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Severe flooding in Nebraska is threatening to swamp the Cooper Nuclear Station near Brownville. The reactor last faced a similar threat from the rising Missouri River during the summer of 2011. Workers have been bolstering a levee with sandbags and making other preparations. /1 
Although the plant operator insists there is no danger, it's worth noting that Cooper Nuclear Station uses a General Electric Mark 1 boiling water reactor, identical in design to the 4 reactors that were flooded and subsequently exploded eight years ago this week in Fukushima. /2
The Fukushima reactors were swamped by a massive tsunami, which destroyed all their backup power generators. With offsite power knocked out and onsite backups unavailable, the reactors overheated, the fuel melted, and they exploded. Spent fuel in cooling ponds also overheated. /3
Absent the tsunami, that scenario is unlikely in Nebraska, thanks in part to the post-Fukushima installation of portable pumps & generators. But it's not impossible. Earlier today, the Nebraska Public Power District declared an "unusual event" as the river continues to rise. /4X
CLARIFICATION: The photo in the tweet above shows Cooper Nuclear Station on June 24, 2011, the last time the Missouri River overflowed its banks and threatened to flood it. Although it illustrates the danger currently facing the reactor, today's floodwaters are not yet this high.
However, if this forecast is correct, they soon will be.
UPDATE: This afternoon, the Nebraska Public Power District began shutting down the Cooper Nuclear Station reactor as floodwaters from the Missouri River reached record heights. omaha.com/news/cooper-nu…
So @NEMAtweets & @NPPDnews assert the 2011 photo above is "FALSE NEWS." Here's a very similar 2015 photo via Google Earth. The complex sits on the banks of the Missouri River. A NPPD spox for says it's 13' above natural grade, but that does not necessarily guarantee protection.
Why does this matter? Because the design basis threat for a nuclear reactor usually doesn't take into account all conceivable risks, just the ones deemed most likely. For example, the Fukushima Daiichi complex was built ~38' above sea level. But the 2011 tsunami was ~49' high.
UPDATE 2: As of late this AM, the reactor remains operational. It is required to shut down when the river reaches 45', but although the National Weather Service gauge just upstream at Brownville now reads 45.7', a plant spox says readings there are lower. ketv.com/article/cooper…
