Estimation of influence of boric acid drop entrainment to its accumulation in the WWER reactor in the case of accident
In framework of implementation of the «WWER-TOI» project special attention is paid to reactor safety assurance in emergency situation with main coolant circuit rupture and loss of all AC power supply for 72 hours. This problem is solved by operation of passive safety systems (PSS), which provide reactor core cooling (RC) by boric acid series feed with concentration of 16 g/kg to the reactor from the hydro accumulator systems. As it known, reactor core at this time is in a boiling state, respectively, take into account low acid concentration in the vapor phase, increase of amount of boric acid in the coolant and achieving its crystallization conditions on the nuclear fuel element outer surface is possible, it may lead to heat transfer deterioration. Consequently, the issues related to the boric acid accumulation in the WWER reactor core and its possible crystallization acquire a special applicability.
In this article the processes of boric acid mass transfer in case of the emergency situation with main coolant circuit rupture for reactors with passive safety systems are considered. The results of the calculation of changes in the boric acid solution concentration in the core for the WWER emergency mode are presented. The positive influence of the boric acid droplet entrainment on the processes of its crystallization and accumulation in the core is shown. The received results allow concluding that the accumulation and crystallization of boric acid in the core is possible. These processes may lead to deterioration of heat removal from fuel rods. The review of the available literature data about thermal physical properties of the boric acid solution (density, viscosity and thermal conductivity) is presented. The fact that available data are of a general nature and does not cover the entire range of parameters (temperature, pressure and concentration of acid) specific for the possible accidents at NPP with WWER is established. The necessity of an experimental studies of the processes of boric acid drop entrainment under conditions specific to the WWER emergency modes, as well as studies of thermal physical properties in a wide range of concentrations of boric acid are shown.
- Kalyakin S.G., Remizov O.V., Morozov A.V. Jur’ev Yu.S., Klimanova Yu.V. Justification of HA- 2 passive reflooding systems design functions of advanced project NPP with VVER. Izvestiya vuzov. Yadernaya Energetika. 2003, no. 2, pp. 94-101 (in Russian).
- Remizov O.V., Morozov A.V., Tsyganok A.A. Experimental study of non-equilibrium thermal hydraulic processes in passive reflooding systems of reactor VVER core. Izvestiya vuzov. Yadernaya Energetika. 2009, no. 4, pp. 115-123 (in Russian).
- Morozov A.V., Remizov O.V. Experimental justification for design functions of additional passive reflooding systems of the reactor VVER core. Teploenergetika. 2012, no. 5, pp. 22-27 (in Russian).
- Kalyakin S.G., Sorokin A.P., Pivovarov V.A., Pomet’ko R.S., Selivanov Y.U. Morozov A.V., Remizov O.V. Experimental research of thermal physical processes for the safety substantiation of new generation VVER. Atomnaya energiya. 2014, v. 116, iss. 4, pp. 241-246 (in Russian).
- Azizov N. D., Ahundov T. S. Thermal properties of boric acid aqueous solutions at 298-573 K. Teplofizika vysokih temperatur. 1996, v. 34, no. 5, pp. 798 – 802 (in Russian).
- WCAP-17021-NP, Rev. 1. Summary of Tests to Determine the Physical Properties of Buffered and Un-buffered Boric Acid Solutions, March 2009. Available at https://www.nrc.gov/docs/ML1122/ML11220A169.pdf (accessed 13.01.2017).
- Avanesyan A.S., Ahundov T.S. Experimental study of the dynamic viscosity coefficient of boric acid aqueous solutions. Preprint AN ArmSSR. Erevan, 1980, 20 p. (in Russian).
- Gusejnov G.G., Gusejnov E.G. Investigation of the thermal conductivity of electrolytes and porous materials saturated by a fluid aqueous solutions. Fizika, Baki, Elm, 2007, v. 13, no. 1-2, pp. 13-25 (in Russian).
- Yassin Hassan A., Serdar Osturk, Saya Lee. Rheological characterization of buffered boric acid aqueous solutions in light water reactors. Progress in Nuclear Engineering, 2015, v. 85, pp. 239-253.
- Tuunanen J., Tuomisto J., Raussi P. Experimental and analytical studies of boric acid concentrations in a VVER-440 reactor during the long-term cooling period of loss-of coolant accidents. Nuclear Engineering and Design, 1992, v. 148, pp. 217-231.
- Morozov A.V., Remizov O.V. Experimental study of the steam generator VVER models in condensing mode. Teploenergetika. 2012, no. 5, pp. 16-21 (in Russian).
- Berkovich V.M., Peresadko V.G., Taranov G.S., Remizov O.V., Morozov A.V., Tsyganok A.A., Kalyakin D.S. Experimental study on Novovoronezh NPP-2 steam generator model condensation power in the event of the beyond design basis accident. Proc. of International Congress on Advances in Nuclear Power Plants. San Diego. CA. USA. June 13-17, 2010, pp. 186-192.
- Luk’yanov A.A., Zaitsev A.A., Morozov A.V., Popova T.V., Remizov O.V., Tsyganok A.A., Kalyakin D.S. Design and experimental study of the non-condensable gases influence on the VVER steam generator model operation in condensing mode during beyond design basis accident. Izvestiya vuzov. Yadernaya Energetika. 2010, no. 4, pp. 172-182 (in Russian).
- Morozov A.V., Shlyopkin A.S. Analysis of the effect of operating factors on the operation of model of VVER steam generator in a mode of steam condensation. VANT. Ser. Nuclear and reactor constants. 2016, no. 3, pp. 91-99 (in Russian).
- Kopytov I.I., Kalyakin S.G., Berkovich V.M., Morozov A.V., Remizov O.V. Experimental investigation of non-condensable gases effect on Novovoronezh NPP-2 steam generator condensation power under the condition of passive safety systems operation. Proceedings of the XYIIth International Conference on Nuclear Engineering, ICONE17, Brussels, 2009, pp. 735-743.
- Schmal I.I, Ivanov M.A. Boric acid mass transfer processes in accidental conditions. Collection of research papers of the IXth International Scientific and technicalconference «Safety Assurance of NPP WWER». Podolsk. JSC EDB «Hydropress» Publ., 2015, pp. 25-29 (in Russian).
- Sterman L.S., Tevlin S.A., Sharkov A.T. Heat and Nuclear Power Plants. Tutorial for Universities. Moscow. Energoizdat Publ.,1982, 345 p. (in Russian).