05000370/FIN-2013005-01
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Finding | |
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| Title | Evaluation of Gas Void Identified in Unit 2 ECCS Piping |
| Description | During the performance of Unit 2 ECCS pipe gas void inspections using ultrasonic test (UT) equipment, a large gas void was found in a 5 foot section of 8 inch diameter piping at high point vent valve 2NV-1056. 2NV-1056 was located on the suction side of both trains of the NI and NV pumps downstream of valve 2ND-58A, which is opened during design basis accident conditions involving cold-leg recirculation to provide the piggyback alignment from the residual heat removal (ND) system. Excessive gas accumulation at 2NV-1056 could result in gas being drawn into the NI/NV pumps causing pump degradation or failure. The licensee vented the piping by opening 2NV-1056, which returned the ECCS piping to water solid conditions. Additional ECCS piping locations were checked for possible gas accumulation and none were identified. The licensee implemented increased frequency UT monitoring for gas accumulation at 2NV-1056 (every 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and subsequently every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />) to ensure timely detection of abnormal gas accumulation until the source was determined. Based on the UT measurements, the licensee determined the size of the gas void to be approximately 2 ft3, which exceeded the existing 0.35 ft3 maximum allowable void volume for this location. The licensee initiated a past operability evaluation to determine if the NI/NV pumps would have been capable of performing their safety function during design basis accident conditions with the void in the piping. In addition, on December 18, the inspectors observed how licensee personnel were conducting the increased frequency UT measurements at location 2NV-1056 using Enclosure 13.7, Supplemental Venting, of procedure PT/2/A/4200/019, ECCS Pumps and Piping Vent. The inspectors noted that personnel were conducting the UT measurement on the 1.5 inch diameter vent piping associated with 2NV-1056 versus the 8 inch ECCS header piping that the vent valve is connected to. The procedure contained a note stating that UT measurement is performed at piping adjacent to valve due to flow being limited by 1/8 inch diameter hole in piping header. The 2NV-1056 vent piping was previously added via a modification to enhance the licensees ECCS piping gas management program. It was installed using a wet tap with a 1/8 inch drilled hole into the top of the header piping with a coupling welded over the hole to connect the vent piping. Due to the small 1/8 inch opening, water tension and/or small trash/debris can inhibit the proper communication of water between the ECCS header pipe and the vent piping. It appeared to the inspectors that the note was directing that the UT measurement needed to be conducted on the ECCS header piping and not the vent piping due to concerns that the vent piping might remain water solid while the ECCS header piping could be voiding. Following discussions with the licensee regarding this note, personnel were directed to conduct the UT measurement in the ECCS header piping. The licensee initiated PIP M-13-11297 to address this issue and to investigate how prevalent past UT measurements were conducted in the vent piping versus the header piping. This issue remains unresolved pending completion of the licensees evaluation of the impact that the gas void would have on the operation of the NI/NV pumps during design basis accident conditions and investigation into the mechanism that resulted in the excessive gas voiding not being identified during routine surveillances designed to identify such conditions. This issue is identified as URI 05000370/2013005-01, Evaluation of Gas Void Identified in Unit 2 ECCS Piping. |
| Site: | [[]] |
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| Report | IR 05000370/2013005 Section 1R22 |
| Date counted | Dec 31, 2013 (2013Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.22 |
| Inspectors (proximate) | G Laska G Mccoy J Heath J Viera J Zeiler M Coursey P Cooperg Mccoyj Heath J Laughlin J Zeiler M Meeks |
| INPO aspect | |
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Finding - Mcguire - IR 05000370/2013005 | |||||||||||||||||||||||||||||||||||||||||
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Finding List (Mcguire) @ 2013Q4
Self-Identified List (Mcguire)
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