This is the first time vitrification has take place since a decommissioning plan for the plant was approved last month by the Nuclear Regulation Authority.
Decommissioning will take about 70 years and is estimated to cost $9bn.
The first major target is to complete the vitrification of all the HLW by the end of fiscal year 2028.
The state-backed JAEA applied for permission to decommission the facility in June 2017.
The Tokai plant began full operation in 1981 but had stood idle since 2006 when a contract for reprocessing used fuel from commercial power reactors came to an end. Since then, only vitrification activities had resumed at the facility, according to Jaif.
The facility was built as part of Japan’s plans to establish a nuclear fuel cycle, in which all spent fuel is reprocessed to extract its plutonium and uranium to make more fuel.
In 2014, the JAEA decided to permanently retire the plant because it would not be financially viable to invest in seismic safety as required by Japan’s strict post-Fukushima regulatory standards.
According to the JAEA the plant has reprocessed about 1,052 tonnes of used fuel comprising 88 tonnes of fuel from the Fugen experimental advanced thermal reactor , 644 tonnes of boiling water reactor fuel, 376 tonnes of pressurised water reactor fuel and nine tonnes of fuel from the Japan Power Demonstration Reactor.