Ah, the horror, the horror....
Monju is a fast breeder reactor that uses sodium as coolant, which catches on fire on contact with air. It uses MOX-fuel.
3.3-tonne, 12-meter "In‐Vessel Transfer Machine" fell into the reactor vessel on August 26, 2010. The manager at the plant in charge of fuel exchange committed suicide in February this year.
From Mainichi Shinbun English (5/24/2011):
TSURUGA (Kyodo) -- The Japan Atomic Energy Agency began preparatory engineering work Tuesday to set up equipment it will use to retrieve a device that fell inside the vessel of its prototype fast-breeder reactor Monju in Fukui Prefecture last August, agency officials said.
The agency aims to collect the cylindrical 3.3-ton device together with part of the vessel's upper lid by mid-June to get the reactor back to normal by autumn, allowing the resumption of a test run of the 280,000-kilowatt prototype, the officials said.
But it is unknown when the test run will begin at the unit on the Sea of Japan coast as Prime Minister Naoto Kan has declared a review of Japan's basic energy plan following the nuclear accident at the Fukushima Daiichi power plant caused by the March 11 earthquake and tsunami.
After the Aug. 26 accident, the agency tried in October to recover the device used in fuel exchange but failed as it had become misshapen, preventing its retrieval through the upper lid.