Experiments on the Release of Gaseous Iodine from Gamma-Irradiated Aqueous CsI Solution and Influence of Oxygen and Methyl Isobutyl Ketone (MIBK)

Abstract

Volatile iodine production due to radiation chemical effects is known to be an important uncertainty source in the evaluation of the source term for severe accidents of light water reactors (LWRs). The gaseous release fractions of molecular iodine and organic iodine from gamma-irradiated 10 À4 mol/L cesium iodide aqueous solution were measured with the dose rate $ 7 kGy/h at room temperature. The solution was buffered with 0.1 mol/L boric acid and sodium hydroxide (pH $7) and contained up to 10 À3 mol/L methyl isobutyl ketone (MIBK) as an organic additive. The concentrations of MIBK in the solution and oxygen in the sweep gas were changed as experimental parameters. The total iodine release fraction of the original aqueous inventory and the fraction released as organic iodine were 2-47 and 0.02-1.5%, respectively, at the end of 2 h of irradiation. They were dependent on both the aqueous MIBK concentration and oxygen concentration in the sweep gas. Under a constant cover gas condition, the total iodine release showed a decreasing trend and the organic iodine release showed an increasing trend when the MIBK concentration increased. This behavior can be explained by the branching of the reaction path of radiolytic degradation of ketones depending on the availability of dissolved oxygen, and competition between iodine and organic compounds on the consumption of radicals produced by water radiolysis.

Results of environmental radiation monitoring at the Nuclear Fuel Cycle Engineering Laboratories, JAEA, following the Fukushima Daiichi Nuclear Power Plant accident

“…The 134 Cs and 137 Cs were detected as gaseous forms which passed through the dust filter and adsorbed on the charcoal cartridge. It is known that deliquescent salts such as CsI are released into containment vessel in case of the severe accident of nuclear power plant [5]. The CsI could be released from containment vessel to atmosphere in case of this accident.…”

Recent advances in the removal of radioactive iodine by bismuth-based materials

“…During the dissolution of spent nuclear fuel, iodine ions will react with free radicals produced by radiation to generate volatile elemental iodine. Part of elemental iodine will also react with organic impurities to generate organic iodine ( Wren et al, 1999 ; Taghipour and Evans, 2000 ; Moriyama et al, 2010 ). These volatile iodine species make the separation and safe storage of radioactive iodine a great challenge.…”

Review of thermal-hydraulic researches in severe accidents in light water reactors

“…The MELCOR code is composed of a control program and many modules, or packages, which model the major systems of a reactor plant and thermal-hydraulic response of the primary reactor coolant system, the reactor cavity, the containment, and the confinement buildings under offnormal or accidental conditions. This code is used for the development of systematic models for aerosol agglomeration and spray removal under SA conditions [46], a real-time prediction technique for accident progression in a PWR containment during a SA when water on the containment floor flows into the reactor cavity (wet cavity) [47], evaluation of containment failure probability by ex-vessel steam explosion in Japanese LWR [21], and evaluation of experiments on the release of gaseous iodine from g -irradiated aqueous CsI solution [48].…”