Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : July 26, 2021 - July 27, 2021
In the Green Growth Strategy presented by the Japanese government in 2020, nuclear power stations are regarded as existing, well-established low carbon power sources and their continuous use is required to achieve the national goal of net zero greenhouse gas emissions by 2050. However, considering the damage caused by the Great East Japan Earthquake and resulting tsunami, the risk from potential accidents must be further mitigated. Prevention of a hydrogen explosion during a severe accident is one of the key issues to improve the safety of nuclear power stations. In this study, the behavior of a packed bed reactor of copper oxide pellets, used as part of a hydrogen treatment system, was examined. Reaction heat from the oxidation of hydrogen into water vapor accompanying complex reactions on the copper oxide surface increases the temperature of the packed bed and consequently the reaction rate. This positive feedback should be controlled to prevent thermal runaway by stabilizing the packed bed at the designed operating temperature of the hydrogen treatment system. The conditions leading to this low temperature positive feedback were experimentally confirmed with a bench-scale packed bed reactor and complementary numerical calculations. At temperatures 233~267 °C, temperature increase is governed by not only temperature-dependent reaction rate but also by competitive adsorption behavior between hydrogen and water vapor. At higher temperatures than 267 °C, hydrogen concentration governs the positive feedback effect, which implies necessity for appropriate design to prevent thermal runaway of the packed bed.
