05000285/FIN-2008006-02
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Finding | |
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| Title | Containment Cooling Design Requirements and Licensing Review |
| Description | On March 17,2008, during the inspection of LER 2007-004, Inadvertent Isolation of Containment Spray due to Inadequate Test Procedure, the team postulated that a containment spray pump coupling failure, a pump discharge check valve failure to open, 0r a pump 480 VAC breaker mechanical failure could result in the inability of one pump to provide any containment spray flow. Consequently, the remaining operating pump \'would operate with both containment spray header isolation Valves HCV-344 and HCV-345, open resulting in a pump runout condition due to a single active mechanical failure. The licensee identified a containment spray pump runout condition in 1990 in which both Valves HCV-344 and HCV-345 were open simultaneously with only one pump running would cause a runout condition and cause the motor to draw more amperage than the vendor allowable criteria of no more than 15 percent above its nameplate rating. The case of a single pump discharging to both spray headers would cause the motor to draw amperage 22 percent above its nameplate rating. After identifying this issue in 1990, the licensee planned to implement a piping modification to the spray header to prevent the runout condition, but elected instead to install additional valve opening logic which was intended to only allow one pump to operate with one spray header valve open or both pumps and both spray headers open. This modification was first installed between the B and C containment spray pumps, SI-3B and SI-3C, 480 VAC breakers and the Train A spray header isolation Valve HCV-344. This modification was also installed in 2006 between the A containment spray pump, SI-3A, and the Train B spray header isolation Valve HCV-345 as well as removing the auto start feature from the containment spray Pump C. Essentially, the modification consisted of an auxiliary contact being installed in each pumps\' 480 VAC breaker cubicle which, when the breaker closed, would allow the opposite train\'s header isolation valve to open. After reviewing CRs 200601606, 200701647,200701647, and LER 2007-004, the team found that the licensees engineering reviews were focused on electrical aspects of single active failures resulting in pump runout and did not consider single active mechanical failure modes. The team noted that a previously submitted license amendment, License Amendment 235, which removed the automatic start feature to the containment spray Pump C also did not consider single active mechanical failures and the potential for pump runout. The license amendment addressed containment sump performance and net positive suction head concerns for the containment spray pumps. The team concluded that the licensee\'s design changes as described above were potentially inadequate due to the failure to evaluate the potential of a single active mechanical failure, such as a pump coupling failure, resulting in pump runout on the remaining operating pump. The licensee subsequently developed an operability evaluation that credited existing operator actions in the EOPs to secure one of the two running containment spray pumps early in an accident, if containment cooling heat removal requirements were met, as well as providing that operators had been previously trained to identify and take actions to prevent containment spray pump runout. The team noted that the licensee did not perform a screening or evaluation consistent with industry guidance on 10 CFR 50.59 for crediting operator actions in lieu of automatic actions. Specifically, although the licensee had preViously credited operator actions to secure one of two running containment spray pumps, the actions were specific and analyzed to address containment sump suction net positive suction head concerns and to minimize postaccident debris transport inside primary containment, not to address pump runout in order to maintain containment spray system design requirements. The team concluded that a 10 CFR 50.59 applicability screening and evaluation was required to credit these operator actions to specifically protect the containment spray system design against single active failures. Subsequently, the licensee conducted a 10 CFR 50.59 review to credit the manual operator actions to support the single active failure design requirements of the containment spray system. The team also noted that the licensee\'s operability evaluation provided that under certain conditions that the running pump would be operated without sufficient net positive suction head for a brief period of time prior to swapping the pump suction to the containment sump resulting in the pump cavitating for a period of approximately five minutes. The licensee determined that cavitation for this short period of time would not result in pump damage. However, the team noted the following additional concerns with the licensee\'s evaluation: (1) pump cavitation was not part of the design of the containment spray system; (2) the licensee did not address whether cavitation would result in air or gas binding of the pump which could result in inoperability of the pump; (3) the licensee\'s determination that the pump motor would operate above its service factor at 22 percent during a runout condition but that a licensee referenced evaluation {CR 200702241), which utilized engineering judgment, qualitatively determined that a .containment spray pump motor would most likely continue to operate without damage in a runout condition, but also stated there is no formal engineering evaluation data to support this judgment for short term operation beyond the service factor of 15 percent; and (4) the evaluation utilized containment overpressure during an accident to justify back pressure on the containment spray pumps which reduces pump run-out and motor amperage. Following the team\'s on-site inspection, the licensee conducted a phone call with the NRC to communicate the station\'s plans to assure containment spray system operability prior to plant startup from the forced outage. During the call, the NRC questioned how the licensee had maintained containment cooling design requirements with respect to not only the containment spray system but also the containment coolers. Apparently, the previously approved License Amendment 235, which allowed removing the automatic start feature of the C train containment spray pump also required that in order to do so, that certain aspects of containment cooler operability be maintained. At the end of the inspection, the team could not come to resolution on the impact of past containment cooler operability and single active failure aspects of the containment spray system. Consequently, an URI was opened pending further licensee and NRC review of the licensing and design requirements of the containment cooling design, including the containment spray system and containment coolers, and the applicability and accuracy of License Amendment 235 to this issue. Additionally, further NRC assessment is required to determine the acceptability of relying on operator actions long term to assure that the containment spray design is maintained under pump runout conditions (URI 05000285/2008006-02; Containment Cooling Design Requirements and Licensing Review) |
| Site: | Fort Calhoun  |
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| Report | IR 05000285/2008006 Section 4OA4 |
| Date counted | Jun 30, 2008 (2008Q2) |
| Type: | URI: |
| cornerstone | No Cornerstone |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 95002 |
| Inspectors (proximate) | J Kirkland P Elkmann L Ellershaw D Stearns J Hanna W Walker M Young S Makor T Patez Dunhamg George C Long C Osterholtz A Della Grec |
| INPO aspect | |
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Finding - Fort Calhoun - IR 05000285/2008006 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Fort Calhoun) @ 2008Q2
Self-Identified List (Fort Calhoun)
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