On the Temperature Increase at Fukushima Daiichi Unit #2

Over the past 24 hours we've seen a number of account concerning rising temperatures inside reactor #2 at Fukushima Daiichi. While we noted this item over at SafetyFirst.nei.org yesterday morning, some accounts of the news have been rather breathless.

If you'd like a sober account of what's actually happening there right now, I'd suggest reading the following account from World Nuclear News. Here's the relevant passage:

This stability of unit 2 was disturbed for a few days, however, when Tepco tried to improve cooling further by tuning the rates of water injection.

[...]

After making this change, Tepco noted a tendency for increasing temperature at the bottom of the reactor vessel. Within a matter of hours the company decided to reverse the change and restore the previous injection rates, but the temperature continued to slowly rise.

Two of the three temperature sensors at the bottom of the reactor vessel edged up by about 2 degrees C. The third, however, rose by around 20 degrees C to hit 72.2 degrees at 5.00am today. Tepco acted to stem this increase by injecting an extra cubic metre of water per hour through the feedwater line, and this stabilised the sensor at about 70 degrees C. It has since decreased to 68.5 degrees C, while the other two sensors were at a new low of around 41 degrees C.

Tepco was able to discount recriticality as a potential cause of the temperature rise after conducting an analysis of charcoal filters in the containment gas control system. These showed very low traces of fission products that were below the threshold that would indicate criticality. Nevertheless Tepco this morning injected boric acid into the reactor vessel as a precaution and increased the core spray injection rate by three cubic metres per hour.

The bottom line here: at no time did the temperature of the bottom of the reactor vessel exceed, or even approach, 100 degrees C, which was one of the important conditions TEPCO has to maintain for cold shutdown conditions.

We're keeping an eye on this and will report back if events warrant.

Comments

Activists' Claims Distort Facts about Advanced Reactor Design

Below is from our rapid response team . Yesterday, regional anti-nuclear organizations asked federal nuclear energy regulators to launch an investigation into what it claims are “newly identified flaws” in Westinghouse’s advanced reactor design, the AP1000. During a teleconference releasing a report on the subject, participants urged the Nuclear Regulatory Commission to suspend license reviews of proposed AP1000 reactors. In its news release, even the groups making these allegations provide conflicting information on its findings. In one instance, the groups cite “dozens of corrosion holes” at reactor vessels and in another says that eight holes have been documented. In all cases, there is another containment mechanism that would provide a barrier to radiation release. Below, we examine why these claims are unwarranted and why the AP1000 design certification process should continue as designated by the NRC. Myth: In the AP1000 reactor design, the gap between the shield bu...

What Happens During a Refueling Outage?

You may have noticed over the past few weeks that a number of nuclear plants are shut down for refueling outages or are resuming operations after just returning from one. This type of routine outage usually occurs in the spring or fall when electricity demand is low so that nuclear reactors can replace about one-third of the spent fuel rods with new fuel and conduct other routine maintenance and repairs at the plant. To get a better sense of how refueling works at a nuclear energy facility, I spoke with Marcus Nichol, NEI’s senior project manager for used fuel storage and transportation, and asked him to explain the basics. Why does a nuclear plant need to replace one-third of its fuel? Nichol: The main purpose of a refueling outage is to replace older fuel that is depleted—meaning it can no longer efficiently produce energy from nuclear fission reactions—with new fuel. This “used fuel” has typically been used in the reactor for four-and-a-half to six years before it is pe...

How Much Land Does Nuclear, Wind and Solar Really Need?

Not too long ago, we reviewed a report that looked at nuclear energy (and other energy sources) as biodiversity agents. This had to do, in part, with the amount of land a facility needs to function. Nuclear energy and fossil fuel plants use relatively little, wind farms and solar arrays quite a lot of land . Based on an objective and transparent analysis of our sustainable energy choices, we have come to the evidence-based conclusion that nuclear energy is a good option for biodiversity conservation (and society in general) and that other alternatives to fossil fuels should be subjected to the same cost–benefit analyses (in terms of biodiversity and climate outcomes, as well as sociopolitical imperatives) before accepting or dismissing them. Writer Barry Brook, who collected 75 scientists to endorse his paper, is interested in land use as it impacts flora and fauna. Biodiversity concerns do not get as much play as they might – and, when they do, it annoys many when land is withdraw...

NEI Nuclear Notes

Search This Blog