Efforts to deal with problems at the Fukushima Daiichi nuclear power plant in northeastern Japan still face many challenges more than a year after the meltdown.

Tuesday will mark one and a half years since the earthquake and tsunami that caused the accident. But the leaking of tainted water and other troubles still plague the clean-up efforts.

Experts say one of the pressing challenges is how to ensure the reliability of emergency facilities built to cool the troubled reactors.

In the aftermath of the March 11th, 2011 disaster that crippled the plant, its operator, Tokyo Electric Power Company, hastily built a system to treat highly contaminated waste water and circulate it as coolant for the reactors.

The government announced last December that the reactors had been brought to a state of cold shutdown.

While the reactors' temperatures and pressures have since remained generally stable, troubles have plagued the cooling water circulation system.

So far, 56 instances of tainted water leaks have been reported. Facilities to decontaminate water have stopped 12 times due to leaks and power supply problems.

On August 30th, coolant water being poured into the 3 crippled reactors temporarily fell below the necessary levels.