Study of the iodine kinetics in thermal conditions of a RCS in nuclear severe accident

Influence of SIC control rod material on the iodine release in case of nuclear severe accident – Chemical reactivity with fission products in thermal conditions of RCS

“…For this test, the sampling in the "Igas speciation line" failed, so that the fraction of other inorganic gaseous iodine species is determined by difference between the "Iaerosol&gas line" and "I2 line" data. Roughly one half of the gaseous iodine is identified as molecular iodine, the rest being attributed to an inorganic form, assumed to be mostly HI because the formation of HOI is less probable in such conditions (Grégoire et al, 2017). Results are comparable to the reference [PL_MoCsI_3] test, indicating that the presence of indium does not significantly alter the chemical Mo-Cs-I-O-H system in steam atmosphere.…”

“…As a consequence, the characterization of the deposited/transported material was limited mainly to y-spectrometry which cannot provide any chemical speciation. Interpretation of such experiments relies thus mostly on computer simulations which in turn needs reliable thermodynamic and thermokinetic data for chemistry of FPs and CR material at high température, even if recent works were performed to improve these data (Grégoire et al , 2017;Miyahara et al, 2019) works are still ongoing on this.…”

“…The experiments performed on the I-O-H system evidenced kinetic limitations for gas phase iodine reactivity (Grégoire et al, 2017). The addition of caesium, in quite large excess relative to iodine to be relevant of severe accident scenarios, resulted in quantitative formation of caesium iodide, preventing thus any gaseous iodine transport whatever the gas atmosphere (steam or steam/hydrogen).…”

Study of the radiolytic decomposition of CsI and CdI2 aerosols deposited on stainless steel, quartz and Epoxy painted surfaces

“…However, an uncertainty remains on the speciation of iodine entering into the containment from the RCS. In fact, once they are released from the nuclear fuel at temperatures ranging from ~ 1500 to 2500 K (for which some FPs could be on their atomic form), FPs are expected to recombine in the RCS as the temperature decreases [14,15,16] down to 373-473 K. The speciation of iodine entering into the containment has largely been debated in the nuclear safety community. Nevertheless, PHEBUS-FP tests [17,18,19,20,21] have shown that iodine can be under two physical forms once it arrives into the containment: gaseous and aerosols.…”