Recovery from any accident will require interim on-site waste storage. The experience at Fukushima Daiichi is presented here as it represents a wide range of waste types needing such storage. An overall picture of the Fukushima Daiichi waste management challenge is in Ref. [9].
The different types of contaminated waste material that are managed within the Fukushima Daiichi on-site areas include trees, buildings and other debris, and very large amounts of contaminated water/secondary water treatment waste. The three waste types are managed independently. Debris and felled trees are segregated and stored in areas based on dose rates and contamination levels.
The initial on-site waste management strategy focused on providing safe, temporary storage for the wastes associated with stabilization and dose reduction efforts. Planned actions included:
(a) Construction of temporary storage facilities (with soil coverage of debris);
(b) Construction of soil covered temporary storage for cut down trees;
(c) Relocation of temporary storage facilities to reduce dose rates at the site boundary;
(d) Construction of a temporary cask storage facility to support removal of nuclear fuel;
(e) Construction of storage facilities for secondary waste from water treatment (e.g. absorption media).
TABLE 3. RANGES OF EVALUATED IMPACTS FOR EVAPORATION OF TMI-2 TRITIATED WATER [73]
Impacts Range of impacts
Bone dose to the off-site population 0–14 person-rem total population (0–0.14 person-Sv)
0–0.4 mrem to the maximally exposed off-site individual (0–4 µSv) Total body dose to the off-site population 0–3 person-rem total population (0–0.03 person-Sv)
0–5 mrem to the maximally exposed off-site individual (0–50 µSv) Thyroid dose to the off-site population Up to 6 person-rem total population (0–0.06 person-Sv)
Up to 4 mrem to the maximally exposed off-site individual (0–4 µSv) Estimated number of radiation caused cancer fatalities
to the off-site population 0–0.0004
Estimated number of radiation caused genetic disorders
to the off-site population 0–0.002
Occupational dose 0–25 person-rem (0–0.25 Sv)
Estimated number of radiation caused cancer fatalities
to the worker population 0–0.003
Land commitment 0–49 000 square feet (0–4552 m2)
Radioactive waste burial ground volume 0–460 000 cubic feet (0–13 026 m3)
Cost to the licensee US $100 thousand to US $41 million
Time to complete 0–36 months
Number of traffic accidents 0–12
Estimated number of traffic fatalities 0–0.8
Maximum individual dose from accidents 0–60 mrem total body (0–600 µSv) 0–3000 mrem bone (0–30 mSv) Population dose from accidents 0–0.7 person-rem bone (0–70 mSv)
0–0.02 person-rem total body (0–0.2 mSv)
FIG. 21. Schematic of a soil covered storage facility for branches, leaves and roots. (Courtesy of TEPCO, Japan.)
It is conservatively estimated that a total of 560 000 m3 of contaminated material will be generated until the end of fuel debris removal, planned for 2027. A new centralized storage facility is being planned with a capacity of approximately 160 000 m3. The difference between the estimated amount of waste and the planned capacity of the storage facility highlights the expectation that waste segregation, volume reduction and recycling will reduce the volume of waste requiring long term management (storage) as radioactive waste.
Contaminated trees are a significant waste stream. As of early 2014, 79 300 m3 of trees were being stored on-site.
The trunks are managed separately from the branches, leaves and roots, as higher activity levels are present on the branches, leaves and roots than on the trunks. It is estimated that the volume distribution is roughly 30% trunks, 40%
branches and leaves, and 30% roots. Further segregation of bark from the trunks could be effective at leaving minimal contamination on the trunks. The tree trunks are temporarily stored in stacks with limitations on the height and measures to ensure airflow in the stacks to reduce the fire hazard. Temperatures are also monitored to further protect against fire.
The branches, leaves and roots are placed in covered temporary storage facilities that include multiple barriers with retaining walls and soil along the sides, and soil and impermeable high-density polyethylene sheets above the waste for shielding and to control the infiltration of water. Ventilation and temperature monitoring reduce the possibility of fires. Figure 21 is a schematic for a covered storage facility for branches, leaves and roots.
Contaminated building parts and other debris must be stored on the site. Activities to stabilize and to reduce dose rates from the damaged reactors resulted in large amounts of debris being collected (see Fig. 22). Debris also continues to be produced as a result of ongoing recovery activities. Some of the debris has high levels of contamination and its management requires additional radiation protection measures for workers. These conditions create challenges for accessing, characterizing and removing debris. Debris has been transported by means of heavy equipment. The waste is transported to collection areas and then stored in different types of facility based on the measured dose rates. The storage types in use include storage buildings, soil covered temporary storage facilities, storage tents and outdoor storage covered by sheets to limit water infiltration (Fig. 23). For soil covered temporary storage, the soil and high-density polyethylene sheets provide shielding and reduce the amount of infiltration of water into the stored waste.
Debris is segregated based on the surface dose rates and type of material (e.g. concrete, steel). Owing to the implementation of planned measures such as volume reduction, recycling and incineration, the volume of stored waste could be significantly reduced. At the same time, the management of solid waste is complicated because in the absence of waste acceptance criteria derived from a disposal concept, only temporary stabilization and storage can be implemented [67].
Guidelines as shown in Table 4 were established to ensure that debris with surface dose rates greater than 1 mSv/h is stored in storage tents, soil covered temporary storage facilities and solid waste storage buildings. These guidelines were developed by the site operator (TEPCO) and approved by the regulator (Nuclear Regulation Authority of Japan) in view of worker protection and to support the maintenance of a dose rate of 1 mSv per year at the site boundary. Several thousand cubic metres of contaminated soil have been generated and are stored separately from other debris. Operational waste (e.g. HEPA filters) is managed similarly to debris.
The third type of waste that needs interim storage is the secondary waste generated by the several water processing systems. The two primary types of waste generated are sludge and used vessels from the caesium removal processes. The processes result in the accumulation of shielded steel vessels containing spent zeolite that has been used to capture caesium and other contaminants such as oil, strontium, technetium and iodine (see Fig. 24).
TABLE 3. RANGES OF EVALUATED IMPACTS FOR EVAPORATION OF TMI-2 TRITIATED WATER [73]
Impacts Range of impacts
Bone dose to the off-site population 0–14 person-rem total population (0–0.14 person-Sv)
0–0.4 mrem to the maximally exposed off-site individual (0–4 µSv) Total body dose to the off-site population 0–3 person-rem total population (0–0.03 person-Sv)
0–5 mrem to the maximally exposed off-site individual (0–50 µSv) Thyroid dose to the off-site population Up to 6 person-rem total population (0–0.06 person-Sv)
Up to 4 mrem to the maximally exposed off-site individual (0–4 µSv) Estimated number of radiation caused cancer fatalities
to the off-site population 0–0.0004
Estimated number of radiation caused genetic disorders
to the off-site population 0–0.002
Occupational dose 0–25 person-rem (0–0.25 Sv)
Estimated number of radiation caused cancer fatalities
to the worker population 0–0.003
Land commitment 0–49 000 square feet (0–4552 m2)
Radioactive waste burial ground volume 0–460 000 cubic feet (0–13 026 m3)
Cost to the licensee US $100 thousand to US $41 million
Time to complete 0–36 months
Number of traffic accidents 0–12
Estimated number of traffic fatalities 0–0.8
Maximum individual dose from accidents 0–60 mrem total body (0–600 µSv) 0–3000 mrem bone (0–30 mSv) Population dose from accidents 0–0.7 person-rem bone (0–70 mSv)
0–0.02 person-rem total body (0–0.2 mSv)
FIG. 21. Schematic of a soil covered storage facility for branches, leaves and roots. (Courtesy of TEPCO, Japan.)
In parallel with ongoing activities, research and development activities focusing on technical solutions for the treatment of salt containing wastewater are being undertaken. The objective is to produce waste forms that are suitable for long term storage on the site. Several techniques such as direct cementation, drying and storage, and drying and subsequent cementation have been investigated. This includes various practical tests with the aim of increasing the salt content in the cement matrix as much as possible, while still meeting the required mechanical strength and homogeneity.
FIG. 22. Whole view of Unit 3 reactor building north side (before large debris removal). (Courtesy of TEPCO, Japan.)
FIG. 23. Examples of facilities constructed for the management and storage of debris. (Courtesy of TEPCO, Japan.)
TABLE 4. GUIDELINES FOR SEGREGATION AND STORAGE OF DEBRIS Surface dose rate of debris (guide value) *
0.1 mSv/h or less 0.1–1 mSv/h 1–30 mSv/h More than 30 mSv/h**
Storage approach
Shielding None None Concrete wall, soil,
containers Containers and building Prevent
dispersion None Sheet cover Tent, soil, containers Containers Temporary storage method Outdoor collection Sheet cover Containers storage
Temporary storage facility
Soil covered temporary storage facility
Container storage Solid waste storage building
* Review guide value as appropriate considering on-site air dose rate.
** For those over 1 Sv/h, temporarily store in containers, solid waste storage building or shielded area.
FIG. 24. SARRY vessels in the operating facilities. (Courtesy of TEPCO, Japan.)