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

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root cause/short term assessment

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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

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Introductory remarks Jim Kobyra

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50.59 self assessment Jeb Kingseed

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Design change self assessment Terry Postlewait

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Integrated design bases program Gary Weber

AMFRÃAN RECTRtC POWER JEB KINGSEED MANAGER, NUCLEAR SAFETY

AMERfCAN Ef,ECf'RfC POWER AGENDA

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Purpose

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Focus

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Scope

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Team composition

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Observations

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Results

'MERfCAN SEC YRN PONER PURPOSE

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Evaluate adequacy of 50.59 process

ANRlfAN HKCYRfC POSER FOCUS

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Operability issues

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Acceptability of screenings and evaluations

~ UFSAR revision

AMERftlAN HH'TRlt'tNER SCOPE

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

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35 procedural 50.59 screenings change sheets and revisions

~ 11 procedural 50.59 evaluations

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25 design change 50.59 evaluations and corresponding screenings

AMERlCAN HHTRlC P4MR TEAM COMPOSITION

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Three teams two procedure teams one 50.59 design change team

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Procedure teams composed of:

QA lead auditor nuclear safety 50.59 reviewer operations procedure specialist

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

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50.59 design change teams composed of:

QA lead auditor nuclear safety 50.59 reviewer design engineers

AIERlfAN El.EtlNlf POWER OBSERVATIONS

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Conclusions were acceptable.

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

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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

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No unacceptable 50.59 screenings

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No new unacceptable 50.59 evaluations

~ UFSAR revision as required

AMiRfNM ELENRf(

PONDER TERRY POSTLEWAIT DIRECTOR, DESIGN ENGINEERING

AMERICAN RECTRIC POMIER AGENDA

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Purpose

~ Focus

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Scope

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Team composition

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Results

ANERlNM HKCYRlC PONR PURPOSE

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

AIIIIERltAN Et,ELTRftl POWER FOCUS

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Functional objectives

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Design intent

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Configuration drawings

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Design bases

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Operability

AMERÃAN.

ElECTRfC POWER SCOPE

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

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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

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RFC DC-12-2213: Upgrade motor CT circuits

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RFC DC-12-2225: RCP motor oil collection

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RFC DC-12-2229: Fire protection hose reels

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RFC DC-12-2276: EDG local controls

AMERl(AN EECTRfC PONDER TEAM COMPOSITION

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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

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Replaced seismic peak recording accelerometers

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Configuration control issues potentially affecting operability: none

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Other configuration control issues: none

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Other operability issues: none

AMERICAN HFCTRIC POWER 4 KV MOTOR CT CIRCUITS

'PGRADE

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Replaced existing cables at current transformers for 4 kv motors

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Configuration control issues potentially affecting operability: none

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Other configuration control issues: none

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Other operability issues: none

ANRltlAN ELEtlTRlt,'OWER RCP MOTOR OIL COLLECTION SYSTEM

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Replaced original oil collection system supplied by original equipment manufacturer

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Configuration control issues potentially affecting operability: none

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

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Other configuration control issues:

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

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Other operability issues: none

ANERlCAN EEtlTRfC POWER FIRE PROTECTION HOSE REELS

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Added additional hose reels and piping in safety related areas

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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

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Other operability issues: none

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

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

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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 ELEC 8(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

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No instances found where operability of SSCs is adversely affected

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Appropriate drawings reflect these design changes

NIERKAN EMCNlC PONDER

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No new operability issues

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50.59 screenings and evaluations are appropriately completed

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Recent 50.59's properly update UFSAR

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Early design changes met functional objectives

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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

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Schedule

NIERltlAN ELECTRIC POWER PURPOSE

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Solidify understanding of and control over plant design and licensing bases

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Prepare for license renewal

~ DBD validation

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UFSAR validation

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Assessment and resolution of issues

AMERlt',AN HFtlTRf(

POWER SCOPE

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Integration of ongoing efforts DBD reconstitution UFSAR revalidation

= NOP upgrade record document control and indexing

AMPRffAN HEQ'Rlt POSER SCOPE cont'd

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

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auxiliary feedwater

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emergency core cooling

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emergency diesel generators

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4KV

~ 250 volt DC calculation index pilot study

AMERICAIII ELECTRIC POWER SCOPE cont'd

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

NIBftlAN HECTRfC PONS SCHEDULE

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Planning nearing completion

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Staffing and logistics in place mid-January

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Draft procedures issued for review per requirements of Appendix B

~ DBDR/UFSAR assessment complete

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Calculation index pilot study in progress

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System assessment start after unit restart

NIERlCAN RECmft',

POSER SCHEDULE cont'd

~ UFSAR revalidation - October 1998

~ DBDR- System March 1999

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NOP - March 1999

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STP - December 1999

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DB validation - pending results of five system pilot

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

A. Alan Blind roject anager Gary Weber roy ect inistration Quality control 1 Sec'y Clerk 1 Cost control 1 Scheduling 1 econstitution eva i ation ec ic ssessmen pgra e rocess mprovemen Mgmt/supv - 3 Mgmt/supv - 2 Mgm supv-4 Mgmt/supv - 2 lvlgmt/supv. - 1 Technical - 5 FI B Technical - 10 Technical - 10 Technical - 12 Clerical - 1 Clerical - 1 Clerical -1 Clerical - 1

c. nex Mgmt/supv -2 Mgmt/supv - 1 Mgmt/supv - 1 echnical - varies Technical - 6 echnical -4 FTE Clerfeat - varies

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/ Current Procedure Non-Intent Change Change Sheet Process Sheet Process. (PMSO-176)

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

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

P

UNIT 1 CONTAINMENTRECIRCULATION SUMP OPERABILITY ASSESSMENT Back round Resolution of the August/September, 1997 AE Design inspection issue on fibrous material in containment led to extensive reviews of both the design basis of and threats to the containment recirculation sump. This document provides an assessment of the operability of the Cook Nuclear Plant Unit 1 containment recirculation sump considering the licensing and design basis of the sump. It also includes a review of the validity of the assumed sump blockage, given the plant configuration and materiel condition and following work during the Fall, 1997 outages. A separate assessment will be provided for the Unit 2 containment recirculation sump upon completion of planned containment work during U2R97.

Affected S stem/Structure/Com onent SSC J

The affected structure is the containment recirculation sump. Blockage of the containment recirculation sump could have an adverse effect on the Emergency Core Cooling (ECCS) and Containment Spray (CTS) systems.

SSC Safe Function The function of the containment recirculation sump is to provide a reliable source of water for the long term cooling of the reactor coolant system and containment building following postulated accidents, which require entry into the recirculation mode of ECCS and/or CTS System operation. The recirculation sump was designed to handle postulated debris threats, while precluding vortexing and air entrainment for the suction of the 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 of the sump screen. Besides meeting the NPSH requirements for the RHR and CTS pumps, the sump is also designed to preclude the entry of particles greater than 1/4" in size to the recirculation sump, which ensures the 3/8" CTS spray nozzles will not 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 ability of the 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 of the sump opening, and the ability of the sump to provide sufficient flow across the sump opening with an acceptable pressure loss such that RHR and CTS NPSH requirements are met.

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

Assessment of Im act of Deficienc 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 "verify that the sump would perform satisfactorily without the development of any severe vortices or other flow irregularities that could affect operation of the 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 of up to 50% was modeled. Loss coefficients (Ci.) determined for various test schemes, and are represented by the equation:

hi.

Ci.= where v /2g hi. = the head loss in ft v = fluid velocity 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 flow of 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 of coarse grating sandwiching a single layer of stainless fine mesh, while the modeled configuration consisted of a 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 of the grating such as screen and grating ligaments, is approximately 37.9 ft (reference calculation ENSM971210TWF). As a point of information, 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 of comparison, the areas of the two 18" Schedule 40 pipes exiting the recirculation sump represent a total area of 3.1 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 flow for 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 of information, the theoretical amount of sump 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 of Hydraulic Resistance republished for the Atomic Energy Commission.

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

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

The diameter of an orifice which would result in a head loss of 9 ft (RHR pump NPSH margin) at a flow of 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 of 94% 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 of much higher than 50% can be tolerated before NPSH margin is completely eroded, it remains important to acknowledge the licensing basis. of 50% plate blockage, and to. provide a basis for why the 50% sump blockage assumption is a reasonable one. Consideration of the 50% blockage assumption must include review of possible post-accident debris generation, and the potential for transport of the debris to the sump.

Debris Generation Resolution of the AE design inspection issue on fibrous material in containment resulted in numerous reviews of the containment for potential debris threats to sump blockage and operability. Extensive walkdowns of containment 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 LOCA generated debris represents a potential threat to the operability of the ECCS and CTS as a result of containment 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 of fibrous material. A portion of fibrous insulation within areas of most concern in the containments (the lower volume or active sump) has been removed; however, it is impractical to perform a 100% removal of all fibrous insulation at this time.

A review was performed of the impact of the remaining fibrous material. They key remaining locations of fibrous mater'ial within the lower volume of the containments include the first few elbows on the steam and feedwater lines near the top of the steam generators in both units. Additionally, the girth welds (except for the channel head to barrel welds) of the 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 a postulated RCS pipe break by the steam generator lower supports, which are large

'rom steel frames that surround the base of the 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 from jets would be localized. Breaks of the steam and feedwater lines themselves are addressed separately, below.

01/06/98 Page 4 of 10

Based on the limited locations of the 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.

A break of either 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 of the 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 of the steam generator at elevation 686', the feedwater line at elevation 661', and assorted fiber pads at the top, middle and lower portion of the 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 of the containment spray will transport some of the fibrous debris to the lower containment floor and will result'in the formation of a pool of water on the containment floor. Analysis for the main feedwater line break concluded that the switchover mode is not required. Appr6ximately 30 minutes after a stea'm line rupture, to'ecirculation both RHR and containment spray trains'uction would. be switched from the RWST to the ECCS recirculation sump. At the time of switchover, 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 of the debris transport from the area around the break location to the lower containment floor will occur in the first few minutes following the break and containment spray activation. There is no break flow for the steam or feedwater line breaks (other than right at the time of the break) and the containment sprays and ice melt are the only source of water for buildup of the water pool on the floor of the lower containment. As such, any turbulence in the floor pool will be 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 of the debris that would be initially suspended in the pool will sediment to the bottom of the floor prior to switchover. The debris on the floor would then need to be transported by water flow to the sump screen. Based on NUREG-0897, the minimum flow velocity needed to transport debris is 0.2 ft/sec. For conservatism, a bulk flow velocity of greater 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 of CTS flow). A cross-sectional area greater than 142 ft yields flow velocities 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 of 4.5 ft from the center of the sump screen, the horizontal bulk flow velocity would be less than 0.1 fi/sec.

01/06/98 Page 5 of 10

Most of the 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 of turbulence, 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 of the screen would remain relatively debris free. Therefore debris generated by potential steam or feedwater line breaks will not adversely impact the performance of the ECCS recirculation sump.

In summary, fibrous material has been removed from the containments with the exception of a 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 vicinity of a 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, following work completed during the Fall, 1997 outages, these systems will not have an adverse effect on the performance of the 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 of repair.

After examining the available original construction coating application and inspection records, a large percentage of items 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 of loose coating particles that could affect the sump screens during a LOCA.

01/06/98 Page 6 of 10

Another key aspect in the evaluation of the 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 of the coatings, but the potential for these particles to reach the screens. Potential for such particles to reach the screens is related to their potential flow path, the settling characteristics of disbonded 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 of high energy lines, the distance from and path to the recirculation sump.

Investigation of the coating systems in containment found the following estimated quantities of unqualified and indeterminate coatings:

UNIT 81 Unqualified Coating Materials Square Feet Lower containment 1358 Upper containment 1826 Annulus 1984 Total 5168 UNIT 82 Unqualified Coating Materials Square Feet Lower Containment 1365 Upper Containment 1830 Annulus 1686 Total 4881 The primary indeterminate coatings identified included piping, including the Containment Purge Air Supply 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 of unqualified and indeterminate coating material is considered insignificant compared to the total amount of coatings in the containments. Loose coatings have been removed, and in many cases, surfaces were repainted. Based on work completed to examine coatings, including removal of any loose coatings,'application of new 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 of information, plans will be 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 of containment led to the identification of various 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 of the items of concern 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 from jets. 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 (tightly wrapped), it is unlikely that the tape would become completely free and transportable following a postulated accident. Furthermore, much of the tape identified was in the annulus regions of the 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 of the 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 of these 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 of the 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 of the sump blockage threats posed by specific materials, the general state of the 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 will act as a filter, and any fines can fill in 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 of the containments. An example of this 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 will not 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 of 50% 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 of handling significantly greater than 50% blockage, and still providing adequate NPSH to the most pumps. Based on the preceding discussion, the containment recirculation sump is 'imiting considered capable of performing 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 of Vortexing and Swirl Within a Reactor Containment Recirculation Sump, Donald C. Cook Nuclear Power Station, Alden Research Laboratory, September, 1978.

2) Test Report: Experimental Investigation of Air Entrainment 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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