ML20207J612
| ML20207J612 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 12/30/1986 |
| From: | Youngblood B Office of Nuclear Reactor Regulation |
| To: | White S TENNESSEE VALLEY AUTHORITY |
| References | |
| GL-85-12, NUDOCS 8701080535 | |
| Download: ML20207J612 (13) | |
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Docket Nos.: 50-327 and 50-328 DEC 3 01986 Mr. S. A. White Manager of Nuclear Power Tennessee Valley Authority 6N 38A Lookout Place 1101 Market Street Chattanooga, Tennessee 37402-2801
Dear Mr White:
Subject:
Request for Additional Information on the Reactor Coolant Pump Trip Issue (Generic Letter 85-12)
Enclosed are the preliminary review results from the staff evaluation of the Tennessee Valley Authority (TVA) submittal on the reactor coolant pump.(RCP) trip issue (Generic Letter 85-12). As you can see from the enclosure there are several areas where clarifications are needed.
It is suggested that TVA personnel evaluate the enclosed report and when appropriate, TVA and the staff have a conference call to discuss the subject.
Once TVA is prepared to discuss the enclosure further, it should contact the project manager for this area, Joseph Holonich, at (301) 492-7270.
It should be noted that resolution of this issue is not reouired for Sequoyah restart.
If you require any additional assistance you can contact Mr. Holonich at the number given above.
Sincerely,
\\M B. J. Youngblood, Director PWR Project Directorate #4 Division of PER Licensing-A
Enclosure:
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l Pr. S.A. White Sequoyah Nuclear Plant Tennessee Valley Authority cc:
Tennessee Department of Public Regional Aaministrator, Region II Health U.S. fluclear Regulatory Conmission, ATTN: Director, Bureau of 101 Parietta Street, N.W., Suite P900 Environmental Fealth Services Atlanta, Georgia 30323 Cordell Hull Building f.'ashville, Tennessee 37219 j
J.A. Kirkebo ATTN:
D.L. Willierrs Fr. Michael H. Mobley, Director i
Tennessee Valley Authcrity Division of Radiological Health j
400 West Sur. nit Hill Drive, W12 A12 T.E.R.R. A. Building Knoxville, Terr,essee 37902 150 9th Avenue North Nashville, Tennessee 37203 t
Mr. Bob Faas Westinghouse Electric Coro.
~ County Judge P.O. Box 355 Hamilton County Ccurthouse Pittsburch, Pennsylvania 15230 Chattancoga, Tennessee 37402
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P. L. Cridley Tenressee Valley Authority 5N 157B Lookcut Place
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Chattanooga, Tennessee 37402-2801 M. R. Harding Tennessee Valley Authority Seoucyah f'uclear Plant P.O. Box 2000 Soddy Daisy, Tenressee 37379 Resident Inspecter/Sequoyah fiPS c/o U.S. Nuclear P.ey.latory Comiss. ion 2600 Iccu Ferry Roao Soddy Daisy, Tennessee 37379 H.L. Abercrcnbie Tennessee Valley tuthority Sequoyah fluclear Plant F.C. Box 2000 Soddy Daisy, Tennessee 37370
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ENCLOSURE PRELIMINARY REVIEW OF REACTOR COOLANT PUMP (RCP) TRIP CRITERIA t
RCP TRIP, SEQUOYAH UNITS 1 AND 2 INTRODUCTION Listed below are the evaluation criteria the staff is applying to RCP trip review and our preliminary appraisal of whether sufficient information was provided for the staff to complete its review. The organization of this Enclosure is a staff provided guidance or evaluation criterion statement based upon Generic Letter 85-12 (Ref.1), generally followed by a staff critique of the initial licensee submittal (Ref. 2).
The staff plan to complete the review is to use this Enclosure as the basis for a tblephone conference call prior to initiation of a significant response effort on the part of the licensee. The staff then plans to document the results of the prelimjpary review and the telephone conference call, and to provide that documentation to the licensee.
Then the licensee can provide a written. response regarding the accuracy of the staff perception of the telephone conference call, together with any desired corrections and supplemental information. This should allow the staff to complete the review and prepare a Safety Evaluation Report (SER). An alternate, if the licensee desires (and which is not presently contemplated), is for the staff to prepare formal questions for licensee consideration.
1 The Tennessee Valley Authority (TVA) submittal contains an enclosure for Sequoyah and another for Watts Bar. The staff has conducted separate reviews since there are differences between the submittals.
However, the reviews are f
closely related, and it may be profitable to coordinate them.
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OVERALL GUIDANCE PERTINENT TO RCP TRIP During a small break accident in certain break size ranges, there exists a window in time during which tripping RCPs will make the accident worse.
Therefore, in a small break situation, one must trip RCPs prior to entering the window.
If one wishes to depend upon manual trip, two criteria are applicable:
1.
One must show that at least 2 minutes exist within which to trip RCPs following " receipt of a trip signal" using licensing calculations as a basis.
2.
One must show that at least 10 minutes exist within which to trip RCPs following " receipt of a trip signal" using best estimate calculations as 1
a basis.
If, for some reason, the RCPs have not been tripped within 10 minutes of the time at'which plant conditions indicate trip should be performed, they are to be left running until after the window is closed. Closure can be indicated by parameters such as regaining both adequate subcooling margin and pressurizer level after they have been lost.
Analyses are required to establish timing relative to items 1 and 2, as well as to establish the dimensions of the window.
It is desirable to leave pumps running for control purposes during other transients and accidents, including steam generator tube rupture accidents of sizes up to one tube broken. Therefore, insofar as is practical, proced'ures and criteria should be developed to attain this goal.
Note that leaving pumps running during "non-break" transients and accidents is not a 100% requirement, as contrasted to the small break, where trip'$ust)e accomplished to remain in y compliance with the regulations.
(Failure to trip as required could lead to exceeding Appendix K specified temperatures.) For "non-break" transients and accidents, RCPs may be tripped when desirable.
If in doubt, the small break criteria are to be applied.
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New plants coming on line should have dealt with RCP trip prior to power operation.
Note much of the work pertinent to the above criteria has been done on a generic basis, and is applicable to individual plants. Where this is the case, it is sufficient to establish applicability, and the generic work need not be repeated on a plant specific basis.
SPECIFIC EVALUATION CRITERIA AND COMMENTS The evaluation criteria are generally those provided in Reference 1, including the Safety Evaluation and its appendices, which were an enclosure to Reference 1.
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A.
Determination of RCP Trip Criteria Demonstrate and justify that proposed RCP-trip setpoints are adequate for 1
small-break LOCAs but will not cause RCP trip for other non-LOCA transients and accidents such as SGTRs. This is to include performance of safety analyses to prove the adequacy of the setpoints.
Consider using partial or staggered RCP-trip schemes.
Staff Evaluation. The licensee has selected a Reactor Coolant System (RCS) pressure of 1250 psig in conjunction with an uncontrolled depressurization as the criterion for tripping the Reactor Coolant Pump (RCP). The RCS pressure option was previously identified by the staff as the least desirable of the three options described by the Westinghouse Owners Group (WDC) in their evaluation of RCP trip, and the staff had not addressed the uncontrolled depressurization aspect.
The staff requests background information pertinent to this selection.
A1.
Identify the instrumentation to be used to determine the RCP trip set point, including the degree of redundance of each parameter signal needed 3
for the criterion chosen.
Establish the quality level for the instrumentation, identify the basis for the sensing-instruments' design features, and identify the basis for the degree of redundance.
Staff Evaluation. The licensee states that two redundant channels of wide range pressure instrumentation are available to the operator for monitoring pressure.
These are identified by transmitter number and the location of the pressure indications in the control room is given. 'Both transmitters are stated to be " qualified Post Accident Monitors and are powered by separate trains."
The point of connection to the RCS should be provided.
A2.
Identify the instrumentation uncertainties for both normal and adverse containment conditions. Describe the basis for the selection of the adverse containment parameters.
Address, as appropriate, local conditions, such as fluid jets or pipe whip, which might influence instrumentation reliability.
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Staff Evaluation. Minimum accuracy requirements are stated as provided in the FSAR, and are 75 psig for Condition IV events. This is not responsive to the question.
Adverse containment conditions are defined as the point corresponding to receipt of a Phase B containment isolation signal. This is 2.81 psig from two of four containment pressure transmitters. The operator is to immediately trip the RCPs upon receipt of this signal, and the RCS pressure signals will not be used as parameters for RCP operation or RCP trip criteria following that operation.
In effect, this response removes any need to consider an adverse environment within containment and further means that RCP operation following Phase B initiation need not be considered since the RCPs are not to be operated. This response does not address RCP restart, nor is it clear that the objective of keeping RCPs operating where practical has been met.
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Local conditions such as fluid jets and pipe whip are not addressed.
Conbitionsoutsideofcontainmentthatmayinfluenceuncertaintyalsoare not addressed.
For example, could a steam line break outside of containment introduce problems with the pressure readings in the control room? Is there any influence of adverse conditions on connections (wiring, piping) between components of the pressure instrumentation system, either inside or outside of containment?
Operator response to instruments under normal and abnormal conditions when one instrument is inoperative should be addressed.
Emphasis should generally be upon abnormal conditions.
A3.
In addressing criterion selection, provide consideration of uncertainties associated with the WOG supplied analyses values. These uncertainties are to include uncertainties in computer program results and uncertainties resulting from plant specific features not representative of the generic data group.
If a licensee determines that the WOG alternative criteria are marginal for preventing unneeded RCP trip, it is recommended that a more discriminating plant-specific procedure be developed.
Licensees should take credit for all equipment (instrumentation) available to the operators for which the licensee has sufficient confidence that it will be operable during the expected conditions.
Staff Evaluation.
Calculations of instrument uncertainties are summarized, and comparisons are discussed between Sequoyah and the Westinghouse Owners Group (WOG) information. TVA states that the calculated overall uncertainty for Sequoyah is from +30 psig to +200 psig for the minimum RCS pressure trip point.
The licensed Westinghouse LOFTRAN computer code is referenced for performance of the non-LOCA analyses.
The computer program result uncertainties evaluation is based on the assumption of no changes in
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initial plant conditions (such as full power, pressurizer level, all Safejy Injection (SI) pumps running, and all Auxiliary Feed Water (AFW) pumps running). The major contributors to uncertainty are stated to be break flow rate, SI flow rate, decay heat generation rate, and AFW flow rate.
Parametric studies are summarized in which the major uncertainties are stated to be due to the break flow model and SI flow inputs.
The licensee has not directly addressed such topics as the accuracy of the numerical solution scheme or of nodalization.
Further, there is no-determination of the' influence of equipment or operational failures.
Information pertinent to the former result from comparisons of the LOFTRAN code to operational and experimental data, and as a result will have been included in the uncertainty number.
Determination of equipment or operational failures is not a necessity as long as the expecte'd configuration of the plant is addressed since the objective of RCP trip is to provide _ reasonable assurarce of not tripping for transients for which a trip is undesirable. Thus, no further information is necessary s
fo~r this topic.
B.
Potential ReactoE Coolant Pump Problems Bl. Assure that containment isolation, including inadvertent isolation, will not cause problems if it occurs for non-LOCA transients and accidents.
Demonstrate that, if water services needed for RCP operations are s
terminated, they can be restored fast enough once a non-LOCA situation is confirmed to prevent seal damage or feilure.
Confirm that containment i
isolation with continued pump operation will not lead to seal or pump damage or failure.
Staff Evaluation. TVA states that containment isolation occurs at two levels, designated as Phase A and Phase B.
Phase A isolation is initiated at a containment pressure of +1.54 psid with respect to the annulus pressure. The RCPs are designed to continue to operate following a Phase A isolation, and all necessary equipment and water services i
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remain in operation.
Therefore, Phase A isolation has no practical effect on RCP operation.
Phash B isolation interrupts water services to the RCPs, and the operators are instructed to trip the RCPs to prevent damage. TVA states that a pressure transient of sufficient magnitude to initiate Phase B would be indicative of a LOCA cr main steam line break of sufficient magnitude that RCP operation would not significantly impact the transient behavior.
TVA also discusses response to loss of seal injection with component cooling water continuing to the thermal barrier heat exchangers. The flow of RCS water up the shaft, with thermal barrier heat exchanger cooling, allows continued operation of the RCPs as long as the lower bearing temperature does not exceed 210 F.
This provides time for attempts to restore seal injection flow.
This is a straightforward description of the response with respect to
' isolation, but there are other aspects of RCP support equipment which need clarification.
For example, do the conditions which lead to containment isolation result in termination of any portion of the Chemical Volume and Control System and is there an indirect effect upon RCP seal injection? If one has a Phase B isolation, what are the implications with respect to total loss of water cooling to the RCP l
seals? If CCW pump operation is terminated, how long does it take for the pump to be restarted and flow restored to the thermal barrier heat exchangers and other RCP associated components? What are the implications? Information should be provided pertinent to restart of RCPs following restoration of services leading to a trip.
Items such as trip parameters, operator response and timing of operations should be 4
identified. The staff does not need a large volume of material on these topics, but does need a brief mention with perhaps reference to i
procedures in the list provided with the submittal.
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t It would also be helpful to provide a probabilistic argument supporting the implied position that stopping RCPs upon Phase B isolation is consistent with the objectives of this program.
B2.
Identify the components required to trip the RCPs, including relays, power supplies and breakers. Assure that RCP trip, when necessary, will Exclude extended RCP operation in a voided system where pump head occur.
is more than 10% degraded unless analyses or tests can justify pump and pump-seal integrity when operating in voided systems.
If necessary, as a result of the location of any critical component, include the effects of adverse containment conditions on RCP trip reliability.
Describe the basis for the adverse containment parameters selected.
Staff Evaluation.
The major components associated with RCP trip are identified, as is their location as being outside containment, and hence they are not affected by adverse conditions inside containment. TVA indicates that the trip coil is energized to actuate, but that if power we're to be lost,"the normal feeder breaker could be manually tripped locally at the switchgear.
A brief consideration should be given to the potential for adverse conditions outside containment and the implications, if any.
For example, can a steam line break outside of containment introduce difficulties with respect to the equipment of interest here?
The timing of operations associated with alternate operator actions required to trip the RCPs should be mentioned.
The loss of power situation mentioned above is one example where the timing may be important. Another is if the operator attempts a trip from the control room and fails, how long will it take to trip from an alternate location, including travel time? (See Item C1, below.)
RCP operation in a voided system is not mentioned.
C.
Operator Training and Procedures (RCP Trip) a 8
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C1.
Describe tho operator training program for RCP trip.
Include the general philosophy regarding the need to trip pumps versus the desire to keep pumps running. Also cover priorities for actions after engineered safety features actuation.
Assure that training and procedures provide direction for use of individual steam generators with and without operating RCPs.
Assume manual RCP trip does not o~ccur earlier than two minutes after the RCP-trip set point is reached Determine the time available to the operator to trip the RCPs for the limiting cases if manual RCP trip is proposed.
Best Estimate calculational procedures should be used. Most probable plant conditions should be identified and justified by the licensee, although NRC will accept conservative estimates in the absence of justifiable most probable conditions.
Justify that the time available to trip the RCPs is acceptable if it is less that the Draft ANSI Standard N660.
If this is the case, then address the consequences if RCP trip is delayed. Also develop contingency procedures and make them available for the operator to use in case the RCPs are not tripped in the preferred time frame.
Staff Evaluation. A general outline of training is presented, and
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background philosophy is discussed, although some of the above points are not addressed.
(What is the general need to trip RCPs as contrasted to keeping them running?) The staff is not clear as to whether the approach is entirely consistent with the licensing requirements which underlay this TMI Action Item. A definition of what constitutes a controlled depressurization as contrasted to an uncontrolled depressurization would be helpful.
A portion of the discussion clearly is beyond the design basis arena in that RCPs are not to be tripped if there is no safety injection during an 9
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F-uncontrolled depressurization.
The staff requests that it be appraised of the background thinking for this operator instruction, and how this approach does not result in operator confusion with the trip requirements under other conditions. The aspect that is of concern is the philosophy which is stated as follows:
"It has been stressed in operator training that if the RCP trip criteria is not fully met, it is more advantageous to continue RCP operation than to trip the RCPs.
In virtually all non-LOCA accidents, RCP operation is desired for its heat removal and pressure control assistance."
Stressing continued operation in general may not be consistent with the licensing requirements.
The staff is also not sure that " virtually all non-LOCA accidents" benefit from RCP operation.
For example, what is the proportion of accidents which involve loss of heat sink and should RCPs remain in operation?
B~rief ir. formation on RCP restart philosophy would be helpful.
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C2.
Identify those procedures which jnclude RCP trip related operation:
(a) RCP trip using WOG alternate criteria (b) RCP restart (c) Decay heat removal by natural circulation (d) Primary system void removal l
(e) Use of steam generators with and without RCPs operating
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(f) RCP trip for other reasons Ensure that emergency operating procedures exist for the timely restart of the RCPs when conditions warrant.
l Staff Evaluation. Th. 11censee has presented a listing of selected procedures which address RCP trip and restart.
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REFERENCES 1.
Thompson, Hugh L. Jr., " Implementation of TMI Action Item II.K.3.5,
' Automatic Trip of Reactor Coolant Pumps' (Generic Letter No. 85-12)",
NRC Letter Addressed to All Applicants and Licensees with Westinghouse Q ) Designed Nuclear Steam Supply Systems (NSSSs), Jun. 28, 1985.
i 2.
Hufham, J. W., Letter to Hugh L. Thompson, NRC, pertinent to response to Generic Letter 85-12, Jan. 13, 1986.
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