New facilities have been installed at ENEA laboratories for pyrochemical process studies under inactive conditions. In particular, PYREL III is a pilot plant which allows to make experiments of electrorefining and electroreduction of simulated fuel. The main component is a zirconia crucible heated by a furnace supported in an externally water-cooled well under the floor of a steel glove-box, where an argon atmosphere is maintained by a continual purge of about 10 L'min-1. The vessel is loaded with LiCl-KCl eutectic salt (59-41 mol%) and is currently operated at 460°C for electrorefining experiments, while electroreduction is made in a bath of LiCl with 1 wt.% of Li2O at 650°C. Treatment of chloride salt wastes coming from pyroprocesses is made inside another argon-atmosphere glove-box, where a matrix termed sodalite is synthesized from a mix of nepheline, simulated exhausted salts and glass frit, through a Pressureless Consolidation (PC) process. The product obtained by heating at 925°C is then fully characterized by means of density measurements, thermal analysis, stereomicroscopy observations, FTIR and XRD spectra, as well as leach tests under static conditions. A novel method proposed by Korea Atomic Energy Research Institute (KAERI) is also applied to the treatment of such wastes. It is based on a matrix, SAP (SiO2-Al 2O3-P2O5), synthesized by a conventional sol-gel process, able to stabilize the volatile salt wastes owing to the formation of metalaluminosilicates, metalaluminophosphates and metalphosphates. The addition of a borosilicate glass as a chemical binder and a treatment at around 1000°C gives the final waste form. With this method a higher disposal efficiency and a lower waste volume can be obtained. A melt crystallization plant (MECRYP) is used for the regeneration of LiCl salts from electroreduction experiments. Alkaline and alkaline-earth metals contained in the waste salt are separated by means of a melt crystallization process, based on the solubility difference of solutes (e.g. CsCl and SrCl2) between molten salt and solid states. In this process, the group I/II radionuclides are concentrated in the melt phase, while the other solid phase contains relatively purified LiCl salt. This crystal phase contains a very small amount of group I/II fission products and is recycled to the electrolytic reduction process for reuse. Another facility, termed off-gas treatment apparatus (OGATA), has been set-up for studies about capture of volatile and semi-volatile fission products, such as cesium, iodine, and ruthenium. It consists of a little furnace which can operate up to 1200°C for the generation of volatile compounds, which then pass through a specific trap able to retain them by virtue of chemical or physico-chemical mechanisms. For example, silver coated mordenite is used for iodine, and zeolite 4A for volatile cesium.
|Titolo:||Facilities for pyrochemical process studies at ENEA|
|Data di pubblicazione:||2013|
|Appare nelle tipologie:||4.1 Contributo in Atti di convegno|