05000482/FIN-2012004-01
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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 IE Electrical Equipment |
| 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 May 29, 2012, Wolf Creek made an unplanned entry into Technical Requirements Manual (TRM) 3.7.23 at 4:45 p.m. for the vital switchgear air conditioning unit B being inoperable. An operator on rounds had noticed a low differential pressure across the air conditioning compressors oil pump that was close to the trip set-point for the air conditioning unit. Wolf Creek decided to replace the compressor. Technical requirements manual (TRM) Limiting Condition for Operation 3.7.23 allows for 7 days restoring the air conditioning unit. Thereafter, TRM 3.7.23 requires entry into the technical specification action statements for the vital buses, switchgear, inverters, and batteries, which are cooled by this unit. The inspectors questioned how the equipment that was required to be cooled by this cooling unit would be able to function without cooling. The licensee explained that they would open doors between trains to allow the functioning unit to cool both trains. The inspectors identified several concerns about the adequacy of the single unit to cool both trains, the current licensing basis supporting this practice, and the lack of an operability determination. After further discussions, on May 31, 2012, Wolf Creek wrote condition report 53672 and requested a prompt operability determination on the inspectors concerns. The train B vital air conditioning unit was replaced and returned to service an hour later. The prompt operability determination was automatically cancelled by procedure. The senior reactor operator agreed with the need to evaluate a potential degraded/non-conforming condition, and wrote another condition report, 53703, to ensure that the reportability evaluation included sufficient analyses to justify or preclude future operation with a single air conditioning unit in operation. On Monday June 4, 2012, at 3:24 a.m., the train A vital switchgear air conditioning unit tripped on low differential pressure across the oil pump. Wolf Creek entered TRM 3.7.23 and posted compensatory measures of opening doors and positioning box fans. No entry was made into technical specification action statements for electrical equipment. Wolf Creek performed an immediate operability determination by initiating condition report 53710, which concluded that the train A vital switchgear and batteries were operable. This conclusion was based on room temperatures presently being below the operability limit of 104 F, room temperatures historically not exceeding 104 F when one air conditioning unit is out of service, and the allowance of compensatory measures per TRM 3.7.23. In condition report 53710, the senior reactor operator requested a prompt operability determination based on concerns previously raised by the inspectors. On June 4, 2012, Wolf Creek had a preliminary GOTHIC room temperature computer model that predicted temperatures of 100 degrees F. The inspectors raised several questions regarding operability. In response, Wolf Creek engineering continued to evaluate the room temperatures and returned a result of inoperable at 2:34 a.m. on June 6 and the shift manager entered Technical Specifications 3.8.4, 3.8.7, 3.8.9, 3.7.8, 3.8.1, and 3.0.3. Operability evaluation GK-12-08 contained GOTHIC computer models that calculated DC switchboard room temperature slightly above the 104 degrees F room temperature limit in TRM 3.7.23. Technical Specification 3.0.3 was entered because there is no specific action for this cooling system, and by virtue of having an inoperable support system necessary to support their function, the licensee declared two inverters and two batteries inoperable, as well as declaring the train A AC and DC power distribution systems inoperable. A power reduction was commenced at 3:27 a.m. The train A vital air conditioning unit SGK05A repairs were completed and was declared operable at 5:05 a.m. and all action statements were exited. From May 29 through August 30, the inspectors identified the following concerns: (1) Wolf Creek relied on compensatory measures to open all doors between trains of batteries and switchgear, posting continuous fire watches, and using non-safety powered box fans to blow air between rooms. The inspectors questioned the reliability and cooling capability of these measures, which were used as a basis for assuring the operability of safety-related systems. Specifically: a. the temporary equipment that did not have a safety-related power source with a diesel generator backup b. the temporary air flow paths did not appear to ensure adequate air flow between trains c. portions of the temporary air flow path and 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 d. the heat loads and cooling capacity were not adequately accounted for (see below) (2) The licensees creation of TRM 3.7.23 appeared to conflict with existing technical specifications that covered the situation. Specifically, cooling was required to support the safety functions of the associated batteries, 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, an SSC must be capable of performing the safety functions specified by its design within the range of specified physical conditions, which would include room temperature. Creating a TRM LCO 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 various revisions of calculation GK-06-W, SGK05A/B Class IE Electrical Equipment Rooms A/C Units, Single Unit Operations Capacity, did not appear to adequately account for heat sources, and may not have provided an adequate technical basis for credited heat removal: a. Draft Revision 2 was non-conservatively low because it did not include heat from a swing battery charger. b. Draft Revision 2 relied on a non-safety air conditioning unit to cool the health physics area under the 4160V vital switchgear rooms. This effectively treated the floor as a plate-type heat exchanger, and credited an inefficient heat transfer mechanism with removing a considerable part of the switchgear room heat load. In doing so, the licensee was crediting non-safety equipment with no diesel generator backup source of power for maintaining the safety-related switchgear operable. c. Calculations for heat removal capability assumed that only sensible heat would be removed from the air. This was inappropriate because humidity is commonly present at the Wolf Creek site. This assumption was non-conservative because this assumption would not account for heat removal used to condense moisture from the air, and would overstate the calculated temperature reduction. d. The inspectors found conflicting references and calculations with different specifications for the capability of the SGK05 units cooling coil. One standard used in design calculations was M-622.1-00133 Reselection Study, which was a vendor study and not a design basis calculation. Condition report 55265 was written to reconcile these standards. e. Heat removal calculations did not account for the heat load in the mechanical equipment rooms containing the air conditioning units and the pressurization fans. f. 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. g. The amount of heat absorption into the concrete structure of the building that was credited in licensee calculations did not include an adequate technical justification. Specifically, the methodology used was not documented, and the room temperatures calculated did not appear to show any significant heat-up of the room air before large heat transfer took place. The amount of cooling seemed disproportionately high for such a small temperature difference between air and concrete. h. The capacity of the air conditioning units cooling coil used in calculation GK-06-W, Revision 2 was approximately 15 percent larger than other Wolf Creek specifications for this component without technical justification. Calculation GK-06-W, also had differing cooling coil capabilities without an explanation in the Assumptions section and the Methodology, Nomenclature and Computations section. (4) The inspectors identified that the licensee had no valid control building system flow and temperature design drawings, and that the existing system flows had not been verified to conform the design through testing. Wolf Creek initiated condition report 54095 to address this issue. Further, the licensee had identified that train B had degraded flow rates in certain portions of the system, further challenging heat removal capability. (5) The inspectors noted that the licensee did identify a direct cause of oil degradation for the May 29, and June 4, 2012, trips or the direct cause of previous compressor trips. The inspectors found that previous trips of the compressor on overpressure were similar to the May and June trips because the oil was becoming acidic and contaminated each time. Previous condition report 27014 did not identify a cause. It proposed more frequent oil and refrigerant changes, but this was never implemented. The inspectors examined the oil removed from the train B compressor in May 2012 and observed a large quantity of metal flakes and black sludge. The oil filter screen for both units was covered in black sludge. There were also what appeared to be copper metal shavings. The qualitative oil test found the oil to be marginally acidic and in need of replacement. Apparent cause 53709 on the June 4 trip of the train A unit did not identify a cause of the oil contamination despite lab analysis of the oil. The above concerns must be addressed before an evaluation of the combined effect of these concerns can be performed. In response, Wolf Creek created a new corrective action, 02-04, in condition report 28252 to reconstitute the design basis of the vital air conditioning system. Wolf Creek also created action 02-05 in condition report 28252 to re-evaluate the environmental qualifications of the Class IE electrical equipment. Pending licensee resolution of the above technical issues, the inspectors will be able to draw a conclusion. Additionally, Wolf Creek initiated condition reports 54155, 55729, 55712, 53549, 53472, 55552, 55551, 55265, 55076, 54234, 53798, 53793, 53791, 53785, 53710, 54865, 54791, 54095, 54652, 53796, 53709, 53703, 53696, 53685, 53672, 53671, 53625, 53393, and 53452. Pending further evaluation of the above issues by the licensee, this issue will be tracked as unresolved item (URI)05000482/2012004-01, Determine Licensing Basis and Capability of One Vital Air Conditioning Unit to Cool Both Trains of Class IE Electrical Equipment. |
| Site: | Wolf Creek  |
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| Report | IR 05000482/2012004 Section 1R04 |
| Date counted | Sep 30, 2012 (2012Q3) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.04 |
| Inspectors (proximate) | S Garchow B Correll A Sengupta H Leake R Kopriva T Farnholtzc Longc Peabody C Speer G Guerra J Laughlin J Watkins L Ricketson N Greene N Makris N O'Keefe R Kopriva S Hedger |
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Finding - Wolf Creek - IR 05000482/2012004 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Wolf Creek) @ 2012Q3
Self-Identified List (Wolf Creek)
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