05000341/FIN-2007003-07
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Finding | |
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| Title | INADEQUATE DETERMINATION OF MINIMUM FLOW SETTING FOR HPCI PUMP (Section 1R21.4.B.1) |
| Description | The inspectors identified an unresolved item concerning the licensees response to Bulletin 88-04, Potential Safety-Related Pump Loss, regarding establishing minimum flow requirements for the HPCI pump. The licensee recognized that the conditions reported in the bulletin were present in all safety-related pumps, including the HPCI pump, but did not determine an appropriate minimum pump flow value to minimize and manage, or to eliminate, the potential for pump damage. Additionally, the inspectors review identified that the calculation used to verify the currently specified minimum flow rate was non-conservative. At the end of the inspection, the licensee dad not received a specific minimum flow value for the HPCI pump from its manufacturer. The inspectors needed this information to complete the assessment of this issue. Description: Bulletin 88-04, in part, identified a concern regarding the adequacy of minimum flow capacities for safety-related centrifugal pumps. The bulletin required licensees to evaluate the capability of safety-related pumps to run long-term at minimum recirculation flow rates. The bulletin stated that many pump vendors had accounted for thermal considerations in setting the minimum recirculation flow rates, but had failed to consider flow instability effects. The latter consideration could necessitate a considerable increase in minimum flow settings, especially for pump operation for extended periods of time. This potential increase occurred because centrifugal pumps demonstrated a flow condition described as hydraulic instability or impeller recirculation at some flow point below approximately 50 percent of the best efficiency point on the characteristic pump curve. These unsteady flow phenomena become progressively more pronounced if flow was further decreased, and could result in pump damage when operated for extended periods of time. The inspectors reviewed the licensees responses to Bulletin 88-04, which were described in a 1988 letter to the NRC. The licensees response for all ECCS pumps was not based on a specific pump vendor evaluation. Hence, the licensee did not properly verify the minimum flow settings with the HPCI pump manufacturer (Byron-Jackson) in accordance with what was stated in their response to the bulletin. The licensee had concluded that the original, manufacturer-supplied minimum recirculation flows contained in the pump purchase specifications were adequate to meet the issues discussed in Bulletin 88-04. The inspectors questioned whether the current minimum flow HPCI setting was reviewed and approved by the pumps manufacturer (now Flowserve), as specified in the licensees response to the bulletin. The licensee had not contacted the pump manufacturer and 18 Enclosure relied upon information provided by General Electric (1988 Boiling Water Reactor Owners Group letter to NRC) to conclude that no changes were needed for ECCS pumps including the HPCI pump. Furthermore, subsequent to the licensees response to the bulletin, the HPCI booster pump impeller was changed from a four to a 5-vane impeller, which may change the required minimum flow rate. Based on the inspectors concern, the licensee contacted the HPCI pump manufacturer to perform a new analysis of the HPCI pumps minimum flow settings. The inspectors noted that this issue might be applicable to other ECCS pumps. The inspectors also identified a related concern with calculation DC-0204, Sizing Restricting Orifice Diameters and Thickness. This calculation established the HPCI minimum flow based on the CST suction alignment and maximum fluid temperature of 100F. These were non- conservative assumptions because the suppression pool suction alignment would have resulted in much higher temperatures (up to 170F) and no suction pressure contribution. As such, these assumptions predicted a non-conservatively high calculated flow through the minimum flow line. Since there was no installed flow instrument the licensee was unable to measure actual flow through the minimum flow line. Several other concerns were also identified including the calculation was not revised to reflect the change from a four to 5-vane impeller for the booster pump and the calculation used a methodology that over-predicted the point of choked flow through the orifice. Furthermore, although this calculation predicted cavitation, it did not evaluate the effect of the cavitation on the orifice and other downstream components and piping. The justification provided in the calculation and in the initial licensees response was that the operating period in minimum flow was short and significant cavitation erosion was not expected. The inspectors review of the operating procedures (normal and emergency) and discussions with the licensees operating staff determined that there were no procedural restraints for the HPCI minimum flow operation. The licensee concurred with the inspectors concerns and initiated CARD 07-24128 that restricted the minimum HPCI flow operation pending further evaluations and potentially an orifice modification. As a result of the response to Bulletin 88-04, HPCI pump was operated since original plant start-up with an increased potential for unusual wear and aging. Based on fact that at the end of the inspection, the licensee did not receive specific minimum flow value for the HPCI pump from its manufacturer, the NRC concluded that additional review and evaluation were required to assess whether or not the licensee has established adequate minimum flow requirement for HPCI pump. Additionally, the same concern may apply to the remaining ECCS pumps since the licensee did not obtain vendor specific minimum flow requirements for these pumps and they may operate at minimum flow conditions for extended periods of time under accident conditions. Also, pending completion of the corrective actions outlined in CARD 07-24128, the ability of the HPCI system to provide the currently required minimum flow of 500 gpm was undetermined. Therefore, this issue is considered an unresolved item (URI 05000341/2007003-07) pending completion of an analysis to assess the HPCI pump minimum flow requirement and the systems ability to provide this flow and subsequent NRC review. |
| Site: | Fermi  |
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| Report | IR 05000341/2007003 Section 1R21 |
| Date counted | Sep 30, 2007 (2007Q3) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.21 |
| Inspectors (proximate) | A Dunlop M Munir B Palagi D Passehl M Shlyamberg F Baxter C Acosta Acevedoa Dunlopj Cassidy T Steadham M Phalen D Jones R Morris A Wilson V Meghani F Tran |
| INPO aspect | |
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Finding - Fermi - IR 05000341/2007003 | |||||||||||||||||||||||||
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Finding List (Fermi) @ 2007Q3
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