ML20214J549
| ML20214J549 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 11/18/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20214J547 | List: |
| References | |
| GL-85-12, NUDOCS 8612010345 | |
| Download: ML20214J549 (11) | |
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Enclosure 1 Filistone Nuclear Power Station, Unit No. 3 Northeast Nuclear Energy Company Docket No. 50-423 Reactor Coolant Pump Trip (G.I.,85-121 e
1 8612010345 861118 PDR P
ADOCK 05000423 PDR a
r ENCLOSURE PRELIMINARY REVIEW 0F REACTOR COOLANT PUMP (RCP) TRIP CRITERIA MILLSTONE 3 RCP TRIP 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 telephone 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 preliminary 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.
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, i
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 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 100% 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.) For "non-break" transients and accidents, RCPs may be tripped when desirable. If in doubt, the small break criteria are to be applied.
New plants coming on line should have dealt with RCP trip prior to power I operation.
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I 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 B
The evaluation criteria are generally those provided in Reference 1, including the Safety Evaluation and its appendices, which were an enclosure to Reference 1.
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.
A. Staff Evaluation. Millstone has selected Reactor Coolant System (RCS) pressure as the parameter to be montiored for the Reactor Coolant Pump (RCP) trip criterion. The staff has previously determined that this is the least desirable of the criteria. Therefore, the staff requests further information pertinent to the selection of this approach as compared to the alternates.
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, identify the basis for the sensing-instruments' design features, and identify the basis for the degree of redundance.
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A1. Staff Evaluation. The licensee identifies that two wide range pressure channels are available that the operators will monitor to determine if tripping the RCPs is necessary. This is the total information provided pertinent to item A1, and it is not sufficient for this review. For example, the instrumentation should be identified, as should its classification (safety related, etc.) and bases for redundancy and qualification. The bases for redundancy and qualification should briefly address all items associated with the pressure determination system, such as connections and associated equipment, in addition to basic equipment such as transmitters and sensors.
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.
A2. Staff Evaluation. The Millstone response is general, and devoid of specific information. For example, uncertainty is addressed as follows:
"In determing the RCP trip setpoints, the effects of instrument accuracy, instrument drift, temperature, and radiation from adverse containment conditions have been considered."
As another example, the Millstone treatment of adverse containment conditions is totally described by:
"The emergency operating procedures include manual RCP trip setpoints for both normal and adverse containment conditions."
The staff will require specific numerical information that is based upon a realistic foundation.
The remainder of the Millstone response for this item deals with localized conditions such as pipe whip and fluid jets. They state:
1 "Because the transmitters are located outside of the missile shield (inside containment), pipe whip and fluid jets are not a concern."
There are high energy pipes located outside of the missile shield inside containment, there are high energy pipes located outside containment, and there may be components associated with the pressure instrumentation that can be affected by localized accident environments that are located both inside and outside of containment. (For example, can a steam line break outside containment reasonably result in an adverse environment which affects pressure indication?)
The staff will require that specific information be provided pertinent to this topic. The staff will further require that appropriate and related topics be discussed. For example, 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.
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 RCP 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.
A3. Staff Evaluation. The response consists of a brief reference to FSAR Chapter 15 accidents and the conclusion that, "...since the limiting events were evaluated assuming offsite power is unavailable, tripping the l
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4 RCPs will not affect the consequences of the accident analyses reported in the FSAR." Whether or not the non-LOCA accidents and transients require or do not require RCPs is not the point, and there is no question as to whether the FSAR analyses represent limiting cases for design basis events. This response does not demonstrate an understanding of the problem.
B. Potential Reactor 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 terminated, they can be restored fast enough once a non-LOCA 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.
Bl. Staff Evaluation. The response begins with "During non-LOCA accident conditions, isolation of water systems to support RCP operation will not occur." It ends with "Because a containment high-3 pressure condition indicates a large LOCA or steamline break in containment, the RCPs should be tripped and maintenance of RPCCW (Reactor Plant Component Cooling Water) to the RCPs is not necessary."
Seal injection is stated to be "... maintained continuously by the charging system during all postulated accident situations with the exception of total loss of AC power." Consideration of RCP trip is not limited to design basis accidents. This may be the intent of the phrase
" postulated ace.ident cituations" if the statement is intended to address the scope of Chapter 15 analyses. One should be dealing with real problems with a realization of the requirements of the regulations so that the requirements are met. The question is not whether seal injection is maintained under " postulated accident condit' ions", but under what conditions seal injection is not maintained so that one has to be concerned with RCP pump response. The concern is further with conditions
that can lead to RCP seal damage. These are not a Chapter 15 types of concern. Further, a major thrust of the effort is maintenance of RCP operation under conditions where operation is desirable, as identified earlier in this document. Millstone does not appear to be addressing RCP trip in this light.
Information should be provided pertinent to trip of the RCPs under conditions such as loss of seal injection or CCW, and restart of the RCPs following restoration of services leading to the trip. Items such as trip parameters, operator response and timing of operations should be identified.
- 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 adverse containment conditions on RCP trip reliability. Describe the basis for the adverse containment parameters selected.
- 82. Staff Evaluation. The Millstone response is that a 6.9 kV supply breaker must be opened to trip an RCP. This can be accomplished remotely from the control room, locally at the breaker cubicle, or by de-energi2ation of the buses since "...they supply no cther safety-related loads. The containment penetration overcurrent protection devices can also serve as a backup to the main RCP breakers. Adverse containment conditions will not affect the operation of the RCP breakers."
There is no mention of time requirements of operations remote from the control room. The location of breakers and associated equipment is not given, and there is no basis for evaluation of the statement that they will not be affected by an adverse containment condition. The rationale that one may de-energize a bus since it serves no safety related loads is unacceptable. Loss of non-safety related equipment is of significance i
since a transient or accident can be made worse by the failure of non-safety related equipment.
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.
Millstone personnel 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 FCP trip will occur when necessary, nor is alternate operator response timing 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.
In general, the staff will require that each of the points raised in the questions and guidance be covered, including associated pertinent topics.
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 +o 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 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. 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 conditior.s.
Justify that the time available to trip the RCPs is acceptable if it is less than the Draft ANSI Standard N650. 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.
C1. Staff Evaluation. The Millstone response is general and does not address the identified points, nor does it establish that the licensee has an understanding of the need to trip RCPs as contrasted to keeping them running.
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.
C2. Staff Evaluation. Millstone has presented a summary listing of selected l
procedures which are stated to cover RCP start and stop operations. The l
staff will require a discussion of selected accidents and equipment i
failures and the interactions with RCP operation as a portion of the review.
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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.
- 2. Northeast Nuclear Energy Company, et. al., " Millstone Nuclear Power Station, Unit No. 3, Response to Generic Letter 85-12," Letter to Hugh L.
Thompson, NRC, Docket No. 50-423, A05034, Sep. 16, 1985.
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