NEW : Tokyo Electric plans a new structure to support the No . one unit 's spent nuclear fuel pool . Robots probe darkened reactor No . one . Radiation readings in 4 town are halfway to the government 's evacuation threshold . Iodine-131 has a radioactive half-life of eight days , and the increase could be either from a fresh leak or from sediment stirred up while placing steel panels around the intakes , said Hidehiko Nishiyama , the top spokesman for Japan 's Nuclear and Industrial Safety Agency . Hosono says it will take Saturday to wind down the nuclear crisis .
NEW : Tokyo Electric plans a new structure to support the No . one unit 's spent nuclear fuel pool . Robots probe darkened reactor No . one . Radiation readings in 4 town are halfway to the government 's evacuation threshold . Hosono says it will take Saturday to wind down the nuclear crisis .