The International Atomic Energy Agency (IAEA) says there have been some positive developments in the last 24 hours at Japan’s Fukushima nuclear power plant, but that the overall situation still remains very serious.

Special Adviser to the IAEA Director General on Scientific and Technical Affairs, Graham Andrew, said Monday that work to connect power from the substation to the reactor building is continuing under difficult conditions.

He said the situation in the reactor’s spent fuel pools is relatively stable, but is still of concern. He added that a positive development is that cooling has been restored to the reactor pressure vessels in reactors number five and six. Andrew said the progress means that the reactors are in a safe mode as cooling systems are stable and under control by being at low temperatures and pressures within the reactor.

Meanwhile, U.S. Energy Secretary Steven Chu told CNN during an interview on Sunday that he believes the worst of Japan’s nuclear crisis was over.