05000321/FIN-2012002-02
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Finding | |
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| Title | Failure to Perform an Adequate Design Modification for Replacement of the TSC Air Conditioning Unit |
| Description | An unresolved item was identified to determine if a violation of regulatory requirements occurred when on December 21, 2011, the Hatch TSC climate control air condition unit tripped due to an overload condition. The cause of the overload condition was attributed to a design modification on November 11, 2011, which installed a control transformer that was undersized to maintain full system air conditioning load. From November 4 to November 10, 2011, Hatch implemented a design change to the TSC ventilation system, DCP SNC330548, Remove/Replace Cooling Coil and Condensing Unit serving TSC (1X75-B001 and 1X75-B002). On November 10, 2011, the TSC ventilation system was returned to service following replacement of the cooling coils and condensing unit. On December 21, 2011, Operations department personnel noted TSC ambient temperature was increasing and the TSC condensing units were not operating. The TSC ventilation system was restarted by resetting the cooling coil and condensing unit control circuit transformer and the licensee commenced an investigation to determine the cause of the trip. Hatch determined that the transformer for the cooling coil and condensing unit control circuit was not rated to supply full control circuit load under high load demand and that a conjectured thermostat adjustment in the TSC had resulted in the HVAC system responding to a cooling demand that exceeded the protective trip set point for the control transformer. The requirements for TSC functionality are documented in Section T 4.0 of the Hatch Unit 1 and Unit 2 technical requirements manual (TRM), Section 3.10.1. The ventilation system for filtration and climate control of the TSC is required for TSC functionality. A suitable environment must be maintained in the TSC for personnel occupancy and equipment operation during radiological events. The licensee performed a functionality assessment (CR 386124) and determined that the heat load of the condensing unit between November 10, 2011, and December 20, 2011, would require only one circuit of the dual unit cooling coil and condensing unit. This determination was made using the maximum ambient temperature recorded during the period (83F) and assuming that the TSC HVAC thermostat was set to maintain the temperature in the TSC at 75 F as recommended in the TSC activation procedure, 73EP-EIP-063-0. With only one circuit of cooling in operation, the electrical load on the control transformer is within the rating of the undersized transformer. Therefore, during this period, the licensee concluded TSC ventilation was functional for climate control of the TSC. On December 21, 2011, at 0522, Operations department personnel noted TSC ambient temperature was increasing. Hatch determined that a thermostat adjustment in the TSC had resulted in the HVAC system responding to a high load cooling demand (both cooling coils and condensing units) that exceeded the protective trip set point for the undersized control transformer. This condition prohibited the TSC ventilation system from cooling the TSC and thus the TSC ventilation system was not available to provide the required climate control function. NRC inspectors concluded since the TSC HVAC thermostat was susceptible to adjustment at any time during the period the undersized control transformer was in service, and that adjustment to the thermostat during a TSC activation could cause high cooling demand which could trip the transformer, the TSC was nonfunctional for the entire period the undersize control transformer was installed in the system. Although the TRM states that the TSC air conditioning system is required for the TSC to be functional, clarification is required by the inspectors to determine if the licensee committed to maintaining climate control for the TSC. Review of the licensees NUREG 0696, NUREG 0737, and pertinent Generic Letter responses is required to determine whether climate control affects functionality and whether this issue constitutes a violation of 10 CFR Part 50.54(q), and the planning standards in 10 CFR 50.47(b) (8). URI 05000321,366/2012002-02, Installation of a transformer for the TSC cooling coil and condensing unit control circuit not adequately designed to provide full system load. |
| Site: | Hatch  |
|---|---|
| Report | IR 05000321/2012002 Section 1R18 |
| Date counted | Mar 31, 2012 (2012Q1) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.18 |
| Inspectors (proximate) | E Morris M Coursey C Dykes D Hardage F Ehrhardtd Berkshiref Ehrhardt W Loo J Laughlin M Miller M Speck B Caballero S Sandal E Morris D Hardage M Schwieg |
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Finding - Hatch - IR 05000321/2012002 | |||||||||||||||||||||||||||||||||||||
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Finding List (Hatch) @ 2012Q1
Self-Identified List (Hatch)
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