Japan on December 27 revised the road map for decommissioning the crippled Fukushima Daiichi nuclear power plant, further delaying removal of thousands of used fuel assemblies that have been held in cooling pools since the 2011 earthquake.
It is the fifth revision of the roadmap by the Ministry of Economy, Trade and Industry. While the decommissioning process is complicated by high radiation and other risks, the government and plant operator, Tokyo Electric Power Co (Tepco), are still aiming for completion within 30-40-years. “It’s a very difficult process and it’s hard to know what to expect. The most important thing is the safety of the workers and the surrounding area,” industry minister Hiroshi Kajiyama told a news conference.
The Japanese government decided to delay the removal of used fuel from units 1&2 by up to five years. The process of removing the fuel had previously been scheduled to begin in fiscal 2023.
More than 4700 used fuel rods remain at the three reactors which suffered meltdown and the two others that survived the earthquake and tsunami. They pose a high risk as their storage pools are uncovered and a loss of water in the event of another major disaster could cause the fuel rods to release massive radiation.
Fuel removal from units 1&2 is now postponed by up to ten years from the initial target of 2018, with further preparation needed to reduce radiation and clear debris and other risks.
Fuel rod removal at the Fukushima Daiichi unit 1 reactor pool will begin sometime in 2027-2028, after debris is cleared away and a rooftop cover installed to contain radioactive dust. Fuel removal from the unit 2 pool is to begin in 2024-2026. Work at the unit 3 reactor pool began in April 2019 and all 566 assemblies will be removed by March 2021.
Tepco has already emptied the pool at Fukushima Daiichi unit 4, which was offline at the time of the accident and only suffered building damage. It aims to have all remaining rods in reactor pools removed by 2031 for safer storage in dry casks.Problems dealing with contaminated water at Fukushima
Tepco faces problems in dealing with 1.2 million tons of treated water, which still contains radioactive tritium, kept in more than 950 tanks at the plant. Plans to release the water into the sea have not been implemented because of possible public repercussions and the impact on the fishing and agriculture.
The amount of water, which is used to cool the melted fuel inside the reactors, is increasing by 170 cubic metres daily. This has been reduced from about 540 cubic metres a day in May 2014. The revised roadmap maintains the current target of reducing contaminated water generation to 150 cubic metres per day in 2020, but sets a new target for reducing this to 100 cubic metres per day in 2025.
Tepco says it can store up to 1.37 million tons of contaminated water, or its current capacity will last until summer 2022. Tepco and the government say the tanks pose risks if they were to spill their contents during another earthquake, tsunami or flood. They also need to free up space to build storage for melted fuel that will be removed from reactors beginning 2021.Fukushima molten fuel removal plans
The most difficult task is removal of an estimated 880 tons of molten fuel from Fukushima's three melted reactors. This is six times more than the amount dealt with in the aftermath of the 1979 Three Mile Island in the USA.
Removal is scheduled to begin in 2021 at Fukushima Daiichi unit 2, where robotic probes have made the best progress. A robotic arm was developed to enter the reactor from the side to reach the melted fuel, which has mostly fallen to the bottom of the primary containment vessel. A side entry would allow the simultaneous removal of fuel rods in the pool from the reactor roof.
The removal of melted fuel will begin with just a spoonful, which will be carefully measured and analysed under International Atomic Energy Agency (IAEA) instructions. The government hopes to gradually expand the scale of the removal, but this depends on better expertise and further robotic development. The decade up to 2031 will be crucial to future future progress.
Fuel removal from Fukushima Daiichi units 1&3 present a more complex problem because of high radiation and water levels respectively, and require more investigation.
Japan has as yet no plans for the disposal of the melted fuel and other debris that come out of the reactors. Managing the waste is expected to require new technologies to reduce its volume and toxicity.
Tepco and the government have mentioned plans to build a site to store waste and debris removed from the reactors, but public consent is a problem.
There will also be an estimated 770,000 tons of solid radioactive waste by 2030. This will include contaminated debris and soil, sludge from water treatment, scrapped tanks and other waste. It will need to be sorted, treated and compacted for safe storage under a plan to be compiled by 2028.Fukushima decommissioniong: cost and labour concerns
According to the government, decommissioning costs are estimated at JPY8000bn ($73 billion). However, compensation, decontamination of surrounding areas and medium-term storage facilities is likely to increase this to an estimated JPY22,000bn. The Japan Centre for Economic Research estimates that decommissioning alone would cost JPY51,000bn if the water is not released and tritium removal technology is pursued.
More than 10,000 workers a year will be needed with about one third assigned to managing the radioactive water. Nuclear Regulation Authority Chairman Toyoshi Fuketa has expressed concerns about a possible labour shortage and Tepco has said it intends to hire workers under Japan's new policy that allows more unskilled foreign labour. However, that plan is on hold in the wake of government instructions to address language and safety concerns.
Photo: Dismantling exhaust stack at Fukushima Daiichi units 1&2 began in December 2019 (Photo: Tepco)