ML20198D730

Forwards Documentation of NRC Understanding of Util Responses to 860410 Request for Addl Info Re Reactor Coolant Pump Trip Procedures.Comments Requested by 860523

ML20198D730
Person / Time
Site:	Seabrook
Issue date:	05/20/1986
From:	Nerses V Office of Nuclear Reactor Regulation
To:	Harrison R PUBLIC SERVICE CO. OF NEW HAMPSHIRE
References
NUDOCS 8605270012
Download: ML20198D730 (19)

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Docket Nos.: 50-443 and 50-444 Mr. ~ Robert J.. Parrision President and Chief Executive Officer Public Service Company of New Hampshire Post Office Box 330 Manchester, New Hampshire 03105

Dear Mr. Harrision:

On April 10, 1986, we had a conference call with personnel ~ representing the Seabrook Station. The Enclosure documents the staff understanding of the Seabrook Station personnel responses to the staff request for additional information during the conference call.

I am transmitting the Enclosure to Public Service of New Hampshire (PSNP) and requesting that PSNP confirm, or correct as necessary, our understanding of the PSNH responses.

'Please provide me your formal comments, if any, by May 23, 1986.

Victor Nerses, Project Manager PWR Project Directorate #5 Division of PWR licensing-A

Enclosure:

As stated cc: See next page Distribution:

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~NRC PDR local PDR PD#5 R/F T. Novak OEl.D J. Partlow

8. Grimes E. Jordan-V. Nerses M. Rushbrook ACRS (10)

C. Belinger W. Lyon PD 5

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wo es Docket Nos.: 50-443 and 50-444 Mr. Robert J. Harrision President and Chief Executive Officer Public Service Company of New Hampshire Post Office Box 330 Manchester, New Hampshire 03105

Dear Mr. Harrision:

On April 10, 1986, we had a conference call with personnel representing the 5eabrook Station. The Enclosure documents the staff understanding of the Seabrook Station personnel responses to the staff request for additional information during the conference call.

I am transmitting the Enclosure to Public Service of New Hampshire (PSNH) and requesting that PSNH confirm, or correct as necessary, our unoerstanding of the PSNP responses.

Please provide me your formal coments, if any, by May 23, 1986.

f  %

Victor Nerses. Project Manager PWR Project Directorate #5 Division of PWR licensing-A-

Enclosure:

As stated cc: See next page

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ENCLOSURE REPORT OF CONFERENCE CALL CONCERNING REACTOR COOLANT PUMP (RCP) TRIP AT SEABP00K STATION UNITS 1 AND 2, APRIL 10, 1986 INTRODUCTION The staff has completed a preliminary review of the Reference 1 submittal from Public Service of New Hampshire ~ pertaining to RCP trip, and has discussed the results of the preliminary review with personnel representing the Seabrook I Nuclear Station. This Enclosure documents both the preliminary review (Ref.

l 4) and the results of the discussion with applicant personnel.

s The purpose of the review was to identify any areas where additional information was needed for the staff to complete its evaluation of RCP trip, and to provide guidance pertinent to submittal of additional information where

) appropriate. The telephone conference call was conducted with the purpose of

obtaining clarification on several points and to obtain additional information. The call took place on April 10, 1986. The applicant was represented by Larry Walsh, Bob Kutcher, Cris Mellow, Bill Fadden, Paul i Christofakis, and Tim Pucko. The staff was represented by Beth Doolittle and Warren Lyon.

This Enclosure begins with an overall guidance discussion, and then covers each of the review criteria by stating the criterion, followed by a staff l

summary and critique. The staff understanding of the applicant response is

! then given, followed by additional staff comments where appropriate.

, 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:

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. 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 b2 left running until after the window is closed. Closure can be indicated by harameterssuchasregainingbothadequatesubcoolingmarginandpressurizer icvel 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, Es 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 cxceeding Appendix K specified temperatures.) For these 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 cperation.

Note much of the work pertinent to the above criteria has been done on a generic basis, and is applicable to individual plants.

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instrumentation environment, and the selected value used for RCP trip is sufficiently high that environmental conditions need not be considered by the operator.

Full consideration was given to the information contained in the WOG Guidelines pertinent to RCP trip criteria (see the first section on generic issues, RCP Trip / Restart). This information is also used during operator training so that the operator will be fully aware of the need for RCP operations, as well as the response that is indicated under various conditions.

s A1. Identify the instrumentation to be used to determine the RCP trip set raint, 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.

Staff Evaluation.

Reference 1 contains the statements: "The RCS subcooling margin is calculated based upon the wide range RCS pressure and compensated core exit thermocouple readings. The value of RCS pressure utilized in the calculation is the output of the data quality algorithm implemented in the subcooling margin monitor. The value of core exit thermocouple temperature is based upon the auctioneered high thermocouple quadrant average temperatures. Using the auctioneered high thermocouple quadrant average temperature in the calculation of core subcooling margin is consistent with the utilization in the WOG Emergency Response Guidelines.

"The Seabrook Emergency Operating Procedure Setpoint Study presents the calculations which support the actual subcooling value of 30 F. The Setpoint Study calculations were performed using pressure temperature instrumentation with the largest calculated errors. By using this approach, the operator is not restricted to a specific type of instrument 4

for determination of RCP trip. As an example, determination of subcooling could be made by:

- direct reading from Subcooling Margin Monitor

- direct reading from Main Plant Computer System, and

- manual calculation using steam tables and any combination of

1) MCB pressure indication (Pressurizer or RCS pressure), and

2) MCB temperature (incore thermocouples or RCS loop wide range s RTDs)."

The referenced calculational procedure leads to subcooling margin results which are reasonable when compared to other plant results the staff has reviewed. The flexible approach provides the operator with options which can be utilized in the event that one instrument is lost. The staff requests that the specific instrumentation be identified, including the location of the connections to the RCS, the transmitters, and any other major components comprising the systems (with the exception of the core exit thermocouples, where the locations and connections are obvious).

The calculational program should be described with respect to discrimination between readings of different value.

Applicant Response. The instrumentation utilized is that pertinent to the subcooling monitor. The Seabrook FSAR, Table 7.5.1, and information contained in Seabrook document SBN-952 provide redundancy location, j calculational methodology, and instrumentation identification data.

1 Individual instrumentation losses or abnormalities are automatically removed from the calculation af subcooling by auctioneering and averaging techniques.

Additional Staff Comment. The discussion revealed a clear understan'ing d of the methodology and the background considerations pertinent to 5

4 determination of subcooling under all reasonably expected plant conditions.

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.

Staff Evaluation. Temperature uncertainty for normal containment conditions is stated as 18.6 F, and 19.6 F is considered applicable for 6 adverse containment conditions. Pressure uncertainty is stated to be 84.6 psi, and is considered to be independent of containment conditions because the transmitters are located outside of containment. Temperature uncertainty is stated to be based on engineering judgement concerning the response of RTDs in an adverse environment.

The staff has the following comments and questions:

1. What are the criteria which separate normal and adverse containment conditions?

2. Some of the instrumentation previously mentioned may have transmitters inside containment, such as pressurizer pressure. Is this correct? If so, how does this affect the uncertainty? Similar questions may be posed for other instrumentation, such as thermocouples, where the uncertainty determinations for RTDs would not be expected to apply. Please discuss.

3. Fluid jets and pipe whip are not mentioned. Please amplify. The concern is with respect to the real operation of the plant as opposed to the licensing approach of a single failure, and the potential impact upon operator decisions. Has the plant been reviewed with respect to fluid jets and pipe whip for this application?

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4. Conditions outside of containment that may influence uncertainty are not addressed. For example, has Seabrook surveyed the wiring and connections between the transmitters and the control room to assure that such accidents as a steam line break outside of containment will not introduce problems with readings in the control room, and have such considerations been factored into the uncertainty evaluation?

5. The uncertainty determinations are stated to be based upon RTDs.

The core exit T/Cs are stated to be the basis for the determination of RCP trip. Please explain the apparent discrepency. (See Item t

A1. )

Applicant Response. Information pertinent to each of the above items is as follows:

1. The generic WOG Guidelines are used for containment conditions. An adverse containment condition is considered to exist if a High-1 containment isolation signal is generated (4.3 psig) or if the integrated radiation dose in containment is greater than 1.4 X 10 Rads.

2. Narrow range pressurizer pressure is the only applicable instrument with a transmitter inside containment. This instrument will not be used in determining subcooling margin since it is not qualified to function in a harsh environment.

The selected subcooling margin is sufficiently high that uncertainty variations due to an adverse containment condition are covered. The same is true with the uncertainty of instrumentation other than that

, automatically used in the subcooling monitor. In rome cases, the uncertainty of instrumentation utilized in determination of the subcooling margin applicable to RCP trip is higher than would be the 7

case with alternate instrumentation. For example, the uncertainty assigned to RTDs is higher than that associated with thermocouples.

3. Studies have been performed in which affected regions have been defined in the vicinity of high energy lines. These have established that, at most, only one instrument can be affected in a redundant system. A plant walk-down is in progress (approximately 90% complete) to evaluate these topics. No problems have been identified. Further information is provided in FSAR Section 3.6.

4. The above identified walkdown applies to this question as well.

v Note the RCS liquid level system was carefully designed to avoid problem areas, and it is installed in protected areas. The instrumentation, including connecting lines, is located away from potential sources of an adverse environment outside containment, such as high energy lines. In addition, all Class 1E instrumentation has been evaluated for conditions which may exist outside containment.

5. See prior response on thermocouples as contrasted to RTDs.

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 j be operable during the expected conditions.

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Staff Evaluation. Determination and use of RCS subcooling as an RCP trip parameter is stated to have been performed in accordance with the generic guidance provided in the Revision 1 version of the Westinghouse Owners Group Emergency Response Guidelines. Please relate this to the information which the staff reviewed and generically approved in Generic Letter 85-12 (Ref. 2). For example, discuss comparisons between Seabrook and the Westinghouse Owners Group (WOG) generic information provided in response to Generic Letter 83-10 (Ref. 3), which was referenced in Reference 2. The staff needs sufficient information regarding the uncertainty of the computer code results used in performance of analyses that it can formulate conclusions in regard to initial plant condition s assumptions, and the major contributors to uncertainty. Where bases are

upon generic accident and transient calculations, the staff needs to understand if.there are any Seabrook specific features which affect the determinations and, if so, what equipment is involved and d at is the impact upon the results.

Applicant Response. All of the information identified by the staff is

contained in the referenced WOG documentation. This can be condensed and provided to the staff if desired, and will be the duplicate of what has been provided by many other utilities in response to this staff question.

l The uncertainties applicable to the Seabrook plant are 138 psig for RCS l pressure, 58 F for subcooling, and 685 psi for pressure difference from

) the RCS to the SG secondary side. There are no unique Seabrook plant

} features that affect the generic WOG information.

1 Additional Staff Comment. The staff briefly identified the pertinent points in the referenced WOG documentation on which there may have been a question, and the applicant was obviously familar with the information.

There is no need for the applicant to " rubber stamp" the information onto an additional response for staff review. The above provided additional plant specific information is sufficient.

B. Potential Reactor Coolant Pump Problems 9

Bl. Assure that containment isolation, including ir. advertent 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.

Staff Evaluation. The RCP seals are cooled by either seal injection via the Chemical Volume and Control System (CVCS) or thermal barrier cooling via the Component Cooling Water (CCW) system. An inadvertent containment t isolation is stated to only affect discharge from the seals, which is re-routed to the pressurizer relief tank. Both seal flow and CCW flow to the RCPs continue.

Seabrook states that the only credible event which would interrupt both of the cooling water sources is a loss of off-site power. This would result in de-energization of the RCPs. One of the seal cooling sources would be restored upon startup and loading of a diesel generator. Either system is stated to provide adequate seal cooling for at least two hours with loss of off-site power.

The staff has a number of comments and' quest' 1s pertinent to the

Seabrook response. These include

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1. The response appears to be based upon consideratio'ns applicable to FSAR transients and analyses. The concern is more pr6perly weighted toward actual plant operation under transient and accident conditions.

2. The response addresses loss of both sources, or seal injection i behavior with a loss of off site power. There are many'other possibilities. For example, does Seabrook have various levels of containment isolation as is common to many Westinghouse plants, and, 1 if so, what is the response to the various levels? Is seal l

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injection lost upon receipt of a Safety Injection (SI) signal due to actions such as closure of charging lines or tripping of charging pumps? Does CCW continue under all conditions of containment isolation?

3. What are the conditions under which RCP operation can be continued, and under what conditions must the RCPs be tripped?

4. What are the conditions under which RCP restart is permitted?

5. If CCW operation is terminated and later restored, what are the u implications and what precautions are taken to assure the RCP .

components are not overstressed? Similar questions may be addressed l to seal injection.

6. 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 identified. The staff does not need a large volume of material on these topics, but does need a brief mention with perhaps reference to procedures in the list provided with the submittal.

Applicant Response. The following information is provided for each of the items:

1, 2. The time associated with loss of all RCP cooling is the time it would take for the RCP seal components to reach a temperature where there may be a temperature concern. Leakage rate would not be expected to be affected at this point. Anything epproaching a large leak rate (LOCA) is not expected for longer times.

The system used for the thermal barrier coolers at Seabrook is somewhat unique, and contributes to a slow thermal response of the RCP seals due to simultaneous loss of both seal injection and CCW, provided there is still AC power to the system pumps. This occurs 11 l

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.A" because there will still be water circulated between the referenced system and the thermal barrier heat exchangers, and the water and sy$tesi components contribute a significant thermal mass. Note, howev'er, that CCW is necessary for RCP motor cooling.

The first level of containment isolation at Se@ rook only affects the seal water return, which is re-routed to the PRT. The high-3 q' containment isolation signal terminates'. C_CW to the RCP motor coolers, but CCW to'the thermal barrier heat exchanger system and RCPsealinjectionareunaffected.

s 3. RCPs are normally not run for more than two minutes without motor cooling. There are additionally a number of trip parameters, such as bearing temperatures, s431! water' return rat.e and seal water pressure differential, which must be met for normal RCP operation.

These would be applied to most circumstances which could exist in s the plant. An exception is Inadequate Core Cooling (ICC). Here, the RCPs would be restarted in accord with information provided in the ,WOG Rev. l'7 Emergency Procedures Guidelines. Note that in ,

general, Seabrook follows those Guidelines.

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4. There are tigIttstemperature rate limitations on reinitiation of RCP operation foll6 wing a loss of all seal cooling. -

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See the above.

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1 Additional Staff Comment. The discussion clearly established that a nu'mber of plant procedures apply to the points identified by the staff,

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' that the personnel _ representing Seabrook were familar with these

'prbcedures and the underlying need, and that the necessary precautions wre reflected in the procedures and understanding.

82. Ideatify the colnponents required to t; rip the RCPs, including relays, powe. supplies and breakers. Assure that RCP trip, when necdssar ,' will cccur. Exclude extended RCP operation in a voided system where pu:np head t~ A 4

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, 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, and their location is established as outside containment.

Control power is also discussed.

A brief consideration should be given to the potential for adverse s conditiuns outside containment and the implications, if any. For example, can a steam line break introduce difficulties with respect to

J the equipment of interest here?

The timing of operations associated with alternate operator actions required to trip the RCPs should be mentioned. For example, if the operator attempts a trip from the control room, and fails, what alternate procedure will be followed such as trip from an alternate location? How long will it take to trip from an alternate location, including travel time?

RCP operation in a voided system is not mentioned.

Applicant Response. All equipment is located in electrical equipment

, areas which do not have high energy lines.

In the event of unsuccessful operator attempts to trip RCPs from the control board, there are alternate techniques which would be applied.

For example, under normal circumstances one could trip the breakers by

, physically walking to the breaker location. One would expect to accomplish this in less then 10 minutes (normally 5 minutes, and in a minimum of about 3 minutes). One could also shed the bus which provides power to the RCPs. There is no safety related equipment on the bus, 13

which also provides power to circulating water pumps and some non-vital motor control centers.

Backup procedures to accomplish these actions are not provided. Such actions are covered in operator training and are considered a normal response which follows from such training, which provides an emphasis on operator understanding of the plant responses and the need for taking certain mitigative actions to plant conditions.

C. Operator Training and Procedures (RCP Trip) s 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 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 conditions.

Justify that the time availalle 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.

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Staff Evaluation. The Seabrook response consists or a brief reference to training in plant specific emergency procedures and "...Seabrook Station has elected to use the reactor coolant subcooling margin as a method of providing guidance to the operator for initiating a manual trip of the RCP in the event of a small break LOCA. The low'subcooling margin temperature only provides guidance and is not meant to be used alone.

Before actually tripping the RCPs, the operator must also ensure that at least one CCP or SI pump is also running."

The staff does not understand these statements. For example:

u 1. This is the first mention of a qualifier which requires other parameters be satisfied prior to tripping RCPs. Why are these qualifiers provided? Are there any others which have not been stated? How is this description consistent with a requirement that the RCPs be tripped under LOCA conditions?

2. The staff believes that if there is no CCW, then there is no cooling to the charging pumps or to the SI pumps. Is this correct? If so, can these pumps operate without cooling? If not, given the situation of no CCW, how can there be seal injection or cooling to the RCPs? Without cooling to the RCPs, how can they continue to be run consistent with the above Seabrook statement?

A description of training and background philosophy is not presented.

The staff expects this information. The staff also expects information pertinent to RCP restart. A paragraph or two is sufficient, the staff does not desire an in-depth treatment. It is sufficient to establish an understanding of the subject.

Applicant Response. The operator is expected to think and not blindly respond to plant conditions. Thus, the subcooling margin utilized for RCP trip is not an absolute, and other plant conditions may appropriately affect RCP trip. Unavailability of any makeup to the RCS represents such a case, and running RCPs as long as is reasonable is a response designed 15

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to extend core cooling beyond what would be obtained if the RCPs were tripped under these unique and unexpected conditions. Note such actions are taken under conditions which are beyond the design basis, and which l l

are beyond the conditions reported in the FSAR. I The staff belief that there is no cooling of the charging and SI pumps under conditions of loss of all CCW is correct. Of these pumps, only the positive displacement pump might operate for more than a few minutes without cooling, and its ability to do so has not been evaluated. (Note this pump has a capacity somewhat above 100 gpm.) See also the prior responses on RCP operation with loss of CCW and seal injection.

s The previously referenced documentation is used during operator training, and provides an understanding of the need for various actions pertinent to RCP operation.

Additional Staff Comment. The staff has not reviewed the tradeoffs between operating RCPs if there is no ability to provide makeup water to the RCS as contrasted to tripping RCPs. There are logical arguments to support both positions. The staff will address this generically. Since many W plants probably have incorporated this WOG provided guidance into their emergency procedures, the present staff thinking is to accept this approach unless there is a clear need for its rejection. No such need is presently apparent.

The discussion with the applicant established that the referenced documents reflected an understanding of the background for RCP operations, and this understanding is in turn being provided to the operators as part of their training.

C2. Identify those procedures which include RCP trip related operation:

(a) RCP trip using WOG alternate criteria (b) RCP restart ,,, ,

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1 (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. Seabrook has presented a listing of selected procedures which address RCP trip. They are not identified with respect to topics (a) - (f). Are these topics included?

w Applicant Response. Yes.

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REFERENCES

1. DeVincentis, John, " Response to Generic Letter 85-12", letter to Hugh L. Thompson, Jr. , NRC, from Public Service of New Hampshire, 58N-976, T.F. B5.3.99, Mar. 31, 1986.

2. Thompson, Hugh L. Jr. , " Implementation of TMI Action Item II.K.3.5,

' Automatic Trip of Reactor Coolant Pumps' (Generic Letter No.

85-12)," Letter from Director, Division of Licensing, NRC, to all applicants and licensees with Westinghouse {W1 designed nuclear steam supply systems (NSSSs), June 28, 1985.

3. Eisenhut, Darrell G., " Resolution of TMI Action Item II.K.3.5,

' Automatic Trip of Reactor Coolant Pumps' (Generic Letter No.83-10d)", NRC letter to all licensees with Westinghouse IW1 designed Nuclear Steam Supply Systems (NSSSs) (except Yankee Atomic Electric Company), Feb. 8, 1983.

4. Berlinger, Carl, "RCP Trip, Seabrook Station Units 1 and 2", NRC Memorandum to Vic Nerses, April 10, 1986.

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