The operator of Japan’s crippled Fukushima Dai-ichi nuclear plant is preparing to open a door of a reactor building to allow workers to install a cooling system and equipment to prevent an explosion.

Tokyo Electric Power says radiation that will be released by ventilating the Unit 2 reactor Sunday will be too small to threaten human health.

Meanwhile, more radioactive water is pooling at the tsunami-hit nuclear plant as workers scramble to restart a key cleanup system. It was shut down on Saturday, hours after beginning full operations, because a component reached its radioactivity limit faster than expected.

Contaminated water could overflow within two weeks if action is not taken. At one location, water is 14 cm from spilling.

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