The graph shows the results of measuring hydrogen (H₂) released into the container space above the simulated slurry (Hydrophilic: Same method as actual slurry, Hydrophobic: Added method to make hydrophilic surface hydrophobic) after the slurry samples at different heights were irradiated with cobalt-60 gamma-rays. The H₂ release rate outside the slurry was determined from measurements when the sample was not stirred just after the irradiation and then when it was stirred (Left figure). From the results of slurries with different adsorption properties of water on solid particles, the effects of the solids and the adsorbed water that trap H₂ in the slurry (Right figure) can be distinguished.

The Advanced Liquid Processing System (ALPS) for treating contaminated water in the TEPCO’s Fukushima Daiichi Nuclear Power Station produces slurry waste containing radioactive materials emitting beta-rays such as strontium. This was because hydrogen (H₂) formed from water radiolysis by beta-rays became bubbles and were retained in the slurry*. This incident predicted the possibility of a large amount of H₂ being suddenly released from the waste. Therefore, experiments such as irradiation experiment using simulated slurry were further carried out to elucidate the mechanism of H₂ retention, along with a model in which H₂ formed from water radiolysis turns into bubbles in the slurry.

Fig. 1 shows the results of irradiation experiment, and indicates that the higher slurry in the container became more difficult for H₂ in the slurry to be released to the outside, in other words, the higher rate of H₂ retained in the slurry. The slurry in which the suspended solid particles strongly adsorb water (hydrophilic) had a higher H₂ retention rate than that in which the particles easily release water (hydrophobic). The results further distinguish the effect on trapping H₂ bubbles in the slurry. In the hydrophobic slurries, a group of solid particles sterically blocks the path of the H₂ bubbles ((1)), whereas in the hydrophilic slurries, in addition to this, the viscosity of water strongly adsorbed to the solid particles also suppresses their movement ((2)). These findings could be utilized to estimate H₂ retention properties based on the slurry properties.

 

^* Tokyo Electric Power Company, Inc., Investigation and Implementation Status of Causes and Countermeasures for Stagnant Water on HIC, 2015, 37p., (in Japanese), https://f-archive.jaea.go.jp/dspace/handle/faa/169249 (Last accessed date: March 17, 2025).

This result is part of the results obtained in a commissioned research project from Tokyo Electric Power Company Holdings, Inc. entitled "Study on Retention and Release of Hydrogen Gas in 1F HIC Slurry" and "Study of 1F Return-Type Slurry on Hydrogen Retention Property."

Ito, T. et al., Retention of Hydrogen Bubbles Generated from Water Radiolysis in Carbonate Slurry, Nuclear Technology, vol.210, issue 8, 2024, p.1427–1443.

Paper URL: https://doi.org/10.1080/00295450.2023.2299893

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