The Horonobe Underground Research Center of the Japan Atomic Energy Agency (JAEA) have been undertaking research and development (R&D) on geological disposal technologies for high-level radioactive waste by constructing and utilising the Horonobe Underground Research Laboratory (URL). Since Japan's fundamental policy is that HLW from the reprocessing of spent nuclear fuel is disposed of safely and over a long period of time in a deep geological repository, the strengthening of the scientific and technological basis for the geological disposal project and the associated safety regulations has been a main focus of our R&D.