Japan's nuclear power industry is responsible for the safe management of all radioactive waste materials. Various types of waste are produced during the production of electricity from nuclear power. Since not all wastes are alike, different methods of treatment and disposal must be used.

Radioactive waste, which is not the same as spent nuclear fuel, is unusable matter that contains radioactive elements. Radioactive waste is generally classified on the basis of how much radiation and the type of radiation it emits as well as the length of time over which it will continue to emit radiation. The purpose of this classification system is to ensure that radioactive waste is handled, stored, and disposed of in ways that are appropriate to its characteristics. There are generally considered to be two types of radioactive waste: High-Level Waste (HLW) and Low-Level Waste (LLW). Different management processes for these wastes apply.

As previously discussed, Japan is well on its way to creating a "closed" nuclear fuel cycle. Despite these efforts, HLW accounts for approximately 3% of the composition of spent fuel (depending on the level of initial enrichment). Specifically, when useable elements are recovered from spent fuel during the reprocessing operation, HLW is the liquid by-product. Though the closed fuel cycle minimizes HLW, that HLW must yet be properly disposed of. Below is an explanation of Japan's plans for the disposal of its HLW.

What then is the ideal method of disposing of high-level radioactive waste? Various methods exist, none without drawbacks; the most significant of which are usually related to risk of accidents or the challenge of political complexities. The most agreeable HLW disposal method involves burying waste deep underground, and this is currently a central feature of research and development programs throughout the world.

Underground disposal offers a number of distinct advantages. To begin with, it is relatively unsusceptible to dramatic shifts in climate. The risk of inadvertent excavation is also minimal, since radioactive waste would be buried several hundred meters under the ground. As the remarkable condition of numerous fossils attest, subterranean burial sites are a superior form of preservation over immense time periods.

With underground disposal, vitrified (formed into glass) waste is cooled for 30 to 50 years in above-ground storage facilities. It is then inserted into metal containers (called overpacks), buried deep underground in stable bedrock, and encased in a buffer layer of viscous shock-absorbing material. This manner of burial minimizes the risk of radioactive material leaking into surrounding groundwater and penetrating neighboring strata. The underground burial location is chosen with a view towards creating a natural barrier, so that even if radioactive material were to leak from the site, the rate at which it would spread would be limited by its absorption into the surrounding ground. This combination of artificial and natural barriers is thought to be sufficient to ensure the safety of underground disposal of high-level radioactive waste for many, many years.

(Research into scientific aspects of the earth's stratum)

Japan's HLW Disposal Program

Japan's current high-level radioactive waste disposal program has formed a private consortium to handle the effort. The Nuclear Waste Management Organization of Japan (NUMO) was created in October 2000. Over the ensuing years, NUMO will be responsible for carrying out assessment studies for site selection, developing and demonstrating reliable disposal technologies, reflecting the opinions from local communities, and obtaining confirmation from the government for the selected site.  The goal is for a site to be operational sometime between 2030 and the mid-2040s.

Japan is not alone in this endeavor. Similar underground disposal programs are already underway around the world. The United States, Sweden, Switzerland, Germany, and Canada are among those countries currently researching and developing underground facilities. Of all countries, the United States is perhaps furthest along in this process at its site at Yucca Mountain, Nevada.

Vitrification
High-level radioactive waste is mixed with glass and poured into stainless steel canisters where it solidifies.

Primary storage
The vitrified waste is stored for 30 to 50 years above ground to allow it to cool.

Underground disposal
When primary storage is complete, the waste is buried in a deep permanent repository. Once in place below ground, the vitrified waste is enclosed in a thick metal container (overpack) and surrounded by a layer of clayey bentonite (buffer).

In Japan, low-level waste (LLW) is considered to be all disposable waste created during the operation of nuclear facilities that is not classified as HLW.

(Workers at a nuclear plant disposing of LLW)

(Contents of an LLW drum)

All commercial nuclear facilities in Japan are required to individually provide storage facilities (see photo above) for their low-level waste. LLW produced at nuclear power plants (such as work clothes, gloves, and cleaning materials) is safely stored on-site in specifically designed, temporary storage facilities. Ultimately LLW can be permenantly and safely disposed of in a landfill.

Japan's low-level waste disposal center (pictured above) is located in Rokkasho Village, Aomori Prefecture. This disposal center is part of the JNFL nuclear fuel cycle facilities. Following temporary on-site storage at nuclear plants, LLW is shipped here from individual plants throughout the country.

Metal drums are emplaced in disposal facilities; the spaces between the drums are filled with morter, and the tops are covered with reinforced concrete, forming a solid block. In order to further seal in the radioactive materials, the sides of the metal drums are covered with bentonite (a kind of clay), soil and sand are spread on top of them, and, finally, trees are planted. Each disposal pit (white, square buildings in the above image) contains approximately 5,000 metal drums.

• More information on Japan's nuclear waste disposal plans (especially for HLW) is available from the Nuclear Waste Management Organization of Japan (NUMO).
• More information on Japan's nuclear waste treatment and research programs is also available from the Radioactive Waste Management Funding and Research Center (RWMC).
• More information on key research into underground repository work being done in the northern island of Hokkaido can be found at this website for the Horonobe Underground Research Laboratory Project.