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Fukushima Radiation Levels High, But Leak Plugged
jmcvetta wrote in with a story about Fukushima radiation levels so high that monitoring devices have been rendered useless. Levels outside the buildings exceed 100 millisieverts in some places. But the good news is that the leak is patched using 1500 liters of sodium silicate.
Helpful radiation chart for those of us who don't have a clue whether 100 millisieverts is a tiny dose or enough to create a Godzilla monster.
In short, it's definitely into the "You might want to step-up your planned schedule on those cancer screenings" territory.
SJW: Someone who has run out of real oppression, and has to fake it.
100 millisieverts? Per hour? Per day? Per century? Thanks, Slashdot, for giving us a useless number.
"I zero-index my hamsters" - Willtor (147206)
The leak that was stopped was from a drain pit to the ocean. The reactor itself is still leaking highly radioactive water. They're running out of places to put it.and are frantically building tanks and ponds.
There is an estimated 50,000 tons of water still on site that will need to be disposed of one way or the other. About 500 tons are pumped into reactor pressure vessels for cooling every day. Some recent information on this is reported here by NHK: Workers face challenge of water storage
To put 50,000 tons of water in perspective, a super tanker will carry about 172,000,000 gallons of oil. 50,000 tons of water is ~12,000,000 gallons. One super tanker could carry all the water on site plus and also receive all new water pumped into the reactors for the next 1332 days. No, I don't need the plausibility of this explained to me; this is an attempt to provide some scale to the problem.
Lurking at the bottom of the gravity well, getting old
Workers are pumping nitrogen into one of the reactors at Japan's damaged nuclear plant in an attempt to prevent an explosion caused by dangerously overheated fuel rods.
Officials at TEPCO, which operates the Fukushima plant, said a dangerous hydrogen buildup is taking place at its number-one reactor. Japan's NHK television quoted officials saying hydrogen is accumulating inside the reactor's containment vessel - an indication that the reactor's core has been damaged.
Crisis at Japan Nuclear Plant Shifts to New Blast Risk
Chemistry 201: Why Is Fukushima So Gassy?
But there are reasons...that Fukushima is particularly vulnerable.
One is its recent use of seawater to cool the reactors's fuel rods and cores. In addition to the oxygen in water molecules, cold seawater can hold a great deal of dissolved oxygen gas. But warm water cannot; so as the seawater was heated in the reactor, the dissolved oxygen emerged and gathered in the empty space above the water.
(Ordinary reactor cooling water has had the oxygen removed from it by plant operators to reduce the possibility of rust.)
In addition, gamma radiation from the nuclear fuel in the reactor would continuously produce small amounts of hydrogen and oxygen by breaking up water molecules --- and the normal method of recombining these elements into water at such plants in a controlled fashion is no longer available.
Plants of the Fukushima variety usually have catalytic converters that accomplish that at the point where steam has run through the turbine and is condensed back into water for another trip through the reactor. But that path has been closed since the plant lost power at the moment of the March 11 earthquake.
Hydrogen can also emerge from the zirconium metal used as fuel cladding. One of the lessons of the Three Mile Island accident in 1979 near Harrisburg, Pa., is that when the cladding comes into contact with steam rather than water, it goes through a reaction that is akin to rusting; it picks up oxygen from the water molecule and gives off hydrogen.
This only happens at high temperatures, but uncertainty reigns at the moment about temperatures in the Fukushima reactor cores. With some cooling channels blocked, they are likely to have hot spots.
By design, boiling water reactors like these have far more zirconium metal in them than pressurized water reactors do. They boil water directly in the core, covering the fuel assemblies with a water/steam mixture rather than keeping them immersed in water. The water has to be directed to each individual fuel assembly and therefore each sits in its own zirconium box.
All of that zirconium is available for an oxidation reaction with steam in which the metal absorbs oxygen from water and turns to a powdery rust, releasing hydrogen.
Well it does look like they have finally got this under control, at least for the most part.
Plugging one leak does not mean the situation is even close to being under control. Hidehiko Nishiyama, a spokesman for the Japan's Nuclear and Industrial Safety Agency, said:
... no further leakage has been detected from the pit. But there is a possibility that the water, which has lost an outlet, could show up from other areas of the plant.
The highly radioactive water is believed to have come from the No. 2 reactor core, where fuel rods have partially melted, and ended up in the pit. The pit is connected to the No. 2 reactor turbine building and an underground trench connected to the building, both of which were found to be filled with highly contaminated water.
Thousands of tons of highly radioactive water had already been found in many places outside the reactor buildings even before the direct leak into the ocean was discovered. Is there anything more substantial than crossed fingers and wishful thinking that makes you think the flow of highly radioactive water will halt now that they've plugged the direct outlet into the ocean?
In addition:
According to estimates by TEPCO announced Wednesday, 25 percent of the nuclear fuel rods have been damaged at the No. 3 reactor. The company earlier said that 70 percent of the No. 1 reactor's fuel rods and 30 percent of the No. 2 reactor's fuel rods have been damaged.
Nishiyama said past hydrogen explosions have likely occurred due to hydrogen accumulation caused by the reaction of melted fuel rods' zirconium with steam from the coolant water. But now there is concern that hydrogen could accumulate in the No. 1 reactor under a different process involving radiation-induced decomposition of water into hydrogen and oxygen.
The installation of billion dollar radiation shielding around the reactor buildings has to be delayed until at least September because, of the high level of radioactivity. In other words, they need to wait for the current levels of radioactivity to decay before it is safe enough to install radiation shielding. So, ISTM, the September date is optimistically assuming the ongoing contamination will magically stop. Yet, even if the shielding could be installed tomorrow:
Some experts were sceptical about the feasibility of the measure as the step would have only limited effects in blocking the release of radioactive substances.
That is because the bulk of the release of radioactivity is downward in the water, not upward into the air. The shielding story highlights the challenge they are up against. The level of radioactivity around the plants (and in the plants) is so high, it is impeding their efforts to control the amount of radioactivity escaping. For example, work to restore the primary cooling system for reactor #2 has been halted for almost two weeks because of the high levels of radiation in the turbine building. The radiation level, due to highly radioactive water in the building, is over one sievert per hour. So a worker hits their lifetime dose limit less than 15 minutes. Someone who lingers there for an 8 hour shift will die regardless of what treatment they receive. It's been reported that the level of radioactivity in reactor buildings 1, 2, and 3 is too high to measure.
They are pouring hundreds of tons of uncontaminated water onto (into?) the reactors every day to cool them. Thousands of tons of this water has come out contaminated with radioactivity and has flooded the turbine buildings, tunnels outside the buildings, and the ground. They don't know how the water is getting contaminated or the routes it is taking
We don't see the world as it is, we see it as we are.
-- Anais Nin
I get what you are trying to say with this, but honestly when everyone says its safe, yet these kind of "accidents" can still occur it makes you step back and really weigh the positives and negatives.
For instance, in these plants they are using plutonium mox fuel. That shit has a halflife of 20,000 years. So it wont be completely nonreactive for approximately 250,000 years or 12000 human generations. Sure it shouldn't happen, and there were no doubt many mistakes by this particular company. But even if it is a possibility that this would happen, and it obviously is, should we not reconsider the long term environmental and other effects when we are possibly going to be affecting forward 12000 generations in the future?
So far in my life time (30 years) there have been 3 major nuclear accidents. Does this not at least warrant a second look? There are plenty of these unsafe plants active in the world, and yes I am aware there are safe reactor designs (CANDU). But when you factor in human greed, nuke plants run by the lowest bidder, should we even be doing it?
I was VERY pro nuclear power before this complete mess that has happened. Even though we will run out of uranium by 2100, even though fuel stays reactive for tens of thousands of years. But honestly, if the japanese cant even do it right, what hope do we have for any country out there?
The timescales alone are enough to make one pause. Can you really trust the next 12,000 generations of man to not have any accidents with spent fuel? Is that something that we should be burdening our future generations with for a short term gain today?
Further reading: 'No safe levels' of radiation in Japan
As a potential lottery winner, I totally support tax cuts for the wealthy