78% reduction in radiation dose around Fukushima Daiichi Nuclear Power

This was just reported today. Sounds pretty good. But I still wonder about the soil contamination around the rice paddies. Although they are not in use, I wonder what the radiation level would be.
A study by the Nuclear Regulation Authority found that radiation dose near the ground surface, a radius of 80 km from TEPCO's Fukushima Daiichi Nuclear Power Station, was reduced by about 78% on average from the year of the nuclear accident.

One lone piece of good news!

I'll take it, true or not... variables or fudged methodology, or not.

I wonder if after the smoke clears, years down the line, if people will consider that area as "cursed" or "taboo" due to the ineptitude of the god called Tepko the Slovenly?

a reply to: musicismagic

The 78% reduction doesn’t really mean anything without knowing what the actual radiation levels were and are currently.

Was it milli sieverts?
Sieverts?
Rems?

a reply to: musicismagic

Reduction probably courtesy of the Pacific Ocean dumping.

Given what we already know would it be much of a stretch to think they were dumping contaminated soils and other crap in there?

originally posted by: Bluntone22
a reply to: musicismagic

The 78% reduction doesn’t really mean anything without knowing what the actual radiation levels were and are currently.

Was it milli sieverts?
Sieverts?
Rems?

This is only information given: www3.nhk.or.jp... might be in Japanese, if so, just use chrome and it will translate it.

a reply to: musicismagic


This is the entire translated article.

“ A study by the Nuclear Regulatory Commission found that radiation dose near the surface, a radius of 80 km from TEPCO's Fukushima Daiichi Nuclear Power Station, was reduced by about 78% on average from the year of the nuclear accident.

The NRA regularly flies helicopters after the Fukushima Daiichi nuclear accident and surveys an area with a radius of 80 km from above.

Then, the radiation dose per hour near the surface of the ground 1m is calculated, painted in nine colors and published on a map.

According to this, when comparing the result of October 2011, which started measurement under almost the same conditions as the present after the nuclear accident, with the latest result of last September, the radiation dose was the average of the entire 80 km area About 78% less.

The
NRA explained that 減少 radioactive materials have the characteristic of decreasing their radiation dose after a certain period of time, which has a large effect, and that, in addition to が decontamination work and ▽ It is said that it may be leaked.”


Not one number on radiation levels...
Go figure.
That article is to journalism what McDonald’s is to fine dining...lol

IDK.

A “100% increase in MJ use” usually means that your buddy showed up at your place a day before he gets paid!! I love that pothole!!



First, the water is still sitting there (as far as I know) and would already have it’s own radiation level. So getting rid of the water would not mean shirt to the surrounding environment.

Second, what they found was basically glass beads of radioactive material spewed out of the melting down reactor. Part good news is that it won’t leach into the soil as radioactive elements. Bad news is that it is micro glass. Think: we are still finding flint arrowheads from ancient civilizations!

I don’t think that radioactive might micro glass can “magically” disappear from the environment like mustard gas dissipating from the the treanches in WW1.

The area will be a mess until several inches of topsoil can be removed and processed (if we even have the tech to remove all contamination).

The whole place is going to be a mess for a while.

That is why we should not just dump contaminated water into the ocean!

The only “good news” that I know of is that they will producing hydrogen somewhere around there!

a reply to: musicismagic

Ummm... radioactive isotopes do not suddenly stop radiating. A 78% decrease would only be expected to happen naturally after about 2 half-lives. U-235 has a half life of about 700 million years, so that would be 1.4 billion years.

Therefore if the radiation levels have decreased, it's not because there's less radiation being emitted. It has to be because the source of the radiation is moving. I consider that bad news; it means the cores are still sinking into bedrock. That could mean that the radiation into the Pacific is happening at lower depths, which could have severe effects on ocean ecology.

Sorry to be the bearer of bad news...

TheRedneck

a reply to: TheRedneck

The cores are still in the containment vessels where they belong.

Unfortunately the article is terrible and doesn’t report type or levels of radiation.
My guess is the already safe levels are now mostly back to normal levels.

a reply to: TheRedneck

Thing is, the longer the half-life, the less radioactive the isotope.
As I recall it was I-131 which was predominant at the disaster site, followed by C-134/137. Substantially more radioactive than Uranium, and substantially shorter half lives.

Was a lot of U-235 spread around Fukushima?

a reply to: Bluntone22

The cores are sitting in bedrock underneath Fukushima. This was a complete meltdown.

The containment vessels are still in the buildings, at least what's left of them.

TheRedneck

a reply to: Phage

I-131 has a half-life of about 8 days; it was spent before the furor died down.

C-134 has a half-life of about two years.

C-137 has a half-life of about 30 years.

All of those are formed during the fission of U-235 by free neutron radiation (not part of the decay chain). The primary radioactive component that ran the reactors is enriched uranium, i.e. U-235. With a half-life of 700 million years, the U-235 is certainly still radiating and is the primary source of any radiation.

TheRedneck

a reply to: TheRedneck

www.world-nuclear-news.org...

originally posted by: Bluntone22
a reply to: TheRedneck

www.world-nuclear-news.org...

Thanks for the site.

a reply to: TheRedneck

I-131 has a half-life of about 8 days; it was spent before the furor died down.

C-134 has a half-life of about two years.

C-137 has a half-life of about 30 years.

Indeed. And this thread is about a reduction in radiation levels from the time of the disaster.

With a half-life of 700 million years, the U-235 is certainly still radiating and is the primary source of any radiation.

Primary source? No, but then the soil of Japan seems to have its fair share of it. Naturally. Very little was released by the reactors. And again, it is the short half-life materials which is most dangerous by weight.

Regarding the U released from the damaged reactor cores of the FDNPP, 235U and 238U have been measured in soil and plant samples collected from contaminated areas, but no anomaly of 235U associated with FDNPP fallout was observed because of the presence of a much larger quantity of natural U.

Therefore, evidence of U release due to the FDNPP accident cannot be obtained by measuring 234U/238U and 235U/238U atom ratios, and if any occurred, the FDNPP-derived U was diluted largely by the higher amount of natural U in Japanese soil (about 1–3 ppm).

www.nature.com...


A 78% reduction of radiation levels in the region is consistent with the decay of more highly radioactive material over the years. Like Iodine and Cesium, the primary contaminants, with shorter half-lives.The area will be dangerous for a while to come, but not because of Uranium.

a reply to: Phage

Primary source? No

OK, Phage, been fun.

When you think nuclear reactors do not use U-235 as fuel, I'm outta here.

TheRedneck

a reply to: TheRedneck

I think phage was saying that the short lived isotopes decaying are the primary reason for the drop in radiation levels. The drop should slow now as the longer lived isotopes remain.

Not that we have any actual numbers on the radiation levels.

a reply to: Bluntone22

Still irrelevant. All of the radiation comes from U-235 initially.

Consider I-131: it is produced as a byproduct of U-235 decay (likely in a secondary decay line). It has a half-life of about 8 days, so a ~75% drop in levels would be observed after about 16 days, assuming no I-131 is being added. That assumption is false because the U-235 is still active and is still, therefore, creating I-131. So as long as the U-235 is active, there will be a constant supply of I-131. C-134, C-137, and a few other isotopes; they simply are created by the alpha decay of U-235 and produce beta/gamma decay (which is why shielding is required; alpha particles from U-235 cannot penetrate skin, but gamma radiation can).

The same goes for the caesium isotopes and any other byproducts. All come from the decay of the enriched uranium which has a half-life of 700 million years.

Phage is trolling. He knows this as well as I do. I'm not in the mood to play games with him, especially when he plays so... poorly... I have an actual scientific interest in Fukushima: this is the first time we have had an actual complete core meltdown (aka "China Syndrome") event. Chernobyl came close, but the core remained (mostly) above ground. When Fukushima melted down, the cores melted their way into the bedrock, but the resultant radiation levels seemed to indicate they had reached an equilibrium point where there was enough external cooling from the environment to offset the heat being produced internally and they stopped. Now, with this reported drop on radiation levels, I suspect that they have continued to descend.

There is no known physical method to stop a nuclear chain reaction once started in a critical mass. It has never been done and no one has thus far developed even a theory of how to possibly do so. Therefore, the cores have not reduced in radiation level by 78%, and must therefore be moving away from the test points or somehow being shielded from them. That's just simple, cognizant reasoning.

TheRedneck

a reply to: TheRedneck

Nuclear reactors don't reach critical mass though.
That would be explosive.
Their fuel is not refined pure enough for that.

When a reactor melts down the chain reaction has already stoped due to the loss of the water moderator.
The isotopes move too fast too start a chain reaction so the water slows the isotopes enough for them to collide and split.
When the heat boils off the water the reaction stops.

Chernobyl didn't use this design and was a crime against humanity.


As for irrelevance...
It's all irrelevant without the levels of contamination being reported.

a reply to: Bluntone22

Nuclear reactors don't reach critical mass though.
That would be explosive.
Their fuel is not refined pure enough for that.

Actually, they do. If they never reached critical mass, they would produce no power.

The fuel is not enriched to weapons grade, true. But it is enriched enough to create a chain reaction. That is the definition of "critical mass"... when the chain reaction is self-sustaining due to enough U-235 atoms in close enough proximity to each other so that the decayed alpha particles from one can initiate decay in others. In a bomb, the enrichment is such that the decay becomes extremely rapid and the resultant heat causes an explosion... in a power plant, the lower enrichment and the presence of control rods to absorb alpha particles (neutrons, mostly) keeps the "explosion" controlled.

It's the same principle as with any other explosive. if you have a tank of gasoline enclosed and ignite it, it will explode violently. Put it into a car and have it injected in smaller amounts and the explosion is controlled. Two things control the decay of U-235 in a power plant: enrichment levels and control rods. The enrichment levels keep it from exploding like a bomb, even under the worst conditions, but can still result in a runaway decay chain. the control rods are used to control it further to keep it at operating temperature.

When a reactor melts down the chain reaction has already stoped due to the loss of the water moderator.
The isotopes move too fast too start a chain reaction so the water slows the isotopes enough for them to collide and split.

No.

The control rods do the moderating by absorbing the neutrons before they interact with adjacent U-235 atoms. They do not need to be slowed down to instigate decay in adjacent atoms; if they are too slow, they are not powerful enough to do so. Water is typically kept on site (with added boron) as a safety protocol to help cool a reactor before it melts down, but it is the boron, not the water, that really does the trick. Boron has the ability to absorb a neutron without becoming radioactive itself.

The reactors do contain water. The water absorbs the heat from the reaction and transfers it to the main steam lines to drive the generators. The water never comes in direct contact with the uranium... it surrounds the containers that hold the fuel pellets. In a PWR reactor (the type I worked on), that water never leaves the primary containment. It simply passes through a heat exchanger which transfers the heat to the steam lines. In a BWR design (like Fukushima), it directly drives the generators. In both cases, external water is used to cool it further before returning it to the source of heat (my plant used cooling towers; Fukushima used ocean water).

The absence of control rods or boron water means the U-235 reacts faster, not slower. Unlike most other generation methods we use, nuclear power is always on until it is turned off by control rods, not off until the control rods are inserted. To start a nuclear reactor, the control rods are fully inserted, the fuel pellets are loaded, and the control rods are removed until the reaction reaches the desired point. That was one of the things that caused the panic at Fukushima: those rods are highly machined to fit precisely between the fuel pellets, and when they became overheated and warped, they wouldn't re-engage.

When the heat boils off the water the reaction stops.

No. The water that was used to flood the reactors was used to cool them to prevent overheating the rods and to try to slow the reaction just a little. The attempt was futile.

To be fair, I went looking for the exact specs on Chernobyl and found some websites that (incorrectly) state what you just did. So I don't hold the misinformation against you. Please understand, however, that this is incorrect information... a lack of moderation causes the chain reaction to continue unabated. Only the lack of enrichment keeps it from becoming a bomb in that case.

Chernobyl didn't use this design and was a crime against humanity.

Chernobyl had advantages in the design. it wasn't that the design was terrible, but that the construction was sub-par compared to today. There weren't as many safety checks as we have at present. I suppose that is inevitable to some degree with any new technology; the reactor that sits 5 miles from me (in the plant I helped build as my first real job out of high school) is the same reactor design as the one at Three Mile Island. Safety measures have been implemented to prevent the same kind of situation, but the design itself is not flawed.

As for irrelevance...
It's all irrelevant without the levels of contamination being reported.

Only so far as human precautions go. Remember, my interest is scientific curiosity: what will happen during a complete core meltdown? The relative levels do offer some insight on that, because they indicate something about where the cores are now in relation to the readings.

But as to precautions being taken for the area of the readings? Certainly the absolute levels are the most relevant. Of course, what's the difference between enough radiation to kill a person in 60 seconds and enough radiation to kill a person in 5 minutes? 4 minutes of agony.

TheRedneck