Sorption/desorption behavior of iodine on graphite. [HTGR]

Fission product plateout and liftoff in the MHTGR primary system: A review

“…The response of these repository locations needs then to be analyzed under specified depressurization conditions. Osborne et al (1982) and Lorenz et al (1982) have shown that iodine chemisorption on steel and graphite is reversible as expected, however not always completely or instantaneously, especially below -700 K. However, presumption of instantaneous absorptive equilibrium during depressurization appears to be a fair approximation. The behavior of iodine associated with plated dust is far more problematical, depending on a series of poorly known chemical and physical items, namely, (1) the dust quantity, (2) its chemical nature with respect to iodine sorptivity, (3) its effective surface area for sorption per unit mass, (4) its distribution between circulating and plated locations, and (5) the behavior of plated dust on depressurization.…”

“…The sorptivity [defined as mols sorbed/(area-partial pressure)] of metallic surfaces of alloys is significantly higher than other surfaces, as may be surmised from the observation that iodine will form chemical compounds with many metals, including iron and chromium, at higher concentrations and lower temperatures. The sorptivity on oxidized surfaces of alloys is perhaps a factor of 100 lower than bare metal (Osborne, et al, 1982) and about a factor of 10^ lower on graphite [Lorenz, et al (1982)], again, relative to bare metal. Since the circulating dust in the PS appears to be principally non-metallic, (see Sect.…”

“…Although other data are sparse, Osbome et al (1982) have shown chemisorption on oxidic surfaces to be roughly two orders of magnimde below that of steel at simUar conditions. Similarly for graphite, the work of Lorenz (1982) indicates significanfly lower sorption for graphite relative to steel. (See Sects.…”

“…The available graphite data at 400°C are summarized in Fig 5.2-2, adapted from Lorenz (1982). As for steel, the 400°C temperature is taken to be an average for the core graphite.…”

“…5.2-2. Assumed Langmuir isotherm for iodine on H451 graphite at 400°C, adapted from Lorenz, et al (1982).…”