Radiation and fire hazard of sodium coolant

Introduction. Nuclear power plants in the Russian Federation produce about 20 % of the total electricity.
On the basis of fast neutron reactors using sodium as a coolant, Rosatom State Corporation is implementing the “Breakthrough” project aimed at the implementation of a nuclear fuel cycle using the energy potential of natural uranium. Study and generalization of information about fire and radiation hazards of sodium coolant is an urgent task to ensure safety in the operation of this type of reactors.

Goals and objectives. The purpose of the article is an analytical study of information about sodium coolant radiation and fire hazard, published in domestic and foreign scientific literature. To achieve it, an analysis of fast neutron reactors operating in the world was carried out, the coolants used in fast reactors were considered. System analysis of radionuclides present in sodium coolant has been carried out, comparative diagrams according to radionuclide radiation properties are presented, the most dangerous radionuclides for humans present in the sodium coolant have been identified. The fire hazard of sodium metal and peculiarities of extinguishing fires associated with the leakage of sodium coolant in the primary and secondary circuits of the reactor plant are analyzed.

Results and its discussion. At the present time, there is 1 experimental-industrial fast neutron reactor in operation in the world, located in Russia, and 1 experimental reactor in India and China. Sodium is used as a coolant in these reactors. As a result of the literature analysis from open sources, it was found that the main sources of impurities in the metal coolant are protective gas, structural and technological materials of the installation, and products of nuclear reactions. A systematic analysis of the properties of radionuclides present in the metal coolant made it possible to determine the most dangerous of them for human life and health. The fire hazard of sodium coolant is mainly due to its chemical activity. The main ways of extinguishing spilled sodium is isolation from oxygen by covering the puddle of metallic sodium with powdered fire-extinguishing MHS, powdered aluminum oxide or reduction of oxygen concentration in the air below 4 % by volume gas extinguishing with nitrogen, carbon dioxide or inert gases.

Conclusions. As a result of the analysis of radionuclides present in the sodium coolant of a fast neutron reactor, it was found that the most dangerous for people are 24Na, 137Cs, 125Sb, 22Na, 239Pu, 54Mn, 110mAg, 131I. Based on the results of the analysis of the fire hazard of radioactive sodium, the most common fire extinguishing agents are established and the features of extinguishing fires that occur when a sodium coolant ignites are described.

1. Nuclear power reactors in the world. Vienna, International Atomic Energy Agency, 2022; 102.

2. Barbin N.M., Titov S.A., Kobelev M. Accidents that occurred at nuclear power plants in 1952–1972. IOP Conference Series: Earth and Environmental Science. 2021; 666(2):022018. DOI: 10.1088/1755-1315/666/2/022018

3. Dhillon B.S. Safety, reliability, human factors, and human error in nuclear power plants. CRC Press, 2017; 62-88. DOI: 10.1201/b22260

4. Titov S.A., Barbin N.M., Kobelev A.M. The analysis of emergency situations related to fires at nuclear power plants. Pozharovzryvobezopasnost/Fire and Explosion Safety. 2021; 30(5):66-75. DOI: 10.22227/0869-7493.2021.30.05.66-75 (rus).

5. Nayak A., Kulkarni P. Severe accidents in nuclear reactors. Woodhead Publishing, 2021; 394.

6. Kumar S. Reliability and probabilistic safety assessment in multi-unit nuclear power plants. Academic Press, 2021; 260.

7. Petrangeli G. Nuclear safety. Butterworth-Heinemann, 2019; 586.

8. Rachkov V.I., Arnoldov M.N., Efanov A.D., Kalyakin S.G., Kozlov F.A., Loginov N.I., et al. Use of liquid metals in nuclear, thermonuclear power engineering and other innovative technologies. Teploenergetika. 2014; 5:20. DOI: 10.1134/S0040363614050087

9. Orlov Y.I., Efanov A.D., Martynov P.N., Gulevsky V.A., Papovyants A.K., Levchenko Yu.D., Ulyanov V.V. Hydrodynamic problems of heavy liquid metal coolants technology in loop-type and mono-block-type reactor installations. Nuclear Engineering and Design. 2007; 237(15-17):1829-1837. DOI: 10.1016/j.nucengdes.2007.03.008

10. Askhadullin R.Sh., Martynov P.N., Rachkov V.I., Legkikh A.Yu., Storozhenko A.N., Ul’yanov V.V., Gulevskiy V.A. Monitoring and control of the oxygen content in heavy liquid-metal coolants for anticorrosion protection of steels. Thermal Physics of High Temperatures. 2016; 54(4):595-604. DOI: 10.7868/S0040364416040013

11. Thomson J.R. High integrity systems and safety management in hazardous industries. Butterworth-Heinemann, 2021; 360.

12. Englander M., Stohr J.A. Chimie et industrie. 1956; 75(2):53-60.

13. Nosov Yu.V., Rovneiko A.V., Tashlykov O.L., Shcheklein S.E. Features of fast reactors decommissioning БН-350, -600. Atomic Energy. 2018; 125(4):195-199.

14. Kozlov F.A., Alexeev V.V., Zagorul’ko Yu.I., et al. The summary of the sodium coolant technology development in application to LMFBRs. Working material TM on the Coordinated Project (CRP) Analyses and Lessons Learned from the Operational Experience with Fast Reactor Equipment and Systems. Obninsk, 14–18 February 2005. Vienna, IAEA, 2005; 237-259.

15. Sorokin A.P., Gulevich A.V., Klinov D.A., Kuzina Yu.A., Kamaev A.A., Ivanov A.P., et al. Studies of high-temperature nuclear energy technology for hydrogen production and other innovative applications. Problems of Atomic Science and Technology. Series: Nuclear reactor constants. 2020; 1:102-119. DOI: 10.55176/2414-1038-2020-1-102-119

16. Kuzina Yu.A., Sorokin A.P. Thermal physics of alkaline liquid metals. Part 2: Physical chemistry, technology and innovative applications (retrospective-perspective view). Questions of Atomic Science and Technology. Series: Nuclear reactor constants. 2019; 3:233-251. DOI: 10.55176/2414-1038-2019-3-233-251

17. Sutyagina R.O., Alekseev V.V., Sutyagin I.A. Review of existing purification systems in the field of liquid metal coolants Preprint FEI-3295. Obninsk, 2021; 53.

18. Kozlov F.A., Volchkov L.G., Kuznetsov E.K., Matyukhin V.V. Liquid-metal coolants of nuclear power plants. Purification from impurities and their control. F. Kozlov (ed.). Moscow, Energoatomizdat Publ., 1983.

19. Bazhenov V.A., Buldakov L.A., Vasilenko I.Ya. Harmful chemicals. Radioactive Substances. Leningrad, 1990; 425-459.

20. Beltyukov A.I., Karpenko A.I., Poluektov S.A., Tashlykov O.L., Titov G.P., Tuchkov A.M., et al. Nuclear power plants with sodium-cooled fast neutron reactors. Part 1. S.E. Shchekleina, O.L. Tashlykova (ed.). Ekaterinburg, 2013; 548.

21. Mikeev A.K. Fire protection of nuclear power plants. Moscow, Energoatomizdat Publ., 1990; 432.

22. Mikeev A.K. Fires at radiation-hazardous objects. Facts, conclusions, recommendations. Moscow, VNIIPO, 2000; 346.

23. Solovyov S.P. Accidents and incidents at nuclear power plants : textbook. S.P. Solovyov (ed.). Obninsk, IATE, 1992; 300.

24. Zhavoronkov I.S., Ilyushonok A.V. Ensuring fire safety of nuclear power plants. Bulletin of the University of Civil Protection of the Ministry of Emergency Situa­tions of Belarus. 2018; 2(3):343-350.