ML24215A095
| ML24215A095 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 08/02/2024 |
| From: | NuScale |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24215A000 | List:
|
| References | |
| LO-169995 | |
| Download: ML24215A095 (1) | |
Text
Response to NuScale Technical Report Audit Question Question Number: A-4.Fluence.TeR-4 Receipt Date: 09/15/2023 Question:
Revise the fluence calculation to obtain a converged reactor pressure vessel fluence value of the MCNP calculations. The staff performed an audit on the MCNP files and found (( 2(a),(c),ECI Passing the relative error is not the basis for accepting the result because relative error is a percentage of the mean value. Follow-up: Provide calculation files that contain information demonstrating that the tallies of the peak fluence at the RPV beltline and the peak fluence in the (( }} 2(a),(c),ECI These regions of interest are shown in red in the figure below. Provide the mean and variance of the converged tallies.
Response
((
}}2(a),(c),ECI During the clarification call on October 17, 2023, NuScale explained that (( }}2(a),(c),ECI NuScale Nonproprietary NuScale Nonproprietary
((
}}2(a),(c),ECI NuScale Nonproprietary NuScale Nonproprietary
(( }}2(a),(c),ECI In response to the follow-up question, TR-118976-P is updated to expand on the method of variance reduction and convergence. ((
}}2(a),(c),ECI NuScale Nonproprietary NuScale Nonproprietary
((
}}2(a),(c),ECI NuScale Nonproprietary NuScale Nonproprietary
(( }}2(a),(c),ECI This provides confidence in the adequacy of the particle sampling in the source as well as through the relevant energy bin, phase spaces, and angles within the model. Markups of the affected changes, as described in the response, are provided below: NuScale Nonproprietary NuScale Nonproprietary
Fluence Calculation Methodology and Results TR-118976-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 15 3.7 Variance Reduction Scheme and Convergence (( Audit Question A-4.Fluence.TeR-4 Audit Question A-4.Fluence.TeR-4 }}2(a),(c)
Fluence Calculation Methodology and Results TR-118976-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 16 (( Audit Question A-4.Fluence.TeR-4 }}2(a),(c) Audit Question A-4.Fluence.TeR-4 Audit Question A-4.Fluence.TeR-4 (( }}2(a),(c) Audit Question A-4.Fluence.TeR-4 Table 3-2 (( }}2(a),(c) (( }}2(a),(c)
Fluence Calculation Methodology and Results TR-118976-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 17 (( }}2(a),(c) Audit Question A-4.Fluence.TeR-4 (( Audit Question A-4.Fluence.TeR-4 }}2(a),(c)
Fluence Calculation Methodology and Results TR-118976-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 22 Audit Question A-4.Fluence.TeR-4 Figure 3-10 X-Y Plot of the Global Fast Neutron Fluence (( }}2(a),(c),ECI
Fluence Calculation Methodology and Results TR-118976-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC C-1 Appendix C Alternative Approaches to Regulatory Guide 1.190 Regulatory Positions RG 1.190 (Reference 7.1) provides guidance for calculating pressure vessel neutron fluence. The NuScale fluence calculation methodology described in this report used some alternative approaches to those recommended in RG 1.190. This appendix describes and justifies these alternatives in Table C-1. The descriptions in Table C-1 are summaries or excerpts of specific portions of regulatory positions in RG 1.190. Audit Question A-4.Fluence.TeR-4 Table C-1 Alternative Approaches to Regulatory Guide 1.190 Regulatory Positions RG 1.190 Regulatory Position Description of Regulatory Position Description of Alternative and Justification 1.1.1 Regional temperatures should be included in the input data. All materials in the NuScale best-estimate fluence model are taken to be at (( }}2(a),(c). The effect of the latter is accounted for in Section B.1.13. 1.1.1 and 1.4.1 In the absence of plant-specific information, conservative estimates of the variations in the material compositions and dimensions should be made and accounted for in the determination of the fluence uncertainty. Uncertainty between the as built and operating and as modeled design is accounted for (( }}2(a),(c) estimates as discussed in Section B.1.3 and Section B.1.4. 1.1.1 The input data should account for axial and radial variations in water density. (( }}2(a),(c) The effect of this modeling simplification is accounted for in Section B.1.13. 1.2 The peripheral assemblies, which contribute the most to the vessel fluence, have strong radial power gradients, and these gradients should not be neglected. Peripheral assembly pin-wise neutron source distributions obtained from core depletion calculations should be used. Assembly-averaged power profiles obtained from core depletion calculations are used in the MCNP6 NuScale best-estimate fluence model. A sensitivity study to establish the effect of this modeling simplification on the NuScale fluence estimates is discussed in Section B.1.5.
Fluence Calculation Methodology and Results TR-118976-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC C-2 1.3.2 The bias introduced by the neutron energy cutoff technique should be estimated by comparison with an unbiased calculation. The MCNP6 NuScale best-estimate fluence model implements a cutoff energy threshold of 0.9 MeV. An additional study involving an MCNP6 model without a cutoff energy threshold is unnecessary. Because there are no processes modeled that would result in a higher energy neutron, the use of a 0.9 MeV cutoff energy threshold makes no difference to the >1 MeV fluence results. 1.3.2 Statement of 10 statistic tests provided by Monte Carlo code (( }}2(a),(c) as discussed in Section 3.7. 1.3.3 The capsule fluence is extremely sensitive to the representation of the capsule geometry and internal water region (if present), and the adequacy of the capsule representation and mesh must be demonstrated using sensitivity calculations. (( }}2(a),(c) 1.4.2 The fluence calculation methods must be validated against (1) operating reactor measurements or both, (2) a pressure vessel simulator benchmark, and (3) the fluence calculation benchmark. The pressure vessel simulator benchmark VENUS-3 is used to validate the NuScale fluence calculation methodology (Appendix A). The VENUS-3 benchmark results are adequate to validate the NuScale fluence calculation methodology. Table C-1 Alternative Approaches to Regulatory Guide 1.190 Regulatory Positions RG 1.190 Regulatory Position Description of Regulatory Position Description of Alternative and Justification}}