ML20247Q856

Summary of ACRS Instrumentation & Control Sys Subcommittee Meeting on 890421 in Bethesda,Md.Implementation Status of ATWS Rule & Related Outstanding Technical Issues Addressed

ML20247Q856
Person / Time
Issue date:	05/03/1989
From:	Advisory Committee on Reactor Safeguards
To:	Advisory Committee on Reactor Safeguards
References
ACRS-2641, NUDOCS 8908070275
Download: ML20247Q856 (13)

Text

DATE ISSUED: 5/3/89 Gg/s-076 A ACRS Meeting Minutes / Summary of the PDR f/*/f Instrumentation and Control Systems Subcomrrittee April 21,1989 Bethesda, Maryland

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Purpose The purpose of this Subcommittee meeting was to review the implementa-tion status of the ATWS Rule and discuss the related outstanding techni-cal issues.

Attendees ACRS NRC W. Kerr, Chairman D. Lynch, NRR H. Lewis, Member S. Newberry, NRR C. Wylie, Member J. Mauck, NRR W. Lipinski, Consultant D. Fieno, NRR L. Oakes, Consultant W. Hodges, NRR M. El-Zeftawy, Staff H. Richings, NRR S. Long, Fellow H. Lee, NRR J. Hannon, NRR V. Thomas, NRR Others G. Gurican, GPU W. Sullivan, GE J. Tunstill, FPC J. MacEvoy, BCP&R J. Taylor, B&W M. Ryan, CE R. Ellison, B&W R. Barnes, AP&L M. Osborne, W M. Tull, AP&L M. Hitchler, W D. Williams, API' R. Miller, }f M. Evans, NUS R. Newton, WEP J. Lumbado, IBM S. Floyd, CP&L J. McPherson, IBM W. Martin, CP&L E. Fotopoulos, Bechtel I?S G. Samstad, GE L. Stalter, TEC l l DESIGNATED ORIGINAL hh

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Instrumentation and Control Systems Meeting Minutes April 21, 1989 l

Meeting Highlights, Agreements, and Requests l

1.

Dr. Kerr,' Subcommittee Chairman, scated the purpose of the Subcom-mittee meeting and introduced the other ACRS members and consul-tants. He emphasized that the subject of this meeting is not to discuss the ATWS Rule, per se, but rather'to discuss its implemen-tation.

1 Dr. Kerr commented that the core damage probability associated with 1

ATWS depends upon the reliability or lack of availability of the automatic shutdown system.

The Subcommittee members are interested in the modifications that were made as a-result of the'ATWS Rule I

and in their effect on reliability.

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Mr. S. Newberry, NRC/ Chief of Instrumentation and Control Systems Branch, NRR, indicated that since the NRR reorganization in the Spring of 1987, his branch has expended considerable resources to resolve the issues of interpretation to implement the ATWS Rule, and to review each plant design.-

Mr. H. Lee, NRC/NRR, indicated that in April 1985, NRR issued Q/A generic letter (85-06) providing guidance to-the industry.on the ATWS modifications needed to implement the Rule.

In May 1985, the staff started the review effort. They have completed 82 safety evaluation reports (SERs) and inspected 30 plants. Mr. Lee pro-vided a sunmary of the ATWS Rule implementation status.

For BWRs (total of 37), 36 plants have implemented recirculation pump trip, 32 plants have implemented alternate rod injection, and 36 have i<nplemented standby liquid control systems.

For W plants (total of 55), 20 plants have implemented the. ATWS mitigating systems actua-tion circuitry (AMSAC).

For CE plants (total of 15), only 3 have implemented the AMSAC.

Six h m implemented the diverse scram system (DSS).

For B&W plants (total of 8), no plants have current-l ly implemented either the AMSAC or the DSS.

However, the projected

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schedule indicates that by the year 1990,.3 B&W plants will imple-ment the AMSAC and DSS. The other remaining 5 plants will. complete.

their implementation by 1992.

Mr. Lynch, 'NRC/NRR, indicated that the s'taff does not give' credit.

1 for implementation until the plant procedures have been revised and -

l the operators have been trained.

Mr. Lee summarized the open issues and the staff's position. There are two main open issues:

(a) BWR plants. instrument diversity -

many BWR plants installed the same type of analog transmitter trip-units (ATTV) for both RTS and the ARI' system. The staff feels that this does not satisfy the ATWS Rule diversity requirement; (b)

Newer CE plant AFW actuation diversity - some newer CE designs.use the same type of components that were used in the existing RTS.

The staff feels that safety benefits justify requiring the design of AMSAC to be diverse and independent from the existing RTS.-

l The staff noted that the acceptable level of component diversity can be achieved in accordance with a combination of allowable methods such as the use of components from different. manufacturer or functional capability.

Identical components used in both.the existing RTS and the diverse scram system are subject to potential common mode failures and thus not acceptable.

The staff indicated. that the meaning of " independence" is derived from the Rule. The Rule states that. logic and actuation device power must be from an instrument power supply independent from the power supplies for the existing RTS. The shared.1E power is i

acceptable if DSS and AMSAC are class IE systems. A failure mode and effects analysis (FMEA) is required to demonstrate that the possibility of common mode failure is eliminated.

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y Instrumentation end Control Systems Meeting Minutes April 21. 1989 j

i Mr. Lynch summarized the exemption process. He indicated that the process is administrative and legal in nature. Any utility has the right to submit an appeal at the branch chief level, the office director or at the division director level. The licensee would be appealing a particular staff position. Appeal provides'an oppor-

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tunity for the industry to assure.itself that each level of manage-ment has had a chance to hear their best case. Mr. Lynch indicated

.l that there is another formal process which is more legalistic in nature.

10 CFR 50.12 allows the licensees to request exemption, provided they meet one of six individual criteria, such as finan-cial hardship. Another criterion that could be met, and which would satisfy the requirement for the exemption, is.that the 1

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licensee's approach meets the intent of the Rule.

Mr. Newberry addressed the BWRs recirculation' pump trip. failure

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issue very briefly. He indicated that some of the BWRS use a trip f

l design that opens the field breaker to the M/G sets for the recir -

culation pumps. Recently, there was an event at Fenni II where a breaker failed tc open when it should have. The results of inves-tigation of this event indicated inadequate _ maintenance was the j

root cause. The staff is searching for a more reliable way to trip the recirculation pumps. The RES staff is proposing a potential new generic issue to investigate the reliability of recirculation pump trips.

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Mr. H. Richings, NRC/NRR, discussed the effect of BWR instability

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on ATWS fixes.

He indicated that the staff is concerned that oscillations might cause an effective power increase during the low flow, part power, SLCS injection mode.

Also, there~is concern about the effect on suppression pool temperature, prior to shutdown by liquid control. Mr. Richings stated that the TRAC-GE-3D code-was used to study oscillation. GE calculations concluded that no significant power increase resulted from the oscillation produced.

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t Mr. Lynch summarized the exemption process. He indicated that the process is administrative and legal in nature. Any utility has the j

right to submit an appeal at the branch chief level, the office director or at the division director level. The licensee would be appealing a perticular staff position. Appeal provides an oppor-

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I tunity for the industry to assure itself that each level of manage -

ment has had a chance to hear their best case. Mr. Lynch indicated that there is another formal process which is more legalistic in nature.

10 CFR 50.12 allows the licensees to request exemption, provided they meet one of six individual criteria,.such as finan-cial hardship. Another criterion that could be met, and which would satisfy the requirement for the exemption, is that the licensee's approach meets the intent of the Rule.

Mr. Newberry addressed the BWRs recirculation pump trip. failure issue very briefly. He indicated that some of the BWRS use a trip design that opens the field breaker to the M/G sets for the recir-culation pumps. Recently, there was an event at Fenni II where a i

breaker tailed tc cpen when it should have. The results of inves-

'!gation of this event indicated inadequate maintenance was the

.oot cause. The staff is searching for a more reliable way to trip j

the recirculation pumps. The RES staff is proposing a potential

.i new generic issue to investigate the reliability of recirculation i

pump trips, i

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Mr. H. Richings, NRC/NRR, discussed the effect of BWR-instability j

on ATWS fixes. He indicated that the staff is concerned that l

oscillations might cause an effective power increase during the. low flow, part power, SLCS injection mode.

Also, there is concern q

about the effect on suppression pool temperature, prior to shutdown by liquid control. Mr. Richings stated that the TRAC-GE-3D code was used to study oscillation. GE calculations concluded that no significant power increase resulted from the oscillation produced.

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Instrumentation and Control Systems Meeting Minutes April 21, 1989 EPRI is investigating operator response to ATWS with oscillations.

BNL personnel have performed calculations using RAMONA-3B and engineering plant analyzer (EPA) codes. These calculations have explored ATWS scenarios, but with no quantification or separate effects of oscillations on thermal power.

4.

Mr. D. Fieno, NRC/NRR, gave a brief presentation regarding PWR ATWS moderator temperature coefficients (MTC).

He indicated that the staff had previously expressed some concern on the validity of earlier PWR ATWS analysis assumptions for MTC values because of charges related to:

Extended cycles of 18 and 24 months Increased discharge burnup Lcw leakage core designs New fuel designs MTC tech-specification change requests.

The staff issued a letter to PWR Owners Groups dated June 12, 1987, requesting the following:

• Information and justification of the conservatism in ATWS based on current MTC values.

Differences in current MTCs with ATWS base MTCs.

Plant data used and assumptions made.

Methodology used to derive ATWS MTCs.

The staff concluded after reviewing the current MTC values and ATWS base values, that the current MTC data is consistent with previous ATWS MTC analyses for all PWR designs.

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Mr. L. Stalter, Toledo Edison Company, representing B&W Owners

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Group. stated that there are no outstanding difficulties with the i

B&W plants at this time.

None of the B8W plants has requested an exemption from the requirements of the'ATWS Rula. Mr. Stalter outlined some of the issues of concern that were identified in the SER such as:

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• The power supplies did not provide independence from the RTS.

The use of isolation devices.

• How total loss feedwater is detected.

• The uses of bypasses and displays.

The items and plant specific concerns are being addressed by each utility in individual submittals. Mr. Stalter indicated that for the (DSS),- the B&W plants have the capability-to de-gate silicon -

controlled rectifiers to de-energize the control' rod drive motors j

allowing the rods to drop into the core.

I Mr. Stalter provided some options to resolve'~the power. supply-j independence issue with the staff, such as:

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• Power DSS /AMSAC with its own non-1E battery, inverter, and l

charger to provide 120V/AC.

Power DSS with a non-battery backed power source, show that i

the rods go in onl loss of offsite power, and show that the j

emergency feedwater initiating system is equivalent to AMSAC, and is Class IE.-

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Instrumentation and Control Systems Meeting Minutes April 21, 1989 Provide a Class IE DSS, and show that the EFW initiating system is equivalent to AMSAC, and is Class 1E.

6.

Mr. R. Newton, Chairman of Westinghouse Owners Group, indicated that there are two main products that address the ATWS Rule, ramely, the AMSAC design and a more recent item in response to NRC request on the MTC values. The W Owners Group has two goals:

(a) to provide generic means for addressing the ATWS Rule, and (b) to allow utility flexibility in rule implementation.

Mr. Newton emphasized that the AMSAC design is ar active system.

It will not trip the plant if it loses power, and in that regard it does not add any unreliability to the plant.

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Ms. M. Osborne, W/ nuclear safety analysis, described the AMSAC functional design.

She indicated that WOG AMSAC has three actu-ation logics:

(a) low steam generator level, (b) low feedwater flow, and (c) main feedwater pump status or main feedwater valve closure.

Implementation of approved functional oesign also re-quires plant specific NRC approval.

Ms. Osborne indicated that WOG structured an ATWS Rule program to assess and respor.d to the June 1987 NRC letter. This program showed continued acceptability of ATWS core damage frequency (CDF) for f plants, given installation of AMSAC. Although AMSAC is required to meet the SECY-83-293 target AkSAC unavailability is not a significant contributor to CDF.

Fuel manugement has a small effect on CDF, depending on availability of pressure relief. This program model is. compatible with IPE.

Mr. Newton, W, described the AMSAC implementation status.

Based on WOG survey in April 1989 of 26 sites and 43 units, there are 22 plant specific sites approved by the NRC, 3 pending, and 1 not yet submitted. As far as the installation on specific units, there are

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22 installed, 7 to be installed shortly or at next-refueling, and 14 not installed yet. Based on this survey, two open items are currently being reviewed:

(a) Tech Specs, and (b) control room human factors review.

Mr. Newton indicated that.the NRC has approved a generic WOG func-tional design for AMSAC. Mr. Newton stated that.W plants are successfully implementing the requirements of the' ATWS Rule with no difficulties.

i 7.

Mr. S. Floyd, Carolina Power & Light Company, representing BWR Owners Group, summarized the ATWS implementation status. He indicated that there are two major implementation problems, namely.

NRC request for. additional diversity for analog transmitter trip units (ATTV's) in alternate rod insertion (ARI) system, and q

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• NRCrequestformodificationstorecirculationpumptrip(RPT) l logic.

There are 37 total units subject to the ATWS-Ru'ie.

30 Units i

essentially complete, and 7 units incomplete (6 having a diversity

-i issue). There are a total of 19 units with the diversity-issue.

There is one exemption that has been_ requested,-and a potential of.

19 others, based on the diversity issue.

1 Mr. Floyd indicated that the NRC staff's position on the ' diversity issue is as follows:

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• Trip unit is not part of the sensor and therefore requires j

diversity.

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• ARI system lacks diversity and does not. comply with ATWS Rule.

The BWR OG's position is as follows:

The trip unit is part of the sensor which is not required to be diverse.

The ARI system meets the diversity requirement and minimizes the potential for common mode failure.

• Staff's position does not offer an improvement in CDF.

1 Mr. W. Sullivan, General Electric, summarized the diversity issue by stating that:

• Trip unit is part of sensor and does not require diversity.

• Diversity is not limited to " equipment diversity" by the ATWS Rule.

• Statement of consideration states equipment diversity where reasonable and practicable.

• Staff's position asks for hardware diversity that is-difficult i

to achieve and ignores cost or. benefit.

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Fabrication diversity for the.Rosemount ATTUs provic:es negif-gible safety improvement.

Mr. Sullivan stated strongly that the current GE design meets both' language and intent of.the ATWS Rule.

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Mr. D. Williams, Combustion Engineering Owners Group. indicated

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that approximately three years ago, the NRC has accepted the DSS, diverse turbine trip designs for CE plants, and the EFW actuation system designs for Arkansas plant.. The CE plant activity in the ATWS area has been plant specific and non-owners group. There are six CE-newer designs-that have a diversity. issue problem. Three plants are currently cooperating.to reach a resolution with the staff. The diversity issue has' to do with the sharing of similar or same equipment in the electronics to trip the plant and the-electronics that actuate the EFW.

However, this issue does not exist for older CE plants.

CE submitted an exemption request based on cost-benefit and the contribution to reduction 4 risk, which has been denied by the'NRC staff.

Mr. Williams indicated that CE Owners Group does not have informa-tion on the individual plant implementation status or licensing activity.

However, Mr. Williams stated that he anticipates that there will be either a resolution or a deadlock that includes a formal action.in-the next 2 or 3 months regarding the three cooperating plants.

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As a result of the Subcommittee's discussion, some of the members and consultants expressed some concerns in regard to the following:

• Dr. Kerr questioned the staff's philosophy regarding the ATWS fixes and commented that the review criteria should emphasize low risk and high reliability rather than just diversity.

' Dr. Kerr commented that he is not convinced that replacing different devices such as replacing Rosemount ATTU circuit 1

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-6 Instrumentation and Control Systems Meeting 'linutes April 21, 1989 board with an equi.alent board manufactured by a different vendor vill significantly improve reliability.

" Dr. Lewis questioned the staff's position that complete diversity would result in minimizing the probability of common mode failures.

Dr. Kerr questioned that purchase of two separate components from two separate vendors would result in enhancing the overall reliability of the system. Mr. Lipinski shared the same sentiment.

Mr. Lipinski indicated that it is very difficult to quantify any benefits from diversity, whereas reliability of individual components could be quantified by collecting data on suffi-cient number of units.

Mr. Lipinski suggested that sensor-transmitters could be built according to military specifications and the staff may con-sider this as a worth investigating alternative.

Mr. Lipinski indicated that the disagreement between the staff and industry on how to define a sensor,.,ensor-transmitter, or a sensor-transmitter-trip unit, stems from the fact that the ATWS Rule requires independence and diversity from, and not including the sensor. Therefore, the distance and location of the sensor plays an important role. He commented that the staff should focus on circuitry down-stream and physically isolated from the sensors to be tested for independence and diversity.

The Subcommittee members agreed to that approach.

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• Dr. Lewis cautioned the staff regarding the implementation I

process.

He urged that it should not to be handled as a m

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a basic goal of making the plants as. safe as is reasonable.

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• Dr. Lewis commented that even if the hardware changes are in terms of simple circuitry and relays as stated by the staff, l

we should not underestimate the reliability of complex systems I

such as the scram systems.

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• Dr. Lewis indicated that'the administrative oppsal process l

would be better handled with technical personnel even if it l

only involves simple relays and wires, rather than handling it!'

with people who are incapable of judging technical issues.

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• Mr. Davis noted that the quantification of increments of risk.

reduction as a result of adding the ATWS Rule systems appears to be a useful way to measure the benefits.

However, this method of measuring the incremental risk changes in CDF only tells part of the story. A preferred quantitative measure.

would be one of public consequences risk reduction as de-termined in a Level 3 PRA.

• Dr. Kerr expressed some concern regarding capability of the TRAC computer code used by GE to handle a large. amplitude oscillations in BWRs coupled with ATWS scenarios.

Future Action The Subcommittee Chairman is planning to'brief the full Committee on May 3-6, 1989 regarding the Subcommittee activities. There is no letter writing expected at the May 1989 ACRS meeting regarding this issue.

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NOTE:

Additional meeting details can be obtained from a transcript of this meeting available in the NRC Public Document Room, 2120 L Street, N.W., Washington, D.C. 20006, (202) 634-3273, or can be purchased from Heritage Reporting Corporation, 1220 L Street, N.W., Suite 600, Washington, E..

20005,(202) 628-4888.

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