1 Février 2015
January 31, 2015
As old nuclear reactors in the country are considered for decommission, the Mainichi Shimbun answers some common questions readers may have about how such decommissioning and the disposal of nuclear waste take place.
Question: What is the background behind the current talk of decommissioning reactors?
Answer: Under current law, nuclear reactors are generally limited to 40 years of operation -- and power utilities are considering decommissioning as an option for nuclear reactors that are approaching this limit. Standard decommissioning involves extracting spent nuclear fuel from the reactor, decontaminating the inside of the reactor building, and then proceeding with the reactor's dismantling. The whole process takes from 20 to 30 years.
Q: Won't high levels of radioactively contaminated waste emerge during a reactor's dismantling?
A: According to power utilities and other sources, most of the waste that comes out during the dismantling process includes items such as concrete structures that do not need to be treated as radioactive waste. Only around 3 percent of total waste products comprise objects that require handling as radioactive waste -- mainly things including structures inside the reactor such as the pressure vessel that housed its nuclear fuel, and the equipment used for the spent nuclear fuel pool.
As an example, around 8,740 metric tons of radioactive waste is estimated to come out from the No. 2 reactor at Chubu Electric Power Co.'s Hamaoka Nuclear Power Plant in Shizuoka Prefecture -- where decommissioning work began in 2009 -- as opposed to 262,800 tons of nonradioactive waste.
Q: How is radioactive waste processed?
A: Except for spent nuclear fuel, the radioactive waste that comes out during decommissioning work has a low level of radiation. Particularly low-level radioactive waste such as filters or workers' clothing is stuffed into barrels, embedded in cement and other materials, and buried less than 20 meters under ground.
This would be the same processing as is already being done at a Japan Nuclear Fuel Ltd. facility in Aomori Prefecture for low-level nuclear waste created by nuclear reactor operations.
On the other hand, objects inside a nuclear reactor -- such as the control rods used to adjust nuclear fission -- are 10 to 100 times more radioactive than low-level waste, and are buried from 50 to 100 meters under ground. Nuclear waste is buried under ground because the bedrock and the soil block radiation.
Q: How will the processed radioactive waste be managed?
A: Shallowly-buried waste will be kept in artificial structures under ground until radiation levels naturally fall -- anywhere from 50 to 300 years. For deeply-buried waste, neither burial locations nor an organization that will retain management responsibility have yet been decided upon. But now that power utilities have started considering reactor decommissions, the Nuclear Regulation Authority began discussions this month geared toward establishing standards for facilities and management of deeply-buried waste. (Answers by Shimpei Torii, Science & Environment News Department)