(1) Secondary Waste from Water Treatment Generated Directly After the Accident and Left in Situ<\/em><\/strong><\/p>\n Secondary waste from water treatment generated directly after the accident is being stored in the Process Main Building (PMB) and High-Temperature Incinerator (HTI) building on the platform at 8.5 m elevation above sea level on the south side of Fukushima Daiichi Unit 4. Prior to the accident, these two buildings were being used to store radioactive waste items temporarily and reduce their volume (through incineration). After the accident, equipment by the name of \u201cSARRY\u201d was installed in the latter, which, as a result of a valve-operation error, caused leakage of contaminated water.<\/p>\n Decontamination equipment sludge<\/strong>: The highly concentrated sludge generated by the operation in June through September 2011 of the decontamination equipment manufactured by Areva remains in Storage Tank D in the basement of the PMB. In September 2018, its ports and through-holes were closed off as a tsunami countermeasure, as there was a risk of efflux to the ocean. However, since this was not a water-tight building to begin with, the contents were scheduled to be transferred after recovery, dehydration and container stabilization to a large waste item storage vault out of reach of tsunamis (a platform at 33.5 m elevation; below, \u201chigh ground\u201d). The recovery was to be completed by FY2025, but radioactivity was confirmed in the tera-becquerel range from strontium-90, and a lot of time has been needed for designing a dust confinement function. Once recovery begins, it is expected to take until at least 2027.<\/p>\n Zeolite sandbags<\/strong>: \u00a0<\/p>\n (2) Secondary Waste from Water Treatment Generated in the Course of Processing Contaminated Water<\/strong><\/p>\n Fuel debris that melted and fell into the basement of the reactor buildings comes into contact with inflowing groundwater, resulting in a continually increasing amount of contaminated water. To deal with that, the contaminated groundwater has been put through cesium-adsorption equipment to remove cesium and strontium radionuclides, then through desalination equipment, then through a multi-nuclide removal facility (ALPS) that removes 62 radionuclide species. Aside from tritium, the contaminants are to some degree strained out through adsorbent materials or otherwise removed, and in the course of doing that secondary waste from water treatment is generated. From TEPCO (2023b) \u201cPolicy for considering solidification of secondary waste from water treatment\u201d (data from technical meeting to review plans for implementing specified nuclear facilities, 4 December 2023, Item 1-2, in Japanese), I will excerpt information on where the waste, including from (1) above, is currently located, how TEPCO intends to treat it, their policy on where it will be stored in the future (Fig. 1) and the amounts of wastes (Table 2). There are three types of ALPS facilities<\/strong>, initial ALPS, added ALPS and high-performance ALPS. The initial and added ALPS facilities perform multi-nuclide removal after a pretreatment. The pretreatment involves injection of a chemical agent that produces a \u201cslurry\u201d consisting of a viscous mixture of fine precipitated matter in the water. The multi-nuclide removal generates \u201cused adsorbent\u201d by straining out the radioactive matter. High-performance ALPS, on the other hand, involves no pretreatment, with the adsorption tower itself replaced, but it is currently not in use. The ALPS slurry has been confirmed to have a maximum dose rate of 13.72 mSv\/h at the HIC-side surface. It is stored in polyethylene containers called \u201chigh integrity containers\u201d (HIC), which are housed in concrete containers that function to shield the radiation as well as release the heat and hydrogen that are generated, but this comes with two risks.<\/p>\n The first is the risk that chemical decomposition caused by the radioactive substances in the slurry could generate hydrogen gas, increasing the water pressure and causing it to leak. As a countermeasure, TEPCO has been considering reducing the volume of water injected into the HICs, and if any HIC is judged as being too full, letting out some of the water from the HIC. A test run using real slurry is scheduled to be conducted in FY2024.<\/p>\n The second risk is deterioration of the HICs themselves from the radiation. For that reason, there are plans to transfer the HICs, which have been found to exceed a cumulative absorbed dose of 5,000 kGy, to reduce the risk of leakage. For example, of the 102 units evaluated to exceed 5000 kGy by the end of March 2023, 45 had been transferred as of the end of FY2022. Fifty-seven are expected to have been transferred by the end of FY2023. From FY2024 onward, there are plans to transfer 23 units, then 26 units, then 48 units gradually year-by-year. A look at the diagram illustrating the procedure, however, shows it to be work accompanied by risk of exposure (Fig. 2). \u00a0<\/p>\n After this risky storage work is completed, the slurry is eventually scheduled to be extracted, dehydrated, solidified, transferred to a metal container and stored near the center of the Fukushima Daiichi premises, on the inland side (Solid Storage Bldg. 9).<\/p>\n Used adsorbent material from ALPS is also stored in HICs.<\/p>\n \u00a0<\/p>\n To reduce storage risks from all of these varieties of secondary waste from water treatment, TEPCO has established the following policies:<\/p>\n \u30fbPromoting transference to storage within buildings.<\/p>\n \u30fbReducing volume through drying and dehydration, decreasing the risk of corrosion and leakage.<\/p>\n \u30fbFrom the standpoint of risks in storage and ensuring storage space, putting higher priority on ALPS slurry, ALPS adsorbent material and decontamination equipment sludge, and taking measures to deal with them.<\/p>\n \u30fbA form of storage is chosen that gives consideration to retrieving the waste from the containers later, and processing it prior to solidifying it, without problems arising such as with processing the empty containers.<\/p>\n \u00a0<\/p>\n It is important to secure storage for the HICs, so 19 plots (for 4,384 units) have been secured to the south of Unit 4 on the inland side. As of the end of FY2022, 4,161 of the spaces were occupied, so the number is to be increased to 4,768 spaces by January 2028 and new plots are expected to be secured elsewhere, capable of holding a maximum of 5,344 units. Meanwhile, with dehydration proceeding, the number of HICs in storage is optimistically expected to decrease (see Graph 1.) \u00a0<\/p>\n![\"\"](\"https:\/\/cnic.jp\/english\/wordpress\/wp-content\/uploads\/2024\/06\/masano-T1-1-e1717386578759.jpg\")
<\/a>Zeolite sandbags (see Table 1) were brought in to purify stagnant water with high concentrations of contaminants that was pooling underground in the second basement of the PMB and under the HTI building, and those have been kept as they are. A maximum dose rate of 4,400 mSv\/h has been confirmed there, but the sandbags have deteriorated, and cannot be recovered with the bags intact. Consideration is being given to pumping them out together with the stagnant water and enclosing it all in containers. Methods for collecting the sludge that will undoubtedly remain at the bottom after the sandbags have been retrieved will be considered in the future. This may also be transferred to the high ground and stored there in the future, but that is a matter for future discussion.<\/p>\n<\/a><\/p>\n<\/a>The cesium-adsorption system<\/strong> consists of three types of devices. the primary adsorption tower \u201cKURION,\u201d a secondary cesium adsorption tower called the \u201cSARRY,\u201d and a tertiary cesium adsorption tower, \u201cSARRY II.\u201d After these cesium adsorption towers have been spent, currently consisting of 779 KURIONs, 257 SARRYs and 17 SARRY IIs, they are placed in box culverts and kept in a temporary storage facility (high ground on the south side of Unit 4). The KURION is also being used as a back-up facility for the SARRY, so the number of spent cesium\u2013adsorption towers will not increase further, but the number of SARRYs and SARRY IIs is increasing together with the treatment of contaminated water.<\/p>\n<\/a><\/p>\n\n
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<\/a> It is unknown whether this will go as planned, however. The scarcity of space for contaminated water tanks has been relieved with the oceanic release of tritium water, but if the amount of contaminated water being processed continues to increase, there is no guarantee that space for storing HICs will not become an issue in the future.<\/p>\n