Nuclear Engineering and Technology

  • 제56권2호
  • /
  • Pages.575-600
  • /
  • 2024
  • /
  • 1738-5733(pISSN)
  • /
  • 2234-358X(eISSN)
한국원자력학회 (Korean Nuclear Society)
권호 표지
DOI QR코드

DOI QR Code

Analysis of fluctuations in ex-core neutron detector signal in Krško NPP during an earthquake

  • 투고 : 2023.04.17
  • 심사 : 2023.10.24
  • 발행 : 2024.02.25
PDF 다운로드
⟨ 이전 논문 다음 논문 ⟩

초록

During an earthquake on December 29th 2020, the Krško NPP automatically shutdown due to the trigger of the negative neutron flux rate signal on the power range nuclear instrumentation. From the time course of the detector signal, it can be concluded that the fluctuation in the detector signal may have been caused by the mechanical movement of the ex-core neutron detectors or the pressure vessel components rather than the actual change in reactor power. The objective of the analysis was to evaluate the sensitivity of the neutron flux at the ex-core detector position, if the detector is moved in the radial or axial direction. In addition, the effect of the core barrel movement and core inside the baffle movement in the radial direction were analysed. The analysis is complemented by the calculation of the thermal and total neutron flux gradient in radial, axial and azimuthal directions. The Monte Carlo particle transport code MCNP was used to study the changes in the response of the ex-core detector for the above-mentioned scenarios. Power and intermediate-range detectors were analysed separately, because they are designed differently, positioned at different locations, and have different response characteristics. It was found that the movement of the power range ex-core detector has a negligible effect on the value of the thermal neutron flux in the active part of the detector. However, the radial movement of the intermediate-range detector by 5 cm results in 7%-8% change in the thermal neutron flux in the active part of the intermediate-range detector. The analysis continued with an evaluation of the effects of moving the entire core barrel on the ex-core detector response. It was estimated that the 2 mm core barrel radial oscillation results in ~4% deviation in the power and intermediate-range detector signal. The movement of the reactor core inside baffle can contribute ~6% deviation in the ex-core neutron detector signal. The analysis showed that the mechanical movement of ex-core neutron detectors cannot explain the fluctuations in the ex-core detector signal. However, combined core barrel and reactor core inside baffle oscillations could be a probable reason for the observed fluctuations in the ex-core detector signal during an earthquake.

키워드

과제정보

We acknowledge the research was funded by the project "Evaluation of ex-core detector position on their response" (3210237) by Krsko Nuclear Power Plant. The research was also funded by the projects "Development of Computational Tools for the Determination of the Neutron Field in the Containment of a Pressurized Water Reactor" (L2-8163), "Stability of nuclear reactors in load follow mode of operation" (L2-2612) and the research core funding No. P2-0073 from the Slovenian Research Agency. T.G. acknowledges the L'Oreal-UNESCO For Women in Science Program for awarding her with Slovenian 2023 fellowship.

참고문헌

  1. North Anna Nuclear Power Plant Seismic Event, Presentation to the Commissioners, 2011, Available at: https://www.nrc.gov/docs/ML1124/ML112420551.pdf, last accessed on 8.3.2023.
  2. Virginia Electric and Power Company (Dominion), Summary of Excerpted Portions of the Roots Cause Evaluation - Dual Unit Trip Following Magnitude 5.8 Earthquake, North Anna Power Station Units 1 and 2, Serial Number 11-578, Docket Nos. 50-338/339, RCE 001061, Rev. 1, 2011.
  3. V. Graizer, C.G. Munson, Y. Li, North anna nuclear power plant strong-motion records of the mineral, Virginia, Earthquake of 23 August 2011, Seismoloical Res. Lett. 84 (2013) 551-557. https://doi.org/10.1785/0220120138
  4. R.D. Campbell, G.S. Hardy, M.K. Ravindra, J.J. Johnson, A.J. Hoy, Seismic reevaluation of nuclear facilities worldwide: overview and status, Nucl. Eng. Des. 182 (1998) 17-34. https://doi.org/10.1016/S0029-5493(97)00271-9
  5. J.K. Lapajne, P. Fajfar, Seismic hazard reassessment of an existing NPP in Slovenia, Nucl. Eng. Des. 175 (1997) 215-226. https://doi.org/10.1016/S0029-5493(97)00039-3
  6. M. Vermaut, P. Monette, P. Shah, R.D. Campbell, Methodology and results of the seismic probabilistic safety assessment of Krsko Nuclear Power Plant, Nucl. Eng. Des. 182 (1998) 59-72. https://doi.org/10.1016/S0029-5493(97)00274-4
  7. A. Gosar, Seismic reflection surveys of the Krsko basin structure: implications for earthquake hazard at the Krsko nuclear power plant, southeast Slovenia, J. Appl. Geophys. 39 (1998) 131-153. https://doi.org/10.1016/S0926-9851(98)00022-6
  8. M. Ursic, A. Stritar, D. Vojnovic, A. Muhleisn, Evolution of the NPP Krsko safety assessment due to seismic hazard, in: Proceedings of International Conference Nuclear Energy for New Europe, Bled, Slovenia, 2005.
  9. Krsko Nuclear Power Plant, Updated Safety Analysis Report, Revision 21, 2014.
  10. L. Sirovich, P. Suhadolc, G. Costa, F. Pettenati, A review of the seismotectonics and some considerations on the Krsko NPP area (SE Slovenia), Bolletino di Geofisica Teorica ed Applicata 55 (1) (2014) 175-195.
  11. Slovenian Nuclear Safety Administration, Slovenian National Report on Nuclear Stress Tests, Final Report, Ministry of the environment and spatial planning, Republic of Slovenia, 2011.
  12. M. Kromar, A. Trkov, Nuclear design calculations of the NPP Krsko core, J. Energy Technol. 2 (2009) 41-50.
  13. Z. Stancar, M. Kromar, L. Snoj, Construction of a Monte Carlo benchmark pressurized water reactor core model, in: Proceedings of 25th International Conference Nuclear Energy for New Europe, Slovenia, 2016.
  14. J.T. Goorley, et al., Initial MCNP6 Release Overview - MCNP6 version 1.0, LA-UR-13-22934, 2013.
  15. T. Goricanec, Z. Stancar, D. Kotnik, L. Snoj, M. Kromar, Applicability of the Krsko nuclear power plant core Monte Carlo model for the determination of the neutron source term, Nucl. Eng. Technol. 53 (2021) 3528-3542. https://doi.org/10.1016/j.net.2021.05.022
  16. L. Snoj, B. Kos, Z. Stancar, M. Kromar, Neutron Streaming Analysis and Shielding Determination, IJS work report, IJS-DP-12106, Ljubljana, 2016.
  17. B. Kos, M. Kromar, Z. Stancar, L. Snoj, Neutron streaming analysis and shielding determination of the Krsko nuclear power plant, in: Proceedings of the International Conference Nuclear Energy for New Europe, Portoroz, Slovenia, 2016.
  18. T. Goricanec, B. Kos, K. Ambrozic, A. Trkov, L. Snoj, M. Kromar, Determination of neutron flux redistribution factors for a typical pressurized water reactor ex-core measurements using Monte Carlo technique, Front. Energy Res. 11 (2023).
  19. S.W. Mosher, et al., ADVANTG An Automated Variance Reduction Parameter Generator, ORNL/TM-2013/416 Rev. 1, 2015.
  20. D.A. Brown, et al., ENDF/B-VIII.0: The 8th major release of the nuclear reaction data library with CIELO-project cross sections, new standards and thermal scattering data, Nucl. Data Sheets 148 (2018) 1.
  21. G. Zerovnik, M. Podvratnik, L. Snoj, On normalization of fluxes and reaction rates in MCNP criticality calculations, Ann. Nucl. Energy 63 (2014) 126-128. https://doi.org/10.1016/j.anucene.2013.07.045
  22. S. Hassani, Mathematical Physics, A Modern Introduction to Its Foundations, Springer, 2013.