Japanese Prime Minister Naoto Kan has appointed two new cabinet ministers to spearhead crisis management at the crippled Fukushima nuclear power plant and reconstruction of the country's earthquake and tsunami-devastated northeast coast.

The appointments, announced Monday, come as engineers at the plant activated a water decontamination system described as a key step toward shutting down reactors disabled by the March 11 twin disasters.

The Tokyo Electric Power Company said its engineers were using the decontaminated water to cool the cores of the number one, two and three reactors Monday afternoon. They hope to begin full-scale operation of the system soon.

TEPCO described the system's activation as a vital step in its plan to achieve a safe shutdown of the reactors by the end of the year. The company is running out of places to store an estimated 100,000 tons of radioactive water that has been poured into the reactors since their regular cooling systems were disabled on March 11.

Prime Minister Kan has faced harsh criticism in some quarters for his handling of the nuclear crisis and what critics say is slow progress in helping tens of thousands of survivors. His new appointments move former environment minister Ryu Matsumoto to the reconstruction post and special aide Goshi Hosono to oversee disaster management at the plant.

The new decontamination system will allow operators to keep recycling the same water through the reactors while emptying contaminated water from the basements and tunnels of the reactor buildings. That will clear the way for other repairs.

The breakthrough, which follows setbacks that delayed the activation of the system for a week, also relieves concerns that radioactive water will overflow the existing reservoirs and spill into the ocean.

The reactors at the plant have been leaking radiation into the atmosphere and ocean since the March 11 earthquake and tsunami, which left about 23,000 people dead or missing.