ML16188A368

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Audit Presentation - Westinghouse Methodology for South Texas Unit 1 LAR: Operation with 56 Control Rods
ML16188A368
Person / Time
Site: South Texas STP Nuclear Operating Company icon.png
Issue date: 07/06/2016
From: Guthrie B, Schmitt D
Westinghouse
To: Lisa Regner
Plant Licensing Branch IV
Regner L, NRR/DORL/LPLIV-1, 415-1906
References
WCAP-9272-P-A
Download: ML16188A368 (8)


Text

Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.

Westinghouse Methodology Impacts from the Removal of the RCCA from Core Location D-6 Brian Guthrie, Transient Analysis Danielle Schmitt, Nuclear Design 1

Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.

Overview of Reload Method (WCAP-9272-P-A)

  • The STP engineering design change process is used to implement the removal of RCCA D-6
  • Impacts of the change on UFSAR Chapter 6 and Chapter 15 analyses have been evaluated through a detailed review of the AORs and the reload design process (WCAP-9272-P-A).
  • As detailed in Table 7 of NOC-AE-16003351, the existing key safety parameters continue to apply (and are confirmed on a cycle specific basis) and no other aspects of the AORs are impacted.

WCAP-9272 methodology is still applicable when control rod pattern is changed 2

Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.

Overview of Reload Method (WCAP-9272-P-A) 3

Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.

Overview of Reload Method (WCAP-9272-P-A)

  • The AORs are established using conservative inputs that are expected to bound future cycles.
  • The key safety parameters that could be impacted by a reload become the Reload Safety Analysis Checklist (RSAC) which is issued every cycle by the Safety Analysis groups to Nuclear and Thermal Hydraulic Design for confirmation
  • Any RSAC limit that is not met for a given cycle is provided to the impacted Safety Analysis group for evaluation
  • Evaluation or re-analysis of the AOR is performed to address the RSAC exception and the results are reported in the cycle specific Reload Evaluation.

WCAP-9272 methodology is still applicable when control rod pattern is changed 4

Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.

Safety Analysis Accidents

  • Example - HZP Steamline Break
  • RETRAN-02 uses a point kinetics neutronics model and does not directly model a control rod pattern
  • Limiting case is generated using assumed physics characteristics.
  • Nuclear Design implicitly confirms acceptability of the physics characteristics by comparing ANC calculated parameters to RETRAN-02 calculated parameters.
  • An unacceptable mismatch requires evaluation or reanalysis of the event using adjusted physics parameters.
  • This approach is consistent with the analysis methodology for the HZP steamline break core response described in WCAP-9226-P-A, Revision 1; the reload methodology for this event is described in WCAP-9272-P-A; and the qualification of RETRAN-02 for use in analyzing HZP steamline break core response is described in WCAP-14882-P-A.

No UFSAR safety analysis calculations explicitly model control rod patterns.

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Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.

Cycle-Specific Core Design Analysis

  • Each cycle the reload core is modeled by Nuclear Design in detail (fuel pattern, control rod pattern, burnable absorbers, etc.)
  • This detailed model is used to calculate cycle-specific values for comparison to the RSAC key safety parameters
  • Key safety parameters assumed in the AOR include values that are impacted by RCCAs such as shutdown margin, total rod worth, and trip reactivity
  • Key safety parameters assumed in the AOR do not include the number of RCCAs, RCCA configuration, or a symmetric RCCA pattern Nuclear Design calculations explicitly model control rod pattern.

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Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.

Cycle-Specific Core Design Analysis

  • Nuclear Design performs the cycle-specific analysis using:

- ANC [WCAP-10965-P-A]

- APOLLO [WCAP-13524-P-A]

- PARAGON/NEXUS [WCAP-16045-P-A, Addendum 1-A]

  • These codes were rigorously benchmarked and qualified for a variety of reactor types, fuel types, and burnable poisons
  • These codes are capable of modeling an asymmetric core:

- Highest worth rod stuck out of the core (N-1) is a conservatism assumption for many RSAC calculations

- Asymmetric core temperature distribution with an N-1 condition is modeled for the Steamline Break accident

- N-2, N-3, etc are calculated for use in plant Operations Nuclear Design codes are capable of modeling the removal of RCCA D-6.

7

Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.

Conclusions

  • Plant changes are handled by STP engineering design change process
  • As a part of the engineering design change process, Westinghouse and the STP Nuclear Fuel and Analysis group performed an impact review of the respective AORs including the continued applicability of WCAP-9272-P-A
  • Nuclear Design codes are capable of modeling the removal of RCCA D-6 8