ML20203F540
| ML20203F540 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 03/20/1986 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20203F519 | List: |
| References | |
| NUDOCS 8604250174 | |
| Download: ML20203F540 (15) | |
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ENCLOSURE PRELIMINARY REVIEW 0F REACTOR COOLANT PUMP (RCP) TRIP CRITERIA FOR THE SOUTP TEXAS PROJECT (STP), UNITS 1 AND 2 MARCH 20, 1986 INTRODUCTION This document provides the evaluation criteria the staff is applying to RCP trip review, a preliminary staff appraisal of the adequacy of the information contained in References 1 and 2, and the staff understanding of additional verbal information received from STP personnel.
The evaluation criteria and preliminary staff appraisal served as an agenda for obtaining additional verbal information via a telephone conference call.
The telephone conference call was conducted between applicant and NRC personnel on March 19, 1986.
Participants in the conference call from Houston Pow'r and lighting were Mike Powell, Terry Roberson, Tom Crawford, John laccf fe, Dan Eldridge, Jim Nesersa, Tim Bowman, and Mark McBurnett.
Bechtel was reuresented by' John Atwell.
Westinghouse was represented by Bruce Lorenz, ledy Giynon, Carl Vernon, and
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Bill Spezialetti.
The staff was represented by Prasad Kadambi and Warren Lyon.
The general organization of the material which follows is a staff provided statement, either guidance or a statement of an evaluation criterion, generally followed by a staff statement in regard to the initial applicant submittal (Refs. I and 2).
The staff perception of the.elephone conference call is then summarized.
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OVERAll GUIDANCE PERTINENT TO RCP TRIP During a small break accident in certair 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 l
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 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, procedures and criteria should be developed to attain this goal.
Note that leaving pumps running during "non-break" transients and accidents is not a requirement, as contrasted to the small break, where trip must be accomplished to remain in compliance with the regulations.
(Failure to trip as required could lead to exceeding Appendix K specified temperatures.1 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 resolve the staff concern with respect to RCP trip prior to power operation.
Note that 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 EVAI.UATION CRITERIA AND COMMENTS The evaluation criteria are generally those provided in Reference 3, including the Safety Evaluation and its appendices, which were an enclosure to Reference 3.
A.
Determination of RCP Trip Criteria Demonstrate and justify that proposed RCP-trip setpoints are adequate for 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 applicant has not selected the Reactor Coolant Pump (RCP) trip criterion, and stated this would be done by March 31, 1986 (Ref. 21.
Staff review cannot be completed until this is accomplished.
The South Texas Project (STP) stated (Ref. 2) that they would use one of the three alternatives recommended by the Westinghouse Owners Group (WOG), as is discussed in the WOG response to Generic l.etter 83-10.
Applicant Supplemental Information. Westinghouse does not support keeping the RCPs run7ing if they should have been tripped, but were not 3
prior to entering the " window" refer red to above.
The Westinghouse position, which is also the STP position, is that the RCPs should be tripped regardless of RCS conditions, unless one is obviously in an Inadequate Core Cooling situation. They argue that if RCPs should be running under 1.0CA conditions, it will be the result of following the Emergency Operating Procedures, since RCPs will be restarted in accordance with those procedures if such action is necessary.
Reference was made to report number WOG-117 from the Westinghouse Owners Group which addresses this situation. Westinghouse personnel also pointed ~out that the staff SER (see Ref. 31 did not disallow this approach, and that it referenced WOG-117 results.
The technical backup for the decision is that Westinghouse Best Estimate (BE) calculations show that the maximum clad temperature never exceeds 2200 F, but always remains significantly below that value.
STP is tentatively planning to use RCS pressure as the criterion for RCP trip, but the final decision has not been reached. An alternate is the pressure difference between the RCS and the Steam Generator (SG) secondary side.
There are a number of factors under consideration pertinent to the final selection.
For example, the pressure difference is displayed directly in the control room so that operators do not have to perform a subtraction in the process of reaching a trip /no-trip decision. Powever, the display position is not as attractive as is the case for RCS pressure. A human factors evaluation remains to be completed prior to selection.
Further information pertinent to the selection is provided in the Section A2 response.
Staff Comment.
The staff has previously stated that RCPS are to be left running if they are not tripped in time to avoid the " window".
Typical concerns are that there is no assurance the RCPs can be restarted under abnormal conditions if they are stopped, it has not been established that the liquid and vapor phases can be rehomogenized if the RCPs are stopped so that the phases separate, and stopping RCPs under "windew" conditions can result in immediate creation of severe core heating conditions where such did not occur as long as the RCPs were running.
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The staff did not refuse to accept the W and STP position on RCP operation, and agreed to review the technical background for both positions.
A1.
Identify the instrumentation to be used to determine the RCP trip set point, including the degree of redundance of each parameter signal needed for the criterion chosen.
Establish the quality level for the instrumentation, identity the basis for the sensing instrument.s' design features, and identify the basis for the degree of redundance.
Staff Evaluation.
The applicant identified that redundant instrumentation is available to support the selected RCP trip criterion.
The instrumentation should be identified, as should its classification (safety related, et. al.) and bases for redundancy and qualification.
The bases for redundancy and qualification should briefly address other items in addition to the transmitters (such as connections and associated equipment).
Applicant Response.
RCS pressure will be determined by using three wide range pressure measurements. The sensing lines are located on three of the four hot legs. The transmitters are located outside containment, and hence are not subject to an adverse containment atmosphere.
They are class IE safety related, and are fully qualified.
There is a program in place at STP to evaluite the influence of an adverse contairment atmosphere on the pre.sure readings as seen by the operator.
It has not been completed, but STP personnel believe they will find little impact.
These pressure sensing devices were previously evaluated for response time with respect to a number of control situations.
The only one encountered where response time was inadequate was for use in control of a cold overpressure conditica.
For that situation, STP uses other connections to the RCS for which the transmitters are located within containment.
These alternate pressures are also available to the operators as a source of further information, should it be needed for RCP trip.
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The steam lines from each SG are equipped with three channels of pressure instrumentation which provide both monitoring and protection functions.
These are fully oualified instrumentation packages.
The transmitters are located in separated cubicles, one for each of the four steam generators.
Hence, only one pressure reading would be expected to be affected by a steam line break in the vicinity of a transmitter.
Staff Response.
The only additional information that is needed is identification of the specific instrumentation.
A2.
Identify the instrumentation uncertainties for both normal and adverse containment conditions. Describe the ba:is for the selection of the adverse containment parameters.
Address, as appropriate, local conditions, such as fluid,iets or pipe whip, which might influence instrumentation reliability.
Staff Evaluation.
The basis for selection of an adverse containment environment is identified as the WOG Emergency Response Guidelines (ERGS), and STP indicates they will address local conditions as appropriate.
This should include local conditions both inside and outside containment.
(For example, can a steam line break outside containment reasonably result in an adverse environment which affects SG pressure indication?)
Operator response to instruments under normal and abnormal conditions when one instrument is inoperative should be addressed.
Emphasis should be upon abnormal conditions when the " good" instrument is providing information with a large uncertainty.
Applicant Response.
Instrumentation inaccuracy and uncertainty investigations have been completed, and STP has determined that either RCS pressure or RCS pressure to SG secondary side pressure differential is satisfactory.
Subcooling margin did not provide satisfactory separation of 1.0CA and steam generator tube rupture.
Draft Emergency Operating Procedures (EOPs-) have been completed for operation with RCS 6
pressure trip.
However, there are other areas where work is needed which is not complete. Overall, less work is reouired if the pressure difference is selected.
The limiting event for RCS pressure has been determined to be a feed line break.
A feed line break analysis for this application has not been completed, and the STP estimate for completion is approximately three months.
The limiting event for pressure difference is steam generator tube rupture.
The uncertainty associated with RCS pressure is approximately 80 psi, and the expected uncertainty for pressure difference is approximately 70 to 90 psi.
Further information will be provided to the staff regarding treatment of sensing line uncertainty and the difference between adverse and normal environmontal conditions.
In the case of RCS pressure, the display processing takes an average of the three readings, analyzes the deviations from the average, and then, if one of the readings is outside of the established range, it is rejected, and a new average determined. This should reduce operator involvement with situations where one instrument is faulty, regardless of the reason.
Pressure information for each steam generator is treated in the same manner.
1 There is an ongoing program of evaluation of pipe whip and the influence of local fluid jets.
This is not complete.
Information will be provided to the staff when it becomes available.
An adverse containment environment is considered to correspond to a Hi-1 containment isolation signal, which is received at a pressure of 5.5 psig.
Staff Response.
The staff indicated that the information that has been provided plus what is anticipated should be sufficient to establish the adequacy of either of the two techniques that are under consideration at 7
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STP. The staff further indicated they would prefer that STP continue a logical investigation of the techniques, and that the selection should be made on technical merit without the pressure of meeting a deadline for preparing input for an SER.
Therefore, the staff plans to prepare an SER on the basis of the available information, and there is no need for STP personnel to meet the deadline committment as specified in Reference 2.
(Note the Reference 2 stated March 31, 1986 date is inconsistent with completion of analyses that may be necessary to technical resolution.)
STP should also provide radiation criteria associated with determination of an adverse containment environment, if any.
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 (or applicant) determines that the WOG alternative criteria are marginal for preventing unneeded RCT trip, it is recommended that a more discriminating plant-specific procedure be developed, licensees (or applicants) should take credit for all equipment (instrumentation) available to the operators for which the licensee (or applicant) has sufficient confidence that it will be operable during the expected conditions.
Staff Evaluation.
No information is provided.
Further Staff Comment.
A brief summary of WOG information as applicable to STP should be supplied.
B.
Potential Reactor Coolant Pump Problems 4
- 81. Assure that containment isolation, including inadvertent isolation, will not cause problems if it occurs for non-LOCA transients and accidents.
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Demonstrate that, if water services needed for RCP operations are terminated, they can be restored fast enough once a non l.0CA situation is
-confirmed to prevent seal damage or failure. Confirm that containment isolation with continued pump operation will not lead to seal or pump damage or failure.
Staff Evaluation.
Essential water services for RCP operation are stated to continue under accident conditions involving Containment Isolation (CII. Seal injection is only isolated when a CI signal is present concurrent with low charging header pressure.
Component Cooling Water (CCW) to the RCP thermal barrier heat exchangers is continued independent of CI, and is stated to be lost only on a low CCW surge tank level.
The applicant further states that the only credible condition which would interrupt both of the sources of cooling water to the RCPs is a loss of offsite power, where the RCP motors are de-energized.
Cooling and injection water are stated to be restored within seconds following start of the diesel generators.
Information should be provided pertinent to trip of the RCPs under conditions such as loss of seal injection or CCW, and restart of thg RCPs following restoration of services leading to the trip.
Items such as trip parameters, operator response and timing of operations should be identified.
The comment in regard to the only credible situation that leads to loss of both sources of cooling water being loss of off. site power could be misleading.
For example, what is the interaction of CCW and the continued operation of the Chemical and Volume Control System, and what are the interactions between availability of cooling water systems and the environment under which the equipment must operate (such as room coolingl? A portion of RCP trip consideration involves licensing concerns and " credible" events, but another part of the consideration is the real operating and potential accident environment one may encounter, which is not necessarily limited to considerations such as are applicable to Safety Analysis Report Chapter 15 analyses.
(These comments are 9
intended to broaden background thinking.
It is not the staff's intent to become involved in these areas as a part of RCP trip review.1 Applicant Response.
The intent of the STP description is to establish that seal injection is always present unless there are major, multiple Equipment failures. Typically, such a situation would result in a low header pressure, which in turn would be followed by valve closure of the supply lines.
The case with cooling water to the RCP components is similar.
This is normally unaffected by all levels of containment isolation.
Response to a loss of seal injection is to trip the RCPs.
Response to loss of cooling water to the oil coolers is to follow the RCP bearing temperatures while continuing to operate the RCPs; RCP trip would be initiated if temperature operational limits were exceeded.
l.oss of cooling water to the thermal barrier heat exchangers would not be a reason for RCP trip as long as a sufficient flow rate existed from the seal injection region into the RCS, as determined from the injection rate and leakoff rate instrumentation.
RCP restart following trip provides a full consideration to the effects of initiation of cooling water to a hot RCP component, and the potential thermal stresses which could be induced.
Staff Response.
Continued discussion provided a clear perception on the part of the staff that the concerns nad been addressed by STP personnel, and there is an understanding of the potential problems associated with RCP trip and restart.
82.
Identify the components required to trip the RCPs, including relays, power supplies and breakers. Assure that RCP trip, when necessary, will occur.
Exclude extended RCP operation in a voided system where pump head 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 10
adverse containment conditions on RCP trip reliability.
Describe the basis for the adverse containment parameters selected.
Staff Evaluation. All components associated with RCP trip are stated to be located outside containment, and therefore are not affected by adverse containment conditions.
The breakers are located in the turbine building. Normally, there are relays associated with tripping the breakers which electrically are located between the breakers and the control room switches.
These relays are not mentioned, nor is the connecting wiring.
The applicant should determine that none of the components will be affected by accident conditions such as high energy line breaks in the turbine building or other accident conditions which could create an adverse environment in the vicinity of the components.
There is no information pertinent to assurance that RCP trip will occur when necessary, nor is an alternate operator response provided if there is a failure to trip upon operation of control switches in the control room.
RCP operation in a voided system is not mentioned.
Applicant Response.
There are no relays outside of the breaker enclosures.
Everything is within these enclosures with the exception of the control room switches and interconnecting wiring.
The review of pipe breaks mentioned previously will encompass consideration of this area.
If an operator were to attempt an RCP trip from the control room, and it was unsuccessful, then trip would be accomplished locally at the breakers.
The required time would be approximately five minutes maximum.
There are no locked doors to impede travel from the control room to the breakers, and an adverse environment that would interfere with the trip operation is not anticipated.
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Operation in a voided system is guided by the WOG Rev 1 emergency operating guidelines.
Note that under this guidance, RCPs are to be restarted under severe ICC conditions.
These operations are a part of operator training.
Staff Response.
This is sufficient information for preparation of an SER.
C.
Operator Training and Procedures (RCP Trip)
C1.
Describe the 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 directicn for use of individual steam generators with and without operating RCPs.
Assume manual RCP trip does not occur 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.
Post probable plant conditions should be identified and justified by the licensee (or applicant),
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 than the Draft ANSI Standard N660.
If this is the case, then i
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.
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Staff Evaluation.
The applicant response is general and does not address the identified points, nor does it establish that the applicant has an understanding of the need to trip RCPs as contrasted to keeping them running.
Further Staff Comment.
The telephone conference call discussion clearly led to the conclusion that the applicant understands the need to trip RCPs as contrasted to keeping them running.
There is a technical disagreement between the staff and STP personnel in regard to whether RCPs should be tripped or left running in the event they should have been tripped, and were not.
As previously identified, the staff will follow up on this item.
The applicant should prepare a brief description of the problems and philosophy behind-RCP trip and restart that establishes a record of applicant understanding, and shows that sufficient information is provided to the operators for dealing with the RCP trip issue.
C2.
Identify those procedures which include 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 (e) Use of steam generators with and without RCPs operating (f) RCP trip for other reasons Ensure that emergency operating procedures exist for the timely restart of the RCPs when conditions warrant.
Staff Evaluation. The applicant has presented a summary listing of selected procedures which are stated to be based upon the WOG Guidelines.
This list appears to be sufficient with the exception that RCP restart procedures and the technical requirements to be met for restart do not 13 l-m.
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appear to be addressed. The staff also expects a brief discussion of these points in the response to C1.
Applicant Response.
The procedures address restart as well as trip.
Restart has been discussed previously.
Staff Coment.
This is sufficient information for preparation of the SER.
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REFERENCES 1.
Wisenburg, M. R., " South Texas Project. Units 1 & 2, Dockets Nos. STN 50-498, STN 50-499, Partial Response to NRC Generic letter 85-12,
' Implementation of TMI Action Item II.K.3.5, Automatic Trip of Reactor Coolant Pumps'", letter to Hugh I.
Thompson, NRC, from Pouston Power &
Lighting, Nov. 6, 1985.
2.
Wisenburg, M. R., " South Texas Project, Units 1 & 2, Docket Nos. STN 50-498, STN 50-499, TMI Item II.K.3.5 and Generic letter 85-12, Automatic Trip of Reactor Coolant Pumps",i.etter to Vincent S. Noonan, NRC, from Pouston Power & Lighting, Jan 28, 1986.
3.
Thompson, Pugh 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 IW)DesignedNuclearSteamSupplySystems(NSSSs),Jun. 28, 1985.
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