Cement-Based Matrix for tritium trapping research project: MACH3

by David LAMBERTIN (CEA/DE2D/SEAD)

Tuesday 5 Dec 2017, 11:00 → 11:45 Europe/Zurich

774/R-013 (CERN)

Abstract:

The Cement and Bitumen for waste Conditioning Laboratory of CEA Marcoule is the coordinator of MACH3 research project (PIA2/ANDRA). One of laboratory activities is to develop and optimize wastes conditioning specific formulations.

The MACH3 research project, which involves three partners (CEA, LML and UCCS laboratories from Lille University), aims at (1) designing cement-based matrix devoted to the conditioning of low-level or intermediate-level radioactive waste, and (2) allowing a strongly limited outgassing of tritium due to the irreversible trapping of its gaseous forms HT and T2.

Radioactive wastes with significant amounts of tritium will be produced in France with the commissioning of the ITER fusion facility. After treatment, they will be stored in dedicated facilities, awaiting conditioning and final disposal. To be acceptable in a repository, tritiated waste packages must exhibit a very low outgassing rate, which is difficult to achieve, unless the waste incorporation rate is drastically reduced or the waste is previously de-tritiated. CEA has been working for several years on the trapping of dihydrogen and tritium using oxide getters. Moreover, it has developed hydraulic binders showing a good chemical compatibility with the waste. Composite matrices incorporating an inorganic getter have also been elaborated for the in-situ trapping of dihydrogen.

Based on this experience, the goal of the MACH3 project is to design and characterize composite cement-based materials, containing getters of the Ag2O/MnO2 type, in order to limit the outgassing of tritium from cemented waste packages. Given the high variety of tritiated waste, these matrices will be prepared as mortars using hydraulic binders with different chemistries (magnesium phosphate cement, calcium sulfo-aluminate cement, Portland cement (CEM I), blended Portland cement comprising blast furnace slag and fly ash (CEM V)), so as to produce pore solution pHs within a large domain (from ~7 to ~13). The getter will be used as powder as cement replacement, or as porous aggregates, as sand replacement. All the formulations will have in common to minimize the residual amount of free water within the capillary porosity in order to keep a good efficiency of the getter. Trials at the lab scale will be performed with real tritiated waste, in order to compare the most promising matrix and determine their tritium outgassing rate.