Dithering and Explosions and Venting- Oh My!

Crossposted from The Stars Hollow Gazette

Fukushima Update- Part 1

First of all let’s survey the damage.  Reactors 1, 2, and 3 suffered core meltdowns that breached the steel containment vessels leaving leaks that have been releasing highly radioactive cooling water AND molten nuclear fuel into the concrete basement below the vessel.

This is kind of a containment vessel too and while there are no current indications that nuclear reactions are continuing in the escaped fuel slag that would burn through this floor and into the uncontained earth foundation of the plants, they’re not waterproof and there is no doubt at all that millions of gallons of highly radioactive water and perhaps some fine particulates are leaking into the environment uncontrolled.

This has led to a re-evaluation of cooling and clean-up strategies that continues because there are no really good answers.  Several radiation peaks indicating continued nuclear reactions in the melted and puddled fuel mean you can’t stop pumping water and the leaking makes it difficult to maintain a sufficient amount in the containment vessel to moderate the reaction (that’s why you get the peaks when the level dips too low).

There’s a continued risk of hydrogen explosions too and one of the reasons I mention that is because the one bit of good news is that it does not look as if the large spent fuel pond at the non working (at the time of the accident) Reactor 4 is having uncontrolled reactions.

At the moment.

A lot of the damage was caused by hydrogen explosions which in turn was caused by malfunctioning vents of the same type currently in use at many U.S. Nuclear Power Plants

Japan Nuclear Watch, May 19: Critical Safety Vent Failures Could Happen Here Too

By: Scarecrow, Firedog Lake

Thursday May 19, 2011 7:19 am

As we’ve explained in previous Japan Watch posts, that sequence led inexorably to near total meltdown of the fuel core inside the reactor vessels at Units 1-3. (All of Unit 4’s fuel was in the storage pool, which presents problems.) TEPCO now concedes these meltdowns were likely total.

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Although earlier expert analyses and TEPCO announcements suggested only partial meltdowns and varying levels of water covering parts of each reactor’s core, it now appears the cores were completely uncovered for some period early on - within the first hours or days - resulting in near total meltdown at each unit. That means the melted fuel is now puddled at the bottom of each reactor vessel, though it is thought (because of low temperatures) to be covered with whatever cooling water can be injected into each reactor vessel.

Earlier this week, they realized Unit 1’s vessel has one or more holes, leaks, allowing water and possibly melted fuel to leak out of the vessel onto the containment structure floor. The reports vary, but they suggest that tons of water, which they’ve been injecting into the core in desperate efforts to keep the core covered, have now found its way into the reactor building’s basement. Water from other units has leaked from other places, including adjacent turbine buildings and some has reached the ocean.

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As we know, there were hydrogen-related explosions in all four units – that is, they waited too long, or, as they’re now discovering, the venting systems failed.

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The Times report very helpfully reminds readers that all of the US reactors with the same GE design have essentially the same (new! improved!) venting systems as the ones that failed at Fukushima Daiichi. GE didn’t comment on the story.

So the next time someone tells you that, unlike those careless Japanese utilities and not too diligent regulators, we have much safer systems and our safety measures are “safer,” just remember this story, because it ain’t so.

The Times report to which Scarecrow refers is this one-

In Japan Reactor Failings, Danger Signs for the U.S.

By HIROKO TABUCHI, KEITH BRADSHER and MATTHEW L. WALD, The New York Times

Published: May 17, 2011

TOKYO – Emergency vents that American officials have said would prevent devastating hydrogen explosions at nuclear plants in the United States were put to the test in Japan – and failed to work, according to experts and officials with the company that operates the crippled Fukushima Daiichi plant.

The failure of the vents calls into question the safety of similar nuclear power plants in the United States and Japan. 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.

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Tokyo Electric in recent days has acknowledged that damage at the plant was worse than previously thought, with fuel rods most likely melting completely at Reactors 1, 2 and 3 in the early hours of the crisis, raising the danger of more catastrophic releases of radioactive materials. The company also said new evidence seemed to confirm that at Reactor No. 1, the pressure vessel, the last layer of protection, was broken and leaking radioactive water.

The improved venting system at the Fukushima plant was first mandated for use in the United States in the late 1980s as part of a “safety enhancement program” for boiling-water reactors that used the Mark I containment system, which had been designed by General Electric in the 1960s. Between 1998 and 2001, Tokyo Electric followed suit at Fukushima Daiichi, where five of six reactors use the Mark I design.

Most the damage at Reactor 4 was cased by an explosion in the vents that it SHARED with Reactor 3.

But there is also this follow up report, also from the Times–

NRC Finds Many U.S. Nuclear Plants Ill-Prepared to Handle Simultaneous Threats

By PETER BEHR of ClimateWire, The New York Times

Published: May 19, 2011

Something under one-third of the 104 U.S. reactors were found to have some vulnerabilities to extreme emergencies, according to the NRC, which is preparing a summary of its post-Fukushima findings.

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At a time when the NRC and industry leaders are calling for a rigorous safety culture within the U.S. nuclear industry, the inspection findings raise questions about whether some plants were following the letter of requirements but not prepared for “unthinkable” events.

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The plant owners’ responses to beyond design basis threats are usually voluntary. “We keep saying, ‘Oh, these are beyond basis events therefore we don’t’ get involved.’ We are happy that the industry responded. We look at it once. That’s it. In the future it’s up to them. I am really bothered by that.”

This piece contains details safety issues at a number of U.S. Nuclear Plants including Indian Point (NYC) and Millstone (Connecticut).

Coming next- The Big TEPCO Bailout.