(A) study of a bismuth-based adsorbent and a precursor for immobilization to manage radioiodine waste

Abstract

Radioiodine released from nuclear facilities has the same chemical behavior as non-radioactive iodine. Internal exposure occurs when radioiodine accumulates in the thyroid gland. As a gaseous emission, radioiodine is typically captured by a solid adsorbent prior to release. Various isotopes of iodine are released depending on whether it originates from a reprocessing facility during normal operation or a nuclear power plant during an accident. Should a severe accident occur at a nuclear power plant, the major iodine isotope released is iodine-131. To adequately capture iodine in the accident environment, an adsorbent has to maintain its adsorption capacity in high temperatures. In fuel reprocessing plants, iodine-129 is the major iodine isotope released. This release occurs through an off-gas system that can control the temperature of the off-gas. Since iodine-129 is a long-lived isotope (half-life: 1.57×10$^7$ years), it should be isolated from the biosphere for a long time after immobilization has assured its physical and chemical stability. In this study, a bismuth-based metal-organic framework (Bi-MOF) is proposed as a reasonable alternative to the commercially used silver-based adsorbent for the following reasons: (1) the raw material (bismuth) is inexpensive and non-toxic, (2) the high iodine adsorption capacity is maintained at high temperatures, (3) the bismuth compound is stable after iodine capture, and (4) the integration from capture to immobilization for disposal occurs in a continuous process.