I.A.E.A. Says Fukushima Plant Operator Should Prepare Better TOKYO - The operator of Japan's stricken Fukushima nuclear plant should stop relying on stopgap measures and better prepare for the unexpected, the United Nations nuclear watchdog agency said Monday, even as a cooling system at the plant was once again shut down because of a dead rat. A team from the International Atomic Energy Agency praised the operator, Tokyo Electric Power Company, for stabilizing the Fukushima Daiichi plant and making progress in the complex task of dismantling its three damaged nuclear reactors. A huge earthquake and tsunami two years ago knocked out the reactors" cooling systems, causing their cores to melt down; the accident spewed radiation across northeastern Japan Juan Carlos Lentijo, the director of the nuclear fuel cycle and waste technology division at the agency and the team's leader, said that the company had accomplished the most urgent job, cooling the damaged reactors, in very difficult conditions of high radiation. However, he said, "there is still room for improvement." He said that while the company, called Tepco for short, has been working to make the plant safer, it was often doing so "with temporary systems or mobile systems - there is a need for more permanent systems." The makeshift nature of some of those cooling systems was exposed again on Monday when Tepco said it had temporarily switched off one of them after a dead rat was found nearby. The system was off for four hours while workers made sure there was no damage to electrical circuits. Last month, a short circuit caused by a dead rat shut down a similar cooling system for more than a day. Tepco said that neither shutdown created any danger, because the systems were cooling pools containing spent fuel, which give off relatively low levels of heat and would remain safe even if left uncooled for a week. There have also been a number of leaks of highly contaminated water from underground storage pools at the plant. Though the leaks have generally been small, they have raised public concerns about whether Tepco was doing enough to stabilize the plant. Mr. Lentijo of the U.N. agency said that Tepco needed to upgrade sensors and other mechanisms for identifying problems so that it could respond more promptly. He said it was essential for Tepco to strengthen its ability to cope with unexpected events as it continues to clean up the damaged reactors, a complex job that may take 40 years. Mr. Lentijo said the company's biggest immediate challenge was managing the huge and growing amount of radioactive water at the plant. Some 100,000 gallons of groundwater a day enters the damaged reactor buildings and becomes contaminated. Mr. Lentijo said his group gave Tepco advice on how to safely store the water in tanks and underground pools that now occupy much of the grounds of the plant.