As of today(13th April), an aftershock occurred at midnight of 7th Aril was the biggest one.
This magnitude 7.1 aftershock made two different nuclear plant's cooling system stop for a while.
One is Onagawa nuclear plant.
This facility has 3 reactors
The other is a Higasidohri nuclea plant.
This facility has 1 reactor.
All of them are under suspension after devastating 311 earthquake. Some of them are under suspension before the earthquake because of maintenance.
By the way, I have learned this, it is just a little complicated.
Reactors have to be kept cool when they are under suspension. In order to run the cooling system, electric power which is independent from the nuclear power plants is must.
Fukushima nuclear plant accident was triggered by the lack of electric power for cooling system. Earthquake destroyed the electric cable which bring external electric to the nuclear plant, Tunami carried diesel fuel tanks for power generator.
The reason of stopping of cooling system at Higasidohri nuclear plant is reported that one part of generator's pump was assembled in the wrong way.
There are a lot of committee, foundation, etc. etc. which declare they are founded for nuclear safety and they are receiving substantial money. Even if the committee and foundation know very well about highbrow nuclear plants, they look not to be interested in last hope generator.