IV. ACCIDENT CLEANUP
The accident at the Fukushima Daiichi NPS has resulted in significant challenges for accident cleanup and waste management. These issues include processing the large volume of contaminated water, debris, soil, secondary wastes, potentially damaged spent fuel within the reactor SFPs, and damaged fuel and fuel debris within the reactors and primary containment structures. Progress has been made in cooling of the reactors, and all the units have reached ambient pressure and temperature conditions, i.e., cold shutdown. Mid-term to long-term waste management issues will continue to be the major technical issues that must be overcome as recovery actions continue toward an acceptable end state. TEPCO (see  for TEPCO information on cleanup status) has established a road map that describes elements of the site cleanup and water management, and it is currently developing more detailed mid-range to long-range plans. There are also waste management challenges associated with
• treatment of contaminated water and the resulting filter and equipment wastes
• storage and disposal of secondary wastes, contaminated soils, vegetation, and debris
• decontamination to allow reinforcement of the weakened structures and installation of cooling
and gas management systems
• installation of new secondary containment structures and material-handling equipment.
Resolving these challenges will be required to allow continued progress for removal of the spent fuel stored within the SFPs and ultimately the retrieval and processing of the damaged fuel within and outside of the RPVs.
As the planning for the cleanup continues to evolve, in early November, the Japanese government ordered TEPCO to draw up a road map to decommission the four damaged reactors at the Fukushima Daiichi NPS in a process that could take decades. The plan, developed by TEPCO in collaboration with the Japanese government, is based on removing fuel rods in SFPs within 2 years and damaged fuel in each of the reactors within 10 years, according to the minister in charge of the nuclear disaster response. TEPCO is developing a road map to be provided early in 2012. Decommissioning the four reactors is estimated to cost at least 1.15 trillion yen [$15 billion (USD)]. Substantial government involvement will be necessary in the decommissioning process. TEPCO must submit a road map of the utility’s corporate structure and financial situation that will be viable. A committee of the Japan Atomic Energy Commission (JAEC) said it may take >30 years to dismantle the reactors. Normal decommissioning takes about half as long according to the JAEC committee. At the Three Mile Island Unit 2 (TMI-2) accident in Pennsylvania in 1979, fuel removal was started ~6˝ years later and was completed in ~14 years.
The Japanese Cabinet also has approved “basic policies” to clean up off-site radioactive contamination resulting from the Fukushima Daiichi accident. Based on recommendations made in 2007 by the International Commission on Radiological Protection, areas contaminated to dose levels with a dose of 20 mSv/year (2 rem/year) above background should be cleaned up to reduce doses by 50% for adults and by 60% for children within 2 years and to bring them to a long-term level of 0.1 rem/year above background radiation levels. This dose level is approximately the same amount of radiation exposure a patient would receive from a full-body CT (computed tomography) scan. The current government policy is that areas where the annual dose levels are above this level are to be given priority in scheduling decontamination activities. The current government policy may prove to be problematic for implementation.
IV.A. Cleanup Issues
The Fukushima Daiichi accident produced radioactive gaseous, liquid, and solid wastes. The gaseous emissions were released in the early days of the accident and have dispersed and decayed to small levels and are no longer a health threat. Based on measurements in November, TEPCO has already declared that significant gaseous releases have stopped and that the temperatures in all three reactors are <75°C (167°F).
Liquid waste management and the cleanup and management of the water that was injected into the reactors and SFPs had been a major concern. For many weeks following the accident, rainwater mixed with the water that had been injected into the reactors and SFPs was accumulating in NPS buildings and tanks. As the buildings and tanks filled up, additional temporary storage tanks were brought in to hold the water. In June, the first of two temporary wastewater cleanup systems was started. As of this writing at the end of 2011, two temporary wastewater processing systems are in service operating at ~90% capacity, cleaning more water than is being injected into the reactors and SFPs. Water levels in the buildings are slowly decreasing, and plans are in place to start work in 2012 on a new, more permanent long-term wastewater processing facility.
The solid wastes at the Fukushima Daiichi NPS consist of
• secondary wastes accumulating as a result of the water treatment processes (such as sludge and filter resins)
• radioactive particles that were released during the reactor building explosions and drifted away and settled across downwind areas
• contaminated rubble and materials from in and around the NPS buildings (including deforestation and other organic debris cleared to make room for storage tanks and buildings)
• radioactive nuclear fuel in the SFPs and in the damaged reactors.
Plans are being developed and implemented to monitor and, if necessary, clean up or remove radioactive contamination from surrounding areas on the Fukushima NPS site. Much of the contaminated rubble and materials around the NPS buildings and in the roadways has been removed, and work has started on rubble removal from the refueling floors of Units 3 and 4. Planning is in progress to start moving the fuel from the SFPs to interim or long-term storage or reprocessing facilities within the next couple of years. Studies are in progress or planned to determine the best methods to be used to defuel the reactors, remove the spent fuel from the SFPs, and treat and dispose of the accumulated radioactive wastes. The initial phase of the complete plan for removal of fuel from the reactor is illustrated below. A complete summary is given at the ANS Web site (http://fukushima.ans.org/), and the detailed plan and progress can be found at the TEPCO Web site .
IV.B. Current Status
Because of damage to the RPVs, PCVs, and reactor buildings, contaminated water injected into the reactor cores is leaking into the turbine buildings. This situation required the quick design of two water treatment systems. One was a short-time-frame installation, and the other was a mid-term installation (Fig. 12). The two water treatment systems are still being used to process wastewater to remove oil, contamination, and brine. The water is being processed at a rate of ~50 m3/hour. Contaminated water is being generated at a rate of 25 m3/hour from reactor core injection and 200 to 500 m3/day from groundwater in-leakage. The processed water is being reused to inject into the RPVs to minimize the volume of new water used. The systems initially experienced equipment and operational problems caused by quick installation and operator unfamiliarity. The systems are currently operating above 90% capacity. TEPCO has been able to reduce the inventory of contaminated water creating enough margin to increase the cooling injection rates into the RPVs. The waste sludge from the oil separator, reverse osmosis membrane, and desalination units is being stored on-site in temporary tanks. In addition, Units 5 and 6 are experiencing groundwater intrusion of 200 m3/day that is slightly contaminated but below release limits. However, TEPCO is unable to release this water because of current environmental policy issues. Therefore, TEPCO is spraying this water on the NPS site to alleviate storage concerns. Similarly, the NPS has a large volume of tritiated water at a tritium concentration of 103 Bq/m3. The total amount of the accumulated water is increasing at ~200 to 720 tons/day. This volume will eventually challenge the storage capacity. Multiple tank farms containing several hundred tanks for a total volume of >111,000 m3 and a megafloat barge to store 10,000 m3 of water have been added to the NPP site.
A similar portable skid-mounted water treatment and desalination system is being used to reduce contamination and chlorine levels in the SFPs of Units 2, 3, and 4. These SFPs had seawater injected into them during the event. The system is being moved to the Unit 2 SFP as cleanup has been completed on Unit 4. In many ways, the Fukushima Daiichi NPS has evolved from a nuclear power electric generation site into a large water treatment facility (Fig. 13).
Site cleanup has been accomplished through the use of ten remotely controlled vehicles including backhoes, bulldozers, and dump trucks. The site has two remote vehicle control rooms that are used to control all the debris-removal construction equipment. One control room operates a backhoe, a dump truck, and a lift truck. The second control room operates two backhoes, a bulldozer, two dump trucks, and two lift trucks. All the items and materials removed from the yard area around the NPS have been stored in metal containers (4- to 8-m3 volume). Larger and less contaminated items are stored in bulk in a new solid-waste building. Each container has an assigned number and is labeled with its container number, where the debris is from, dose rate, and type of debris. This will be used to maintain inventory control during eventual transport off-site and waste disposal.
Removal of reactor building structures damaged by the explosions will be required to allow removal of spent fuel and ultimately core material. Planning is currently in progress for removal of fuel from the SFPs (Fig. 14) to storage containers within the next few years after the structures are removed .
Frequent monitoring and development of plans for environmental cleanup or removal of harmful levels of radioactive contamination from areas surrounding the NPS are progressing. The magnitude of the cleanup outside of the NPS site has required the Japanese government to take ownership for these tasks. A number of demonstration projects have been initiated, and the complete road map
is to be provided in early 2012. A complete summary is given at the ANS Web site (http://fukushima.ans.org/), and the detailed plan and current progress can be also found at the TEPCO Web site .