Non-Radioactive Cyclohexane Method vs. Radioactive Methyl Iodide Method: A Comparative Evaluation of Nuclear-Grade Activated Carbon Adsorber Test Methods

Nuclear-grade activated carbon adsorbers are the primary engineered barrier against release of radioactive organic iodine species from nuclear power plant ventilation, hospital nuclear-medicine exhaust, radiochemical laboratory exhaust, and emergency air-cleaning systems. This white paper presents a systematic comparison of the two dominant carbon qualification test methods: the non-radioactive cyclohexane method (DIN 3754) and the methyl iodide method (ANSI N509/N510, ASTM D3803), referenced by U.S. NRC Regulatory Guide 1.52. It covers test conditions, TEDA impregnation chemistry, regulatory acceptance criteria, and method selection guidance, concluding that the two methods are complementary: cyclohexane testing serves as a fast, non-radioactive field surveillance tool, while methyl iodide testing is the only method that directly verifies the chemisorption chemistry responsible for actual radioiodine capture and is required for NRC regulatory compliance.