ML20237A776

SER Accepting Licensee Response to NRC Bulleting 95-002, Unexpected Clogging of RHR Pump Strainer While Operating in Suppression Pool Cooling Mode

ML20237A776
Person / Time
Site:	Peach Bottom, Limerick
Issue date:	08/10/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20237A773	List: ML20237A771 ML20237A776
References
IEB-95-002, IEB-95-2, NUDOCS 9808170097
Download: ML20237A776 (5)

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• • • • • f SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO NRC But i FTIN 95-02 PECO ENERGY COMPANY L[MERICK GENERATING STATION. UNITS 1 AND 2 PEACH BOTTOM ATOMIC POWER STATION. UNITS 2 AND 3 DOCKET NOS. 50-352 50-353. 50-277. AND 50-278

1.0 INTRODUCTION

NRC Bulletin 95-02 entitled, " 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 licensees or holders of construction permits 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 letter dated November 16,1995, PECO Energy Company (PECO, the licensee) submitted its responses to NRC Bulletin 95-02. By letters dated May 9,1996, and March 4,1997, the staff forwarded two requests for additional information (RAl) to the licensee. The licensee's responses to the RAls were provided in letters dated June 10,1996, and April 3,1997. In its response, the licensee stated that: 1) the suppression pool at Limerick, Unit 1, was last cleaned and destudged in September 1995; 2) the suppression pool at Limerick, Unit 2, was last cleaned ard desludged in January 1995; 3) the torus at Peach Bottom, Unit 2, was last cleaned and desludged in September 1994; and 4) the torus at Peach Bottom, Unit 3, was last cleaned and desludged in 1991. Peach Bottom, Unit 3, also conducted an inspection of one half of its torus and the strainers located within the inspection area during its refueling outage in January 1995.

Based on this inspection, the licensee concluded that additional cleaning at that time was not l

necessary. The following describes the requested actions in NRC Bulletin 95-02 and the licensee's responses to each requested action:

l Action 1: . Verify the operability of all pumps which draw r action from the suppression pool when l performing their safety functions (e.g., ECCS, containment spray, etc.), based on an ev1uation

of suppression pool and suction strainer cleanliness conditions. This evaluation should be based I

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 poolwas last cleaned.

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Resnonse: In response to requested action number 1, the licensee concluded that all pumps taking suction from the pool were operable. The licensee's conclusion was based on satisfactory results from PECO Energy's program to demonstrate adequate pool cleanliness.

The four parts of the program consist of the following: .1) analysis of water and sludge samples for presence of fiber,2) inspection of pump strainers,3) inspection of suppression chamber floor, and 4) trending of pump suction strainer differential pressure.

ENCLOSURE 9808170097 980810 PDR ADOCK 05000277 0 PDR

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In its response to the bulletin, PECO stated that bou e of Umerick were thoroughly ,

cleaned and inspected during recent outages for each uria. Unit 1's suppression pool and strainers were thoroughly cleaned during the September 1995 outage following Unit 1's strainer clogging event. This strainer clogging event was the basis for the staff's issuance of NRC Bulletin 95-02. Additional follow-up cleaning and strainer inspection was performed during the Unit 1 refueling outage in February 1996. Following this outage, visibility in the suppression pool was 20 25 feet, and divers were able to easily see small objects located on the pool floor. Unit 2's suppression pool and strainers were thoroughly cleaned and inspected during its refueling outage in February 1995. Water and sludge samples taken from both units found no fibrous material in Unit 2 and only trace amounts in Unit 1.

Quarterly pump test results have shown no indication of degraded pump performance at j

either unit. The licensee stated that the experience at Limerick, Unit 1, has shown that

- appreciable accumulations of fibrous material on the suction strainer can be detected before accumulations reach a level in which pump performance is degraded.

PECO also stated that Peach Bottom, Unit 2 torus was thoroughly cleaned and inspected during its refueling outage in October 1994. Unit 3 torus was last cleaned in 1991; however, the licensee conducted an inspection of one half or the torus and the strainers located within the inspection area during the Unit 3 outage in October 1995. The inspection results showed that the torus was covered by a thin layer of sludge which was approximately 1/64 of an inch or less in depth. The only foreign material consisted of 3 isolated fibers of approximately 1 inch in length and one small piece of duct tape. The licensee concluded that the visibility in the pool was sufficient for ensuring that the pool was adequately clean.

Visibility was estimated to be 10-12 feet. Analyzed samples of torus water and sludge taken to date have not detected the presence of fibers. Quarterly pump test results have shown no indication of degraded pump performance at either unit. '

Based on the results of the tests, inspections and analyses discussed above, the licensee concluded that all pumps drawing suction from the suppression pool or torus to perform their safety function are operable. ,

l 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.  !

Response: In response to requested action number 2, the licensee concluded that additional pump testing other than quarterly inservice tests (IST) was unnecessary. The licensee stated that the program for cnsuring adequate suppression pool / torus cleanliness described in its response to action 1 above provides equivalent or better assurance of ECCS pump operability than a single multi-pump test. However, the licensee did provide the staff i with operational data which indicated significant operating experience over the operating I cycles prior to and following the issuance of NRC Bulletin 95-02 where more than one

pumps were run in suppression pool cooling or IST mode. The reason for these multiple j l- pump runs was primarily for the maintenance of suppression pool / torus water temperature -

during high pressure coolant injection (HPCI) pump testing. The following describes the .

operating experience provided by the licensee in its responses: l t

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1) Peach Bottorn, Unit 3: two loops of the RHR system were run for approximately 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> on May 30,1996 to ensure that torus water temperature was maintained within allowable limits during a HPCI test. No anomalies were identified in any RHR system parameters.

2) Limerick, Unit 2: two loops of RHR pumps were run in suppression pool cooling mode during HPCI testing for approximately two hours with no anomalies noted in any RHR system parameters.

3) Limerick, Unit 1: two loops of RHR pumps were run simultaneously in suppression pool mode for approximately.18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> during HPCI testing. An additional 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> was spent with one loop in suppression pool cooling mode and one loop in IST mode. The licensee also stated that during the safety relief valve discharge / strainer clogging event identified in NRC Bulletin 95-02, the licensee operated two loops of suppression pool cooling simultaneously for approximately 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br />. Other than the strainer clogging event described in NRC Bulletin 95-02, no anomalies were noted in any RHR system parameters. -

Action 3: Schedule a suppression pool cleaning. The schedule for cleaning the pool should be consistent with the operability evaluation in requested action 1 above. In addition, a 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.

Response: Prior to the completion of this review, the licensee began implementing its resolution to NRC Bulletin 96-03 for all four units. The licensee has installed (or will install during each unit's upcoming refueling outage) new suction strainers on RHR and core spray pumps for all four units. The strainers are sized with significant margin to allow large periods between pool cleanings, in response to requested action number 3, the licensee i committed to cleaning the suppression pool eveiy 10 years based on the installation of the new strainers. However, the licensee will inspect the strainers and the suppression pool during two consecutive refueling outages, and may adjust the periodicity of the pool cleanings based on the inspection findings. In addition, if these inspections indicate that

l. corrosion product and foreign material accumulation in the pool are well within the design I bounds for the strainers, the licensee will adjust the suppression pool / suction strainer inspection frequency to every other refueling outage.

I Action 4. Review foreign material exclusion (FME) precedures and their implementation to l 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 i

FME controls have been established to prevent materials that could potentially irnpact ECCS operation from bsing introduced into the suppression pool, and that workers are sufficiently aware of their responsibilities regarding FME. Any identified weaknesses should 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 weaknesses noted may have on the operability of the ECCS should be assessed.

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Response: In response to requested action number 4, the licensee has reviewed its FME practices and concluded they are adequate. The licensee's conclusion is based on l procedural controls currently being used at both sites, such as: 1) loose items must be secured (e.g., by a lanyard or taped *.n a pocket) when entering an FME zone such as the suppression chamber,2) visualinspections of personnel entering an FME zone are conducted by control point personnel to ensure unnecessary items are not taken into an FME zone and to ensure that loose items are secured,3) a dropped item log is maintained at the FME control point,4) materials that could clog strainers are not authorized in an FME zone unless the worker has specific approval from the Maintenance Manager, 5) periodic inspections are performed by management and supervisory personnel to verify job site cleanliness is being maintained,6) waming signs are posted in areas that communicate with the suppression chamber (e.g., downcomers), and 7) extensive closeout inspections are -

conducted prior to' securing an FME zone. In spite of this, the licensee also committed to having an independent assessment of its FME program performed by its Nuclear Quality Assurance (NQA) organization with additionalimprovements made to the FME program as necessary. The licensee also indicated that its workers have a heightened awareness of cleanliness controls in the area of the drywell and suppression pool, and that work groups at both stations receive cleanliness controls training.

Action 5: Consider additional measures such as suppression pool water sampling and trending -

of pump suction pressure to detect clogging of ECCS suction strainers.

Response: In response to requested action number 5, the licensee committed to trending of pump section strainer differential pressure, periodic sampling of suppression pool / torus water and analysis to determine if fibrous materials are present in the pool, and evaluation of ways to potentially minimize the accumulation of sludge in the pool. The licensee will evaluate routine operation of the Suppression Pool Cleanup systems to determine if this would minimize the amount of suspended solids in the pool, in addition, the licensee will evaluate the use of a new system designed to reduce the dissolved oxygen concentrations in the pool water which may reduce corrosion product buildup in the suppression pool / torus.

In its RAI response of April 3,1997, the licensee indicated that it will discontinue periodic sampling of the torus water and pump suction differential pressure trending after the installation of the new suction strainers because of the large margin built into the design. In addition, the licensee believes that trending of differential pressure with the new strainers would not provide meaningful data due to the large size of the strainers. The differential pressure will be very small.

. 2.0 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 which would prevent them from performing their safety function. Requerted action 1 requested licensees to evaluate the operability of their pumps based on the cleanliness of the suppression pool and strainers. Requested action 2 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 experiencing unacceptable debris buildup. Requested actions 3,4 and 5 serve to ensure tha, appropriate measures are taken in the long term to prevent debris accumulation in the pool.

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The licensee has performed an assessment of the operability of all pumps drawing suction from the suppression pool to perform their safety function and concluded that they are operable based on the results of suppression pool and strainter inspections, sludge and pool water sample analyses, and IST testing of pumps. The licensee concluded that an extended duration, multiple-pump test was not necessary based on the pool and strainerinspections and the IST results.

The staff notes, however, that the licensee has a large amount of operating experience with multiple-pump runs over the last @ rating cycle (see response to action 2 above). No anomalies in RHR system parameters were identified in approximately 31 hours3.587963e-4 days <br />0.00861 hours <br />5.125661e-5 weeks <br />1.17955e-5 months <br /> of multiple-pump operation at Limerick, Units 1 and 2, and Peach Bottom, Unit 3. This data supports the licensee's claim that their program to demonstrate adequate pool cleanliness is sufficient in lieu of an extended-duration, multiple-pump test. The data also supports the licensee's conclusion that all pumps drawing suction from the suppression pool or torus are operable. However, during the fall 1997 ECCS suction strainer modification of Peach Bottom, Unit 3, the licensee failed to i

provide adequate FME controis. The failure resulted in foreign material entree into and clogging of core spray pump 3A and inadequate pump flowrate. This lapse ofimplementation of the FME controls was documented in the NRC staff Notice of Violation, integrated Inspection Report No.

50-277/98-05 and 50-278/98-05, and proposed Civil Penalty dated June 11,1998. In spite of this lapse, the staff has noted that the licensee's corrective actions described in its response to the Notice of Violation adequately correct the deficiencies which led to failure of FME controls during the ECCS suction strainer modification. Therefore, 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 commitments to its program to ensure adequate suppression pool / torus cleanliness in both the short term and the long term, have the NQA organization perform an independent assessment of the FME program and to make improvements as necessary, trend pump suction strainer differential pressure, and assess other potential ways for removing suspended solirts in the pool water and reducing corrosion product formation in the pool, meet the intent of requested actions 3,4, and 5 and are acceptable.

l The staff notes that it is necessary to clarify one point. NRC Bulletin 95-02, action number 3 requested licensees to establish a suppression pool cleaning program. The times between periodic strainer / suppression pool cleanings and inspections established by the licensee (every other refueling outage for inspection /10 years for cleaning) are large; however, they are considered to be adequate by the staff based on the new strainer design they are installing in l( response to NRC Bulletin 96-03 (See licensee submittals dated October 10,1997 for Limerick, Units 1 and 2, and August 22,1997 for Peach Bottom, Units 2 and 3.) The licensee's l new strainer design is sized with more than 100% margin over its new licensing basis. Because of this margin, the staff believes that extending the time between inspections and cleanings is appropriate and that the frequencies established by the licensee for strainer / suppression pool inspection and cleaning are adequate.

3.0 CONCLUSION

l Based on the staff's evaluation of the licensee's submittals, the staff finds the licensee's response to NRC Bulletin 95-02 to be acceptable.

Principal Contributor: R. Elliot Date: August 10, 1998