ICONE23-1093 RADIATION-INDUCED ELECTROLYSIS (III) : A POTENTIAL ROOT CAUSE OF HYDROGEN EXPLOSIONS IN THE FUKUSHIMA DAIICHI ACCIDENT

Abstract

Since the scientific cause for a series of hydrogen explosions during the Fukushima accident has not been established, the author investigated his basic theory named "radiation-induced electrolysis" by applying the estimation of the amounts of H_2 generation during the active phase of the Fukushima accident. The author's theory was originally developed by including Faraday's Law of electrolysis into the basic time-dependent material balance equation of radiation-chemical species for his study on accelerated corrosion phenomena which is widely observed in aged plants. Through this mechanism as much as 5,300 m^3-STP of accumulated hydrogen gas is estimated to be inside the PCV just prior to the hydrogen explosion which occurred a day after the reactor trip in Unit 1. With this large volume of hydrogen gas the explosion was a viable possibility upon the "venting" operation as stated in previous reports. In view of this, this paper intends to continue the investigation of the Fukushima accident while focusing on hydrogen generation from the spent fuel pools, as the author's previous estimation for 1F4 SFP indicated a rapid initiation of hydrogen generation when the pool water temperature exceeded 40 degrees centigrade. These observations lead to investigate the potential mechanism by changing the pool water temperature and flow velocity in the spent fuels. During the trial calculations it was discovered by chance that SBO induced a rapid initiation of electrolysis when the pool water temperature surpassed 40°C with a range of low water flow velocity through the spent fuels as reported in NPC-2014. Due to a difference in the absorbed dose rate of water through γ-decay heat, an electrochemical potential difference should exist in the highly radioactive region of spent fuels stored by evacuating the core and less radioactive fuels stored for several years. All these spent fuels were stored in spent fuel racks placed at the bottom of the pool covered with a stainless steel lining. The metallic contacts enabled electric conduction between the highly radioactive fuel assemblies and cooled spent fuels. This hypothesis leads to a simple solution of inserting ceramic insulator to prevent direct metallic contact of the spent fuel racks to the liner and each other in order to disconnect the closed circuit. However, the author has reservation of this hypothesis, without first having the appropriate experimental verification. The estimation of the amount of hydrogen was calculated without experimental evidence of the electric current going through the spent fuel racks.