After the venting failed at the Fukushima plant, the hydrogen gas fueled explosions that spewed radioactive materials into the atmosphere, reaching levels about 10 percent of estimated emissions at Chernobyl, according to Japan’s nuclear regulatory agency.
It’s a very interesting story and at least feels like the start of the narrative of what happened at Fukushima Daiichi. But the discussion of valves and venting careens off in very odd ways.
American officials had said early on that reactors in the United States would be safe from such disasters because they were equipped with new, stronger venting systems. But Tokyo Electric Power Company, which runs the plant, now says that Fukushima Daiichi had installed the same vents years ago.
Gulp! Did anyone ask the Nuclear Regulatory Commission or perhaps a utility here in the states about this? Nope.
Tokyo Electric has said the valves did not work at Fukushima Daiichi after the power failed.
That would suggest that operators of similar plants in the United States and Japan could protect reactors by moving generators to higher floors if the equipment is currently in places that could be affected by tsunamis or flooding from rivers.
But a redesign of the venting system itself might also be necessary.
Matt Wald, who wrote this story, seems to have had second thoughts, particularly about the similarity of Japanese and American plants when it comes to the implementation of valves.
Yet since 1989, when the Nuclear Regulatory Commission told American plant operators that it liked the venting idea, the thinking has changed further on the operation of boiling water reactors. For one thing, most American reactors have been allowed to bolster their steam output so they can make more electricity. To get permission to do this, a reactor owner must arrive at a calculation that the emergency core cooling system could still work in case of excess heat.
Some plants now anticipate high pressure, and, in fact, require it for safe operation.
So there was divergence, at the least. Here’s a little more, specific to valves:
If the vent is operated with an electrically driven valve, as in the current design, operators can control how much steam they let out and how much pressure they keep in. The alternative is probably a rupture disk, a thin piece of steel that breaks at a pre-designed level, just below the pressure that is likely to rupture the containment.
Wald goes on to express some doubts, but the point is that he learned more about valves and venting and shared that with his readers. What started out fairly damning became considerably less so with some further research.
---
Some of the concern with valves comes from an engineer named Anthony Sarrack:
Anthony Sarrack, working with another Monticello engineer, wrote a white paper in 2005 raising concerns about a venting system designed to rid boiling water reactor containment vessels of excessive pressure during accidents by releasing it outside.
…
But Sarrack says he left the industry in 2006 after spending a frustrating 19 months trying to persuade the regulators and industry officials to consider his proposed solution.
"As an industry, they don't want to make changes," he said.
Monticello is in Minnesota, which is why reporter David Shaffer tells this story in the Minneapolis Star-Tribune.
The Union of Concerned Scientists has caused some mischief with Sarrack’s findings, but as usual, there’s more to the story. There’s this:
The Monticello plant has a backup system powered by compressed nitrogen that officials said would power the vents if the plant lost all power. The venting system has never needed to be used, the utility said.
So one of the big concerns – that the vents would lose power if a plant does - is not really so.
Then, this:
Doug True, president of Erin Engineering and Research, a Walnut Creek, Calif., nuclear consulting firm, said Sarrack's proposal "never got any traction" in the industry because many people disagreed with its merits.
"There was lot of consideration on how to use these vents, and on balance people generally felt the way they were installed was the preferred way," he said.
So Sarrack may have been frustrated that his ideas didn’t get much pickup – fair enough - but suggesting that they weren’t given consideration isn’t really true. (Sarrack also says his bosses at Monticello never tried to silence him and that he later left of his own accord – so conspiricists do not have much of a stick to use here.)
The subject is a little esoteric, I know, but because the New York Times made a pitch of it, it picked up more interest than it probably warranted. But the interesting thing is that reporters – including the original reporter - kept digging into it and finding it, at best, rather problematic. On the other hand:
An NRC spokeswoman said the vents will be reviewed as the agency studies the lessons from the Fukushima disaster.
Well, why not? Where’s the harm? It’s even as it should be.
Monticello. The valves are – okay.
0 comments:
Post a Comment