Determination of Conservative Conditions of the Model of Reactivity Accident at RBMK‑1000

V. I. Borysenko, V. V. Goranchuk

Institute for Safety Problems of Nuclear Power Plants,
NAS of Ukraine, 12, Lysogirska st., Kyiv, 03028, Ukraine

DOI: doi.org/10.31717/2311-8253.22.2.2

Abstract

Analytical studies have been performed on the model of a reactivity accident at the 4th Unit of the Chornobyl NPP with an RBMK-1000-type reactor. The model of the RBMK-1000 reactor was developed based on the equations of nuclear reactor kinetics. In the model, the reactivity changes as a result of external influences (the movement of control rods; changes in the coolant temperature at the reactor inlet), as well as a result of feedback on reactivity effects (changes in fuel temperature, coolant density, 135Xe concentration). The change in the coolant density takes into account the formation of steam in the reactor core, and the coolant pressure is introduced into the model as an external factor, according to the results of the registered data during the accident on 26.04.1986. There is a high sensitivity of the RMBK-1000 reactivity model to the absolute values of reactivity coefficients that have occurred on the eve of the accident (negative reactivity coefficient by fuel temperature, positive steam coefficient of reactivity). Therefore, the study is conducted for different combinations of values of the efficiency of the control rods, reactivity coefficients, as well as other factors affecting the course of the accident — emergency protection triggering time, and reactor power level before the accident. Considering that the main stage of the accident lasted less than 10 s, fuel destruction is possible when the critical value of fuel enthalpy is reached, at which the fuel dispersion process begins. The results of modeling of reactivity accident on RBMK-1000 with the values of parameters of reactivity effects, which best correspond to the chronology of recorded events as well as to the recorded values of technological parameters, are presented.

Keywords: RBMK-1000, reactivity, reactivity coefficient by fuel temperature, reactivity coefficient by coolant density, fuel enthalpy, end effect, graphite displacer.

References

1. Khalimonchuk V. A., Kuchin A. V. (2011). [Simulation of the Chornobyl accident]. Nuclear and Radiation Safety, vol. 51, no. 3, pp. 20–28. (in Rus.)

2. Khalimonchuk V. A., Kuchin A. V., Tokarevskyi V. V. (2016). [Research of neutron characteristics of ChNPP RBMK-1000 in the Institute for Nuclear Research in preand post-emergency period: retrospective analysis]. Nuclear and Radiation Safety, vol. 69, no. 1, pp. 14–19. (in Rus.)

3. Bertrand Mercier, Di Yang, Ziyue Zhuang, Jiajie Liang (2021). A simplified analysis of the Chernobyl accident. EPJ Nuclear Sci. Technol, vol. 7, 1, pp. 1–12.

4. Borysenko V. I., Goranchuk V. V. (2021). [Model of reactivity accident of the RBMK-1000 of the Chornobyl NPP 4th power unit]. Nuclear Power and the Environment, vol. 21, no. 2, pp. 39–48. (in Ukr.)

5. Borysenko V. I. (2017). [On some parameters of nuclear safety of uranium-graphite reactors]. Atomic strategy of XXI, vol. 122, pp. 18–21. (in Rus.)

6. Steinberg N. A. (2020). [While witnesses are still alive]. Atomic strategy of XXI, vol. 162, pp. 9–11. (in Rus.)

7. Nigmatulin B. I. (2020). [In the development of the theme]. Atomic strategy of XXI, vol. 162, p. 12. (in Rus.)

8. Kopchinski G., Steinberg N. (2020). [Chornobyl. Reasons]. Atomic strategy of XXI, vol. 163, pp. 20–22. (in Rus.)

9. Kopchinski G., Steinberg N. (2020). [Chornobyl. Instead of conclusion]. Atomic strategy of XXI, vol. 164, pp. 21–23. (in Rus.)

10. Borysenko V. I. (2021). [Model of reactivity accident of RBMK-1000]. Atomic strategy of XXI, vol. 174, pp. 6–9. (in Rus.)

11. Karpan N. V. (2006). Chernobyl. Mest mirnogo atoma. [Chornobyl. Revenge of the Peaceful Atom]. Available at: http://www.twirpx.com/file/121267/ (in Rus.)

12. Dmitriev V. M. Prichiny Chernobylskoy avarii izvestny. [The causes of the Chornobyl accident are known]. Available at: http://www.accidont.ru (in Rus.)

13. INSAG-7. The Chernobyl Accident: Updating of INSAG-1. A report by the International Nuclear Safety Advisory Group. Vienna: International Atomic Energy Agency, 1992, 135 p.

14. Kuznetsov I. A. (1987). Avariynyye i perekhodnyye protsessy v bystrykh reaktorakh. Biblioteka ekspluatatsionnika AES [Emergency and Transient Processes in Fast Reactors]. Мoscow: Energoatomizdat, 176 p. (in Russ.)

15. Adamov E. O., Domoradov A. E., Mironov Yu. V., Nikitin Yu. M. (1993). [Role of individual factors in the development of the Chornobyl accident]. Atomic Energy, vol. 75, no. 5, pp. 336–341. (in Rus.)

16. Abramov M. A., Avdeev V. I., Adamov E. O. (2006). Kanalnyi yadernyi energeticheskiy reaktor RBMK. [Channel-type nuclear power reactor RBMK]. Moscow: SUE NIKIET, 632 p. (in Rus.)

17. Borysenko V. I., Goranchuk V. V. (2013). [Determination of conservative parameters of model of reactor for research of transient of VVER-1000]. Problems of Nuclear Power Plants Safety and of Chornobyl, vol. 20, pp. 28–36. (in Rus.)

18. Rumyantsev A. N. (2011). Chernobyl v 2009 godu. [Chornobyl in 2009]. Available at: http://www.proatom.ru/modules.php?name=News&file=article&thold=1&mode=-flat&order=1&sid=2842 (in Rus.)

19. Borysenko V. I., Goranchuk V. V. (2022). [Model of reactivity accident of the RBMK-1000 reactor]. Nuclear Physics and Atomic Energy, vol. 23, no. 2, pp. 99–106. (in Ukr.)

20. 1E-C–II. Technological regulations for operation of Units 3 and 4 of Chornobyl NPP with RBMK-1000 reactors. Came into force by the Order no. 953 dated 15.12.1983. Chornobyl. 98 p. (in Rus.)

Full Text (PDF)

---