Izvestiya vuzov. Yadernaya Energetika

The peer-reviewed scientific and technology journal. ISSN: 0204-3327

A Study of Flammable Gas Generation and Radionuclide Release during Underwater Handling of AM Reactor Spent Fuel

6/15/2021 2021 - #02 Fuel cycle and nuclear waste management

Gaiazov A.Z. Leshchenko A.Yu. Smirnov V.P. Ilyin P.А. Teplov V.G.

DOI: https://doi.org/10.26583/npe.2021.2.07

UDC: 621.039.546

The paper presents the research results on the accumulation of flammable gases under conditions simulating the underwater handling of leaking spent nuclear fuel from the AM reactor. Two fuel compositions as fuel rod fragments were examined, i.e., uranium-molybdenum dispersed in magnesium and uranium carbide dispersed in calcium. The experiments were carried out in the in-cell automatic test rig of the Material Testing Division at JSC «SSC RIAR».

The experiments measured the 137Cs release during underwater storage of uranium-molybdenum fuel. Data were also obtained on the kinetics of hydrogen yield for both fuel compositions as well as on the kinetics of methane generation for the carbide SNF. The kinetics are best approximated by exponential dependences, which formally correspond to first-order chemical reactions.

A calculated estimate was made of the contribution of radiolytic hydrogen to the volume of the gases generated during the experiments. It was shown that the determining source of the gases was the chemical interaction between the spent fuel under study and water.

An experiment with the uranium-molybdenum fuel revealed a pronounced effect of passivation of chemical processes on the fuel surface due to the formation of insoluble corrosion products. The depth of the corroded fuel composition for the fuel segment edges was estimated to be equal to 370 μm when calculated from the amount of hydrogen released during the experiment as a result of the reaction of magnesium with water.

As for the experiments with the carbide SNF, an incubation period of about 20 hours was observed followed by a vigorous release of hydrogen and methane. A comparative analysis was carried out for the results of the experiments and published data on the behavior of the components of the fuel compositions in water.

The methane release obtained from the experiment for the carbide SNF does not correlate with foreign publications in the sense that uranium carbide irradiated higher than 4300 MW·day/tU poorly reacts with water.

The findings can be used to justify fire and explosion safety of underwater handling of the damaged spent nuclear fuel with the considered fuel compositions (SNF from reactors AM, AMB, EGP-6, etc.), for instance, to justify underwater preparations of the AMB SNF for reprocessing.

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fire and explosion safety damaged SNF AM (AMB) reactor radiolysis hydrogen methane storage in wate