ML20198P370

Discusses Expansion of Work Being Performed Under GSI-191, Assessment of Debris Accumulation on Pressurized Water Reactors Sump Performance. Sketches of Various Sumps Encl

ML20198P370
Person / Time
Issue date:	05/14/1997
From:	Marshall M NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
To:	Shao L NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
Shared Package
ML20198P288	List: ML20198P284 ML20198P325 ML20198P337 ML20198P370
References
FOIA-99-52, REF-GTECI-A-43, REF-GTECI-ES, RTR-NUREG-0896, RTR-NUREG-896, RTR-REGGD-01.082, RTR-REGGD-1.082, TASK-*****, TASK-A-43, TASK-OR GL-85-22, NUDOCS 9901070042
Download: ML20198P370 (16)

Text

,

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1 May.14, 1997 L

1 MEMORANDUM TOi Lawrence C. Shao, Director Division of Engineering Technology Office of Nuclear Regulatory Research THROUGH:

Franklin Coffman, Chief

/s/ FCoffman-

. Generic Safety issues Branch Division of Engineering Technology Office of Nuclear Regulatory Research

' FROM:

Michael L Marshall, Jr., Task Manager

/s/ MLMarshall Generic Safety issues Branch Division of Engineering Technology Office of Nuclear Regulatory Research

SUBJECT:

EXPANSION OF WORr e _.t.G PERFOdMED UNDER GSI-191,

" ASSESSMENT OF DEBRIS ACCUMULATION ON PRESSURIZED WATER REACTORS SUMP PERFORMANCE"

REFERENCES:

(1) Rao, D., et. al., " Interim Letter Report: Assessment of Debris Accumulation on Pressurized Water Reactors Sump Performance," SEA 97-3702-010-A:1, Science and Engineering Associates, Inc.,

l

- Albuquerque, NM, March 28,1997.

(2) Memorandum to W. Russell, NRR, from D. Morrison, RES,

" Response to NRR's third Supplemental User Need Request for Loss of ECCS Cooling in BWRs Due to Clogging of ECCS Suction Strainers,"

March 4,1996.

(3) Memorandum to D. Morrison, RES, from W. Russell, NRR, " Third Supplemental User Need Request Regarding Potential for Loss of Emergency Core Cooling in a Boiling Water Reactor Due to Clogging of the Suction Strainers by Loss-of-Coolant Accident Generated Debris,"

December 7,1995, l:

(4) Generic Letter 85-22," Potential for Loss of Post-LOCA Recirculation

[

.Due to insulation Debris Blockage," USNRC, December 1985.

(5) Regulatory Guide 1.82, Rev. 2

• Water Sources for Long-Term j

Recirculation Cooling Following a Loss-of-Coolant Accident," USNRC, May 1996.

(6) Serkiz, A., "USl A-43 Regulatory Analysis," NUREG-0896, USNRC, Washington, DC, October 1985.

l-9901070042 990104 i

l PDR FOIA i

O'NEALIA99-52 PDR

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l L.Shao.

In December 1995, the Office of Nuclear Regulatory Regulation (NRR) asked the Office of Nuclear Regulatory Research (RES), via an user need memorandum (Ref. 3), to reevaluate the resolution of pressurized water reactor (PWR) sump blockage to determine if there is a need for further action beyond the onginal resolution (Refs. 4,5, and 6). The safety concern is the same concem the NRC had during the recent reevaluation of BWR strainer blockage; the ECCS will not be able to provide long-term cooling as required by 10 CFR 50.46. In the "new" study, we will consider two types of failures: (1) " localized" loss of water depth and (2) loss of NPSH margin.

A PWR sump blockage study was part of unresolved safety issue (USI) A-43, " Containment l

Emergency Sump Performance." USI A-43 was resolved in 1985. NRR requested this reevaluation because the reevaluation of boiling water reactor (BWR) strainer blockage resulted in regulatory action beyond its original resolution. BWR strainer blockage resolution was included in the USI A-43 resolution. RES agreed to conduct the reevaluation (Ref. 2), but the start of the study was delayed until January 1997 because of resource constraints. RES has l

designated this issue generic safety issue (GSI) 191, " Assessment of Debris Accumulation on Pressunzed Water Reactors Sump Performance " The reevaluation of the technical basis and resolution of the PWR sump blockage had four plausible conclusions:

1.

original technical basis and resolution are adequate.

l 2.

onginal technical basis is adequate, but the resolution is not aceouate 3.

original technical basis is not adequate, but the resolution is adecuate. or-4.

original technical basis is not adequate.

j i

The reevaluation of the adequacy of the PWR sump blockage technical basis and resolution is I

being performed by Science and Engineering Associates, Inc. (SEA). SEA is the contractcr

[

that assisted the NRC with the reevaluation of BWR strainer blockage. SEA was asked to perform several specific tasks:

1.

review the technical basis for the resolution of USI A-43 (75%

completed),

2.

identify information or models used in the USl A-43 evaluation that are obsolete (0% completed),

3.

identify and review debris sources in PWRs (25% completed).

4.

identify differences between PWR and BWR guidance (0% completed).

5 review concerns raised by Finirh and Swedish regulators (25c4 completeo) and i

6 ioentify ano review citferences among PWR containments anc sumrs

,m_.

m

L Shao (75% completed).

April 1997, SEA submitted an interim letter report that documented their preliminary findings.

Their principal findings were.

.l 1.

effect of particulate debris on head loss was not investigated, 2.

the variabihty in sump designs and other pertinent plant features is considerable; it is unknown if the reference plant used in USl A-43 is a worst-case or best-case design (see Att.1),

3.

in addition to head loss or instead of head loss, the ability of water to travel from the containment floor into the sump should have been a failure mode modeled (see Att. 2).

,4.

the sole use of bulk flow rate across a containment floor is not a good measure of the ability of debris to reach debris interceptors, and 5

head loss correlations used will und-er precict head loss So the conclusion that can be crawn from SEA's findings is that the USl A-43 study did not j

completely address all the aspects associated with PWR sump blockage. Based on SEA's i

findings ano my famihanty with this issue. I recommend that the scope of GSI-191 be 1

expanded, beyond merely' reevaluating the USl A-43 technical basis and resolution. to conducting a full comprehensive study, that encompasses the 76 operating units, to determine l

the significance of PWR sump t'!ockage. A *new comprehensive study should involve (see l

Att. 3):

1.

analysts of five to ten reference plants, because of the variabihty in sump designs (NOTE: the reference plants chosen should bound the sump designs in operating PWRs').

2.

survey (see Att. 4) of all or most of PWRs' to collect information (e.g., sump dimension) so an informed decision can be made regarding typicality of the reference plants chosen and collect information that is not readily available (NOTE: this may be the most time consuming part of the study),

3.

continue identifying and reviewing debris sources in PWR containments, j

l 4.

use computational fluid dynamics codes to develop flow networks of the containment floor in the reference plants, l

5.

more applicable (e.g, inclusion of particulate debris) and accurate (e g more representative debns sizes and amounts) head loss correlations Esg Rock Point snouic tm anctucea in in6 ocputatior.

1 L.Shao 6.

include all debris sources (e.g., paint flakes, boron precipitates, etc.) in the analysis, and 7.

estimate the impact of debris blockage over a period of time will be considered.

If the study shows that debris blockage of the sump will prevent the ECCS from drawing water from the sump during the period that it is expected to be available, then the RES staff will work with the NRR staff to devise additional regulatory actions beyond those taken as a result of the USl A-43 study. So the results of the "new" study will be used to respond to NRR's request for 4

an assessment of the original resolution (Ref. 3). The is will be performed to demonstrate the validity and extent of the sump debris blockage safety concern. Also, the study may provide a systematic framework for the NRC to address debris blockage concerns regarding coatings.

a This study should cost approximately S 486.000.00 and should be completed within 17 months from authorization (i.e., funding) to expand the work scope of the GSI-191 work (see Att. 5 and 6). Currently the branch does not have the fiscal resources to fund this work. If funds cannot be redirected towards this effort then the resporise to NRR's request wjll be delayed again.

NRR had originally requested that the work be completed by December 1996, but agreed to the one fiscal year delay (see Ref. 2) During a recent telephone conversation with the NRR Lead Technical Reviewer for this issue. he expressed a desire to have at least preliminary findings by the end of the 1997 calender year Attachments:

1.

Sketches of Various Sumps 2.

Conceptual Description of Debns Blockage impact on Sump Availability 3.

Overview of Proposed Study 4.

Partial List of Possible Survey Questions 5.

Draft of Proposed Modification to NRC-04-97-036 TO OO2 Statement of Work 6.

RES GANTT Chart cc:

J. Craig F. Cherny A. Serkiz DISTRIBUTION:

CENTRAL FILES GSIB c/f s

DOCUMENT:P:\\SHAO16.MEM To receive a copy of this document. indicate in the box: "C" = Copy without enclosures "E" = Copy with enclosures "N" = No copy (OFFICE DET/GSIB DET/GSIB,,

c.

MME MLMarshal1 if FCoffman

• i h

DATE 05/

/97 05/. N 97 05/

,97 05,

,97 i06/

,9-

!j OFFICIAL RECORD COPY (RES " le Code) RE :D '<

c __ _ _

SKETCHES OF VARIOUS SUMPS GSI-191: Assessment of Debris Accumulation on Pressurized Water Reactors Sump Performance The following sketches (Fig.1a to Fig. 9b) were taken (except where noted) from utilities' Updated Fina! Safety Analysis Report (FSAR). To date Science and Engineering Associates.

Inc. has reviewed over 50 FSAR and Individual Plant Examination Submittals, as part of the GSI-191 effort. Many of the FSAR did not have sketches of their sumps and/or the dimensions of their sumps. The sketches shown may not encompass all the different sump designs installed in PWRs, but the sketches do illustrate the variability among PWR sump designs.

Also, the sketches should illustrate the need to collect sump design information for each operating PWR so that we can make informed decisions during the course of the "new" study.

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CONCEPTUAL DESCRIPTION OF DEBRIS BLOCKAGE IMPACT ON SUMP AVAILABILITY

\\

GSI-191: Assessment of Debris Accumulation on Pressurized l

Water Reactors Sump Performance i

i l The safety concem is the same concem the NRC had during the recent reevaluation of BWR strainer blockage l study; the ECCS will not be able to provide long-term cooNg as required by 10 CFR 50.46. In the "new" study, we l will consider two types of failures: (1)" localized" loss of water depth and (2) loss of NPSH margin.

1 1.

"LOCAllZED" LOSS OF WATER DEPTH l

As debris collects against the trash rack / debris screen, the height of the debris mass may increase to the height of the water on the containment floor a'd the permeability of the debris mass may retard the flow of water into the sump. So the 1ocalized" water depth will decrease below the containment water depih, if the ECCS pump is removing water from the sump faster than it is being replenished. Thus, effecting the NPSH l

available and amount of water available for cooling. This failure is predicated on the assumptions that the l

water depth on the containment floor is not very deep or there is enough debns to build a mass as hioh as i

the water depth. If this can be moc,ea usino the equations for seepage. then the orincioal carameters/ variables neeceo :c catu.a.

COVER FLATE TRASH RACK / DEBRIS SCREEN A

DEBRIS 7

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the flowrate through the debris bed are the coefficient of permeability, water depth, debris mass length, and

-debris mass area.

2.

LOSS OF NPSH MARGIN j

As debris collects against the debris screen (i.e., strainer) attached to the suction piping of a pump th'e resistance to flow i'. increased, so the available head loss is decreased. If a pump losses its NPSH, then cavitation will occui leading to a reduction of flow and damaged to the pump. This assumption assumes uniform blockage of debris screen. This has been modeled using equations for flow through a porous media. The principle parameters / variables needed to calculate the head loss across a debris bed are tne porosity, debns mass thickness, water velocity, and viscosity.

OVERVIEW OF PROPOSED STUDY GSI-191: Assessment of Debris Accumulation on Pressurized Water Reactors Sump Performance 1.

DATA COLLECTION AND SCOPING CALCULATIONS:

Because of the variability in sump designs, the NRC should collect all pertinent information for each PWR (see Att. 4) to facilitate meaningful and well-informed analysis of sump blockage. While the NRC is assembling the pertinent information, SEA and the RES staff will develop or refine the equations and methods needed to conduct an evaluation of sump blockage. Also, SEA will conduct a series of calculation (in some cases engineering judgement will be used) to determine (and/or verify) which plant features have the largest impact on an analysis.

2.

SELECTION OF REFERENCE PLANTS:

Based on the plant data and scoping calculations. RES staff and SEA would select several plants that woulo represent or counc me sa'iaL.hty of sump cesign ana other pertinent conditions in operating PWRs. SEA Analysts and RES staff will need to review plant drawings for each of the reference plants and may need to meet once or twice with p! ant personnel to determine the zone of influence of a pipe rupture. Currently, SEA anc I have put the following plants on our short iist of potentral reference plants: ANO Unit 1 (B&W LLP, dryamb), Comanche Peak Unit 1 (4LP W. dryamb), H.B. Robinson (3LP W, dryamb), Maine Yankee (CE, dryamb). Palo Verde (CE80, dryamb), Prairie Island Unit 1 (2LP W, dryamb), Salem Unit 1 (4LP W. dryamb). Sequoyah Unit 2 (4LP W icecnd).

and Zion (4LP W, dryamb). These plants were placed on the ' snort list" because they were used in the USI A-43 study or recommended by NRR staff.

3 ANALYSIS:

The reference plant analysis will be more similar to the analysis conducted for the reference plant during the recent BWR strainer blockage study than the reference plant analysis performed under the USl A-43 study. The analysis will be divided into three distinct but closely related parts: t1) determination of debris sources and amounts, (2) l estimation of debris transport to sump, and (3) determination of impact of debris accumulation on ECCS. The first part of the analysis would involve reviewing plant specific piping drawings, meeting with plant personnel, estimating the amount and I

location of debris sources to determine the amount of debris generated during a pipe rupture. Some of the debris sources in PWRs are thermalinsulation, paint flakes. Boron precipitate, rust, etc. The second part of the analysis would estimate the amount of debris that will be transported from the vicinity of the oipe rupture and the containment floor to the sump based on the existing excenmerW cata Onc! the ongoing PES detM cryweli transport stuoy) anc comoutat;ona; rr ccenr: Tne in:rc can 0; me anaivsd

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would estimate if enough debris has been transported to the sump (s) to cause a

" localized" loss of water depth and/or (2) loss of NPSH margin. Also, a parametric analysis (single and multivariate) will be conducted to better understand the generic implication of the analysis and a regulatory analysis will be conduded to determine the impact of any proposed regulatory actions on the industry. All the analyses will be conducted by SEA.

4.

ASSESS AND UPDATE RESOLUTION:

i The RES staff will review the analysis results provided by SEA and the data collected during the survey to determine the revisions that need to be made to regulatory guide 1.82 and to make a case for taking or not taking addrtional regulatory actions.

i 1

l

7 PARTIAL LIST OF POSSIBLE SURVEY QUESTIONS GSI-191: Assessment of Debris Accumulation on Pressurized Water Reactors Sump Performance s

1.

. minimum containment flood level (depth of water on the floor)

~ 2.

maximum containment flood level 3.

maximum containment sump temperature

'4 required NPSH for RHR and CS pumps

. 5.

available NPSH for RHR and CS pumps 6.

maximum flowrate for RHR and CS pumps 7.

description of containment sump (incl. drowings) l 8.

dimensions (e.g., cepth below containr.r.1t floor, volume. etc ) of containment sump (s) (i.e, sump that RHR draws sue:icr' 9.

de.scription of trasn rack 10.

dimensions (e.g., hole size. height. area. etc ) cf trash rack 11.

oescription of sump screen 12.

dimensions (e.g., height, hole size, area, etc.) of sump screen 13.

containment floor area 14.

position (s) and location (s) of containment sump (s) containment 15.

. list of qualified coatings in containment

~ 16.

list of unqualified coatings in containment 17.

thickness and amount of. listed coatings

- 18.'

list of thermalinsulations used in containment 19.

installation, location, and amount of thermalinsulation 20.

. volume of water in accumulators

-21.

volume of water in RWST 22.

slope of containment floor in vicinity of containment sump 23.

debris curb arrangement

-24.

numt;er of containment sumps

l y

Attachment S

' DRAFT OF PROPOSED MODIFICATION TO NRC-04-97-036 TO 002 SOW AND IGCE NOTE: NRR and RES management have not reviewed this SOW modification, so the scope and cost estimate may change.

BACKGROUNQ The United States Nuclear Regulatory Commission (NRC) first addressed the concern with pressurized water reactors (PWRs) sump performance as part of the resolution of unresolved safety issue (USI) A-43," Containment Emergency Sump Performance." The resolution was published in 1985 (Refs. 6,13, and 15). The USl A-43 evaluation and resolution focused primarily on PWRs, but its results were considered applicable to boiling water reactors (BWRs).

In light of the resolution of S-081, Potential for Loss of Emergency Cooling in BWR Due to LOCA Generated Debris,"(i.e., the BWR suction strainer blockage issue) the NRC decided to reassess debris blockage of PWR sumps to determine if there is a need for further actions to be taken for PWRs beyond the onginal resolution of USl A43 in January 1997, the NRC placed a task order with SEA for technical assistance during the NRC's reassessment of adequacy of tne USI A43 resolution for PWR sump blockage. NRC has designated this issue genene safety i oue (GSI) 191. Assessment of Debris Accumulation on Pressunzed Water Reactors Sump Performance."

OBJECTIVES The objectives of this task are being altered from (1) assess the adequacy of the t7chnical basis

- of the USI A-43 resolution and (2) assess adequacy of regulatory guide 1.82. Rev.1 guidance concerning debris blockage of PWR sumps to studying debris blockage of PWR sumps to assist the NRC in determining if actions beyond those taking dunng the resolution of USl A-43 are warranted. The study will involve several parts and sub parts.

1.

DATA COLLECTION AND SCOPING CALCULATIONS:

The NRC will collect pertinent information for each PWR to facilitate a meaningful and well-informed analysis of sump blockage. While the NRC is assembling the pertinent information, the contractor will develop or refine the equations and methods needed to conduct an evaluation of sump blockage. Also, the contractor will conduct a series of calculations (in some cases engineenng judgement may be used) to determine (and/or verify) which plant features have the largest impact on an analysis of sump blockage.

l

i

. SCHEDULE ASSUMPTION $

e 1,

NRC will collect plant data on all PWR - not SEA.

2.

' SEA will form multiply teams to collect data from reference plants and NRC staff will supervise each plant visit.

)

l 3.

Reference plant analyses will not start untii NRC data collection is complete,

4..

. The reference plants selected will be v. 'ing to participate in study and the NRC will approve of the staff working with those plants.-

5. -

if experiments are required, the need will be identified during their scoping calculations and the.

experiments can be started and finished within four months.

6.

RES and NRR staff will make final decision based draft NUREG/CR reports.

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