05000456/FIN-2011004-02
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Finding | |
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| Title | Use of Mesh Strainer Bags in Auxiliary Building Floor Drains |
| Description | The inspectors identified an Unresolved Item (URI) related to the use of fine mesh strainer baskets in auxiliary floor drains. Specifically, the strainer baskets in auxiliary building ventilation inlet plenums had repeatedly clogged, causing flooding inside the plenum that overflowed into various electrical penetration areas. At the end of the inspection period, the inspectors had not completed an evaluation to determine whether the issue adversely affected the ability to achieve safe shutdown due to a moderate energy line break in the auxiliary building ventilation plenum area. During routine daily reviews of the licensees CAP documents, the inspectors noted several IRs documenting clogged floor drains in auxiliary building ventilation inlet plenums that resulted in water pooling on the floor and dripping into various electrical penetration areas. The specific IRs reviewed included the following: IR 1230829; Water in Auxiliary Building Ventilation Inlet Plenum Following Storm; June 20, 2011; IR 1249503; Operations Auxiliary Building Floor Drain Overflowing; August 9, 2011; IR 1259300; Area Evaluation Required After Water Exposure; September 4, 2011; and IR 1260053; Clogged Floor Drain Basket in 0VA01CC/CD Supply Plenum; September 7, 2011. On August 9, 2011, as documented in IR 1249503, the licensee noted that the floor drain in the Unit 2 auxiliary building ventilation supply plenum overflowed. This resulted in about 4 inches of standing water in the plenum and 10-20 gallons of water that seeped into the electrical penetration area below. The water pooled around the pressurizer heater substations, but did not penetrate the cabinet. No actions were assigned in the IR and it was closed on August 14. On September 4, the licensee generated IR 1259300, which requested an area equipment evaluation for the auxiliary building electrical penetration area (Elevation 426) due to water flowing into the area from above. The water originated from the Unit 2 auxiliary building ventilation supply plenum due to a clogged floor drain. Operators replaced the mesh basket and the water then drained out of the plenum properly. The licensee noted that no safety-related equipment was wetted from the dripping water. The IR referenced existing WO 1045973 and WO 970365 scheduled for December 2011 to remove corrosion that was clogging the floor drains. Action Item 2 was assigned to review a recommendation from Engineering to include a note in the operator rounds to inspect the floor drain baskets and replace them as necessary to ensure no flooding occurred. This action was initially due on October 7, but had been extended to December 7 at the end of the inspection period. The licensee documented the September 4 overflow event in IR 1260053 and initiated a monthly recurring action to inspect the floor drain baskets. The inspectors recalled a prior violation (NCV 05000456/2010007-04; 05000457/2010007-04, Adverse Impact of Flood Drain Strainer Design Modification on Flooding Analysis) that was issued to Braidwood in 2010 regarding auxiliary building floor drain basket strainers. In that violation the inspectors concluded that the licensee failed to adequately ensure that bag-type strainers installed in the auxiliary building floor drains, for the purpose of preventing debris from blocking the floor drain piping, would not adversely impact the analysis of record for internal flooding. As a corrective action to the NCV, the licensee developed Engineering Change (EC) 379355 to analyze the impact of clogged floor drains on the auxiliary building flooding calculation. The analysis focused on critical floor drains, which were defined in procedure BwMS 3350-009, Auxiliary Building Floor Drain Strainer Basket Surveillance, Revision 9, as drains that are credited to remove water in the auxiliary building flood calculation. The licensee concluded in EC 379355 that there was no detrimental impact to auxiliary building flooding evaluations. However, the inspectors questioned whether the auxiliary building ventilation plenum floor drains should have been analyzed in EC 379355. The inspectors discussed the issue with licensee personnel and IR 1264201, Incorrect Floor Drains Classification in BwMS 3350-009A2, was generated. The Unit 2 auxiliary building ventilation plenum floor drains on the 451 elevation appeared to have been mischaracterized as non-critical floor drains in procedure BwMS 3350-009, Attachment 2, and thus were not included in the analysis performed in EC 379355. The licensee concluded in IR 1264201 that there would be no impact on safe shutdown capability with a clogged auxiliary building ventilation plenum floor drain and a medium energy line break. At the end of the inspection, the inspectors had not yet validated that there would be no impact on the ability to achieve safe shutdown due to a moderate energy line break in the auxiliary building ventilation plenum area. Due to clogged drains, there were known leakage paths from the auxiliary building ventilation plenum area into the electrical penetration areas, which contained safe shutdown equipment through penetrations that were not classified as flood seals. The inspectors had not validated that the design interactions between the auxiliary building floor drains, the auxiliary building ventilation plenums, non-flood penetrations, and safe shutdown equipment in the electrical penetration rooms was adequate. (URI 05000456/2011004-02; 05000457/2011004-02, Use of Mesh Strainer Bags in Auxiliary Building Floor Drains) |
| Site: | Braidwood  |
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| Report | IR 05000456/2011004 Section 1R06 |
| Date counted | Sep 30, 2011 (2011Q3) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.06 |
| Inspectors (proximate) | A Garmoe B Jose E Duncan J Benjamin J Gilliam M Holmberg M Perrya Garmoeb Palagi D Reeser E Duncan G O'Dwyer J Benjamin M Perry R Ng |
| INPO aspect | |
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Finding - Braidwood - IR 05000456/2011004 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Braidwood) @ 2011Q3
Self-Identified List (Braidwood)
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