Today a magnitude 7.1 quake that registered an upper 6 on the Japanese scale near the epicentre in Miyagi prefecture exposed how vulnerable nuclear sites other than the wrecked plant Fukushima 1 still are.

The nuclear reprocessing plant and high level waste storage site in Rokkasho village, Aomori prefecture was without external power – again. Luckily its diesel backup generators are providing emergency power, as they already did after the site lost grid power on March 11.

Two of the three grid connections at Onagawa nuclear power station north of Fukushima are down. Backup diesels are working.

The Higashidori nuclear power station is also running on diesel power right now.

Luckily none of these sites got hit by tsunamis this time, but after the core damage and massive radiation release at Fukushima 1 following a loss of grid power and failed backup generators, any incident in which nuclear sites are only one or two failed diesel engines away from disaster will make a lot of people very nervous, especially as Fukushima 1 is still not secured almost four weeks later.

UPDATE 2011-04-08:

Grid power was restored at Higashidori at 03:30 JST on Friday, 2011-04-08. Grid power was restored at Onagawa the same morning.

Due to the loss of grid power the spent fuel pool cooling system failed for 20-80 minutes at Onagawa and Higashidori, which was not long enough for temperature to rise significantly.