ML18024A793
| ML18024A793 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 01/25/2018 |
| From: | Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation |
| Schaaf R, NRR/DORL/LPLII-2 | |
| References | |
| Download: ML18024A793 (15) | |
Text
Watts Bar Nuclear Plant Unit 2 Pre-Submittal Meeting for Proposed License Amendment Request Regarding the use of PAD4TCD in the Large Break Loss of Coolant Accident Analysis January 25, 2018
Opening Remarks Original Watts Bar Unit 2 (WBN 2) Large Break Loss of Coolant Accident (LBLOCA) Analysis PAD4 Thermal Conductivity Degradation (PAD4TCD)
Nuclear Regulatory Commission (NRC) Approval of PAD4TCD Revised LBLOCA Analysis Key Points in the Proposed PAD4TCD License Condition LAR Licensing Schedule Overview Proposed License Condition Change Schedule for Submittal Summary and Closing Remarks Agenda l 2
Original WBN 2 LBLOCA Analysis Information Notice (IN) 2009-23: Nuclear Fuel TCD Pellet thermal conductivity decreases as burnup increases Consequently, stored energy in the pellets increases as burnup increases Original WBN 2 LBLOCA analysis used PAD 4 that did not model TCD Concern was that the higher burnup fuel would have a higher peak clad temperature (PCT) than fresh fuel when the effects of TCD are modeled in the fuel performance code l 3
PAD4TCD To address the concern with the original LBLOCA analysis A revised fuel performance code (PAD4TCD) was developed that explicitly modeled the effect of TCD on fuel pellet stored energy The LBLOCA was revised to determine the PCT for burned fuel using PAD4TCD The revised LBLOCA analysis accounted for reduced peaking in the burned assemblies The revised LBLOCA analysis determined that fuel in its 2nd cycle of operation produced the highest PCT Fuel in its 2nd cycle of operation had the highest PCT due to a relatively small amount of reduced peaking being credited in the analysis l 4
NRC Approval of PAD4TCD l 5 NRC reviewed the TCD model in PAD4TCD and concluded there is good agreement of the temperature dependent and exposure dependent coefficients between PAD4TCD and FRAPCON3.4 thermal conductivity models NRC also compared PAD4TCD fuel rod temperature predictions to the Halden high burnup fuel temperature measurements and found good agreement NRC concluded that PAD4TCD adequately accounts for TCD Safety Evaluation Report (SER) on Original License SER on Current License Condition
Revised LBLOCA Analysis Revised LBLOCA analysis credits reduced peaking for fuel in its 2nd and 3rd cycle of operation The reduced peaking partially offsets the lower thermal conductivity of the higher burnup fuel so the temperature / stored energy of the higher burnup fuel is similar to that of fresh fuel As part of the core design process for each cycle, analysis checks are in place that ensure the peaking limits for the higher burnup fuel are less than used in the LBLOCA analysis l 6
Key Points in the Proposed PAD4TCD License Condition LAR l 7 PAD4TCD adequately accounts for the effect of TCD on fuel rod temperature and stored energy LBLOCA analysis, as described in the WBN dual-unit Updated Final Safety Analysis Report (UFSAR), includes the effect of TCD on higher burnup fuel to determine limiting PCT Checks in the core design process ensure the peaking limits used in the UFSAR LBLOCA analysis for higher burnup fuel are not exceeded The LBLOCA PCT is sufficiently low (1766°F as compared to 2200°F) that there are no concerns that LBLOCA PCT will exceed regulatory limits should a newer fuel performance code be used (i.e., PAD 5)
No new technical content
Replacement of PAD4TCD with PAD 5 in the LOCA Analysis l 8 TVA will update the LBLOCA analysis to use newer, recently approved fuel performance code PAD 5 (as part of the recently approved full spectrum LOCA (FSLOCA) Evaluation Methodology)
The LBLOCA analysis using PAD 5 will be for both WBN 1 & 2 with replacement steam generators (RSGs)
WBN 1 has RSGs WBN 2 currently has smaller, older steam generators than the RSGs The LBLOCA analysis using PAD 5 will be submitted in June 2019 Effective for Unit 1 upon NRC approval Effective for Unit 2 upon replacement of the original steam generators
WBN Unit 2 TPBAR LAR Department of Energy (DOE) Tritium requirements drive TVA schedule Tritium Production Burnable Absorber Rod (TPBAR) LAR Submitted on December 20, 2017 Approval requested by May 31, 2019 Based on currently approved LOCA analyses Load TPBARs for WBN 2 Cycle 4 (November 2020)
Schedule allows time for Cycle 4 fuel design and fabrication l 9
WBN Units 1&2 FSLOCA LAR WBN 1 has RSGs WBN 2 RSGs planned for operation in Cycle 5 FSLOCA analysis that is bounding for both units with RSGs will be complete by December 2018 FSLOCA LAR submittal following Unit 2 TPBAR LAR approval Approval requested by March 2021 Implementation in Unit 1 Cycle 18 (October 2021) and Unit 2 Cycle 5 (June 2022) l 10
Licensing Schedule Overview l 11 ID Task Name 2017 2018 2019 2020 2021 2022 2023 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 1
WBN 2 TPBAR LAR - NRC Review 3
WBN 2 Cycle 4 Fuel Design & Fabrication 4
WBN 1&2 RSG FSLOCA LAR Development 5
WBN 1&2 RSG FSLOCA LAR - NRC Review 6
WBN 1 Cycle 17 7
WBN 1 Cycle 18 8
WBN 2 Cycle 4 (w/ TPBARs) 10 WBN 2 Cycle 5 9
WBN 2 RSG Installation ID Task Name 2017 2018 2019 2020 2021 2022 2023 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 1
WBN 2 TPBAR LAR - NRC Review 3
WBN 2 Cycle 4 Fuel Design, Fab & Delivery 4
WBN 1&2 RSG FSLOCA LAR Development 5
WBN 1&2 RSG FSLOCA LAR - NRC Review 6
WBN 1 Cycle 17 7
WBN 1 Cycle 18 8
WBN 2 Cycle 4 (w/ TPBARs) 10 WBN 2 Cycle 5 9
Proposed License Condition Change Currently, WBN Unit 2 Operating License, License Condition 2.C(4) states that PAD4TCD may be used to establish core operating limits for Cycles 1 and 2 only. PAD4TCD may not be used to establish core operating limits for subsequent reload cycles.
The proposed change reads as follows: PAD4TCD may be used to establish core operating limits until the WBN Unit 2 steam generators are replaced with steam generators equivalent to the existing steam generators at WBN Unit 1.
l 12
Schedule for Submittal l 13 PAD4TCD LAR will be submitted in February 2018 Request NRC approval within one year of submittal date to support WBN Unit 2 Cycle 3 operation
Summary and Closing Remarks The WBN 2 LBLOCA analysis adequately accounts for the effects of TCD and evaluates higher burnup fuel to determine the limiting PCT The core design process ensures that the power peaking for fuel in its 2nd and 3rd cycle of operation remains below the power peaking limits used in the UFSAR LBLOCA analysis WBN 2 has a very low LBLOCA PCT so any increase in PCT resulting from an LBLOCA analysis that uses the new fuel performance code PAD 5 can be accommodated without approaching the PCT acceptance criteria No safety concern exists with maintaining the current LBLOCA analysis until the WBN 2 steam generators are replaced l 14