Olkiluoto geology

[Blind groper]

MiM

With the greatest of respect I have to tell you that you are wrong on the statement that there is no evidence for a threshold.

The effects of radiation on human health have been studied in enormous detail, and most especially in relation to cancers. While it is not possible to nail down an exact value for a threshold, the mass of evidence shows that the threshold is a reality. I suggested that anything less than 100 millisieverts per year does not cause extra cases of cancer, and the evidence points strongly to that. The more conservative government regulations give a maximum of 50 millisieverts per year, and that is probably sensible.

In any case, what I suggested would not come within an order of magnitude of either, even with some serious bioaccumulation of radioisotopes.

[MiM]

here I am convinced you will fail, because accumulation in the food chain is a well established process for many toxins and many radionuclides (including caesium).

How much accumulation are you talking about?

I mean, if we assume occasional accumulation to increase the spot radiation levels to three orders of magnitude higher than background, it will still be safe. The concentrations we are discussing are really, really small. As I said before, there is already 50 million tonnes of weakly radioactive U235 in the ocean. Is that not accumulated also?

Bearing in mind both the immense dilution and the decay into harmless by products, such things as Cs 137 will never, ever, be able to reach harmful levels, even with bioaccumulation.

I did the calculation on Cs-137 for you, above. With current energy production, if we dump everything and mix it evenly in the oceans the activity will reach a steady state of 0.1 Bq/l sea water. That's the point, when the caesium decays as fast as we pour more in.

Many years back, as a part of my masters thesis, I did modelling of Chernobyl caesium fallout behaviour in a big Finnish lake. There, a short pulse of initially 5 Bq/l in water lead to measured values of up to 5000 Bq/kg in predatory fish. But that was a very short duration pulse, the levels in water quickly dropped, whereas they stayed high in fish. In those studies, the accumulation from water to plankton used was 5000 times, and plankton is just the beginning of the accumulation chain. Of course those numbers are not directly applicable, as a fresh water lake and salty sea water would behave differently, but the chronic burden your scheme would lead to would worsen the situation compared to my Chernobyl scenario.

[MiM]

MiM

With the greatest of respect I have to tell you that you are wrong on the statement that there is no evidence for a threshold.

The effects of radiation on human health have been studied in enormous detail, and most especially in relation to cancers. While it is not possible to nail down an exact value for a threshold, the mass of evidence shows that the threshold is a reality. I suggested that anything less than 100 millisieverts per year does not cause extra cases of cancer, and the evidence points strongly to that. The more conservative government regulations give a maximum of 50 millisieverts per year, and that is probably sensible.

In any case, what I suggested would not come within an order of magnitude of either, even with some serious bioaccumulation of radioisotopes.

With greatest respect, show me the evidence. Why is that government maximum of 50 mSv only used for a small special group, and not for the general public? At least in Finland the allowed exposure to the public is 0.1 mSv/y.

Edit: maybe to be exact - of course there is evidence to be found pointing towards any conclusion, in any question as complex as this. But there is no conclusive evidence, and the debate is still ongoing. As an argumentation style, you like to flash "greenpeace" here and there, but the LNT (linear non-threshold) model is still used by governments and serious organisations over the world.

[Blind groper]

Evidence for no threshold.
The main evidence comes from studies of Hiroshima survivors. However, here is another reference.
http://www.world-nuclear.org/education/ral.htm

I quote :

"The prevailing assumption is that any dose of radiation, no matter how small, involves a possibility of risk to human health. However there is no scientific evidence of risk at doses below about 50 millisievert in a short time or about 100 millisievert per year (40 times average annual dose from natural background)."

You asked about varying government recommendations. That is correct, of course. Governments try to be very conservative, and set limits well below that which might cause harm. Limits for radiation exposure are incredibly variable from place to place. Japan, for example, raised its limit for the sake of expediency, for Fukushima workers, to 250 millisieverts in a single dose. Some other nations have very low levels.

Government recommended levels do not show the minimum likely to cause harm, since their levels are way below that level, with the probable exception of Japan. Hiroshima studies indicate that levels below 100 millisieverts per year are likely not to raise cancer rates. Even this may be conservative, since there are some places where background radiation is much higher still, and local populations do not seem to suffer excess cancers.

[Blind groper]

I did the calculation on Cs-137 for you, above. With current energy production, if we dump everything and mix it evenly in the oceans the activity will reach a steady state of 0.1 Bq/l sea water.

Natural radiation in the oceans is 15 becquerels per litre. I have already pointed out the level of tolerance life has for radiation. Do you really think an addition of 0.7% extra is going to be a problem?

[JimC]

I have an interesting perspective on this one. Once a year, I conduct an experiment using radioactive sources and a geiger counter for my Year 11 physics students. Here is the introduction to the practical activity:

Introduction
This practical investigation will be carried out by your teacher, and you will record the data as it is produced, and analyse it later. The key instrument in this investigation is a Geiger-Müller counter, which records individual particles or photons of ionising radiation as they enter a tube. A clicking sound is produced, and a count is recorded. For convenience, a timer allows us to record a “count per 10 seconds”, which will be our standard measurement.
In this investigation, we will be using 3 radioactive sources, prepared for schools by the Lucas Heights nuclear reactor in Sydney. The 3 radioisotopes are:
1. Cobalt 60 (Co-60, a 200 kBq gamma emitter, with a half life of 5.8 years)
2. Americium 243 (Am-243, a 20 kBq alpha emitter, with a half life of 7370 years)
3. Strontium 90 (Sr-90, a 70 kBq beta emitter, with a half life of 27 years
The sources themselves are in plastic disks. The Co-60 and the Sr-90 are fully sealed, but the Am-243 has a hole exposing the bare metal. You should be able to work out why...
These sources are relatively low intensity, but they still need to be treated with respect and care. They are normally stored in a lead-lined box, within a larger wooden lead-lined box. When I am using them, I will handle them with tongs, and keep the ones I am not currently using under a lead sheet.
If time, we may also test the activity of a range of mineral samples.

The counter roars in some situations. Even though it's not hands on for them, the kids love it, and talk about it later. Such a good prac...

Later in the course, after a lot of teaching about nuclear energy, the lads do this exercise:

Year 11 Physics Essay on nuclear issues
In this task, you are to write an essay of around 2 pages (typed) in length on the issues surrounding the use of nuclear energy. The essay will be argumentative in style, but must attempt to give a balanced view of the arguments for and against the use of nuclear energy to generate power. The issues could be global, or you may wish to specifically look at the possibilities for nuclear power in Australia. It must be clearly in your own words. An essay style assignment like this does not require diagrams. You do not need to give a detailed account of the nuclear reactions involved, but some of the consequences of the reactions (e.g. the generation of highly radioactive waste) will obviously be important.
It may be worthwhile looking at the websites found on your MyClasses physics page, and one of the Unit 1 Detailed Studies found on the CD that accompanies your textbook may also be helpful.

[MiM]

Evidence for no threshold.
The main evidence comes from studies of Hiroshima survivors. However, here is another reference.
http://www.world-nuclear.org/education/ral.htm

I quote :

"The prevailing assumption is that any dose of radiation, no matter how small, involves a possibility of risk to human health. However there is no scientific evidence of risk at doses below about 50 millisievert in a short time or about 100 millisievert per year (40 times average annual dose from natural background)."

You asked about varying government recommendations. That is correct, of course. Governments try to be very conservative, and set limits well below that which might cause harm. Limits for radiation exposure are incredibly variable from place to place. Japan, for example, raised its limit for the sake of expediency, for Fukushima workers, to 250 millisieverts in a single dose. Some other nations have very low levels.

Government recommended levels do not show the minimum likely to cause harm, since their levels are way below that level, with the probable exception of Japan. Hiroshima studies indicate that levels below 100 millisieverts per year are likely not to raise cancer rates. Even this may be conservative, since there are some places where background radiation is much higher still, and local populations do not seem to suffer excess cancers.

So there, another political statement, used in a debate that should be science driven. I believe you just made my point, with that reference.

The Hiroshima data has been interpreted to show a threshold, to show no threshold, or to show that lower doserates actually are more dangerous than the non-threshold hypothesis would give. The data simply isn't strong enough to make a final conclusion from it.

All governmental and other limits are based on some kind of cost/benefit analysis. I agree that the limits for the public are generally conservative, where conservatism is possible. But limits for workers already allow for some degree of occupational risk, as there are many other hazardous workplaces.

[Blind groper]

Here is another reference that may be more to your liking.

http://www.ajronline.org/content/179/5/1137.full

I quote from the conclusion .

"The evidence presented in this review leads to the conclusion that the linear no-threshold theory fails badly in the low-dose region because it grossly overestimates the risk from low-level radiation. This means, for example, that the cancer risk from diagnostic radiography is much lower than is given by usual estimates, and may well be zero."

Hidden in the body of that report is this gem.

"A $10 million study of shipyard workers involved in servicing United States Navy nuclear-propelled ships compared those who were and were not occupationally exposed to radiation [29]. In the former group, workers had exposures greater than 0.5 cSv (0.5 rem) and average exposures of 5 cSv, whereas the latter group had exposures of less than 0.5 cSv. The exposed workers had a cancer mortality rate that was only 85% of that for the unexposed workers, a difference of more than 4 SDs. Hiring procedures, medical surveillance, job type, and other factors were the same for both groups, so the often-used explanation of “the healthy worker effect” does not apply here. "

In this very large study, it appears that exposure to low level radiation actually is protective against cancer.

[MiM]

Now you are talking I am afraid I don't have time to look closely at that right now, but I will be back.

[MiM]

Took a bit of digging. The DOE report that is referenced in the snippet you present isn't available on line (you can get a draft of it for 35$), but I found a scientific article written by the same guy who wrote that original report, on the same issue Health effect of low level radiation in shipyard workers

I quote a part of the conclusions in that article. Gives a somewhat different picture than the one B. Cohen presents . Actually professor Cohen is fairly well known in the business, and his claims has been rejected by eg a WHO expert panel (http://en.wikipedia.org/wiki/Bernard_Co ... ysicist%29)

The consistency of the finding of an increased risk with
increasing dose for each cancer in the dose-dependent anal-
ysis is highly suggestive that radiation is associated with the
risk of these cancers. In addition, the LHC cancers, which
include leukemias and multiple myelomas as well as non-
Hodgkin lymphomas, are recognized or suspected to be
associated with an increased risk from radiation exposure.
These cancers show a significant and very high five to six-
fold excess risk in 50 mSv or more radiation-exposed work-
ers compared to those in the low dose reference group.
Therefore, these data on increasing risks from radiation
exposure for LHC support the findings from similar studies
in the literature. The consistency of the increase in risk with
dose for each cancer and the significantly high risk of LHC
associated with radiation doses of 10 mSv or more indicate
that the shipyard population, which was still very early in
follow up at the time of termination of the study, needs to
have additional follow up to determine the risks of leukemia,
LHC and solid tumors. These early data suggest the workers
may have a risk of some cancers from low dose radiation.

[Tero]

MiM, I have yet to find anyone but the artos and the gropers in message boards. Where did the scientists go? Duh! They are too busy doing science!

[Blind groper]

MiM

Here is a better account of that study, presented by the chief author, Professor John Cameron.

http://www.radscihealth.org/rsh/Docs/9411a4Cameron.htm

This clarifies points. For example mesothelioma. This was associated with asbestos exposure, which occurs to some degree in ship workers. Only 36 mesothelioma deaths were reported, and they occurred with both nuclear and conventional ship groups.

More to the point, nuclear ship workers had a statistically very, very significant reduction in overall cancer deaths compared to conventional ship workers.

[MiM]

MiM

Here is a better account of that study, presented by the chief author, Professor John Cameron.

http://www.radscihealth.org/rsh/Docs/9411a4Cameron.htm

This clarifies points. For example mesothelioma. This was associated with asbestos exposure, which occurs to some degree in ship workers. Only 36 mesothelioma deaths were reported, and they occurred with both nuclear and conventional ship groups.

More to the point, nuclear ship workers had a statistically very, very significant reduction in overall cancer deaths compared to conventional ship workers.

What do you mean "chief author" His name isn't even on the DOE report, which is attributed to Matanoski alone. Matanoski is also the main author of the article I linked. The difference Cameron refers to dealt with in that article.

[Blind groper]

What do you mean "chief author" His name isn't even on the DOE report, which is attributed to Matanoski alone. Matanoski is also the main author of the article I linked. The difference Cameron refers to dealt with in that article.

The original study was carried out by a team under Prof. John Cameron, and financed by the military. Your DOC report is a review, using the data that Cameron's team generated. Matanoski merely looked at data. He did not generate it.

[MiM]

What do you mean "chief author" His name isn't even on the DOE report, which is attributed to Matanoski alone. Matanoski is also the main author of the article I linked. The difference Cameron refers to dealt with in that article.

The original study was carried out by a team under Prof. John Cameron, and financed by the military. Your DOC report is a review, using the data that Cameron's team generated. Matanoski merely looked at data. He did not generate it.

And as a courtesy to your discussion partner, you might give the reference to that information too

Anyway, this discussion should be enough to make my point, that this issue is still open. The existing data can be interpreted in very different ways, and there is no more certainty about the existence of a threshold, than about the no threshold theory.