I dunno about 70%, but that one plant is obviously trying to avoid a meltdown and the other one nearby is shutdown as well. As a result a lot of connected hydroelectric and gas plants connected to them shut down as well. A lot of the north should still be powerless.
As for Niigata, they got hit by the second 6.6 quake. The 8.9 probably felt like a 6 or so to them as well.
Edit: Apparently 10 Nuclear plants are shutdown. No idea what coverage area that is.
Edit #2: And to brighten your day I just found and article saying that no fatalities have been reported from the Niigata quake. Just sit tight I suppose. Besides power, most phones are down as well ... some from obvious damage, others intentionally shut down for emergency uses only.
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