 4
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""Y USNRC February 4, 1994 Page 3 4.7%.
These MOV's were shown to have sufficient margin to compensate for the loss in torque; however, a more thorough initial review should'have been done to preclude operability concerns. The licensee will. request additional information from Limitorque in order to evaluate some MOV motors and detailed calculations will be performed for each MOV affected.
by the Part 21.
This is considered an inspection followup item that will be evaluated in a future inspection (50-282/93012-02; 50-306/93012-02(DRS)).
Epsoonse A review of MOV's for which we have data has been completed.
Six MOV's still need review upon receipt of motor curve and torque derate data from Limitorque. The results indicate that all the MOV's reviewed retain sufficient margin to compensate for the torque capability changes arising from the Part 21 report. Results of the review are summarized below.
1) 104 of 110 MOV's which have had their torque switches set diagnostically-with either VOTES or MOVATS have been verified to have sufficient margin to compensate for the torque capability changes.
H The 6 remaining MOV's were not addressed in the Part 21 report.
Limitorque was contacted by letter dated 10/15/93, and numerous followup calls, requesting motor curve and torque derate data.
To date'this data j
has not been received.
Upon receipt of the requested motor data from Limitorque, the remaining 6 MOV's shall be reviewed.
Based on current margins, no operability concerns are expected.
- 2) Of the remaining Generic Letter 89-10 MOV's:
1 Six of the MOV's (not the same six as in 1 above) are not motor stall limited, and remain as such after application of the Part 21 report. The Part 21 report has no impact on these valves.
The remaining MOVS are non-environmentally qualified and therefore have a l
maximum temperature of 130 degrees F when required to operate during an accident. The resulting torque capability increase due to Limitorque's allowance to use an application factor of 1.0 instead of 0.9 more than offsets'any torque loss at this temperature. Torque capability increases for these MOV's as a result ofEthe Part 21 report.
The results of this Part 21 review of MOV's will be' incorporated into'the next revision of the Site Engineering Manual MOV target thrust calculations (ENG-ME-046).
The complete implementatior of this revision will be ccnpleted 30 j
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Nodhem States Power Company USNRd
' February 4, 1994 Page 4 1
days after receipt of the remaining motor data from Limitorque.
Inspection Followuo Item 3 The licensee evaluated the susceptibility of 122 gate valves to pressure locking and thermal binding.
The evaluation disclosed that 12 valves were susceptible to pressure locking and 8 valves were susceptible to thermal binding. The licensee responded to these problems as follows:
Two valves on each unit (RHR to vessel injection) considered susceptible to both pressure locking and thermal binding were changed from normally closed to normally open, thereby avoiding the problem. The licensee j
indicated that PRA evaluations confirmed the actions to be appropriate.
Four valves on each unit (RHR to SI and RHR to CSP) considered susceptible to pressure locking were not modified.
The licensee reviewed MOV capability and indicated that the valves could open against i
maximum bonnet pressure with a 100% margin of safety.
Two valves on each unit (FW to SC isolation). susceptible to thermal J
binding, were modified by changing to an SB-3 actuator with compensating spring pack, which the licensee feels will ameliorate the effects of inertia on closing I
Ten MOV's (RHR to loop B, Loop A hotleg RHR suction, and loop B hotleg RHR suction) are potentially susceptible to pressure locking during normal
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shutdown to cold shutdown. The licensee indicated that cooldown and j
depressurization rates are slow enough so that bonnet depressurization occurs before the valves are needed.
The inspectors recommended that the evaluation be reconsidered, because valve seats which are designed to be leak-tight should not ba relied upon to leak at a prescribed rate.
The inspectors noted that eight sump B MOV's were classified as not susceptible to either pressure locking or thermal binding.
However, the licensee was provided with two scenarios by which the inspectors felt the valves might be susceptl.ble to pressure locking.
The licensee had not considered these scenarios but committed to review them and to take appropriate action. The licensee's actions regarding pressure locking is considered to be an inspection followup item that will be evaluated in a future inspection (50-282/93012-04; 50-306/93012-04(DRS)).
Response
Re-evaluations of the 18 valves listed in the preceding two paragraphs were made, and Safety Evaluation #373 was produced. The conclusion of the Safety j
Evaluation is that the 18 valves are operable. Modifications to the Sump B to RHR suction valves will be made to provide increased assurance of long term I
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l Nodhem States Power Company February 4, 1994 Page 5 operability. The schedule for modifications is not yet defined due to uncertainties in parts availability.
Please contact Jack Leveille (612-388-1121, Ext. 4662)'if you have any questions related to this letter.
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Roger O Anderson Director Licensing and Management' Issues c: Regional Administrator - Region III, NRC Senior Resident Inspector, NRC NRR Project Manager, NRC J E Silberg i
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