ML20205N115
| ML20205N115 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 04/22/1986 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20205N113 | List: |
| References | |
| GL-85-12, NUDOCS 8605010443 | |
| Download: ML20205N115 (11) | |
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ENCLOSURE INTERIM REPORT CONCERNING REVIEW OF RCP TRIP AT BEAVER VALLEY UNIT 1 INTRODUCTION The staff briefly reviewed the Reference 1 submittal, and prepared preliminary comments and questions which served as an agenda for a telephone conference call with Beaver Valley Unit 1 personnel. The initial conference call occurred on February 19, 1986, and there was a followup telephone call on February 26, 1986. Both calls involved Ed Coholich of Duquesne Light and Warren Lyon of NRC. This Enclosure expands upon and documents all items contained ih the agenda, and also provides the staff understanding of licensee responses obtained during the conference.
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 perception of the telephone conference call is then sunnarized.
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, i
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- 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 ont 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 t3 the small break, where trio must be. accomplished to remain in compliance with the regulations. (Failure to trip as required could lead to exceeding Appenfix K specified temperatures.) For "nsn-break" transients and accidents, RCPs may be tripped when desirable. If in doubt, the small break criteria are to be applied.
New plants cc:ning on line should have dealt with RCP trip prior to power operation. 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.
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SPECIFIC EVALUATION CRITERIA AND C099 TENTS 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 j small-break LOCAs but will not cause RCP trip for other non-LOCA transients and accidents such as SGTRs. This is to include perfomanca l
of safety analyses to prove the adequacy of the setpoints.
Consider using partial or staggered RCP-trip schemes.
Staff Evaluation. The licensee has selected the secondary pressure dependent RCS pressure criterion as the basis for RCP trip. This is one
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of the three criteria which the staff previously found acceptable on a
! generic basis, and is the one which the staff recomended as the first 1
choice, again, on a generic basis.
a The staff requests that the licensee provide a sumary of the selection process which illu:strites tiie r6Lional leading tu the selected trip l criterion.
1 A1. Identify the instrumentation to be used to detemine the RCP trip set i point, including the degree of redundance of each parameter signal needed l 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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- Staff Evaluation. Reactor Coolant System (RCS) wide range pressure instrumentation and steam generator pressure instrumentation is ;
) identified by number and manufacturer. This includes racks and.
indicators. The wide range indicators are stated to be safety grade and redundancy exists. Three secondary pressure indicators are stated to
! exist for each loop. All instruments are stated to be environmentally i i 3 i
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qualified for the design basis accident which they are required to mitigate.
A2. Identify the instrumentation uncertainties for both nomal 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 l instrumentation reliability. )
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Staff Evaluation. Normal and post-accident indication accuracies are i provided. The selection basis is the Emergency Procedures for the Beaver Valley Power Station. Containment pressure above 5 psig or containment 5
radiation in excess of 10 R/hr result in use of adverse containment l parameters by the operator. Otherwise, nonnal parameters (uncertainties) l are used. l l
The licensee reported a review of plant drawings, instrument locations, '
sensing lines, and electronics, and concluded that no single failc.e
- would result in a fluid jet or pipe whip causing loss of all instrumentation used to monitor the RCP trip setpoint.
The applicant does not address permanent damage that may have occurred to instrumentation due to exposure to an adverse environment.
1 Licensee Response. The seconoary pressures are determined via three channels for each of the three steam generators. As discussed in the Beaver Valley submittal, the pertinent connections, wiring, et. al. are widely separated and it is unlikely all would be affected at the same time or during the same accident. Additional redundency is provided by sensors on each of the steam lines, which are used for control of the atmospheric dump valves. Operators are instructed to use all available instrumentation in determination of the status of the plant and in the planning of a response to a plant upset condition.
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f The reactor coolant system (RCS) is more limited, with two pressure indicators which cover the full pressure range. Pressurizer pressure indication is also available, but these are limited to the range above i about 1750 psi. If there is difficulty with pressure readings, the' operators would use RCS temperature measurements to provide additional information. (They would assume the temperatures corresponded to l
saturation conditions to determine a pressure, and use that for guidance in planning their response.)
A3. In addressing criterion selection, provide consideration of uncertainties associated with the WOG supplied analyses values. Theseuncerta)inties l 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 cre marginal for preventing unneeded RCP trip, it is recommended that a more discriminating plant-specific procedure be developed. Licensees (or I 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 ext "ed f conditions.
Staff Evaluation. The computer program result uncertainties evaluation j is based on the assumption of no changes in initial plant conditions (such as full power, pressurizer level, all SI pumps running, all AFW i
pumps running). The major contributors to uncertainty are stated to be break flow rate, SI flow rate, decay heat generation rate, and auxiliary '
i feedwater flow rate. The break flow model is stated to be about 30%
high, SI flow rate has roughly a +/- 10% uncertainty, and decay heat is about 5% high when contrasted to best estimate models. (AFWisbest estimateasusedinthecode.) Parameter study results are mentioned which show little sensitivity to decay heat and AFW flow. The applicant concluded that the calculational uncertainty is -30 to +300 psi for the RCS/ Secondary Differential Pressure RCP setpof nt based upon uncertainty '
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in the break flow model and SI flow rate. (Other parameters were not included since they were felt to be negligible.)
The WOG analyses were performed with the licensed Westinghouse LOFTRAN computer code for plants under non-LOCA conditions.
The applicant 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 expected configuration of the plant is addressed since the objective of RCP trip is to provide reasonable assurance of not tripping for transients for which a trip is undesirable. It is not necessary to establish that one will never trip since the plant is capable of being safely controlled if an unnecessary trip does occur. Thus, no additional information is needed for the staff to complete review of this item.
B. Potential Reactor Coolant Pump Problems
- 81. 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 I
isolation with continued pump operation will not lead to seal or pump damage or failure, i
Staff Evaluation. Water services are identified as the component cooling water (CCW) system which cools the RCP thermal barrier heat exchangers and RCP oil, and the RCP seal injection flow which is provided by the charging /high head safety injection pumps. Seal injection is not !
affected by containment isolation, and is stated to be adequate to ,
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prevent seal damage. CCW is maintained under phas~e A cont < Nment isolation conditions, but is terminated upon receipt of a phase B signal.
In the event of a phase B isolation, flow cannot be restored fast enough that the RCPs can be allowed to continue to run, although operation for a limited time is stated to be possible without damage. A variety of alarms and operator instructions pertain to stopping RCPs. Restart instructions are provided in the Emergency Operating Procedures.
B2. 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.
4 Staff Evaluation. The various equipment items are identified by number and plant location. The licensee states that none are located where they are influenced by conditions associated with the accident in question.
Various options are covered. Manual trip of the RCPs from the pump breaker in the switchgear room is mentioned, but the time to accomplish this action is omitted.
There is no discussion of 10% degraded operation.
Licensee Response. If the operator tries to trip from the main control board and is unsuccessful, then the following time sequence is believed reasonable:
- 1. The operator will take 15 seconds to deterinine that a manual remote trip is necessary.
- 2. The operator will walk at a fast pace from the control room to the location of the RCP trip breakers. This will take about 50 seconds 7
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(determined by timing an operator walking from one location to the other).
- 3. The operator will trip the three breakers in about 20 seconds."
These estimates are sufficient to establish a rough response time, and clearly indicate that an undue delay will not occur upon failure to trip from the control room (unless an operator error is involved, which was not the intent of the staff concern).
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 direction for use of individual steam generators with and without operating RCPs.
Assume manual RCP trip does not occur 2arlier 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 than 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. Selected methodology is stated to be based upon the WOG approach, and a brief description is provided in regard to use of the information in operator training. The licensee has provided a reasonable discussion of background concerns and the need for RCP trip as contrasted to running RCPs.
The RCP trip criterion is stated to be to trip the RCPs if the RCS pressure is 145 psi greater than the highest steam generator pressure for normal containment conditions, or 510 psi greater for adverse containment conditions. However, the statement is also made that "If primary to secondary delta-P decreases to the trip setpoint of 145 psi and high head SI flow is verified, the RCP's must be tripped." These do not appear to be consistent statements.
What would happen if there were an isolated steam generator which remained at high pressure as the remainder of the plant was cooled down?
"The non-LOCA events analyzed are a steam break and a feedline break.
The analysis shows that primary to secondary delta-P should not decrease below 350 psi for these events. RCP's will not be tripped during a SGTR 1 or non-LOCA event unless containment pressure rises to 10 psig and CIB actuates." This does not appear consistent with the previously stated 5
criterial of trip at 5 psi or 10 R/hr.
i Licensee Response. RCP trip criteria, as addressed here, are applicable to the first few minutes of a transient or accident, and are not applicable to the regime of controlled RCS cooldown.
The operator will know if a steam generator is isolated so that its pressure can " hang up", and will respond accordingly.
i Staff Response. Timing should extend into the transient sufficiently far that RCP restart beyond the window of vulnerability is covered. ,
i C2. Identify those procedures which include RCP trip related operation: I 9 I l
(a) RCP trip using WOG alternate criteria
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(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 licensee references the WOG Emergency Response Guidelines, and identifies differences between Beaver Valley and the generic guidelines. It does not appear that this is sufficient information for the staff to be able to audit or review the response.
Licensee Response. The Beaver Valley submittal of October 10, 1985 identified changes between the Westinghouse Owners Group procedures and those at Beaver Valley. The Beaver Valley procedures are in the possession of the on-site NRC Resident Inspector, and hence are i immediately available for staff review.
Staff Response. This is sufficient for staff purposes since it is beyond the scope of the present review to perform an in-depth evaluation of procedures. ;
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REFERENCES
- 1. Thompson, Hugh L. Jr., " Implementation of TMI Acticn 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) Designed Nuclear Steam Supply Systems (NSSSs), Jun. 28, 1985.
- 2. Carey, J. J., Letter to Director of Nuclear Reactor Regulation, USNRC, from Vice President, Nuclear, Duquesne Light, Oct. 10, 1985.
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