Vitrification of high-level radioactive waste (HLW) has been scientifically proven to be the safest and most effective means of dealing with this material. Since Japan is pursuing a "closed" nuclear fuel cycle, the vitrification of 3% of spent fuel (depending on initial enrichment level) is the most logical method of disposal. Once the interim "cooling off" period of this waste has ended in 30 - 50 years, final disposal of the waste will commence.

After the interim storage period, allowing for the decay of most short-lived fission products, and thus the cooling of the vitrified high level waste in corrosion-resistant canisters, it can be disposed of in a deep geological site for isolation from the biosphere.

Geological disposal (see graphic below) of high level and long-lived waste is recognized world-wide as a technically sound concept. The multiple barriers enclosing the waste, that is to say the borosilicate glass itself, the canister as well as other engineered barriers, and the rock formations surrounding the repository (natural barrier) will prevent a return of radioactivity from the waste to the human environment over a very long period.

Japan is undertaking such a program, which involves several successive careful actions, to design and construct the most suitable repository site in terms of technical feasibility, environmental impact, economic considerations and public acceptance.

Technical developments are being continued by dedicated organizations. Current plans expect that repository operations in Japan will start by the 2030s. More on the handling of nuclear wastes can be found in the Nuclear Waste Management section.