Milestone Report - M4FT-14OR0312022 - Co-absorption studies - Design system complete/test plan complete
Objective The objective of this test plan is to describe research that will determine the effectiveness of silver mordenite and molecular sieve beds to remove iodine and water (tritium) from off-gas streams arising from used nuclear fuel recycling processes, and to demonstrate that the iodine and water can be recovered separately from one another. Background The need to control emissions of the gaseous radionuclides to the air during nuclear fuel recycling is widely recognized. Gaseous
... d. Gaseous radionuclides can partition to off-gas streams emanating from the various individual processes used in the recycle plant, for example, from the mechanical head end (shear), fuel dissolver, vessel vents, cell ventilation, and melting operations. In traditional recycle plants the bulk of the volatile fission products (i.e., Kr, Xe, I, and H) are released during the dissolution process. The noble gases report almost quantitatively to the dissolver off-gas stream. About 95% of the iodine partitions to the dissolver off-gas stream. Tritium is retained in the aqueous dissolver solution as tritiated water and enters the dissolver off-gas stream as a small fraction of the water vapor rising from the solution. Most of the water vapor is returned to the process using a condenser, but nevertheless some water vapor escapes into the off-gas system. Dissolver off-gas is also accompanied by nitrogen oxides and nitric acid vapors. Because of the corrosive nature of these gases and vapors, it has been proposed that silver substituted mordenite may be used for iodine removal because mordenite is resistant to degradation by these oxyacids. Tritium is allowed to accumulate in the plant water systems until the concentration is such that the water vapor escaping the plant causes release limits to be reached. The plant water may then be replaced and the contaminated water appropriately treated and disposed. Other techniques for tritium disposal, such as water feed-and-bleed, can be implemented but all involve disposing of significant amounts of water that must be immobilized for decades.