ML17334A615

Containment Sump Operability Determination

ML17334A615
Person / Time
Site:	Cook
Issue date:	01/06/1998
From:	INDIANA MICHIGAN POWER CO.
To:
Shared Package
ML17334A614	List: ML17334A613 ML17334A615
References
AEP:NRC:1260G6, NUDOCS 9801200084
Download: ML17334A615 (71)

Text

ATTACHMENT 1 TO AEP:NRC: 1260G6 OVERHEAD SLIDES USED DURING JANUARY 8,

1998, PUBLIC MEETING

ANERfCAN

HECTRlC POMtER ADDITIONALREVIEWS JANUARY 8, 1998

NIERtt,'AN RECTKIC pomER JIM KOBYRA CHIEF NUCLEAR ENGINEER

AMER!CAN RECTRfC NNB

~ December 16, 1997 Public meeting on CAL response

~ December 22, 1997 Public meeting on three follow-up items

~ calculations

~ root cause/short term assessment

~ 50.59 program We agreed to additional reviews

AINRKAN SEC mlC POWER (cont'd)

~ LETTER AEP:NRC:1260G4 December 24, 1997.

Summarized December 22 meeting Commitment to perform additional reviews

~ Letter AEP:NRC:1260G5 December 31, 1997 Docketed results of additional reviews

ANBl(AN HHTRlL POSER

~ Introductory remarks Jim Kobyra

~ 50.59 self assessment Jeb Kingseed

~ Design change self assessment Terry Postlewait

~ Integrated design bases program Gary Weber

AMFRÃAN RECTRtC POWER JEB KINGSEED MANAGER, NUCLEAR SAFETY

AMERfCAN Ef,ECf'RfC POWER AGENDA

~ Purpose

~ Focus

~ Scope

~ Team composition

~ Observations

~ Results

'MERfCAN SEC YRN PONER PURPOSE

~ Evaluate adequacy of 50.59 process

ANRlfAN HKCYRfC POSER FOCUS

~ Operability issues

~ Acceptability of screenings and evaluations

~ UFSAR revision

AMERftlAN HH'TRlt'tNER SCOPE

~ Random selection of screenings and evaluations from 1/96-9/97

~ 35 procedural 50.59 screenings change sheets and revisions

~

11 procedural 50.59 evaluations

~ 25 design change 50.59 evaluations and corresponding screenings

AMERlCAN HHTRlC P4MR TEAM COMPOSITION

~ Three teams two procedure teams one 50.59 design change team

~ Procedure teams composed of:

QA lead auditor nuclear safety 50.59 reviewer operations procedure specialist

AMERlt,'Atll HH,'Nlt,'OSER TEAM COMPOSITION cont'd

~ 50.59 design change teams composed of:

QA lead auditor nuclear safety 50.59 reviewer design engineers

AIERlfAN El.EtlNlf POWER OBSERVATIONS

~ Conclusions were acceptable.

~ 11 of 60 50.59 screenings were not documented to a level of detail that would meet today's standards.

~

1 of 36 safety evaluations did not contain justification that would be considered adequate by today' standards.

AMERICAN EI,ECTRIC POWER OBSERVATIONS cont'd

~ A previously identified and addressed issue was re-verified on DCP-0049 Rev.

0 and 1. CR 97-2491 and LER 97-023 had previously been written to correct and report this issue.

ANERft,'AN

'Kl'Rl(

POWER OBSERVATIONS cont'd

~ Improving trend in the adequacy of 50.59 screenings and safety evaluations from 1/96 to 9/97. Fewer negative observations'on recent 50.59s.

ANERltlAN HHlBft.'OWER RESULTS

~ No new operability issues

~ No unacceptable 50.59 screenings

~ No new unacceptable 50.59 evaluations

~ UFSAR revision as required

AMiRfNM ELENRf(

PONDER TERRY POSTLEWAIT DIRECTOR, DESIGN ENGINEERING

AMERICAN RECTRIC POMIER AGENDA

~ Purpose

~ Focus

~ Scope

~ Team composition

~ Results

ANERlNM HKCYRlC PONR PURPOSE

~ Confirm adequacy of safety related design changes approved during same time frame as recirculation sump modifications RFC-2361, 1979

AIIIIERltAN Et,ELTRftl POWER FOCUS

~ Functional objectives

~ Design intent

~ Configuration drawings

~ Design bases

~ Operability

AMERÃAN.

ElECTRfC POWER SCOPE

~ Review sample of safety related design changes approved within six months of RFC 2361

~ Ten safety. related design changes were approved between 10/6/78 and 10/6/79 RFC-2361 approved 4/6/79

~ Five design changes chosen at random

AN)It;W RECTRIC POWER SCOPE RFC DC-1-1508:

Seismic accelerometers

~ RFC DC-12-2213: Upgrade motor CT circuits

~ RFC DC-12-2225: RCP motor oil collection

~ RFC DC-12-2229: Fire protection hose reels

~ RFC DC-12-2276: EDG local controls

AMERl(AN EECTRfC PONDER TEAM COMPOSITION

~ Three Teams one each led by experienced mechanical, structural, or electrical/l8 C design engineer one or more discipline engineer team members, as required each team had a qualified 50.59 reviewer

AMERICAN EEtlTRftl POWER

~ Replaced seismic peak recording accelerometers

~ Configuration control issues potentially affecting operability: none

~ Other configuration control issues: none

~ Other operability issues:

none

AMERICAN HFCTRIC POWER

'PGRADE 4 KV MOTOR CT CIRCUITS

~ Replaced existing cables at current transformers for 4 kv motors

~ Configuration control issues potentially affecting operability: none

~ Other configuration control issues: none

~ Other operability issues:

none

ANRltlAN ELEtlTRlt,'OWER RCP MOTOR OIL COLLECTION SYSTEM

~ Replaced original oil collection system supplied by original equipment manufacturer

~ Configuration control issues potentially affecting operability: none

NlERfL'AN ELE(fR)L PONER RCP MOTOR OIL COLLECTION SYSTEM cont'd

~ Other configuration control issues:

non-conforming weld identified and dispositioned in 1989, documented under the corrective action program

~ Other operability issues:

none

ANERlCAN EEtlTRfC POWER FIRE PROTECTION HOSE REELS

~ Added additional hose reels and piping in safety related areas

~ Configuration control issues potentially affecting operability:

LER 86-003 reported inadequacy of piping supports over safety related components.

Rev.

1 to design change corrected by providing seismic supports.

AMERICAN ELECTRfC POWER FIRE PROTECTION HOSE REELS cont'd

~ Other configuration control issues: none

~ Other operability issues:

none

AIERlt,'AN El,BYRD POWER EDG CONTROLS ON LOCAL SUBPANEL

~ Provided local start, stop and control of emergency diesel generators EDG

~ Configuration control issues potentially affecting operability: none

ANERfCAN Hit.'mlC POMR EDG CONTROLS ON LOCAL SUBPANEL cont'd

~ Other configuration control issues:

could not locate documentation that addressed additional relay loads to EDG inverter. This has been dispositioned.

several relays were not found in a vendor technical manual.

AMERlCAN ELEC8(C POWER EDG CONTROLS ON LOCAL SUBPANEL cont'd

~ Other configuration control issues:

cont d condition report 97-3587 written 12/11/97 to document reversed wires on U2 EDGs potentiometers.

Drawings correct. U2 CD wires corrected.

U2 AB scheduled 1/9/98.

~ Other operability issues:

none

AMERltlAN ELECTRIC POMR RESULTS

~ No instances found where operability of SSCs is adversely affected

~ Appropriate drawings reflect these design changes

NIERKAN EMCNlC PONDER

~ No new operability issues

~ 50.59 screenings and evaluations are appropriately completed

~ Recent 50.59's properly update UFSAR

~ Early design changes met functional objectives

~ Results support our.confidence that safety related systems are operable

ANERlCAN ELECTRIC POWER Gary Weber Executive Staff Engineer

AMERlt,'AN ELEt,'Nlt,'OWER

~ Purpose

~ Scope

~ Schedule

NIERltlAN ELECTRIC POWER PURPOSE

~ Solidify understanding of and control over plant design and licensing bases

~ Prepare for license renewal

~ DBD validation

~ UFSAR validation

~ Assessment and resolution of issues

AMERlt',AN HFtlTRf(

POWER SCOPE

~ Integration of ongoing efforts DBD reconstitution UFSAR revalidation

= NOP upgrade record document control and indexing

AMPRffAN HEQ'Rlt POSER SCOPE cont'd

~ Assessment activities effectiveness of DBDR and UFSAR projects ongoing system assessment of DBD validation

~ auxiliary feedwater

~ emergency core cooling

~ emergency diesel generators

~ 4KV

~ 250 volt DC calculation index pilot study

AMERICAIII ELECTRIC POWER SCOPE cont'd

~ Technical assessment group dedicated team for assessment and resolution of issues issue tracking augmented through task authorization mechanism

NIBftlAN HECTRfC PONS SCHEDULE

~ Planning nearing completion

~ Staffing and logistics in place mid-January

~ Draft procedures issued for review per requirements of Appendix B

~ DBDR/UFSAR assessment complete

~ Calculation index pilot study in progress

~ System assessment start after unit restart

NIERlCAN RECmft',

POSER SCHEDULE cont'd

~ UFSAR revalidation - October 1998

~ DBDR-System March 1999

~ NOP - March 1999

~ STP - December 1999

~ DB validation - pending results of five system pilot

AMERff,'AM HEtlf'Rff POWER ORGANIZATIONALCHART uc ear ngrg.

A. Alan Blind roject anager Gary Weber royect inistration Quality control 1

Sec'y Clerk 1

Cost control 1

Scheduling 1

econstitution Mgmt/supv - 3 Technical - 5 FI B Clerical - 1 eva i ation Mgmt/supv - 2 Technical - 10 Clerical - 1 ec ic ssessmen Mgm supv-4 Technical - 10 Clerical -1 pgra e

Mgmt/supv - 2 Technical - 12 Clerical -

1 rocess mprovemen lvlgmt/supv. -

1 Mgmt/supv -2 echnical - varies Clerfeat - varies Mgmt/supv - 1 Technical - 6

c. nex Mgmt/supv -

1 echnical -4 FTE

ERI(AN EI KCTRIC POMtlR Review cases where changes may have been made without a 50.59 evaluatio during the period 1988 - 1994

~ Results by January 31, 1998

Previous and Current Procedure Change Sheet Processes At Cook Nuclear Plant Former Temporary/

Non-Intent Change Sheet Process.

Current Procedure Change Sheet Process (PMSO-176)

Temporary Procedure Change Sheet That Does not Affect Intent of Procedure Tech Spec 6.5.3.1.a Any Procedure Change Sheet InitialApproval by Two Members of Plant Staff One Holding SRO ech Spec 6.5.3.1.a Perform Normal 50.59 Screening Process Within 14 Days ech Spec 6.5.3.1.a ech Spec 6.5.3.1.a Approved with Subsequent 50.59 Screening and Safety Evaluation ifnecessary Approved with Subsequent 50.59 Safety Evaluation if necessary

ATTACHMENT 2 TO AEP:NRC:1260G6 CONTAINMENT SUMP OPERABILITY DETERMINATION 9801200084 980i08 PDR ADQCK 05000$ i5 P

UNIT 1 CONTAINMENTRECIRCULATIONSUMP OPERABILITY ASSESSMENT Back round Resolution ofthe August/September, 1997 AE Design inspection issue on fibrous material in containment led to extensive reviews ofboth the design basis ofand threats to the containment recirculation sump.

This document provides an assessment ofthe operability ofthe Cook Nuclear Plant Unit 1 containment recirculation sump considering the licensing and design basis ofthe sump. It also includes a review ofthe validityofthe assumed sump blockage, given the plant configuration and materiel condition and followingwork during the Fall, 1997 outages.

A separate assessment willbe provided for the Unit 2 containment recirculation sump upon completion ofplanned containment work during U2R97.

Affected S stem/Structure/Com onent SSC J

The affected structure is the containment recirculation sump.

Blockage ofthe containment recirculation sump could have an adverse effect on the Emergency Core Cooling (ECCS) and Containment Spray (CTS) systems.

SSC Safe Function The function ofthe containment recirculation sump is to provide a reliable source ofwater for the long term cooling ofthe reactor coolant system and containment building following postulated accidents, which require entry into the recirculation mode ofECCS and/or CTS System operation. The recirculation sump was designed to handle postulated debris threats, while precluding vortexing and air entrainment for the suction ofthe Residual Heat Removal (RHR) and CTS pumps and also while providing adequate Net Positive Suction Head (NPSH) to these same pumps.

Postulated debris threats considered in the sump design included up to 50% plate blockage ofthe sump screen.

Besides meeting the NPSH requirements for the RHR and CTS pumps, the sump is also designed to preclude the entry ofparticles greater than 1/4" in size to the recirculation sump, which ensures the 3/8" CTS spray nozzles willnot be blocked by debris.

The sump screen also provides particle exclusion protection for small ECCS valves.

01/06/98 Page 1 of 10

SSC Deficienc Questions have been raised regarding the abilityofthe recirculation sump to meet design basis requirements and credible debris threats, including debris blockage with different characteristics than the 50% plate blockage assumed during original sump design.

Specific design requirements in question relate to the effective area ofthe sump opening, and the ability ofthe sump to provide sufficient flow across the sump opening with an acceptable pressure loss such that RHR and CTS NPSH requirements are met.

Assessment ofthe sump operability must consider whether design basis assumptions for blockage are reasonable, based on determination and consideration ofcredible post-accident debris threats.

Assessment of Im act ofDeficienc on Abili of Recirculation Sum to Perform Its Safe Function The Cook Plant containment recirculation sump design was modeled extensively during the late 1970s (reference

1) to "verifythat the sump would perform satisfactorily without the development ofany severe vortices or other flowirregularities that could affect operation ofthe pumps in the Emergency Core Cooling System (ECCS) during its recirculation mode." A by-product from th'e model testing, which included testing for various "plate blockage" schemes. at the sump entrance, included empirical head loss data at the sump screen, at minimum water level (El. 602'-. 10"). Sump entry screen blockage ofup to 50% was modeled.

Loss coefficients (Ci.) determined for various test schemes, and are represented by the equation:

Ci.=

hi.

where v /2g hi. = the head loss in ft v = fluidvelocity at the sump exit pipes

~ g = 32.2 ft/sec Data from the Alden Test report indicated that the configuration with the highest observed head loss at the sump entrance occurred with a loss coefficient and corresponding flowof 0.26 and 13.79'fUsec, respectively.

For these conditions, the corresponding flow was 15,400 gpm (7,700 gpm per sump outlet pipe). This data is taken from Table 10 of the 1978 Alden Labs report. The observed head loss with these conditions was 0.77 ft.

01/06/98 Page 2 of 10

Although the configuration modeled by Alden Labs was similar to the current Cook Plant sump configuration, it is not identical. The existing sump entrance design employs two aligned layers ofcoarse grating sandwiching a single layer ofstainless fine mesh, while the modeled configuration consisted ofa single coarse grating and a single fine mesh screen.

For the existing (as-left) sump screen design, the open flow area, after subtracting structural elements ofthe grating such as screen and grating ligaments, is approximately 37.9 ft (reference calculation ENSM971210TWF).

As a point ofinformation, the sump screen was recently aligned as an enhancement under design change DCP-869 to optimize

~

open flow area.

Prior to this optimization, the worst case open flow area was determined by calculation, assuming possible grating misalignment, to be as low as 18 ft (reference calculation ENSM971128TWF). By way ofcomparison, the areas ofthe two 18" Schedule 40 pipes exiting the recirculation sump represent a total area of3.1 ft.

Calculation ENSM970128AF, Rev.

1 has been performed to determine the available NPSH for the ECCS pumps.

The head loss through the existing sump screen was analytically determined to be 0.62 ft at 15,600 gpm flowfor the existing sump configuration with 50% plate blockage, consistent with the plant licensing basis.

Since this analytically determined head loss correlated well with empirical results from the Alden sump model tests (0.77 ft at 15,400 gpm), a conservative head loss of 1 ft across the sump screen was assumed in the NPSH calculation, at 15,600 gpm. Using this head loss, NPSHA was calculated for the RHR and CTS pumps. NPSHA was found to exceed required NPSH for both the CTS and RHR pumps with margin (NPSH margin was 9 ft for the RHR pumps and 22 ft for the CTS pumps for worst case conditions).

Thus, for sump screen blockage assumed in the licensing basis (50% plate blockage), for the existing sump design, NPSH margin is preserved.

As a point ofinformation, the theoretical amount ofsump screen area blockage required to achieve a head loss equivalent to NPSH margin is calculated below, to determine how much screen blockage could be tolerated.

The grating and screen arrangement was treated as an orifice, which is consistent with the methodologies presented in the Handbook ofHydraulic Resistance republished for the Atomic Energy Commission.

Using equations from Cameron Hydraulic Data, flowthrough an orifice is determined by the equation:

Q = 19.636 C di h", where, Q = flow, in gpm di= diameter oforifice or opening h = differential head, in ft ofliquid C = discharge coefficient (0.61 for square edge orifice)

The diameter ofan orifice which would result in a head loss of9 ft (RHR pump NPSH margin) at a flowof 15,600 gpm was determined to be 20,83 inches, which corresponds to a 2.4 ft for a circular flow area.

This open flow area corresponds to blockage of94% of, the current sump area (37.9 ft ). Considering that the sump outlet pipes total 3.1 ft in area, this result is not unexpected.

01/06/98 Page 3 of 10

Although it has been shown above that blockage ofmuch higher than 50% can be tolerated before NPSH margin is completely eroded, it remains important to acknowledge the licensing basis. of50% plate blockage, and to. provide a basis for why the 50% sump blockage assumption is a reasonable one.

Consideration ofthe 50% blockage assumption must include review ofpossible post-accident debris generation, and the potential for transport ofthe debris to the sump.

Debris Generation Resolution ofthe AE design inspection issue on fibrous material in containment resulted in numerous reviews ofthe containment for potential debris threats to sump blockage and operability. Extensive walkdowns ofcontainment were performed to identify potential debris sources.

Among the threats identified and considered were fibrous insulation materials, coatings, material stored in containment, tape, cable tie-wraps, anti-slip tape on ladders and labels.

Fibrous Insulation Materials It is well documented that LOCAgenerated debris represents a potential threat to the operability ofthe ECCS and CTS as a result ofcontainment sump blockage.

Pipe and equipment insulated with fibrous materials is a potential significant debris source.

The piping and components within the containment that are insulated have been reviewed to determine the location offibrous material. Aportion offibrous insulation within areas ofmost concern in the containments (the lower volume or active sump) has been removed; however, it is impractical to perform a 100% removal ofall fibrous insulation at this time.

A review was performed ofthe impact ofthe remaining fibrous material. They key remaining locations offibrous mater'ial within the lower volume ofthe containments include the first few elbows on the steam and feedwater lines near the top ofthe steam generators in both units. Additionally, the girth welds (except for the channel head to barrel welds) ofthe Unit 1 steam generators are insulated with pads containing fibrous material. Potential break locations on the RCS piping were considered to assess ifthere was fibrous insulation in proximity (considered to be within approximately five pipe diameters) to the postulated break locations. For this review no credit was taken for leak-before-break.

The fibrous material on the steam generator girth welds is largely shielded

'rom a postulated RCS pipe break by the steam generator lower supports, which are large steel frames that surround the base ofthe SG just above the channel head.

The shielding afforded by these frames, and also by nearby floor grating, would limitjet impingement and consequently debris generation to localized areas.

The fibrous insulation on the steam and feedwater lines is sufBciently removed from the RCS piping that debris generation from RCS piping jet impingement'on these lines was not considered likely. Once again, any effects fromjets would be localized.

Breaks ofthe steam and feedwater lines themselves are addressed separately, below.

01/06/98 Page 4 of 10

Based on the limited locations ofthe fibrous materials, the probable localized nature ofjets from RCS pipe breaks, and considering shielding from structural elements, debris generation from fibrous materials due to postulated RCS pipe breaks is not considered to be sufficient to challenge the recirculation sump beyond its capabilities.

Abreak ofeither the a main steam line or a feedwater lines was considered to evaluate if the break could generate fibrous debris that could potentially challenge the ECCS recirculation sump screen.

The sources ofthe fibrous material are on the main steam line at elevation 635'lose to the reactor building penetration, the main steam line close to the top ofthe steam generator at elevation 686', the feedwater line at elevation 661', and assorted fiber pads at the top, middle and lower portion ofthe Unit 1 steam generators Either a main steam line or feedwater line break (MSLB or FLB) would initiate containment spray operation for containment pressure greater than 2.9 psig. The outflow ofthe containment spray willtransport some ofthe fibrous debris to the lower containment floor and willresult'in the formation ofa pool ofwater on the containment floor. Analysis for the main feedwater line break concluded that the switchover to'ecirculation mode is not required.

Appr6ximately 30 minutes after a stea'm line rupture, both RHR and containment spray trains'uction would. be switched from the RWST to the ECCS recirculation sump. At the time ofswitchover, the lower containment water pool depths are approximately 7 ft over the minimum required for pump suction (reference 4).

The debris generated by the break could potentially challenge the ECCS recirculation sump by clogging the sump screen with debris.

To challenge the ECCS sump screen, the debris must be transported to the sump screen.

Most ofthe debris transport from the area around the break location to the lower containment floor willoccur in the first few minutes followingthe break and containment spray activation. There is no break flowfor the steam or feedwater line breaks (other than right at the time ofthe break) and the containment sprays and ice melt are the only source ofwater for buildup ofthe water pool on the floor ofthe lower containment.

As such, any turbulence in the floor pool willbe limited to the top few inches, with no viable turbulence mechanism available for the water close to the floor. Consequently, it is anticipated that any ofthe debris that would be initiallysuspended in the pool willsediment to the bottom ofthe floor prior to switchover. The debris on the floorwould then need to be transported by water flowto the sump screen.

Based on NUREG-0897, the minimum flowvelocity needed to transport debris is 0.2 ft/sec. For conservatism, a bulk flow velocity ofgreater than 0.1 ft/sec is assumed to be required to transport debris. The maximum flow'through the ECCS recirculation sump for a MSLB is 6,400 gpm (2 trains ofCTS flow). A cross-sectional area greater than 142 ft yields flowvelocities less than 0.1 ft/sec (142 ft = [6400 gpm /450] /0.1). Using the minimum pool height of 10 fi (approximately 7ft above elevation 602'-10"), at distances greater than a radius of4.5 ft from the center ofthe sump screen, the horizontal bulk flowvelocity would be less than 0.1 fi/sec.

01/06/98 Page 5 of 10

Most ofthe break locations would generate debris that would reach the containment floor and sediment at distances sufficiently removed from the sump screen such that transport to the sump screen is not considered likely. Furthetmore, given the lack ofturbulence, it is unlikely that the debris that could be transported to the sump screen would be uniformly distributed across the entire axial extent. It is expected that the upper portions ofthe screen would remain relatively debris free. Therefore debris generated by potential steam or feedwater line breaks willnot adversely impact the performance ofthe ECCS recirculation sump.

In summary, fibrous material has been removed from the containments with the exception ofa few select areas, which are jacketed with stainless steel, consistent with the plant licensing basis.

These select areas have been evaluated and determined not to be a significant threat to recirculation sump screen blockage.

Additionally, thermal insulation has been extensively inspected during numerous walkdowns during the Fall, 1997 outages, and repairs have been made where the insulation jacketing was not in good repair. This included ensuring that jacketing adequately covers insulation material (no excessive joints) and that insulation is secure (banding is tight). Based on these observations and repair, fibrous insulation material 'other than that in the direct vicinityofa break, is not expected to come loose and migrate to the recirculation sump.

~Coatin s

s The coatings systems in both units have undergone extensive investigation and it is concluded that, followingwork completed during the Fall, 1997 outages, these systems willnot have an adverse effect on the performance ofthe recirculation sump screens following postulated accidents.

The existing coatings systems can be categorized as either qualified (N-grade), unqualified (typically manufacturer's standard paints on such things as electrical boxes/cabinets, pumps, fans and motors) or indeterminate (coating systems that appear to be qualified but where there is incomplete documentation).

The coatings at risk for disbondment include unqualified coating systems, indeterminate coatings and qualified coatings that are in need ofrepair.

After examining the available original construction coating application and inspection records, a large percentage ofitems previously believed to be indeterminate were in fact found to be @edifie coatings.

This includes the coating systems and their applications on the containment liner, the concrete floors and walls, major equipment provided by Westinghouse, the polar and manipulator cranes and most structural steel.

This greatly limits the potential quantity ofloose coating particles that could affect the sump screens during a LOCA.

01/06/98 Page 6 of 10

Another key aspect in the evaluation ofthe containment coating systems was to determine which coated surfaces are at risk for adversely effecting the sump screens.

Determinations were based not only on the potential for disbondment ofthe coatings, but the potential for these particles to reach the screens.

Potential for such particles to reach the screens is related to their potential flowpath, the settling characteristics ofdisbonded coating particles and existing obstructions such as curbs and walls. For example, coating particles released in the annulus were considered a relatively minor threat to the recirculation sump based on the lack ofhigh energy lines, the distance from and path to the recirculation sump.

Investigation ofthe coating systems in containment found the following estimated quantities ofunqualified and indeterminate coatings:

UNIT81 Unqualified Coating Materials Lower containment Upper containment Annulus Total Square Feet 1358 1826 1984 5168 UNIT82 Unqualified Coating Materials Lower Containment Upper Containment Annulus Total Square Feet 1365 1830 1686 4881 The primary indeterminate coatings identified included piping, including the Containment Purge AirSupply piping and other piping found to have an unusual appearance when compared to the qualified coating system, and structural steel including that associated with the steam generators.

This relatively small amount ofunqualified and indeterminate coating material is considered insignificant compared to the total amount ofcoatings in the containments.

Loose coatings have been removed, and in many cases, surfaces were repainted.

Based on work completed to examine coatings, including removal ofany loose coatings,'application ofnew qualified coatings and on the relatively small amount of unqualified or indeterminate coatings, this material is not considered to pose a significant threat to the recirculation sump. However, as a point ofinformation, plans willbe formulated to further improve coatings during future outages, consistent with industry guidance (pending Generic Letter on coatings) to be issued in early 1998.

01/06/98 Page 7 of 10

Material Stored in Containment Walkdowns ofcontainment led to the identification ofvarious items that were intentionally stored in the containments during past operation.

Reviews were conducted prior to their storage in containment and typically included evaluation for seismic restraint. Typical items stored in the containments included vacuums, welding machines and lift-a-loAs. The majority ofthe items ofconcern were stored in the lower volume, in the refueling cavity tunnel area.

Further consideration indicates that these items could generate debris when exposed to impingement fromjets. Additionally, these items may be coated with unqualified coatings, and their presence may result in local flow acceleration for water flowing to the sump, which could enhance debris transport.

Therefore, items which are not required to remain in containment, have been removed.

This includes the containment charcoal auxiliary ventilation units, which were removed under design change DCP-860.

~Ta es P

Various tapes used in the containment building were also considered.

These included white glass tape and black electrical tape, in addition to duct tape. Duct tape has been aggressively removed as it was identified. Although qualification documentation could not be produced for white and black tapes identified, this material has been

'extensively examined through walkdowns.

Loose tape was removed.

Tape that is tightly affixed is not being removed, since it was judged that due to typical installation methods for tape (tightlywrapped), it is unlikely that the tape would become completely free and transportable following a postulated accident.

Furthermore, much ofthe tape identified was in the annulus regions ofthe containment, which is not in good communication with the active sump containing the recirculation sump.

Ladder rung (anti-slip) tape is being removed. In summary, tapes remaining in the containments are not considered a significant threat to the recirculation sump given planned work and inspections during the Fall, 1997 outages.

~Cbl Ti W Cable tie wraps were also considered as to potential to threats the recirculation screen.

Experience indicates that the tie wrap material may become brittle with age.

However, it has also been demonstrated that the tie wraps are negatively buoyant (i.e., they sink).

Therefore, considering that many ofthe cable tie wraps are enclosed in cable trays, that the containment design includes curbing to trap debris, and finally, that this material has been shown to sink, the existence ofthese materials is not considered a significant'threat to the recirculation sump.

01/06/98 Page 8 of 10

Labels Labels were dispositioned similar to tape and coatings in that they were reviewed to determine qualifications, and they were extensively examined during walkdowns.

Labels that were qualified for post accident environment were left in place, provided they were in good repair. Labels which were not qualified for the post-accident environment were removed from the lower volume (active sump). Vnqualifiied labels in other areas ofthe containment were examined and left in place provided they were tightly adhering and in good condition. Labels in poor repair were removed.

In summary, labels left in containment were either qualified, or they were not considered a threat to the sump based on their tight adherence and their distance from and path to the sump.

General Combined with the consideration ofthe sump blockage threats posed by specific materials, the general state ofthe containment materiel condition was also considered.

Miscellaneous materials (such as dirt, rust, etc) are important since any fibrous material that transports to the recirculation s'ump willact as a filter, and any fines can fillin flow paths through the fibrous material, significantly increasing head loss across the sump screen.

Although containment cleanliness has been on an improving trend in recent years, containment remediation efforts during the Fall, 1997 outages included extensive focused cleaning ofthe containments.

An example ofthis focused effort involved the removal of steam generator walkway platforms, so that the areas beneath could be vacuumed.

These efforts further reinforce the confidence that the sumps willnot be subject to excessive blockage during postulated accidents.

Conclusion In conclusion, credible post-accident debris threats have been shown to be limited. Thus, there is reasonable assurance that the design basis assumption of50% sump screen blockage can be met. Furthermore, the calculated head loss across the sump screen for assumed blockage results in acceptable NPSHA for the RHR and CTS pumps, with margin. Finally, the recirculation sump screen has been shown to be capable ofhandling significantly greater than 50% blockage, and still providing adequate NPSH to the most

'imiting pumps.

Based on the preceding discussion, the containment recirculation sump is considered capable ofperforming its function, and therefore should be considered operable.

Prepared y

Mechanical Systems Manager 01/06/98 Page 9 of 10

References

1) Test Report: Hydraulic Model Investigation ofVortexing and Swirl Within a Reactor Containment Recirculation Sump, Donald C. Cook Nuclear Power Station, Alden Research Laboratory, September, 1978.

2) Test Report: Experimental Investigation ofAirEntrainment at a Reactor Containment Sump Due to Break and Drain Flows, Donald C. Cook Nuclear Power Station, Alden Research Laboratory, December, 1979.

3) Condition Report 97-2457, Fibrous Material in Containment Cable Trays.

4) FAI/97-140, D. C. Cook Containment Response to a Main Steam Line Break, Fauske 8c Associates, Inc., December, 1997.

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