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| Quarter | Site | Title | Description | |
|---|---|---|---|---|
| 05000454/FIN-2015008-01 | 2015Q3 | Byron | Question Regarding the Maximum Wet Bulb Temperature Value Assumed in the SXCT Tornado Analysis | Question Regarding the Maximum Wet Bulb Temperature Value Assumed in the Emergency Service Water Cooling Tower Tornado Analysis Introduction: The team identified an unresolved item (URI) regarding the maximum wet-bulb temperature value assumed in the SXCT tornado analysis. Specifically, the team noted the analysis used a value which was less restrictive than the highest 3-hour wet-bulb temperature recorded for the site as described in the UFSAR. Description: In Section 3.5.4 of the UFSAR, Analysis of Missiles Generated by a Tornado, stated that, An analysis of the UHS cooling capability for a tornado missile event has been made. It also stated that, A maximum outside air wet-bulb temperature of 78 degrees Fahrenheit is assumed and is conservatively held constant throughout the transient. In addition, this UFSAR section stated that, The analysis was performed using service water cooling tower performance curves generated using the method described in UFSAR Section 9.2.5.3.1.1.2 (...). The analysis of the UHS cooling capability for a tornado missile event was calculation BYR09-002, UHS Capability with Loss of SX (Emergency Service Water) Fans due to a Tornado Event, which used a constant maximum outside air wet-bulb temperature value of 78 degrees Fahrenheit consistent with UFSAR Section 3.5.4. However, the team noted the assumed maximum outside air wet-bulb temperature value of 78 degrees Fahrenheit appeared to be inconsistent with the method described in UFSAR Section 9.2.5.3.1.1.2, Steady State Tower Performance Analysis. Specifically, it stated that, The design wet-bulb temperature during warm weather operation is 82 degrees Fahrenheit (Refer to UFSAR Section 2.3.1.2.4). In Section 2.3.1.2.4 of the UFSAR, Ultimate Heat Sink Design, stated that, This analysis (described in Section 9.2.5.3.1.1) includes scenarios with the highest 3-hour wet-bulb temperature, 82 degrees Fahrenheit, which was recorded on July 30, 1961, at 3:00 pm. This UFSAR section also stated that, Per Regulatory Guide 1.27, the ultimate heat sink must be capable of performing its cooling function during the design basis event for this worst case 3-hour wet-bulb temperature. In addition, it stated, However, the design operating wet-bulb temperature of the ultimate heat sink is 78 degrees Fahrenheit (ASHRAE 1 percent exceedance value). This issue is unresolved pending further review by the Office of Nuclear Reactor Regulation (NRR) of the licensing basis related to the wet-bulb temperature value applicable for the SXCT tornado analysis, and the team determination of further NRC actions to resolve the issue. (URI 05000454/2015008-01; 05000455/2015008-01, Question Regarding the Maximum Wet-Bulb Temperature Value Assumed in the SXCT Tornado Analysis) |
| 05000454/FIN-2015008-02 | 2015Q3 | Byron | Maximum Wet Bulb Temperature Value Assumed in SXCT Analysis Was Not Monitored | Maximum Wet-Bulb Temperature Value Assumed in Emergency Service Water Cooling Tower Analysis Was Not Monitored Introduction: The team identified an URI regarding the lack of monitoring the maximum wet-bulb temperature value assumed in SXCT analysis. Specifically, the team noted the maximum wet-bulb temperature value was a critical parameter for the SXCT analyses, but the licensee had not established a testing program to verify actual values were bounded. Description: In Section 3.5.4 of the UFSAR, Analysis of Missiles Generated by a Tornado, stated that, An analysis of the UHS cooling capability for a tornado missile event has been made. It also stated that, A maximum outside air wet-bulb temperature of 78 degrees Fahrenheit is assumed, and is conservatively held constant throughout the transient. In Section 9.2.5.3.1.1 of the UFSAR, Design Basis Reconstitution, stated that, The design basis event for the Byron ultimate heat sink is a LOCA coincident with a loss-of-off-site power (LOOP) in one unit, and the concurrent orderly shutdown from maximum power to cold shutdown of the other unit using normal shutdown operating procedures. It also stated that, The design wet-bulb temperature during warm weather operation is 82 degrees Fahrenheit (Refer to the UFSAR Section 2.3.1.2.4). In Section 2.3.1.2.4 of the UFSAR, Ultimate Heat Sink Design, stated that, This analysis (described in Section 9.2.5.3.1.1) includes scenarios with the highest 3-hour wet-bulb temperature, 82 degrees Fahrenheit, which was recorded on July 30, 1961, at 3:00 pm. The analysis of the UHS cooling capability for a tornado missile event was calculation BYR09-002, UHS Capability with Loss of SX Fans due to a Tornado Event, which used a constant maximum outside air wet-bulb temperature value of 78 degrees Fahrenheit consistent with UFSAR Section 3.5.4. The analysis of the UHS cooling capability for a LOCA coincident with a LOOP was calculation UHS-01, Ultimate Heat Sink Design Basis LOCA Single Failure Scenarios, which used a constant maximum outside air wet-bulb temperature value of 82 degrees Fahrenheit consistent with the UFSAR Section 9.2.5.3.1.1. However, the licensee had not established a testing program to verify actual environmental conditions were bounded by these analyses and design basis limits. In response to the team questions, the licensee stated that this approach was acceptable because historical data showed wet-bulb temperature had a cyclic nature, maximum wet-bulb temperature lasted for relatively short durations, and the analyses assumed constant wet-bulb temperature values. This issue is unresolved pending further NRR review of the acceptability of the licensee approach to ensure the SXCT analyses bounded actual environmental conditions, and the team determination of further NRC actions to resolve the issue. (URI 05000454/2015008-02; 05000455/2015008-02, Maximum Wet-Bulb Temperature Value Assumed in SXCT Analysis Was Not Monitored) |