Thermometers a Hot Topic at Fukushima Daiichi / Wall Street Journal / February 15, 2012 /

Fukushima Daiichi operator Tokyo Electric Power Co. on Tuesday said that one of the thermometers attached to its No. 2 reactor was almost certainly on the blink.

The news prompted a collective sigh of relief that the steadily rising temperatures the thermometer had been logging weren’t a sign that the damaged reactor was once more spinning out of control.

But the malfunctioning thermometer is also the latest troubling reminder of how fragile Tepco’s grip on the stricken nuclear plant is.

The antics of that thermometer -– one of six key gauges that tell the outside world how hot the fuel in the crippled No. 2 unit likely is — have transfixed Fukushima Daiichi watchers this month. The No. 2 reactor is one of those whose fuel rods are thought to have melted during the March accident at the nuclear plant.

In December, Tepco said that all the reactors had cooled to well below 100 degrees centigrade, meaning they were no longer releasing radiation or in danger of restarting a nuclear reaction. But in early February, Tepco said one of No. 2’s thermometers was registering steadily rising temperatures — from around 50 degrees C on Feb. 1 to around 70 C five days later.

By Sunday, Feb. 12, Tepco said the temperature was heading up toward 90 C, despite weeks of cooling counter-measures like an increase in the amount of water pumped into the reactor, and the injection of boric acid -– a chemical that helps prevent a nuclear reaction from occurring.

By Tuesday, the thermometer reading was hovering around 250 C – even as the two others in closest proximity were logging a steady 30 C. Tepco said that discrepancy, as well as the lack of other signs of a nuclear reaction such as an increase in steam or radiation levels, probably meant a broken wire somewhere.

Still, a faulty thermometer at No. 2 raises troubling questions. With all the punishment Fukushima Daiichi’s equipment has gone through –- nuclear meltdowns and explosions, not to mention the magnitude 9 earthquake and tsunami that started everything off – it’s no wonder things are breaking down.

But radiation levels are still so high around many of the reactors that the equipment can barely be checked, let alone replaced. That’s the case with the thermometer in question, which is inside the highly radioactive containment vessel of No. 2.


Other Reactor 2 Thermometer News:

TEPCO: No.2 reactor thermometer likely broken – NHK
Possible sensor failure throws Fukushima reactor temp. data into doubt – Mainichi Daily

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