05000254/FIN-2013003-02: Difference between revisions
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{{finding | {{finding | ||
| title = Question Concerning Licensing Bases | | title = Question Concerning Licensing Bases of the Ultimate Heat Sink | ||
| docket = 05000254, 05000265 | | docket = 05000254, 05000265 | ||
| inspection report = IR 05000254/2013003 | | inspection report = IR 05000254/2013003 | ||
Revision as of 20:05, 20 February 2018
Finding | |
|---|---|
| Title | Question Concerning Licensing Bases of the Ultimate Heat Sink |
| Description | The inspectors identified an unresolved item (URI) concerning the current licensing bases with respect to failure of Lock and Dam No. 14 on the Mississippi River. The inspectors reviewed several documents to ascertain the current licensing bases for the UHS. The river serves as a source of raw water for the station as well as one of the heat sinks. The licensee designated the UHS as non-safety related and as described in UFSAR Sections 2.4.4 and 9.2.5.3, the UHS is required if the river can no longer support its functions. The inspectors noted the current UFSAR states the loss of river results from damage to the Lock; however, historical documents state the event promulgates from a loss of Dam No. 14. Specifically: Section 2.4 of the Final Safety Analysis Report (FSAR) states, in part, the following: The river level at the station is assumed to drop to elevation 561 feet 0 inches if Dam No. 14 were to fail [emphasis added]. Elevation 561 feet, 0 inches is the normal river level downstream of Dam 14. The station design includes the feature that at the time that Dam 14 fails [emphasis added] the only systems requiring the use of river water would be the RHR service water pumps. If in the unlikely event the broken dam condition occurs [emphasis added], it is necessary to open the gate on the ice melting line to permit the discharged water to return to the intake flume. This procedure permits the use of the water impounded in the intake flume and discharge flume to be used as an evaporative heat sink. This technique will impound 3,960,000 gallons of water. The maximum amount of water required by the system at this stage will be approximately 7000 gpm, which means that without any recirculation, the impounded water will last a minimum of 9.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. It will be necessary to make up water to the intake flume under this condition by portable pumping equipment which will move water from the main river channel to the plant. Pumps capable of pumping 7000 gpm water will be maintained on site and backup pumps available from the local fire stations. In a letter dated November 6, 1970, to the U.S. Atomic Energy Commission (now NRC), Commonwealth Edison (the licensee) addressed questions regarding the use of portable equipment to move water from the main river channel to the plant under frozen river conditions. In response to Question 2.8, the licensee stated the portable pumps would not be required under these conditions. In addition, the licensee afforded the opportunity to clarify some statements in Section 2.4 of the Final Safety Analysis Report (FSAR). Specifically, the licensee stated the portable pumps would not be needed for makeup under a loss of dam event because the evaporative losses were about 20 gpm, not 7000 gpm as written. Although not stated in the licensees response, the inspectors noted the original description in FSAR Section 2.4 did not account for the ice melt line used to recirculate water back to the UHS; hence stating the need for makeup to the closed volume of the UHS. The licensees clarification (the need for 20 gpm makeup) accurately reflects the actual losses that need to be replenished. In the safety evaluation dated August 25, 1971, Section 2.3 states, the facility is also designed to provide an adequate supply of cooling water to the plant by providing a reservoir of about 3.8 million gallons of water in the intake bay so that, even if the river level dropped below a level of 565 feet MSL due to an assumed failure of Dam 14 downstream of the site [emphasis added], the water trapped in the intake bay would supply an adequate source of water for safe cool-down of the reactor primary system. In 1989, the licensee determined the original evaporative losses cited in the November 6, 1970, letter did not account for the worst case conditions. The licensee performed a calculation assuming worst case summer conditions and determined the evaporative losses were about 54 gpm. The licensee concluded the two 2000 gpm portable pumps were more than sufficient to address these losses. In NRC Inspection Report 05000254/1998-201, 05000265/1998-201(ML9805180380), the NRC team identified errors with the 1989 calculation and the licensees approach. Specifically, the team determined that in an evaporative mode, the trapped volume of UHS would increase in temperature and during summer operation, could be driven well above the 95 degrees Fahrenheit design temperature established for the RHRSW system. The licensee performed a preliminary calculation assuming 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> cool-down time on the main condensers from dam failure to loss of contact with the river [emphasis added] and determined the UHS could reach 112 degrees Fahrenheit. The team noted this evaluation used a method of makeup different than the current UFSAR. The team initiated an Unresolved Item 05000254/1998-201-12, 05000265/1998-201-12 to determine the resolution of the dam failure effects on the UHS. In May 1998, the licensee completed 10 CFR 50.59 Safety Evaluation SE-98-068. The purpose of this evaluation was to assess proposed changes to the UFSAR to incorporate the results of the study and revised temperature calculations. It described the change from dam failure to Lock and Dam failure as a clarification of the event to include a timeline and credible failure modes for the Lock and Dam. The licensee concluded these changes did not constitute an un-reviewed safety question, was not a change to a license condition and did not require a TS change. In May 1998, the licensee revised the UFSAR to reference the study and include details on the expected timeline and actions associated with a transportation accident impacting the Lock. The revised UFSAR also reiterates the portable pumps are onsite with backup pumps provided from another facility or leasing facility. In November 1998, an inspection was conducted to follow up on the licensees actions to address this URI. As documented in NRC Inspection Report 05000254/1998-019, 05000265/1998-019 (ML9812290045), the NRC team noted the licensee performed a hydraulic study of the Mississippi River in April 1998. This study assessed the possible failure modes of Dam No.14 and concluded the most credible and reasonable worst case scenario involved a transportation accident whereby a river barge impacts the Lock and Dam. The study determined the time for the river to separate from the UHS was about 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br />. The licensee used this information in Calculation QDC-3900-M-0692 to determine the cooling needs for the UHS. The calculation concluded three portable pumps delivering a total of 5100 gpm of cooler water were needed to ensure the inlet temperatures remained within design limits. A violation for the failure to assure the design basis information was consistent with actual plant design was issued. As described in Section 1R07.1b(3), in April 2001, the licensee completed a 10 CFR 50.59 Safety Evaluation Screening, QC-S-2001-0026, to assess removal of the portable pumps from onsite and relocating the pumps to an offsite leasing facility located a few hours away. The licensee revised the UFSAR and removed the portable pumps from the site. The inspectors noted the original FSAR did not provide the detail as to the cause of the dam failure or a time line for the loss of river event. The licensee stated their response to Question 2.8, (and as reiterated in the August 1971 Safety Evaluation) implies the loss is not immediate because water level would recede in the condenser box and the unit would be shutdown due to loss of condenser vacuum. The licensee contends the main condenser would remain functional following a dam failure up until the vacuum can no longer be maintained by the UHS supply. The inspectors noted the licensee had assumed 1-hour of such operation in their preliminary calculation performed in November 1998. The inspectors were concerned the licensee redefined the loss of river event from the original Section 2.4 of the FSAR description of an unlikely event of a broken dam to a transportation accident impacting the lock. Therefore, this issue is considered an Unresolved Item (URI 5000254/2013003-02; 05000265/2013003-02, Question Concerning Licensing Bases of the Ultimate Heat Sink) pending further consultation with the Office of Nuclear Reactor Regulation. |
| Site: | Quad Cities  |
|---|---|
| Report | IR 05000254/2013003 Section 1R07 |
| Date counted | Jun 30, 2013 (2013Q2) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.07 |
| Inspectors (proximate) | A Dahbur C Mathews J Cassidy J Neurauter K Carrington K Stoedter M Domke M Garza R Murray V Meyersb Cushman C Lipa C Mathews D Szwarc G O'Dwyer J Bozga J Mcghee L Jones R Langstaff S Bel |
| INPO aspect | |
| ' | |
Finding - Quad Cities - IR 05000254/2013003 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Quad Cities) @ 2013Q2
Self-Identified List (Quad Cities)
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