ML20045B282

Responds to NRC Bulletin 93-002, Debris Plugging of ECC Suction Strainers. Results of Evaluation of Existing Primary Containment Strainers Including Design,Maint & Insp Activities to Maintain Operability Encl

ML20045B282
Person / Time
Site:	Quad Cities
Issue date:	06/10/1993
From:	Chrzanowski D COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
References
IEB-93-002, IEB-93-2, NUDOCS 9306170132
Download: ML20045B282 (4)

Text

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.. _ Ctmmenwrith Edison 2 1400 Opus Place Downers Grove, tilinois 60515 June 10,1993 Office of Nuclear Reactor Regulation U'.S. Nuclear Regulatory Com. mission Washington, DC 20555 Attention: Document Control Desk

Subject:

Quad Cities Station Response to NRC Bulletin 93-02,

" Debris Plugging of Emergency Core Cooling Suction Strainers" Quad Cities Station Units-1 and 2, (NRC Dockets 50-254 and 50-265)

The purpose of this letter is to provide the Quad Cities Station response to the subject Bulletin. The details of the Quad Cities response are provided in the attachment. In summary, Quad Cities has performed the requested actions of the Bulletin. Because no fiberous air filters or other temporary sources of fibrous ma-terial, not designed to withstand a LOCA, were identified at Quad Units 1 and 2, no compensatory measures were required.

The verification activities completed for Unit I will be supplemented with a visual inspection and strainer inspection during the upcoming Quad Cities Unit I refueling outage, presently scheduled for Spring of 1994. Commonwealth Edison will notify the NRC of the results of this inspection.

To the best of my knowledge and belief, the statements contained in this docu-ment are true and correct. In some respects these statements are not based on my personal knowledge, but on information furnished by other CECO employees, con-tractor employees, and/or consultants. Such information has been reviewed in ac-cordance with company practice, and I believe it to be reliable.

If there are any questions or comments, please contact me at (708) 663-7292 state of I county of bei Sincerely, Signed before en this / N d/

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J/ /-7 David J. Chrzakow. ski Nuclear Regulatory Services Attachments: Quad Cities Response to Bulletin 93-02 cc: Regional Administrator-RIII SE^

J. Hickman, Project Manager-NRR/PDlII-2

~ 30[QC ALC L so7tay Pusuc. STAiE or ituNo:s C. Patel, Quad Cities Project Manager-NRR/PDIII-2 rn C0rTSS!0N EXPIRES 0/25/94 T. Taylor, Senior Resident Inspector (Quad Cities) "*** ~

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ATTACHMENT QUAD CITIES STATION RESPONSE TO BULLETIN 93-02 Per the requirements of NRC Bulletin 93-02, Quad Cities Station has per-formed an evaluation of the existing Primary Containment strainers including design, maintenance and inspection activities to maintain operability. The results of this evaluation are described below.

To summarize the evaluation, the Unit 2 ECCS strainers were inspected i prior to Unit startup on 5/26/93 as required by the Bulletin. No adverse debris buildup was noted on the strainers and no air filters or other temporary sources of i fibrous material were identified. Unit 1 Primary Containment strainers will he inspected at the next refuel outage, number Q1R13, presently scheduled for Spring 1991 This is in keeping with the requirements of the Bulletin.  ;

Quad Cities Station is of the BWR Mark I design, which makes it less sus-ceptible to the debris build-up noted at the Perry Station, a BWR Mark III.

Actions Taken in Response to Bulletin 93-02 The Unit 2 Primary Containment (drywell and torus) was visually inspected for fi-brous material. The intent of the inspection was ta identify any glass wool, fiber glass, nylon netting, fabric or other material that is capable of being separated into fibers. The inspection did not identify any fibrous air filters or other tempo-rary sources of fibrous material inside the primary containment.

The Unit 2 Torus was inspected using a submersible camera. The results of this inspection found the four ECCS suction strainers in good condition. Some foreign material was found during this inspection and removed. This material included a piece of string, a dosimeter, a scaffolding knuckle, a pipe fitting and some tie-wraps. The string was found lodged in a strainer. The remainder of the items were found on the bottom of the torus. All of the items were removed. None of these items would have affected the operability of the ECCS pumps.

The Unit 1 Primary Containment is in the same condition as Unit 2. This state- '

ment is based on:

• The results of the Unit 2 Primary Containment inspection.

• The Containment close-out walkdowns that have been performed previ-ously on both units are similar. Therefore there is no reason to believe the Unit I containment is any different condition than the Unit 2 con-tainment. )

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The equipment in both containments is the same and therefore similar results are expected when the Unit 1 containment is inspected. 1 i

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ATTACHMENT QUAD CITIES STATION RESPONSE TO BULLETIN 93-02 The Unit 2 Primary Containment was inspected for final closcout prior to startup. Part of this inspection included identification of any fibrous filter material or other temporary sources of fibrous material. This was completed prior to unit startup on 5/26/93.

Actions Planned in Response to Bulletin 93-02 The Unit 1 drywell will be inspected to identify fibrous air filters or other tem-porary sources of fibrous material at the next outage during which the contain- ,

ment is deinerted. This will be completed no later than 4/1/94 which is the next scheduled refueling outage. .

The Unit 1 ECCS suction strainers will be inspected during the refuel outage in 1994. This will be completed no later than 4/1/94.

Clarifyine Infhrmation concernine Bulletin 93-02 Quad Cities Station is less susceptible to fbreign material intrusion than BWRs of the Mark III design. The suppression pool is contained within the torus and is not accessible during normal operation. Material which would cause plug-ging of the ECCS suction strainers would have to come from the Drywell, un-less material was left in the torus from the previous outage. The material would have to take a circuitous flow path from the drywell to ECCS suction strainers. The flow path from the drywell leads through the 1 x 1% foot open-ings of the jet deflector plates through the 6 foot 9 inch vent lines. Inside the torus, the vent lines connect to large spherical shells that are interconnected by the 4-foot 10-inch diameter inner torus ring header. From this header, the path to the torus is through the 96 24-inch diameter downcomers that extend below the water line. The path then proceeds through the large torus volume to the four suction strainers, located about 1/3 of the water level height above the bottom of the suppression chamber. The path provides many places to trap foreign objects, and would spread the particles that do get through uniformly throughout the torus volume. Larger pieces of metal would settle to the bottom of the torus and lighter materials would float rather than be sucked into the strainers.

Inerting of the Quad Cities Primary Containment also leads to less corrosion products available for the potential pre-filtering effect described in IEB 93-02.

The torus is desludged every outage. The previous desludging efforts have not ,

identified an abnormal amount of foreign materialin the torus.

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A'ITACIIMENT

, QUAD CITIES STATION RESPONSE TO BULLETIN 93-02 The ECCS suction strainers are made from stainless steel having perforations .

of 1/16th inch effective area. Hydraulic design of the ECCS is based on the si-multaneous operation of all ECCS equipment at full rated flow and 100% plug-ging of one of the four strainers, plus 1-foot of head loss across each of the remaining s, trainers. The design basis of the strainers is:

Each strainer shall pass 10,000 gpm with an entrance head loss across the screen of one foot of water minimum.

The strainers are cylindrical and sized to remove particles greater than 1/8th inch diameter.

The strainers are in areas of minimum water turbulence ( not directly under a downcomer).

The bottom of the strainers is more than three feet off the bottom of the torus.

The average water velocity in the torus during ECCS equipment operation is less than 0.1 ft/sec, which is not suflicient to transport material except the smaller  ;

particles in suspension. However, during a blowdown from the drywell to the to-rus, the torus will be agitated and a certain portion of contaminants will be trans-ported to the suction strainers. The effective flow area of the strainers may be reduced.

For long term ECCS operation, not all of the ECCS pumps would be required to remove decay heat. For the immediate post-accident time period, two LPCI pumps and one core spray pump would be sufficient. On a long term basis, satisfactory cooling could he accomplished with one LPCI pump and one core spray pump, which would require only 1/8 of the total suction screen area.

In summary, there are relatively few sources of potentially damaging material, and the amount of contaminants is small compared to the torus water volume. ,

Furthermore, it is difficult for contaminants to reach the suction strainers. These '

considerations have led to the conclusion that the probability of torus contamina-tion creating a safety problem is extremely remote.