ML20056D752
| ML20056D752 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 08/12/1993 |
| From: | Donnelly P CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-89-10, NUDOCS 9308170435 | |
| Download: ML20056D752 (8) | |
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consumers Patrick M Donnepy Mant Manager hiKMGAN'S PROGRESS Big Rock Pomt Nuclear Plant,10269 US 31 Nonh, Charlevoin, MI 49720 August 12, 1993 Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT - RESPONSE TO A REQUEST FOR ADDITIONAL INFORMATION WITH REGARDS TO A NUCLEAR REGULATORY COMMISSION ASSESSMENT OF THE BIG ROCK POINT'S EMERGENCY CONDENSER AND MAIN STEAM ISOLATION VALVES, DATED JUNE 29, 1993.
Please find attached the response to the Office of Nuclear Reactor Regulation's (NRR) assessment of Big Rock Point's Emergency Condenser and Main Steam Isolation Valves. This assessment was performed as a result of a Region III Inspection conducted on our program developed in response to Generic Letter (GL)'89-10, Safety-Related Motor-0perated Valve Testing and Surveillance.
NRR requested that certain actions be taken to provide additional assurance that these valves will close as required. Of the seven actions required, five have _been reviewed and will be addressed in this response. An additional response within 45 days of the date of this letter will address the remaining actions '. requiring establishing or modifying current operating / emergency operating procedures and position indication.-(The Emergency Operating.
Procedures have recently undergone an extensive rewrite and verification /.
-validation program, and are still in draft form expected to:be issued by the end of August 1993. An informal review of NRR's requirements-in regards to procedures was' performed, and the concerns that NRR has-is expected to be addressed. However, a more formal review is required, and is expected to be completed in 45 days).
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Patrick Donnelly-Patrick M Donnelly
- Plant Manager
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CC: Administrator, Region III, USNRC.
NRC Resident Inspector : Big Rock Point ATTACHMENT 170052
,3 9308170435 930812 e
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ATTACHMENT CONSUMERS POWER COMPANY BIG ROCK POINT PLANT DOCKET 50-155 RESPONSE TO A REQUEST FOR ADDITIONAL INFORMATION WITH REGARDS TO A NUCLEAR REGULATORY COMMISSION ASSESSMENT OF THE BIG ROCK POINT'S EMERGENCY CONDENSER AND MAIN STEAM ISOLATION VALVES, DATED JUNE 29, 1993 4
i August 12, 1993 6 Pages
' ATTACHMENT TO RAI DATED 6/29/93
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, EMER'GENCY CONDENSER INLET ISOLATION VALVES MO 7052 AND MO 7062 EMEB/NRR CONCLUSION EMEB/NRR believes that neither the licensing basis nor NUREG-0737 requires the Big Rock Point licensee to upgrade the EC inlet isolation valves to full safety-related. status. However, EMEB/NRR considers that staff findings regarding Item II.K.3.14 of NUREG-0737 to have~been based on EC inlet isolation valves being capable of isolating an EC tube break. EMEB/NRR believes that, if tested and maintained properly, the EC inlet isolation valves are sized sufficiently to isolate flow in the event of a line break, although the torque switch might trip prematurely and these MOVs might need to be resignaled to close. The staff should request the licensee to perform the following actions to provide assurance that the EC inlet isolation valves are maintained capable of isolating an EC tube break:
(1) raise the torque switches to their maximum allowable setting (without exceeding structural and motor capability limits),.
(2) maintain and test these MOVs to ensure their continued capability (such as through the program established in response to Generic' Letter 89-10, and (3) modify the emergency procedures and position indication, if necessary, to ensure that MOVs closed fully following a break.
LICENSEE'S RESPONSE l
(1) -MD-1052 and MO-7062 have Limitorque type SMA-0 motor operators. The rated' thrust and torque for these operators are as follows:
Torque - 370 ft-lbs Thrust - 18,000 lbs During the 1993 refueling outage, the torque springs on both of these
. actuators were replaced, which now allows the actuators to deliver the maximum torque / thrust allowable.
VOTES diagnostic testing was also performed to verify the thrust output of these actuators under static conditions. ~The maximum thrust measured during this testing is as follows:
- M0-7052 - 17,030 lbs M0-7062 = 17,461 lbs.
Due.to torque switch repeatability and VOTES system inaccuracies,_these thrust values actually exceed the rated thrust-(but ~are within the 10%
range allowed by Limitorque) and therefore.are the maximum settings for-M0-7052 and MO-7062.
Additionally, the evaluation provides a calculation,; based on the valve factor methodology, of the minimum thrust.and torque required to close-the valve with a maximum differential pressure of 1445 psid. The calculation utilizes an assumed valve factor equal to 0.3.
This valve factor is based on Limitorque's recommended valve factor for flexible -
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wedge gate valves.
Industry testing of valve closure under blowdown conditions has indicated a 0.3 valve factor may not be conservative for blowdown valve closure and that actual valve factors are probably in the range of 0.4 to 0.6.
However, a valve factor of 0.3 is used since the postulated break of a 5/8 inch o.d., 0.058 inch thick condenser tube with a line pressure of 1445 psig is not indicative of. the blowdown conditions (6 inch line size) during industry testing.
t The calculation shows the thrust required to close the valve is 13013 lbs and the equivalent torque required to close the-valve is 258 ft-lbs (assuming a stem factor based on a conservative coefficient of friction of 0.20). Comparison of the required thrust and torque to close the valve with the output torque and thrust at maximum torque switch setting of 3-I/2 shows the operator can deliver sufficient torque and thrust at torque switch trip to close the valve.
(2) BRP will maintain and test the EC inlet valves M0-7052 and MO-7062 to provide assurance of continued operability. The valves are included in the BRP ASME Section XI IWP and IWV testing program.. The valves are stroke time tested for both the open and closed direction on a quarterly frequency and have their remote position indication verified every reactor refueling for operability verification in accordance with the requirements of ASME Section XI.
The valves are included in the BRP Preventative Maintenance (PM) program which provides for regularly scheduled maintenance / overhaul.
Additionally, the valves are subject to post maintenance testing and acceptance testing for operability verification prior to return to service which includes stroke time testing, motor rotation checks, continuity checks, motor current measurement, remote position indication testing and VOTES static testing subject to the maintenance activity performed.
NOTE: The valve actuator for M0-7062 was overhauled in early 1992'and had preventive maintenance performed in the current 1993 outage.
The valve actuator for M0-7052 was overhauled in the current 1993 refueling outage.
Post maintenance testing, including V0TES diagnostic testing, was also performed on both of these MOVs during this outage.
BRP considers the inclusion of EC inlet valves M0-7052 and M0-7062 in the existing preventative maintenance, post maintenance testing / acceptance testing, and ASME Section XI IWP and IWV testing programs as adequate for providing assurance of continued operability of the valves.
(3) The emergency procedures and position indication modifications will be evaluated in an additional response made within 45 days of the date of i
L this letter.
MAIN STEAM ISOLATION VALVE (MSIV) MO 7050 l
EMEB/NRR CONCLUSION i
EMEB/NRR concludes that the accident scenarios analyzed in the Big Rock Point FHSR require as part of the plant's licensing basis that the MSIV be.able to close against low differential pressure. The FHSR does not include small steam-line break scenarios which might result in the need for the MSIV to l
. ATTACHMENT TO RAI DATED 6/29/93 3
close against high differential pressure. EMEB/NRR considers the MSIV to not be capable of closing against its original design-basis differential pressure
-specification (1500 psid) that might credibly occur during a small steam-line break or plant transient when the valve might receive an automatic or manual signal to close. The staff would need to justify any modification to upgrade the MSIV as a backfit because the licensing basis for the MSIV does not include high differential pressure conditions. In lieu of processing a backfit analysis, EMEB/NRR recommends that the licensee be requested:
(1) to verify the calculational assumptions, (2) to set the torque switch to the maximum allowable setting (without exceeding structural of motor capability limits),
(3) to establish operator procedures to prevent premature attempts to close the valve prior to differential pressure being within that capability of the MSIV, and (4) to ensure that the plant Technical Specifications do not require the MSIV l
to close either automatically or manually under conditions which the MSIV is not capable of operating.
EMEB/NRR considers that these minimal cost actions would provide an acceptable level of confidence that the MSIV could close against high differential pressure and reduce the risk associated with a small steam-line break or other l
plant transients. If the licensee took these actions, EMEB/NRR believes that a modification to upgrade the MSIV would not be necessary if evaluated as part of a backfit cost-benefit analysis.
LICENSEE'S RESPONSE (1) For verification of the torque / thrust calculation assumptions, in-situ testing at design basis differential pressure and flow conditions would provide the best possible data.
In-situ testing of M0-7050, is not practicable given the existing plant configuration, and since Generic Letter 89-10 states that testing MOVs at design-basis conditions is not recommended where such testing is precluded by the existing plant configuration, no in-situ design-basis testing of M0-7050 will be performed at BRP. The conservative assumptions in the BRP Torque / Thrust Calculation include a 0.5 valve factor for closing used.in calculating the differential pressure load, a rate of loading factor of 10% used to account for reduced operator output thrust under differential pressure loading versus under static conditions, and a stem factor based on a coefficient of friction of 0.20.
Since M0-7050 will not be design-basis tested, BRP is evaluating M0-7050 using the "2 phase" approach as permitted by Generic Letter 89-10. The first phase is a conservative calculation methodology for predicting required MOV thrust and torque and performance of diagnostic testing under static conditions to set-up the valve's control switches. The second phase consists of a comparative analysis of the best available information which supports verification of MOV operability.
BRP will use this second phase for verification of calculational assumptions. The best available information from design-basis testing of similar valves in the industry, for any future information available through the MOV Users
ATTACHMENT TO RAI DATED 6/29/93 4
Group (MUG), and from the EPRI Performance Prediction Program when published will be used in verifying calculational assumptions and for verifying MO-7050 is capable of performing its design-basis function to close.
(2) M0-7050 has a Limitorque type SMA-2 motor operator. The rated thrust and torque for this operator are as follows:
Torque - 1,500 ft-lbs Thrust = 60,000 lbs During the 1991/92 refueling outage, M0-7050 was diagnostically tested using the VOTES system. The maximum thrust measured during this testing (adjusted for Liberty Technologies' 10CFR21 notification), was 55,807 lbs. Accounting for system inaccuracies and torque switch repeatability, this value could go as high as 61,611 lbs. Although this value is higher than the thrust rating, it is within the 10% band allowed by Limitorque for inertial thrust. Thus, M0-7050's torque switch is set to the maximum setting.
An evaluation of the acceptability of this torque switch setting shows the operator thrust output at torque switch trip is sufficient to close i
the valve under design-basis conditions, and shows that the installed springpack prevents potential overtorquing of the operator.
(3) The operating procedures will be evaluated in an additional response made 45 days from the date of this letter.
(4) Big Rock Point Technical Specifications do not contain any specific reference requiring the MSIV to close automatically or manually under conditions the MSIV is not capable of operating.
BRP Technical Specifications were reviewed and the following sections either j
specifically mention M0-7050 or contain requirements applicable to MO-7050:
j 3.4.3.c Specifies the closing time for M0-7050 for containment sphere penetration isolation to be 60 seconds.
3.7 Specifies that M0-7050 is to be leak tested at each reactor shutdown for refueling.
3/4.7.1.3 Provides requirements for Alternate Shutdown System equipment to be operable during power operation.
Included in this equipment is a control switch for MD-7050 located at M0-7050 Motor Starter.
9.0 Provides requirements for Inservice Inspection and Testing of ASME Code Class 1, 2 and 3 components, Inservice Testing applies to M0-7050 to meet the requirements for operability l
verification in accordance with ASME Section XI, IWV.
6.1.2 Applies to operation of components in the Reactor Safety System during power operation. Three of the sensors listed directly affect M0-7050 when the sensor's associated trip device trips at its SCRAM setting and generates signals to close the
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containment sphere isolation valves, thus signaling M0-7050 to close.
Sensor and Coincidence SCRAM Trio Device "'
In Each Channel Settino Low Reactor 1 out of 2 2 2'9" Above l
Water Level Top of Active Fuel (4 level switches)
High Enclosure 1 out of 2 s 1.0 psi above Pressure (4 atmospheric pressure switches)
Loss of Auxiliary 1 out of 1 52120 volts Power Supply (voltage relay)
(1) For a postulated small steam line break downstream of M0-7050, a reactor scram as a result of low steam drum level (-8 inches below centerline) or a manual scram as a result of an observed steam flow / feed flow mismatch, would occur prior to reaching the Low Reactor Water Level trip point. For these conditions, M0-7050 would not be called upon to close. Since the postulated line break is expected to be outside containment, the High Enclosure Pressure setpoint will not be challenged either. Additionally, a postulated small steam line break and a concurrent Loss of Auxilliary Power is beyond the licensing basis of Big Rock Point, and should not be considered credible for automatically closing M0-7050 against a high differential pressure.
l In addition, a review of six FHSR Chapter 15 Transients was performed to determine the impact of automatic or manual operation of the MSIV as specified -
in the Technical Specifications:
1.
Decrease in Feedwater Temperature The MSIV is not important to this event. The MSIV could be used as a recovery action if the bypass valve fails open. With a stuck open bypass valve at the start of the transient the dp across the MSIV would be less than 200 psi.
2.
Increase in Feedwater Flow There is no reason for the MSIV to~ close for this transient. The transient was evaluated for both an open and closed turbine bypass valve, which is equivalent to an open or closed MSIV. The change in MCPR was the same for both cases because the bypass valve did not begin to open until after the minimum CPR occurred.
3.
Increase in Steam Flow The MSIV is not important in the IPR (initial pressure regulator) event.
The MSIV could be used as a recovery action in this sequence when the dp i s ' l ow.
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ATTACHMENT TO RAI DATED 6/29/93 6
4.
Turbine Trio Without Bvoass The MSIV has no impact on this event. Turbine trip without bypass bounds a turbine trip with MSIV closure since the bypass valve is a faster acting valve, hence the greater the negative reactivity.
5.
Loss of AC Power
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The MSIV has no impact on thi.s event. The MSIV will receive a close signal when offsite power fails; however, valve performance has no affect on the transient since the bypass valve and stop valve are assumed closed.
6.
Loss of Coolant Accident
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The MSIV receives a close signal upon a loss of off-site power (Appendix K). At the time of valve closure reactor pressure will have lowered to less than 200 lbs for the.375 ft2 break. Failure of the bypass valve in
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the open position would have little impact on this analysis.
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