Abstract:
The mechanisms of boric acid mass transfer in a VVER-1200 reactor core are
studied in this work in the event of a major circulatory pipeline rupture and loss
of all AC power. The VVER-1200's passive core cooling technology is made up of
two levels of hydro accumulators. They use boric acid solution with a
concentration of 16 g H3BO3/kg H2O to control the reactivity. Because of the
long duration of the accident process, the coolant with high boron content starts
boiling and steam with low concentration of boric acid departs the core. So,
conditions could arise in the reactor for possible accumulation and subsequent
crystallization of boric acid, causing the core heat removal process to
deteriorate. Calculations were carried out to estimate the likelihood of H3BO3
build-up and subsequent crystallization in the core of the VVER reactor.
According to the calculations, during emergency the boric acid concentration in
the reactor core is 0.153 kg/ kg and 0.158 kg/kg in both the events of solubility
of steam and without solubility of steam respectively and it does not exceed the
solubility limit which is about 0.415 kg/kg at water saturation temperature. No
precipitation of boric acid occurs within this time during the whole emergency
process. Therefore, findings of the study can be used to verify whether the
process of decay heat removal is affected or not.
