ML17164A859
| ML17164A859 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 10/27/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17164A858 | List: |
| References | |
| IEB-95-002, IEB-95-2, NUDOCS 9810300202 | |
| Download: ML17164A859 (10) | |
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UNITED STATES NUCLEAR REGULATORY COlVIMISSION WASHINGTON, D.C. 20555-0001 GU U
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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, to address the potential for Emergency Core Cooling System (ECCS) suction strainers to be clogged during normal operations by debris which is present, or accumulates in, the suppression pool during normal operation.
Industry experience has shown that during operation of the suppression pool cooling system, the strainers may filterout fibers that are present in the pool water. The resulting mat of fibers then improves the filtering action of the strainers, thereby collecting corrosion, products and other material (sludge) on the surface of the strainer. This strainer clogging may then result in loss of cooling flow.
The bulletin requested all holders of boiling-water reactor (BWR) operating licenses or 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 15, 1995 (PLA-4391), Pennsylvania Power and Light Company (PPSL, the licensee) submitted their response to NRC Bulletin 95-02 for Susquehanna Steam Electric Station, Units 1 and 2. Updated information was contained in letters dated October 4, 1996 (PLA-4512), and April24, 1998 (PLA-4880). In its response, the licensee provided information on actions that had already been completed, or were ongoing, to demonstrate compliance with the requested actions in the bulletin.
The following describes the request'ed actions in NRC Bulletin 95-02 and the licensee's response to each requested action.
Verifythe operability of all pumps which draw suction from the suppression pool when performing their safety functions (e.g., ECCS, containment 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.
98i0300202 98i027 PDR ADQCK 05QQQ38T 6
PDR ENCLOSURE
J' Sum of o se The licensee performed a detailed operability evaluation of the pumps associated with the RHR, Core Spray (CS), High Pressure Coolant Injection (HPCI), and Reactor Core Isolation Cooling (RCIC) systems in accordance with the NRC Bulletin as well as the more detailed September 29, 1995, BWR Owners'roup guidance referenced by the bulletin. 'This evaluation concluded that all of the pumps evaluated are operable based on the results of strainer/suppression pool cleanliness inspections, suppression pool water/sludge sampling, foreign material exclusion (FME) controls, and RHR/CS pump suction pressure trend data.
During the 1995 Refueling and Inspection Outages (RFIOs), the licensee used divers to perform inspections of the strainers and the pool floors. Allstrainers were found to be free of accumulation of fibers, and a relatively small amount of foreign material was found in each pool.
These items were either retrieved or determined, through formal evaluation, to have no detrimental effect on the pumps ifleft in place.
Pool sludge accumulations were found to be "a very light dusting of corrosion products" in Unit 1, and less than 1/8" in Unit 2. Additionally, no fibers were found in any samples taken of pool water or sludge.
The licensee's evaluation of the potential for the introduction of debris or other material that could clog the strainers concluded that the results of the strainer and pool inspections would remain satisfactory.
This was based on the small number of foreign objects found during the inspections (which were the first purposeful cleanings since shortly after initial plant startup) and enhancements which had been made to the FME program prior to the 1995 RFIOs.
Finally, the licensee performed a review of historical suction pressure measurements of the CS and RHR pumps, taken during quarterly flowtests and RHR suppression pool cooling operations, for adverse trends.
No indications of strainer degradation were identified, which is consistent with the results of the divers'nspections.
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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.
Sum a
of es o se The licensee concluded that additional confirmatory tests/inspections were not required based on: (1) satisfactory results of the strainer/pool inspections performed in 1995 prior to the NRC issuance of Bulletin 95-02, (2) the removal of foreign material from the pool (or satisfactory evaluation of remaining items), (3) absence of fibers in pool water/sludge samples, (4) enhanced FME controls, and (5) acceptable pump suction pressure data trends.
The licensee did, however, take advantage of a forced outage on Unit 1 to sample and analyze the suppression pool water.
Quarterly surveillance testing of the RHR and CS pumps, and strainer/pool floor inspections
'uring RFIOs, has continued with no indication of strainer degradation.
Furthermore, subsequent to their 120-day response to this bulletin, as discussed in their fetter dated April24, 1998, the licensee performed multiple pump runs to confirm the absence of fiber in the pool. These
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involved extended runs of multiple RHR pumps in order to achieve sufficient agitation, such that any fibers would be suspended and then drawn to the suction strainer.
This testing was most recently performed during the Unit 1 ninth and tenth RFIOs and the Unit 2 eighth RFIO, and revealed no accumulations of fibrous material. This not only confirms the absence of fiber in the pool, but provides additional confirmation of the licensee's operability evaluation for Bulletin 95-02.
~CQQ 3 Schedule a suppression pool (torus) cleaning. The schedule for cleaning the suppression 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.
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f esose The licensee had removed foreign materials from the suppression pools of each unit during the RFIOs preceding issuance of NRC Bulletin 95-02. Any material left behind had been formally evaluated.
The licensee implemented a program for periodic inspection and cleaning, ifneeded, of the suppression pools.
Based on the results of the inspections performed during the 1995 RFIOs, which are discussed in the response to Item 1, the licensee concluded that suppression pool cleaning was not required prior to the next RFIO.
As discussed in their October 4, 1996, and April24, 1998, letters, the licensee subsequently filtered or desludged the suppression pools and conducted FME inspections with divers during the 1997 and 1998 RFIOs.
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Review 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 ifcomprehensive FIVIE controls have been established to prevent materials that could potentially impact ECCS operation from being 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.
Summa o Res o se The licensee concluded that, based on the results of the pool inspections performed during the 1995 RFIOs, FME controls in place prior to 1995 were adequate.
However, the licensee implemented program'enhancements which included:
(1) daily walkdowns of the drywell and wetwell during refueling outages for the presence of foreign material, (2) installation of temporary covers over the downcomers during refueling outages, (3) installation of downcomer drain fittings during draining'evolutions, and (4) additional FME training for site personnel.
Action 3 Schedule a suppression pool (torus) cleaning. The schedule for cleaning the suppression 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.
Summa of Res onse The licensee had removed foreign materials from the suppression pools of each unit during the RFIOs preceding issuance of NRC Bulletin 95-02, Any material left behind had been formally evaluated.
The licensee implemented a program for periodic inspection and cleaning, ifneeded, of the suppression pools.
Based on the results of the inspections performed during the 1995 RFIOs, which are discussed in the response to Item 1, the licensee concluded that suppression pool cleaning was not required prior to the next RFIO.
As discussed in their October 4, 1996, and April24, 1998, letters, the licensee subsequently filtered or desludged the suppression pools and conducted FME inspections with divers during the 1997 and 1998 RFIOs.
Action 4 Review 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 ifcomprehensive FME controls have been established to prevent materials that could potentially impact ECCS operation from being 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.
Summa of Res onse The licensee concluded that, based on the results of the pool inspections performed during the 1995 RFIOs, FME controls in place prior to 1995 were adequate.
However, the licensee implemented program enhancements which included:
(1) daily walkdowns of the drywell and wetwell during refueling outages for the presence of foreign material, (2) installation of temporary covers over the downcomers during refueling outages, (3) installation of downcomer drain fittings during draining evolutions, and (4) additional FME training for site personnel.
Action 5 ti Consider additional measures such as suppression pool water sampling and trending of pump suction pressure to'detect dogging of ECCS suction strainers.
Summa of Res onse The licensee samples suppression pool water and sludge during RFIOs, and is evaluating potential methods for taking unfiltered samples of suppression pool water, ifneeded, while the units are on-line. Additionally, the licensee trends the RHR and CS pump suction pressure data taken during quarterly pump surveillance testing.
No further measures were proposed.
Since the initial response, however, the licensee has also implemented a program to reduce the potential sources of fibrous material within the containment.
As discussed in the October 4, 1996, and April24, 1998, letters, this included replacement of fibrous insulation in the drywell with reflective metallic insulation or, in the case of the Reactor Building Chilled Water System, a phenolic foam insulation.
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 build-up of debris that could clog strainers during normal operation which 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 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 build-up. Requested actions 3, 4 and 5 serve to ensure that appropriate measures, such as cleaning of suppression pools and strengthening of FME practices, are taken in the long term to prevent debris accumulation in the pool.
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.
The licensee conducted an inspection to confirm that the ECCS systems were not affected by an unacceptable build-up of debris that could clog the pump strainers.
Initial strainer cieanliness was considered good. 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 meet the intent of requested Actions 3 and 4, and are acceptable.
The licensee's programs for trending pump suction pressure data, sampling torus water/sediment, and periodically inspecting the strainers and torus provide additional opportunity for eariy identification of potential strainer fouling. The staff has concluded that these additional actions meet the intent of requested Action 5 and are acceptable.
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4.0 CONCLUSION
Based on the staff's evaluation of the licensee's submittals, the staff finds the licensee's response to NRC Bulletin S5-02 to be acceptable.
Principal Contributors:
D. Collins J. Hickman R. Elliott October 27, 1998
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