Aftershocks jolt eastern Japan; extra nuclear safety steps ordered

Japan has ordered nuclear plant operators to put in place new safety measures by April 28 in addition to steps imposed late last month that are soon due for checks by authorities to confirm implementation, the trade ministry said, as another series of aftershocks jolted the eastern region.

There has so far been no serious damage reported at five nuclear plants in northeast Japan, including the crippled Fukushima Daiichi plant, as a result of today's magnitude-6.6 earthquake.

The order came after a 7.4 magnitude aftershock on Thursday, the biggest since the deadly March 11 quake, had temporarily disabled all three power lines supplying offsite power to Tohoku Electric Power Co's Higashidori plant, which has been shut for regular maintenance since February.

The ministry's Nuclear and Industrial Safety Agency (NISA) on Saturday ordered nuclear power companies to install at least two emergency diesel engines even at reactors that are not in operation and are kept at low temperatures, such as at the Higashidori plant.

Previously, one emergency power source had been required to be ready for use at reactors under such conditions, while only reactors that are in operation or are shut but not fully cooled down had been required to have two or more power sources.

Aiming to avoid a repeat of the tsunami-triggered crisis at the Fukushima Daiichi plant, the ministry on March 30 ordered nuclear plant operators to take immediate steps to improve emergency preparedness.