ML20154L103
| ML20154L103 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 10/14/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20154L098 | List: |
| References | |
| IEB-95-002, IEB-95-2, NUDOCS 9810190145 | |
| Download: ML20154L103 (4) | |
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30se6-0001
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j SAFETY EVALUATION BY THE OFFICE OF NUCI FAR REACTOR REGULATION'
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RELATED TO NRC But i FTIN 95-02 DETROIT EDISON COMPANY FERMI 2 l
DOCKET NO. 50-341
1.0 INTRODUCTION
i NRC Bulletin (BL) 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.
I It requested all holders of boiling-water reactor operating licenses or construction permits for j
nuclear power reactors to take five actions to ensure that unacceptable buildup of debris that i
could clog strainers does not occur during normal operation. By letters dated November 16, 1995, and November 15,1996, Detroit Edison (the licensee) submitted its response to BL 95-02 for Fermi 2. In its response, the licensee stated its intent to comply with the requested actions in the bulletin.
2.0 DISCUSSION The following describes the requested actions in BL 95-02 and the licensee's response to each requested action.
Action i Verify the operability of all pumps which draw suction from the suppression pool when performing their safety functions (e.g., ECCS [ emergency core cooling system), 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.
Response
The eight RHR and core spray system (CSS) pumps are tested quarterly by drawing water from the suppression pool through the suction strainers. The licensee reviewed the pump flow and pump suction pressure data from the tests for the prior 7 years and identified no sign of strainer degradation. Although the high pressure coolant injection (HPCI) and reactor core isolation i
cooling (RCIC) pumps do not take suction from the suppression pool during surveillance tests, 1
based on the similarity of the HPCI and RCIC strainers with the RHR and CSS strainers, on the satisfactory results of the RHR and CSS flow tests through the suppressicn pool strainers, and 9810190145 981014 PDR ADOCK 05000341 4
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l the satisfactory visual inspections performed on all the suction strainers, the licensee determined that there was reasonable assurance that the HPCI and RCIC strainers were also operable.
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.
Resoonse l
The licensee committed to inspect the suction strainers during refueling outages as part of j
Fermi's preventive maintenance program. The first such inspection was performed during the first refueling outage after BL 95-02 was issued. The visual inspection, by divers, found only fine particle accumulation with no sludge, fibrous material, or other debris observed in quantities or locations that wo' ld constitute a strainer blockage concem. The inspection identified items on the torus floor that were addressed as part of a revision to the foreign material exclusion (FME) program discussed in the response to Action 4.
Quarterly surveillance testing of the RHR and CSS flow paths has continued with no indication of strainer degradation.
Fermi has a Torus Water Management System (TWMS) which is used to maintain torus water quality by transferring torus water to the condensate system and returning clean condensate water to the torus. This system is also used to routinely sample the torus water. As part of the response to BL 95-02 the licensee obtained samples from the RHR pump suction during a pump and valve operability surveillance. Sampling during the RHR pump surveillance was intended to facilitate increased water mixing compared to the TWMS operation. Small numbers of fibers less than 4 mm in length were identified in the sample. However, the licensee i
concluded that the fibers found in the torus water samples were too small relative to the ECCS suction strainer hole size to constitute a strainer blockage concem.
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.
j Resoonse i
The licensee had cleaned the suppression pool in the last refueling outage preceding the issuance of BL 95-02. The licensee implemented a program for periodic inspection of the l
suppression poolincluding criteria of evaluating the adequacy of pool cleanliness, determining the appropriate cleaning frequency, and procedures for cleaning the poolif needed. The j
licensee implemented this inspection program during the first refueling outage after BL 95-02 4
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t 3-was issued. Based on the inspection performed the licensee concluded that torus cleaning was not required prior to the next scheduled refueling outage.
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 j
exists. This review should determine if comprehensive FME controls have been established to l-prevent materials that could potentially impact ECCS operation from being introduced into the t
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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Resoonse The licensee performed a review of the housekeeping procedure and related administrative l
controls prior to the first refueling outage after BL 95-02. The review resulted in a revision to l
the plant housekeeping procedure, which, in part, upgraded FME and housekeeping l
requirements in the drywell and suppression chamber. Adherence to the enhanced provisions for material and tool control in the suppression chamber is expected to preclude the possibility j
of leaving objects such as those identified during the refueling outage inspection (lapel air j
sampler and skimmer) in the suppression pool.
Action 5 Consider additional measures such as suppression pool water sampling and trending of pump l
suction pressure to detect clogging of ECCS suction strainers.
Resoonse l
The licensee will be reviewing and trending the pump suction inlet pressure data, taken before starting the pumps and after the pumps have reached a steady state, from the quarterly surveillance tests of the RHR and CSS pumps.
Samples of suppression pool water, from the TWMS, will be analyzed monthly for conductivity and the amounts of selected elements. Additionally, torus water samples taken during RHR pump surveillance tests will be analyzed for suspended solids and fibers at least quarterly.
3.0 EVALUATION l
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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, preventing the strainers 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 L
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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
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appropriate measures, such as cleaning of suppression pools and strengthening of FME 3
practices, are taken in the long term to prevent debris accumulation in the poo!.
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 provides a reasonable basis for concluding that all of the pumps evaluated are operable. The licensee conducted an j
inspection to confirm that the ECCS systems were not affected by an unacceptable buildup of debris that could clog the pump strainers. The licensee indicated initial strainer cleanliness was 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 its 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 i
pressure data, sampling torus water /sedimer t, and periodically inspecting the strainers and i
torus provide additional opportunity for early dentification of potential strainer fouling. The staff has concluded that these additional actions meet the intent of requested action 5 and are i
acceptable.
4.0 CONCLUSION
Based on the staff's evaluation of the licensee's submiMals, the staff finds the licensee's i
response to BL 95-02 acceptable.
Principal Contributors: John B. Hickman Robert B. Elliott (By precedent) l Date: October 14, 1998 i