A comparison of core degradation phenomena in the CORA, QUENCH, Phébus SFD and Phébus FP experiments

Water Hammers Exploded The Nuclear Power Plants at Fukushima Daiichi

A fundamental theory, the Leishear Explosion Theory, explains many small nuclear power plant explosions, as well as major explosions at Three Mile Island and Fukushima Daiichi. Focusing on the Fukushima Daiichi explosions, autoignited explosions hammered the largest seismic response at Unit 1 on March 12, 2011. At Unit 3 on March 14, a larger explosion ignited with an observed fireball and smoke cloud but lower seismic forces. On March 15, a Unit 2 reactor system explosion ignited hydrogen in the Unit 4 reactor building to cause damages following ignition, and seismic responses were negligible. Note that a Unit 2 reactor building explosion did not occur, and this fact is questionably attributed to the destructive removal of one of the walls of Unit 2 due to the earlier Unit 1 explosion. All of these explosions were ignited by fluid transients that exploded flammable hydrogen that was created during nuclear reactor core meltdowns, which were initiated by loss of power due to a tsunami. The conclusions presented here build upon earlier publications, where fluid transients autoignite hydrogen to explode buildings. Also, research from Argonne National Laboratory provides background to explain this common cause for nuclear power plant explosions. Although different than the Argonne report conclusions, conclusions here are consistent with observations provided by the Argonne report. New ideas challenge existing beliefs, but the stakes are high since nuclear reactor safety is important to prevent loss of life and catastrophic environmental damages. The next nuclear power plant explosion can be stopped!

Post-Test Analyses of the CMMR-4 Test

Understanding the final distribution of core materials and their characteristics is important for decommissioning the Fukushima Daiichi Nuclear Power Station (1F). Such characteristics depend on the accident progression in each unit. However, boiling water reactor (BWR) accident progression involves great uncertainty. This uncertainty, which was clarified by MAAP-MELCOR crosswalk, cannot be resolved with existing knowledge and was thus addressed in this work through core material melting and relocation (CMMR) tests. For the test bundle, ZrO2 pellets were installed instead of UO2 pellets. A plasma heating system was used for the tests. In the CMMR-4 test, useful information was obtained on the core state just before slumping. The presence of macroscopic gas permeability of the core approaching ceramic fuel melting was confirmed, and the fuel columns remained standing, suggesting that the collapse of fuel columns, which is likely in the reactor condition, would not allow effective relocation of the hottest fuel away from the bottom of the core. This information will help us comprehend core degradation in boiling water reactors, similar to those in 1F. In addition, useful information on abrasive water suspension jet (AWSJ) cutting for debris-containing boride was obtained in the process of dismantling the test bundle. When the mixing debris that contains oxide, metal, and boride material is cut, AWSJ may be repelled by the boride in the debris, which may cut unexpected parts, thus generating a large amount of waste in cutting the boride part in the targeted debris. This information will help the decommissioning of 1F.

Metallic Fast Reactor Separate Effect Studies for Fuel Safety

Sodium-cooled Fast Reactors (SFR) are one of the advanced nuclear reactor concepts to be commercially applied for electricity production. The benefits of SFR are well-known and include: the possibility of a closed fuel cycle, proliferation resistance, nuclear waste minimization via actinides burning, and fissile breeding capabilities. Metallic fuel used in SFR has well demonstrated irradiation performance. However, more studies are necessary to optimize and extend operational and safety limits for their commercialization and licensing. This could be achieved through a better understanding of fuel behaviors during transient and of fuel failure thresholds. This paper describes the experimental Research and Development (R&D) program aimed at providing the necessary data to support the development of SFR-optimized safety limits. This program integrates separate effects testing and integral effects testing, combined with advanced Modeling and Simulation (M&S). This R&D program, finally, focuses on delivering the science-based information necessary for supporting the licensing and utilization of SFR based on metallic fuel. In this paper we will describe the three research areas centered on fuel development and focused on separate effect testing, namely: (1) microstructural, chemistry, and material properties; (2) thermo-mechanical behavior; and (3) source term and fission product behavior. Preliminary results from these Separate Effect Tests (SET) studies and the current instruments and experimental plan are also presented.