ML11136A054
| ML11136A054 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 04/18/2011 |
| From: | Office of Nuclear Reactor Regulation |
| To: | Division of Operating Reactor Licensing |
| References | |
| Download: ML11136A054 (3) | |
Text
WBN2Public Resource From: Poole, Justin Sent: Monday, April 18, 2011 3:49 PM To: Crouch, William D Cc: WBN2HearingFile Resource
Subject:
Draft Request for Additional Information regarding GL 2004-02
- Bill, Below, for your review, are preliminary Request for Additional Information (RAI) questions regarding Watts Bar Nuclear Plant (WBN), Unit 2. Please review to ensure that the RAI questions are understandable, the regulatory basis is clear, there is no proprietary information contained in the RAI, and to determine if the information was previously docketed. Please also let me know how much time Tennessee Valley Authority (TVA) needs to respond to the RAI questions.
Justin C. Poole Project Manager NRR/DORL/LPWB U.S. Nuclear Regulatory Commission (301)4152048 email: Justin.Poole@nrc.gov
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The staff has reviewed the applicants March 4, 2011, documentation related to the actions and evaluations taken to resolve Generic Letter (GL) 2004-02, Potential Impact of Debris Blockage on Emergency Recirculation during Design Basis Accidents at Pressurized-Water Reactors, dated September 13, 2004. The staff has determined that the following additional information is required in order for the staff to complete its review:
Debris Generation
- 1) According to the Break Selection Evaluation, mineral wool is installed in limited locations, but was stated to not be within any loss of coolant accident (LOCA) zone of influence (ZOI). No ZOI size was provided for the mineral wool material. The basis for excluding the mineral wool as potential debris was not provided. Provide information to justify that the mineral wool cannot become transportable debris.
Alternately, provide information to justify that the design basis debris load bounds any alternate debris load that includes the mineral wool.
Head Loss and Vortexing
- 1) The design basis assumes 750 ft2 sacrificial strainer area for miscellaneous debris (Section 3.b of submittal). During testing, the staff understood that scaling included a 200 ft2 sacrificial area, as documented in the staffs trip report (ML102160226). Please reconcile this discrepancy.
- 2) The application did not include a plot of the test strainer head loss as a function of time for the design basis test, annotated with significant events during the test, as described in the revised content guide for GL 2004-02 supplemental responses (ML073110278. Staff reviews the plot to validate extrapolation of test results to the mission time, and to ensure that pressure-driven bed discontinuities did not affect the debris head loss (such that temperature scaling may be inappropriate). Provide an annotated plot of the design basis test.
1
- 3) Provide the methodology used for extrapolation of head loss values to the 30 day mission time, including any statistical methodology employed.
Net Positive Suction Head
- 1) It is unclear how the margins reported for residual heat removal (RHR) switchover time and containment spray system (CSS) switchover time are consistent with the strainer submergence values reported in section 3.f.2 of the Watts Bar 2 application. For the limiting case of small-break LOCA (SBLOCA), the minimum sump level is stated to increase from 5.78 ft to 6.91 ft from the time of emergency core cooling system (ECCS) recirculation to the time of CSS recirculation. This would contribute to a net positive suction head (NPSH) margin of 1.1 ft. The NPSH section of the application states that NSPH margin increases by about 3.7 ft when comparing similar conditions. The change in submergence for a large-break LOCA (LBLOCA) reported in section 3.f.2 (3.4 ft) is closer to this value. There may be a discrepancy in the reported minimum sump level at CSS recirculation for the SBLOCA case. Clarify the water levels and discuss how the NPSH margins reported in section 3.g.16 were calculated.
- 2) For SBLOCAs, Enclosure 3 indicates that the minimum water level calculation assumes the reactor coolant system (RCS) will contribute inventory to the reactor cavity. The applicant calculates RCS shrinkage, due to cooling of the primary inventory, and subtracts this value to reduce the amount of water that reaches the containment sump. It is not clear to the staff that the calculations account for the inventory required to refill the RCS. , such that the stated amounts provide for conservative estimates of minimum sump level. The staffs position is that the applicant should account for the potential for the RCS to become completely filled with water at its ultimate equilibrium temperature. The staff understands that the levels may have been calculated correctly and that ice melt will contribute inventory at a rate exceeding the rate required to account for RCS refill and cooldown. Provide information to demonstrate that the minimum sump level has determined properly considering the above discussion.
2
Hearing Identifier: Watts_Bar_2_Operating_LA_Public Email Number: 345 Mail Envelope Properties (19D990B45D535548840D1118C451C74D7F6E4FCEB0)
Subject:
Draft Request for Additional Information regarding GL 2004-02 Sent Date: 4/18/2011 3:48:48 PM Received Date: 4/18/2011 3:48:50 PM From: Poole, Justin Created By: Justin.Poole@nrc.gov Recipients:
"WBN2HearingFile Resource" <WBN2HearingFile.Resource@nrc.gov>
Tracking Status: None "Crouch, William D" <wdcrouch@tva.gov>
Tracking Status: None Post Office: HQCLSTR02.nrc.gov Files Size Date & Time MESSAGE 4867 4/18/2011 3:48:50 PM Options Priority: Standard Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:
Recipients Received: