The use of the facsimile program in the speciation of iodine in a pwr reactor containment following a loss of coolant accident

Iodine is released in a loss of coolant PWR accident from defected fuel as caesium iodide which ionises to produce the I-ion on contact with water whether this water be the original coolant water before blowdown, or the water from the reactor storage tank during the refill phase. Iodine exists in a variety of oxidation states of which I- is the lowest, the more oxidised form of I2, or its hydrolysis product HOI, are volatile and have the potential to constitute a radiological hazard. Recent work has suggested that thermal oxidation of I- to I2 by oxygen is not important but that radiolytic oxidation can produce I2 by oxygen is not important but that radiolytic oxidation can produce I2 from I- usually up to a limiting concentration. Computer simulation of the chemistry of laboratory observation has proved to be reasonably successful. This paper explores the extension of such modelling to the detailed situation of a reactor accident where the aqueous medium exists in the forms of aerosol, spray, sump and reactor water, being mixed and contacted with the large volume of containment air in a way dictated by the thermal hydraulics of the accident. The chemical modelling is flexible and produces credible results which suggest, for example, a large degree of volatilization when the iodine is released before blowdown, but a very small proportion of vaporised iodine when iodide is released below the water surface during refill