AVS: EXPERIMENTAL TESTS OF A NEW PROCESS TO INDUCTIVELY VITRIFY HLW INSIDE THE FINAL DISPOSAL CONTAINERS AT VERY HIGH WASTE LOADINGS

摘要

The design and performance capabilities of the Advanced Vitrification System (AVS) arerndescribed, together with the results of experimental tests. The AVS is an in-can melting systemrnin which high-level waste (HLW) is vitrified directly inside the final disposal container.rnThe AVS container, or module, consists of an outer stainless steel canister and an alumina-lined,rninner graphite crucible, which is thermally insulated from the outer stainless canister. Therngraphite crucible is inductively heated to very high temperatures (up to 1500℃) by an externalrnlow frequency (30 Hertz) alternating current (AC) transformer coil. The actively cooled outerrnstainless canister remains at near ambient temperature. The HLW/frit mixture is fed into the hotrngraphite crucible, where it is vitrified. After cooldown, the HLW/frit feed and off-gas pipes arerndisconnected from the top of the module, which is then sealed and readied for shipment orrnstorage. All radioactively contaminated melter components inside the module are disposed ofrnalong with the vitrified waste. The graphite crucible also provides a geologically stable barrierrnfor the vitrified product.rnThe AVS potentially can double HLW loading over that obtained from Joule melters; lowerrnvitrification costs by about half; reduce the number of disposal canisters required by about half;rnhandle diverse waste feeds with high concentrations of problem elements such as chromium andrnzirconium; and reduce the time needed to vitrify a given inventory of HLW.rnThe AVS can operate at temperatures up to 1500℃ because its refractory materials are at meltrnconditions for only a few hours, instead of years required for conventional melters. This permitsrnmaking a wide range of vitrified products from borosilicate glass to highly leach resistant glassrnceramics. The AVS process minimizes the necessity for waste feed blending and eliminates therncold cap, the need to control melt viscosity and electrical conductivity and the requirement forrnpouring. Since the Advanced Vitrification System is modular, with multiple canister-processingrncells, it provides operational redundancy and minimum technical risk. It also eliminates thernpossibility of a single point failure. Because each AVS module contains a single-use melter,rnthere is no subsequent melter decontamination and decommissioning requirement.rnBench scale tests of the AVS were carried out at the DIAL (Diagnostic Instrumentation AnalysisrnLaboratory) at Mississippi State University. The tests produced 5-inch diameter AVSrnborosilicate glass logs with simulated HLW loadings of 35 and 50% by weight. The simulatedrnHLW material was supplied by the Department of Energy (DOE) and corresponded to HanfordrnEnvelope D waste. The product glasses met or exceeded DOE’s Product Consistency Testrn(PCT), and the Environmental Protection Agency’s Toxicity Characteristic Leaching Procedure