05000482/FIN-2007003-01
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Finding | |
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| Title | Circulating water roof loading exceeds design |
| Description | On May 7, Wolf Creek received heavy rains and water leaks from the circulating water screen house roof were observed. On May 8, 2007, it was observed that the roof of the circulating water screen house had accumulated approximately eight inches of standing water and that the drains were blocked by debris. That same day, the drains were cleared and the roof was drained. It was not until inspector questioning that the design calculation for the roofs steel structure was reviewed for possible impacts; however, no roof damage was visually observed. The roof drains are described in Drawing A-121 and SPEC A-3862 with domed drain covers. The steel screens inside the drains became plugged with debris because outer dome covers over the screens were missing. On May 31, 2007, the dome drain covers were replaced. A work order was written in May 2001 because of standing water on the circulating water screen house roof caused by clogged drains due to missing dome covers. The debris was removed from the clogged drains in June 2001; however, the missing dome shaped drain covers were not replaced until after the May 7, 2007, occurrence. Based on the inspectors questioning of the May 2007 rains, Wolf Creek evaluated the impact of eight inches of water on the roof. The eight inches of water exceeded the design stress of approximately 16 ksi for the roofs most limiting I-beams. However, after reviewing the calculation, the loading did not exceed the yield stress for the A36 steel used in the most limiting I-beam of the roof. Directly below the most limiting I-beam is located all of the circulating water pump circuit breakers and the feeder circuit Breaker 4-26 for Bus SL-31. Bus SL-31 feeds the normal service water Pumps B and C and the electric fire water pump. Calculation A-3862-02 W01 describes the design stress for the load bearing steel structure of the circulating water screen house. Calculation A-3862-02 W01 provides for roof loading of snow, but not for standing water since the roof is designed with water drains. This calculation allows for a roof load of 20 pounds per square foot or approximately 3.8 feet of snow. The 3.8 feet of snow is approximately 3.8 inches of standing water. Thus, the added weight of eight inches of water was in excess of the loading specified in Calculation A-3862-02 W01. Based on the onsite meteorological tower, winds during the time the eight inches of standing water were on the roof ranged from 0 to 20 mph, however, this was determined not to be a significant contributor to roof stresses. On May 26, 2007, inspectors walked down the circulating water screen house roof to see the new dome covers and found them to be covered with insect debris. On May 26, 27, and 28 this issue re-occurred as Wolf Creek experienced heavy rains but only minor water depth was observed. Mechanics subsequently re-cleared the roof drains. This occurrence also called into question the ability of the dome covers to prevent roof gravel from migrating downstream to the drains because the gravel is smaller than the dome cover grating. This issue and the corrective actions are being tracked by Wolf Creek in Condition Reports 2007-001897 and -002599. Since additional inspection is needed to evaluate the facts and significance of all instances, this issue is being treated as an Unresolved Item (URI)05000482/2007003-01, circulating water roof loading exceeds design. |
| Site: | Wolf Creek  |
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| Report | IR 05000482/2007003 Section 1R06 |
| Date counted | Jun 30, 2007 (2007Q2) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.06 |
| Inspectors (proximate) | K Clayton D Dumbacher P Elkmann G Pick S Cochrum C Long S Alferink V Gaddy D Deese E Rueschc Longj Cruz S Cochrum |
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Finding - Wolf Creek - IR 05000482/2007003 | |||||||||||||||||
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Finding List (Wolf Creek) @ 2007Q2
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