ML20237E399

SER Accepting Licensee Response to NRC Bulletin 95-002, Unexpected Clogging of Residual Heat Removal Pump Strainer While Operating in Suppression Pool Cooling Mode, for Clinton Power Station

ML20237E399
Person / Time
Site:	Clinton
Issue date:	08/27/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20237E397	List: ML20237E395 ML20237E399
References
IEB-95-002, IEB-95-2, NUDOCS 9808310260
Download: ML20237E399 (4)

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p k UNITED STATES 5 y NUCLEAR REGULATORY. COMMISSION WASHINGTON, D.C. speeH001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO NRC Bul i FTIN 95-02 I

ILLINOIS POWER COMPANY l CLINTON POWER STATION DOCKET NO. 50-461 i

1.0 INTRODUCTION

NRC Bulletin 95-02, " Unexpected Clogging of a Residual Heat Removal (RHR) Pump Strainer While Operating in Suppression Pool Cooling Mode," was issued on October 17,1995. It  !

requested all holders of boiling-water reactor (BWR) operating licenses or construction permits l

for nuclear power reactors to take five actions to ensure that unacceptable buildup of debris that could clog strainers does not occur during normal operation. By letters dated November 15, 1995, December 21,1995, and October 9,1996, Illinois Power Company (the licensee) submitted their response to NRC Bulletin 95-02 for Clinton Power Station (Clinton). In its response, the licensee stated their intent to comply with the requested actions in the bulletin.

The licensee noted that Clinton uses a continuous suppression pool cleanup system to maintain pool cleanliness and that visual observation indicates that overall pool cleanliness is good. In addition, pump suction pressure data for the systems which draw suction most frequently from the suppression pool have not indicated that any buildup of material has occurred.

2.0 DISCUSSION The following describes the requested actions in NRC Bulletin 95-02 and the licensee's response to each requested action.

i Action i Verify the operability of all pumps which draw suction from the suppression pool when j performing their safety functions (e.g., ECCS (emergency core cooling system), containment l spray, etc.), based on an evaluation of suppression pool and suction strainer cleanliness  ;

conditions. This evaluation should be based on the pool and strainer conditions during the last inspection or cleaning and an assessment of the potential for the introduction of debris or other  !

materials that could clog the strainers since the pool was last cleaned.

. Response The Clinton suppression pool was last cleaned in April of 1994, by vacuuming the bottom.

l However, Clinton has a continuously operating suppression pool cleanup system. In normal ,

operation this system processes the suppression pool water volume once very 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br />. The 9808310260 980827 l" l PDR ADOCK 05000461>

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l o 2 in-line strainers on this system have not experienced excessive fouling and have had only seven cleanings in 9 years of operation. The suppression pool cleanup system processes the water through filter /demineralizers, which remove fibrous material and sediment before retuming the water to the pool.

The suction pressure date for the RHR A and B pumps, which have the most frequent operation with the suppression pool as a source, did not indicate any clogging taking place. There have also been no abnormal suction pressures identified by the inservice inspection program for any other ECCS or the reactor core isolation cooling system (RCIC) pumps.

l The existing programs to prevent the inadvertent introduction of material in the suppression L pool were reviewed and no further actions were required. Details on the programs were l provided in the response to requested action 4.

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Action 2 Confirm the operability evaluation in requested action 1 above through appropriate test (s) and strainer inspection (s) within 120 days of the date of this bulletin.

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Response

The RHR A, B, C, and low-pressure core spray (LPCS) pumps have operability tests performed l quarterly, taking suction from the suppression pool. An examination of the pump suction history for these pumps showed no adverse trends, so the licensee determined that no further testing was required. The high-pressure core spray (HPCS) and RCIC pumps are also tested quarterly, although they take suction from the RCIC storage tank. An inspection and cleaning of the ECCS and RCIC suction strainers was completed on December 12,1995. The as-found condition of the strainers did not require cleaning as there was insufficient debris to negatively affect ECCS and RCIC operation. However, cleaning was performed tc., establish a baseline condition for future examinations.

In addition, in an April 1996 event, the licensee operated various safety relief valves to control reactor pressure. Subsequently, RHR B was operated for over 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br /> to remove the decay heat from the suppression pool. During this event there were no indications of inadequate j suction pressure for any of the pumps taking suction from the suppression pool. A visual  !

inspection of the RHR B suction strainer following the event identified some debris accumulation but it was an insufficient amount to affect operability.

Action 3 Schedule a suppression pool (torus) cleaning. The schedule for cleaning the suppression pool i should be consistent with the operability evaluation in requested action 1 above. In addition, a l program for periodic cleaning of the suppression pool should be established, including _

procedures for the cleaning of the pool, criteria for determining the appropriate cleaning

. frequency, and criteria for evaluating the adequacy of the pool cleanliness.  ;

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Response

!- As previously stated, the suppression pool was last cleaned in April of 1994; however. the suppression pool cleanup system provides continuous filtering and demineralizing of the pool.

An additional cleaning of the suppression pool was conducted in refueling outage 6, which began in 1996. A program addressing future inspection frequency, inspection crite;ia, and additional cleanings will be included in the response to NRC Bulletin 96-03, "Poter,tial Plugging of Emergency Core Cooling Suction Strainers by Debris in Boiling Water Reactors."

Action 4 Review foreign material exclusion (FME) procedures and their implementation to determine whether adequate control of materials in the drywell, suppression pool, and ' systems that interface with the suppression pool exists. This review should determine if comprehensive FME controls have been established to prevent materials that could potentially impact ECCS

, operation from being introduced into the suppression pool, and if workert are sufficiently aware of their responsibilities regarding FME. Any identified weaknesses shov2d be corrected in addition, the effectiveness of the FME controls since the last time the suppression pool was cleaned and the ECCS strainers inspected, and the impact that any w9aknesses noted may have on the operability of the ECCS should be assessed.

Response

l In response to requested action number 4, the licensee has revie wed their FME practices and concluded that they are adequate. This conclusion is based on 'axtensive procedural controls l for FME and a review of condition reports which indicated no aaverse trend in the area of FME for the suppression pool. f j Action 5 Consider additional measures such as suppression pool water sampling and trending of pump j suction pressure to detect clogging of ECCS suction strainers.  !

l Resoonse

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l The licensee currently conducts a suppression pool sampling program with required actions if a 9 parameter falls into an abnormal range. In addition, ECCS and RCIC pump suction pressure is recorded and trended as part of the ISI program. The licensee concluded that the sampling and testing programs are adequate and no further actions are required.

3.0 EVALUATION The purpose of the requested actions in the bulletin is to ensure that ECCS and other pumps

- drawing suction from the suppression pool do not experience unacceptable buildup of debris that could clog strainers during normal operation and would prevent them from performing their safety function. Requested action 1 requested licensees to evaluate the operability of their

- pumps based on the cleanliness of the suppression pool and strainers. Requested action 2

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4 l then requested a verification of the licensee's assessment through a pump test and strainer

( inspection. These two actions serve to ensure that the pumps are currently operable and not i experiencing unacceptable debris buildup. Requested actions 3,4 and 5 serve to ensure that I

appropriate measures, such as cleaning of suppression pools and strengthening of FME L practices, are taken in the long term to prevent debris accumulation in the pool.

L The staff has concluded that the licensee's assessment of the ability of all pumps drawing

! suction from the suppression pool to perform their safety function has a reasonable basis for concluding that all of the pumps evaluated are operable, in addition, the licensee conducted an inspection to confirm that the RCIC and ECCS systems were not affected by an unacceptable l buildup of debris that could clog the pump strainers. Initial strainer cleanliness was considered l

good. Each strainer had a uniform covering of iron oxide dust that was easily removed by slight agitation. Although no cleaning was necessary, the strainers were cleaned to provide a l baseline for future examinations.

The staff has concluded that the licensee's response meets the intent of requested actions 1 and 2 and is acceptable. The staff has also concluded that the licensee's evaluation of their FME program and suppression pool cleaning program meets the intent of requested actions 3 and 4, and is acceptable. The licensee's existing programs such as trending of pump suction pressure data, sampling of torus water / sediment, and periodic inspections of the strainers and torus provide additional opportunity for early identification of potential strainer fouling. The staff has concluded that these additional actions meet the intent of requested action 5 and are acceptable. The staff has also concluded that the schedule forimplementation of the actions proposed by the licensee is appropriate given the actions already taken.

4.0 CONCLUS!QN Based on the staff's evaluation of the licensee's submittal (s), the staff finds the licensee's response to NRC Bulletin 95-02 to be acceptable.

Principal Contributors: John B. Hickman R. Elliott (by precedent)

Date! August 27, 1998 l

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