The last working reactor at Ukraine's Chernobyl nuclear power station - scene of the world's worst nuclear accident-was shut down yesterday for four months of repairs, a spokesman for national nuclear power company Energoatom said. The repair will last until November 9, the spokesman said, without giving further details. Chernobyl used to have four working nuclear reactors. The fourth reactor exploded in April 1986, sending radioactive dust over Ukraine, Russia, Belarus - all then in the Soviet Union - and parts of Europe.