ML20077F386
| ML20077F386 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 07/21/1983 |
| From: | Jackie Cook CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.K.3.05, TASK-TM 24080, GL-83-10E, NUDOCS 8308010354 | |
| Download: ML20077F386 (9) | |
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o Consumers Power Company General Offices: 1945 West Parnait Road, Jackson, MI 49201 e (517) 788-Od50 July 21, 1983 Mr Darrell G Eisenhut, Director Division of Licensing United States Nuclear Regulatory Coannission Washington, DC 20555 MIDLAND ENERGY CENTER PROJECT -
RESOLUTION OF ACTION ITEM II.K.3.5
" AUTOMATIC TRIP OF REACTOR COOLANT PUMPS" GENERIC LETTER 83-10e -
FILE 0926.2 SERIAL 24080 Attached is Consumers Power Company's response to your letter of February 8, 1983 concerning TMI Action Item II.K.3.5, " Automatic Trip of Reactor Coolant Pumps." As a member of the B&W Owners Group (BWOG) we will be participating in a generic subiaittal to resolve this issue.
The attached plan and schedule is submitted in accordance with 10 CFR 50.54(f).
W Y JWC/JRW/mfm CC RJCook, Midland Resident Inspector JGKeppler, Administrator, NRC Region III 8300010354 830721 PDR ADOCK 05000329 k
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Plan for Resolution of TMI Action Item II.K.3.5 l
" Automatic Trip of Reactor Coolant Pumps" i
INTRODUCTION The criteria for resolution of NUREG-0737, Item II.K.3.5, " Automatic Trip of I
Reactor Coolant Pumps", are provided in letters from D G Eisenhut (NRC) to all 4
applicants and licensees with B&W designed Nuclear Steam Supply Systems (83-10 e and f), dated February 8, 1983. The B&W Owners Group has been i
formulating a plan to demonstrate' compliance with those criteria. The following represents this overall position and plan.
' PLAN FOR' TREATMENT q RC PUMP OPERATION' The treatment of reactor coolant pumps during accidents and transients has received extensive attention over the past several years. The B&W'O'ners w
Group has performed. analyses evaluating the effect ofLa delayed RC pump trip _
using Appendix;Kl assumptions during the course of a-small break LOCA1 accident and-has determined that an early trip'of RC pumpsLis_ required to show i
i conformance tci 10 CFR 50.46 for.a range.of break sizes. Therefore, to be
-consistent with~the conservative analyses performed, fit is our. position that' 7
the-reactor coolant pumps should be. tripped if indications.of a small break
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LOCA exist.
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2 The B&W Owners Group and B&W maintain that it is highly desirable to maintain RC pump operation during non-LOCA events, as an aid in the mitigation of the transient. Consistent with this philosophy, the concept of subcooling margin was chosen as an indicator for the need to trip RC pumps in 177FA plants.
It is our intention to demonstrate that this concept is consistent with our philosophy for handling RC pumps during transient conditions and complies with the intent of the criteria stated in Generic Letter 83-10.
The symptom approach of subcooling margin, developed as part of the Abnormal Transient Operating Guidelines Program, is intended to replace the present guidelines of tripping solely on the presence of a low RC pressure ESFAS signal.
It is the position of the B&W Owners Group and B&W that reactor coolant pump trip can be achieved safely and reliably by the operator.
It has been determined that a loss of subcooling margin will occur for those SBLOCAs where a pump trip is required to show compliance with 10 CFR 50.46.
The B&W Owners Group will undertake a program based on the above position to demonstrate that the concept of subcooling margin is an appropriate indicator of the need to trip RC pumps, yet still allows continued RCP operation for SGTRs less than or equal to a double ended rupture. The concept of subcooling margin will be examined for the more likely non-LOCA transients to demonstrate that under realistic conditions an indication requiring RC pump trip is unlikely.
This program is also intended to provide the required justification for manual RCP trip on indication of loss of subcooling margin. Tripping on loss of subcooling margin will assure pump trip prior to the development of significant system voids. No attempt will be made to demonstrate oc0783-5060b112 L
3 acceptability of continued RCP operation during small break conditions. No request for an exemption of 10 CFR 50.46 will be made to allow continued RCP operation during SBLOCA.
The specific plan for resolution of the RC pump trip issue is structured to address the specific criteria stated in Generic Letter 83-10.
A description of the plan, related to the criteria with which it is intended to comply, follows:
I.
Pump Operation Criteria Phich can Result in RCP Trip During Transients and Accidents 1.
Setpoints for hCP Trip:
The RCP trip criteria, based on loss of subcooling margin, was a.
developed with the intent of assuring that an indication for RC pump trip would occur for those SBLOCAs where pump trip was required to meet the criteria of 10 CFR 50.46. A spectrum of analyses has been performed using Appendix K assumptions which demonstrate that a loss of subcooling will-always occur for small breaks that have the potential to uncover the core and violate 10 CFR 50.46 criteria if.the RCPs are tripped under certain two--
phase conditions. Therefore, it is our position that loss of subcooling can be used_ as - an indicator of the need for RCP trip.
The actual value of the setpoint will be determined to ensure that-this-indicator will allow continued forced RCS flow during realistic SGTRs up to.and including the design basis SGTR - a
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single double ended rupture. The setpoint will also be oc0783-5060b112
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4 determined to include consideration for minimizing the indication for need to trip RC pumps for more likely non-LOCA events such as a mild overcooling transient due to excessive steam flow.
b.
No partial or staggered RCP trip schemes will be considered except for the extreme case where mechanical damage to the pump is likely as this adds to increased decision making on the part of the operator during transient conditions.
c.
The RCP trip criteria based on subcooling margin precludes operation of the RC pumps in a highly voided system.
d.
A primary objective of the parameter and setpoint selection is the avoidance of reactor coolant pump trip for non-LOCA events particularly SGTR. Realistic operator actions in accordance with the ATOG procedures are expected to avoid loss of subcooling and-the need to trip the reactor coolant pumps for the STGR event.
Furthermore, since subcooling margin would be quickly regained following makeup or HPI initiation, without loss of natural circulation even if the operator failed to take actions to prevent RCP tripping and ESFAS actuation, restart of the pumps would be allowed. Consequently, reliance on the PORV for depressurization is unlikely.
e.
The significance of primary system voiding due to flashing of bct coolant is discussed as part of operator training. The subject
,of~ void treatment.in the Abnormal Transient' Operating Guidelines ~
(ATOG) is.being supplemented by additional-guidance on.
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j prevention, det ection, and mitigation of voids. This is considered to be a post Emergency Operating Procedure s
implementation issue.
f.
Actions following containment isolation signals will be reviewed to ensurc consistency in the treatment of availability of cooling water and seal injection to prevent pump damage.
Instructions for pump trip are provided in the ATOG guidelines in the event of I
likely niechanical pump damage.
Criteria for restart of RC pumps include assuring that cooling water and seal injection are available.
g.
Instructions for maintaining or reinitiating forced RC flow are contained in ATOG for ICC conditions.
2.
Guidance for Justification of Manual RCP Trip s
f a.
A spectrum of small break LOCAs has been analyzed for 177 FA li plant type using the CRAFT 2 code. Using the Appendix K l
evaluation techniques, there-exits a combination of break sizes and RC pump trip times which result in a violation of 10 CFR-50.46 limits. For the worst break size,.ie, that size which.
requires the quickest pump trip, trip'aust occur within two.
minutes of the indication of.need.for pump. trip. As break size decreases, longer time is. ' vailable for.~ operator action. The a
critical time period;of high. void formation;(>70%) when RC pump trip is not recommended has also been determined. The-critical time period for the. break requiring the, quickest' operation action'
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6 time is short (five minutes) when pump trip could result in violation of 10 CFR 50.46 criteria.
b.
A best estimate SBLOCA analysis will be performed for each general plant type, over the spectrum of sizes determined by the conservative analyses to determine (a) the time available for a required RC pump trip, and the period of time when RC pump trip is not recommended or (b) the lack of indication for a required pump trip.
If it is determined that a need for RC pump trip exists, the time for operator action will be determined and justified by comparison to ANSI standards and operating experience. An indication of reasonable operator action time is expected to justify manual RCP trip.
3.
Other Considerations a.
The level of quality of instrumentation, as described in the enclosure of Generic Letter 83-10, used to produce the signal' indicating the need for RC pimp trip, will be provided.by Consumers Power Company to supplement the BWOG generic submittal for treatment of RC pumps duriag transients.
b.
The ATOG guidelines and plant specific Emergency Operating.
Procedures contain criteria for the timely restart of reactor.
coolant pumps when conditions which will support safe. pump operation exist. Table 6 in Part II,. Volume 1.of'ATOG provides the conditions when RC pumps'can be restarted. The Plant-Limits and Precautions document provide further instruction, oc0783-5060b112
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c.
Plaat operators have been trained in their responsibility for performing RCP trip in the event of a small break LOCA.
Instructions for plant operation are reinforced by regular requalification class and simulator training. Operators will be trained on the concept of RC pump trip on subcooling margin and appropriate priorities as the plant implements the ATOG
. philosophy.
The B&W Owners Croup's response to this section of requirements will be reported by the end of 1983.
II.
Pump Operation Criteria Which Will Not Result in RCP Trip During Transients and Accidents.
Since it is the position of the BWOG and B&W that the safest method for RC pump operation following SBLOCA is manual trip, the criteria stated in this section will not be addressed.
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1 CONSUMERS POWER COMPANY Midland Units 1 and 2-Pocket No 50-329, 50-330 Letter St rial 24080 Dated July 21. 1089 At the request of the Commission and pursuant to the Atomic Energy Act of 1954, and the Energy Reorganization Act of 1974, as amended and the Commission's Rules and Regulations thereunder, Consumers Power Company submits the proposed plan and schedule for resolution of II.K.3 5, " Automatic Trip of Reactor Coolant Pumps" (Generic Letter 83-10) i CONSUMERS POWER COMPANY J/)Y By JW odf,Wice 7 reside.it Project, Engineering and Construction Sworn and subscribed before me this h day of
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