Hydrogen and methane oxidation performances of hybrid honeycomb catalyst for a tritium removal system

Effect of a modified 13X zeolite support in Pd-based catalysts for hydrogen oxidation at room temperature

This study investigated the effect of a modified 13X zeolite to Pd/zeolite catalyst on the oxidation of hydrogen to ensure safety from hydrogen leakage. The catalytic activity of Pd/zeolite catalysts was significantly affected by acid treatment of 13X zeolite support and various calcination temperatures (300 °C, 400 °C, 500 °C, 600 °C) of the Pd/zeolite catalyst. To understand the correlation between the activity and physical properties of the catalysts, activity test, XRD, BET, TEM, TPR, and TPO were performed; Pd/13X (400) was shown to have a high catalytic activity, which depended on the dispersion and particle size of palladium. Also, a strong PdH on the catalyst surface was formed, and a high catalytic activity at a low hydrogen concentration was obtained.

Atmospheric tritium concentrations under influence of AREVA NC La Hague reprocessing plant (France) and background levels

In-air tritium measurements were conducted around the AREVA NC La Hague reprocessing plant, as well as on other sites that are not impacted by the nuclear industry in northwest of France. The results indicate that the dominant tritium form around the AREVA site is HT (86%). HT and HTO levels are lower than 5 and 1 Bq. m^-3 for hourly samples taken in the plume. No tritiated organic molecules (TOM) were detected. 26 measurement campaigns were performed and links were established between near-field ⁸⁵Kr, HT and HTO activities. Environmental measurements are in line with those taken at the discharge stack, and tend to demonstrate that there are no rapid changes in the tritium forms released. Out of the influence of any nuclear activities, the levels measured were below 13 mBq.m^-3 for HT and 5 mBq.m^-3 for HTO (<0.5 Bq. L^-1). HTO level in air seems to be influenced by HTO activities in surrounding seawater.

Development of an active tritium sampler for discriminating chemical forms without the use of combustion gases in a fusion test facility

A new type of active tritium sampler that can discriminate between chemical forms in a fusion test facility without the use of combustion gases was developed. The proposed tritium sampler was operated using water vapour instead of combustion gases. To test the operation and performance of the device when water vapour is used, we evaluated the catalytic oxidation properties, and the evaporation and collection of water vapour under actual sampling conditions. The properties of the added water mass and the operation temperature of catalysts in the proposed sampling system were then determined. Thereafter, we carried out air sampling for tritium monitoring. The levels of tritium concentration measured by the proposed tritium sampling system were similar to the values measured by the conventional sampling system. Our findings show that the proposed tritium sampling system without combustion gases is a good replacement for the conventional tritium sampling system in a fusion test facility.

The VATO project: An original methodology to study the transfer of tritium as HT and HTO in grassland ecosystem

Tritium (³H) is mainly released into the environment by nuclear power plants, military nuclear facilities and nuclear reprocessing plants. The construction of new nuclear facilities in the world as well as the evolution of nuclear fuel management might lead to an increase of ³H discharges from the nuclear industry. The VATO project was set up by IRSN (Institut de Radioprotection et de Sûreté Nucléaire) and EDF (Electricité de France) to reduce the uncertainties in the knowledge about transfers of ³H from an atmospheric source (currently releasing HT and HTO) to a grassland ecosystem. A fully instrumented technical platform with specifically designed materials was set up downwind of the AREVA NC La Hague reprocessing plant (Northwest of the France). This study, started in 2013, was conducted in four main steps to provide an hourly data set of ³H concentrations in the environment, adequate to develop and/or validate transfer models. It consisted first in characterizing the physico-chemical forms of ³H present in the air around the plant. Then, ³H transfer kinetics to grass were quantified regarding contributions from various compartments of the environment. For this purpose, an original experimental procedure was provided to take account for biases due to rehydration of freeze-dried samples for the determination of OBT activity concentrations in biological samples. In a third step, the ³H concentrations measured in the air and in rainwater were reconstructed at hourly intervals. Finally, a data processing technique was used to determine the biological half-lives of OBT in grass.