Considering Monju’s peculiarities as a sodium-cooled reactor, the NRA has established a safety oversight team to follow JAEA’s activities. The decommissioning, to be completed over the course of some three decades, is divided into four phases. The immediate priority is to remove the fuel, which will be done during the first phase, to be completed by fiscal 2022 (April 2022 to March 2023).
The “Lonely” Reactor
Monju started construction in October 1985, with first criticality achieved in April 1994; it was connected to the power grid in August 1995. In December of that year, however, a sodium leakage occurred from piping in the secondary cooling system during test operations to confirm performance.
The accident had originally been classified as an “incident,” but a series of revelations and missteps soon drew the public’s ire: (1) a video showed the sodium reacting with air; (2) the public relations system at the Power Reactor and Nuclear Fuel Development Corporation (PNC), the operator of Monju at the time, was antiquated and insensitive to public expectations; and (3) operational errors and design mistakes were publicized nationwide.
Thereafter, Monju remained shut down for an extended period. and its operator (PNC) went through a series of organizational restructurings, becoming the Japan Nuclear Cycle Development Institute (JNC) and eventually JAEA. In May 2010, JAEA resumed trial operations at Monju after fourteen years.
The long shutdown of the reactor, however, produced many adverse effects, with frequent occurrences of trivial problems. In August 2010, the so-called “in-vessel transfer machine” fell into the reactor vessel when it was being withdrawn after a scheduled fuel replacement, and could not initially be recovered. Eventual removal and restoration took two years, coming at tremendous cost.
There was additionally a series of omissions in safety inspections under operational safety programs, which generated another round of public anger.
Monju became “lost technology” in the sense, at least in part, that a generation of workers retiring during the long shutdown had left an insufficient number of staff members who were proficient in its operation. The other side of the coin was that inexperienced workers caused new problems, continuing the negative spiral, with another suspension following.
Monju was supposed to have been the core of Japan’s nuclear fuel cycle policy. Nevertheless, in December 2016, the Japanese government, the implementer of that policy, decided that the reactor would be decommissioned, with few objections from the domestic nuclear industry. Though Japan advocates a policy based on the nuclear fuel cycle, it has no means for implementing one. “Monju” was essentially abandoned.
Monju was believed to be an ideal reactor, “producing more fuel than it consumed.” Its life of nearly thirty-five years, however, was mostly a lonely one.
