Izvestia Vysshikh Uchebnykh Zawedeniy. Yadernaya Energetika

The peer-reviewed scientific and technology journal. ISSN: 0204-3327

Estimation of influence of boric acid drop entrainment to its accumulation in the WWER reactor in the case of accident

11/28/2017 2017 - #04 Global safety, reliability and diagnostics of nuclear power installations

Morozov A.V. Pityk A.V. Ragulin S.V. Sahipgareev A.R. Soshkina A.S. Shlyopkin A.S.

DOI: https://doi.org/10.26583/npe.2017.4.07

UDC: 621.039.58

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.

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WWER emergency mode boric acid accumulation droplet thermal physical properties of boric acid solution density viscosity thermal conductivity