Key important roles of water chemistry contributing to the Fukushima recovery issues and the plant restart activities

摘要

After the severe accidents at Fukushima Daiichi Unit 1 through 3 of Tepco HD on March 11,2011,all the commercial BWRs and PWRs in Japan were forced to shut down.The regulatory requirements for the plant restart have been strictly settled and only few plants have been approved to operate but most of the plants have been waiting for the approval.Historically the water chemistry for commercial light water reactors have been developed and advanced in order to overcome the problems associated with the plant operation,such as keeping material integrity and reducing radiation exposure.However,after the Fukushima accident,the surrounding situation of the water chemistry has been totally changed and it should be noticed that most of the water chemists have to deal with not only the operating plant water chemistry but also various kinds of chemistry related issues such as radioactive contaminated water purification,desalination,anti-corrosion countermeasure application,decontamination,sea water radiolysis,and so on.On the other hand many of the LWRs in Japan are under review process for restart and have been equipped with the new devices as a severe accident countermeasure.Firstly,the water chemistry consideration is necessary for the plant start up after a long storage period.Furthermore,it is also important to evaluate the effectiveness of those severe accident countermeasure devices,such as a alkaline injection system in order to keep the pH high to suppress iodine carry over.In this paper the roles of water chemistry for the Fukushima recovery issues and the plant restart activities are briefly summarized.