05000483/FIN-2012005-03
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Finding | |
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| Title | Determine Licensing Basis and Capability of One Vital Air Conditioning Unit to Cool Both Trains of Class 1E |
| Description | The inspectors identified an unresolved item involving the licensing basis and cooling capability of the safety-related air conditioning units and the ability to cool both trains of safety-related switchgear, batteries, battery chargers, and inverters with a single train of cooling. On December 5, 2012, the inspectors identified an issue with the licensees plan to cope with / mitigate an inoperable vital switchgear Class 1E air conditioning unit. This system has two trains, each comprised of a chiller, fans and ductwork to cool the rooms containing its associated safety-related switchgear, battery, battery charger, and inverters. This system and its cooling function are not explicitly covered by technical specifications, while the supported systems are covered by technical specifications. In 2004, in an attempt to address the fact that these cooling trains are not covered by technical specifications, and therefore have no allowed outage time, the licensee created Final Safety Analysis Report Administrative Technical Specification 16.7.13. This specification states that if one of the trains of cooling is inoperable, the ESF switchgear and vital batteries/chargers may be considered operable for up to 7 days provided the following conditions are met: (1) all doors between trains are open; (2) safety-related transformers XNN05 and XNN06 for 120VAC are de-energized; (3) thermostats on the operable cooling unit are set below 80F; and (4) at least one Class 1E air conditioning unit is operable and capable of operating at full capacity. As described in Callaway Action Request 201009024, if one train of cooling were inoperable, operators would declare the associated switchgear, battery, charger, and inverters inoperable and enter associated technical specification action statements, then implement/verify the compensatory measures, then exit the action statements for up to 7 days. The inspectors questioned the technical basis for how the equipment that was cooled by this air conditioning unit would be able to function without cooling. Specifically, the inspectors questioned the adequacy of the single unit to cool both trains. On December 6, 2012, while the licensee was reviewing the inspectors concerns, they identified that heat load calculations GK-10, DC SWBD, Battery and ESF SWGR Room Temperatures with One 1E A/C Unit Inoperable, and GK-22, Eval. Inverter Loads, 92-1014, did not account for both trains of control building pressurization heaters being energized. This increases the heat load assumed in the calculation and required additional compensatory actions beyond the Final Safety Analysis Report 16.7.13 actions. The licensee revised a standing order to direct operations to secure the control room emergency ventilation system associated with the affected Class 1E air conditioning unit. This is achieved by placing three fans in pull-to-lock when using one cooling train to cool both electrical trains. The licensee initiated Callaway Action Request 201208550 to address this issue. The inspectors have the following concerns: (1) Callaway relies on compensatory measures to open all doors between trains of batteries and switchgear, posting fire watches, and de-energizing plant equipment (which is safety-related). The inspectors questioned the appropriateness and cooling capability of these measures, which were used as a basis for assuring the operability of the supported safety-related systems. Specifically: a. the temporary air flow paths did not appear to ensure adequate air flow between trains b. portions of the temporary air flow path went through a corridor that was not cooled, allowing unaccounted-for heat, as well as loss of cooled air, since there was no way to efficiently move all the cooled air to the other trains room with a corridor between the individual train rooms c. one safety-related control room ventilation system is rendered inoperable by implementing the compensatory measures d. the heat loads and cooling capacity were not adequately accounted for (see below) (2) The licensees creation of Final Safety Analysis Report Administrative Technical Specification 16.7.13, appeared to conflict with existing technical specifications that covered the situation. Specifically, cooling was required to support the safety functions of the associated safety-related batteries, battery chargers, inverters, and switchgear. The definition of operable in technical specifications stated that for a system to be considered operable, all necessary cooling systems must also be capable of performing their related support functions. Part 9900 guidance for assessing operability further states that, in order to be considered operable, structures, systems and components must be capable of performing the safety functions specified by its design within the range of specified physical conditions, which would include room temperature, and accident loading Creating a Final Safety Analysis Report specification and limiting condition for operation allowing the support system to be out of service would not alleviate the need to consider the impact to the operability of the supported systems. (3) The inspectors found that the electrical equipment heat load evaluated in calculation GK-10 did not appear to adequately account for all heat sources, and may not have provided an adequate technical basis for credited heat removal. a. Sensible and latent heat added to the switchgear rooms by outside air from the control building pressurization fans were not included in calculations. During accidents, the control building pressurization fans add outside air to raise the pressure in the control building to minimize in-leakage, but would add sensible and latent heat that was not included in heat removal calculations. b. The DC switchgear and battery rooms are located directly above the AC switchgear rooms. An assumption for the DC switchgear and battery rooms stated that heat will be removed through the floor, while another assumption for the AC switchgear room stated that heat will be removed through the ceiling. (4) The inspectors questioned whether both trains of supported equipment would satisfy the design and licensing basis of the plant with a single train of cooling. Specifically, loss of the single operable cooling train would lead to failure of both trains of supported equipment such that the plant would no longer be able to withstand a single failure without prior NRC approval. The inspectors noted that the licensee has actually implemented the compensatory measures described above and declared the supported systems operable by relying on one train of cooling, including December 17- 18, 2012, when train A chiller had a refrigerant leak and again on December 22, 2012, through January 5, 2013, when train B chiller had a refrigerant leak. The above concerns must be addressed before an evaluation of the combined effect of these concerns can be performed. In response, the licensee created Callaway Action Request 201208908 to re-evaluate their current practice and the basis for using a single cooling unit. The inspectors were concerned that the licensee implemented a Final Safety Analysis Report change that conflicted with existing requirements in technical specifications and created a condition where the plant would be subject to loss of both trains with a single failure of the operating train of cooling without prior NRC approval. In addition, the technical basis for this Final Safety Analysis Report change may not have adequately accounted for the maximum expected heat loads, and may not have demonstrated air flows to remove heat loads from both trains simultaneously. Additional information was needed to determine whether the concerns discussed above involve one or more violations of 10 CFR Part 50, Appendix B, Criterion III, Design Control, 10 CFR 50.59, Changes, Tests and Experiments, Technical Specification 3.8.1, AC Sources Operating, Technical Specification 3.8.4, DC Sources Operating, Technical Specification 3.8.7, Inverters Operating, and Technical Specification 3.8.9, Distribution Systems Operating. Pending further evaluation of the above issues by the licensee and subsequent review by inspectors, this issue will be tracked as unresolved item (URI)05000483/2012004-03, Determine Licensing Basis and Capability of One Vital Air Conditioning Unit to Cool Both Trains of Class 1E Electrical Equipment. |
| Site: | Callaway  |
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| Report | IR 05000483/2012005 Section 1R15 |
| Date counted | Dec 31, 2012 (2012Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.15 |
| Inspectors (proximate) | P Elkmann T Hartman G Apger L Willoughby N Makris N O'Keefe |
| INPO aspect | |
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Finding - Callaway - IR 05000483/2012005 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Callaway) @ 2012Q4
Self-Identified List (Callaway)
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