Meltdown

About a year ago, I wrote this blog, in which I mentioned my “conversion” from optimistic nuclear fan to nuclear sceptic. Essentially, what changed my mind was the realization that nuclear power was subject to human frailties, combined with our natural creativity to come up with new ways to make things go wrong. Actually, that blog was prompted by the closure, on schedule, of Europe’s last RBMK reactor; the kind that went ‘foom’ at Chernobyl in 1986.

The RBMK design, from the 1950s, had serious safety flaws which contributed directly to the nuclear accident. That was why I was relatively blasé about the problems experienced in Fukushima in Japan after the earthquake and tsunami. After all, even the oldest reactor on site dated to 1971, benefitting from over a decade of design improvements compared to Chernobyl (particularly in that they incorporate a concrete containment vessel); and anyway, the three operating reactors had shut down automatically when the quake was detected, while the other three were already shut down for maintenance.

explosion siteOne thing which hadn’t occurred to me was that even when the nuclear reaction is shut down, the decay of short-lived nuclear byproducts is still generating heat. In fact, initially, it’s a substantial fraction of the amount of heat when the reactor is fully functional. For the six Fukashima reactors, that’s many megawatts of surplus heat that has to be removed from each.

It takes several days of cooling with pumped water before the heat generation subsides to safe levels. At Fukushima, electrical power for the pumps was lost in the earthquake (and, of course, the reactors themselves had stopped producing power). Backup diesel generators immediately took up the load, until these in turn were wiped out by the floodwaters of the tsunami. Batteries took over, capable of running the pumps and control systems for several hours.

What was supposed to happen during that period was that external generators would be brought in and connected up, but the reactors’ switch rooms were in basement areas and were under water.

That was why the pumping of cooling water stopped.

After a week, the situation seems only to have got worse. Several explosions and fires have been caused by hydrogen released by the reaction between water and overheating fuel rods. Stored fuel rods are boiling off the water from the pools in which they sit. In the reactor cores, the fuel rods have been damaged, and are in danger of melting.

In other words, the situation is bloody serious. And the reason is that things haven’t happened the way the designers thought. Maybe they should have predicted that the backup generators and switch rooms would be vulnerable to flooding if placed at or below ground level. Maybe they should have designed in passive cooling systems which could still work in the absence of electrical power. Maybe they should have designed a better way of storing spent fuel.

But that’s the whole point. For every improvement that closes a loophole, nature or human stupidity will find another. That’s why I think that nuclear power is simply too dangerous to pursue.

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