Putting Radiation Dose in Perspective 4

[WoodyPE]

Fukushima Daiichi #3 had a second explosion on March 14, 2011. Soon after the explosion the radiation level was measured at 50 microsieverts per hour in the service hall and 20 microsieverts per hour at the plant gate. The allowable dose for a typical nuclear worker is 20 millisieverts per year. Hence at the plant gate the worker would reach dose in 1000 hours.

1 Sv = 1000 mSv (millisieverts) = 1,000,000 ?Sv (microsieverts)

Radiation dose benchmarks courtesy of the Wikipedia:

Yearly Dose Examples

? Living near a nuclear power station: less than 0.01 mSv/year
? Cosmic radiation (from sky) at sea level: 0.24 mSv/year
? Terrestrial radiation (from ground): 0.28 mSv/year
? Natural radiation in the human body: 0.40 mSv/year
? Typical individual's natural background radiation: 2 mSv/year; 1.5 mSv/year for Australians, 3 mSv/year for Americans
? Radon in the average US home: 2 mSv/year
? Average American's total radiation exposure: 6.2 mSv/year
? New York-Tokyo flights for airline crew: 9 mSv/year
? Smoking 1.5 packs/day: 13 mSv/year Current average limit for nuclear workers: 20 mSv/year
? Background radiation in parts of Iran, India and Europe: 50 mSv/year
? Lowest clearly carcinogenic level: 100 mSv/year


Lifetime Dose Examples

? Criterion for relocation after Chernobyl disaster: 350 mSv/lifetime


Symptom Benchmarks

Effects to humans of acute radiation (within one day):
? 0–0.25 Sv: None
? 0.25–1 Sv: Some people feel nausea and loss of appetite; bone marrow, lymph nodes, spleen damaged.
? 1–3 Sv: Mild to severe nausea, loss of appetite, infection; more severe bone marrow, lymph node, spleen damage; recovery probable, not assured.
? 3–6 Sv: Severe nausea, loss of appetite; hemorrhaging, infection, diarrhea, skin peels, sterility; death if untreated.
? 6–10 Sv: Above symptoms plus central nervous system impairment; death expected.
? Above 10 Sv: Incapacitation and death.

 

[trottiey]

I do not see what the "lowest clearly carcinogenic level" could be based on. The science to date does not support any safe threshold of radiation. Such a threshold may in fact exist, and lower levels may even be beneficial, but there exists insufficient scientific evidence for such at this time.

Similarly, the "Symptom Benchmarks" only describe acute radiation effects and neglect the stochiastic effects such as cancer. So a dose of 0.25 Sv may have no immediate detectable clinical effect, but that does not mean it has no effect at all. The best science indicates that such as dose would carry with it a 1% extra chance of developing a fatal cancer, over and above the natural rate of about 22%. In addition, that dose would carry a 0.2% chance of hereditary risk if the patient has children after the exposure.

I would also point out, as explained in thread466-294445, that the dose rates reported at Fukushima do not include internal radiation doses for inhaled or ingested contaminants.

 

[ScottI2R]

Whoa whoa whoa! What is this smoking 1.5 packs a day exposure? I assume this would be considered an internal exposure and exposures are cumulative over time. In this case, a year. So is it correct to say that a nuclear worker is using up 65% of his / hers allowable exposure limit if the said person is a smoker?

Another reason to quit I guess.....I wonder what the exposure level is from my nicotine gum.

I really am a good egg, I'm just a little scrambled!

 

[ScottI2R]

Please disregard my previous post. It contains lead 210 and polonium 210. I found this below:

Cigarette Smoking
Besides carbon dioxide, tar, and nicotine, cigarette smoke also contains radioactive lead and polonium, enough to result in a radiation exposure of 1300 mrem/year to a 1.5 pack a day smoker. Each cigarette smoked can also be equated to one chest x-ray, and a non-smoker living with a smoker may receive the equivalent of 12 chest x-rays per year as a result of second-hand smoke. Perhaps the easiest radiation exposure to control is this one: If you smoke, stop; if you don’t smoke, don’t ever start. Whenever possible, minimize your exposure to other people’s smoke. For more information about smoking, see the Quitting Smoking Fact Sheet.

Definite incentive that I never heard of! Thank you Woody!

Scott

I really am a good egg, I'm just a little scrambled!

 

[WoodyPE]

trootiey:

As we're discussing basic health-physics and radiation dose -- there is no known "risk-free" dose for nuclear radiation. This is true for lead-dust exposure as well as many other toxic substances we could talk about.

As Scott brought up, heavy cigarette smoking can give the equivalent of a full-year's allowable radiation dose. In practice it isn't counted toward the 20 millisievert/yr allowable maximum dose for nuclear workers that smoke. In other words a nuclear worker that smokes heavily could get as much as 40 millisieverts of dose in a year with only 20 millisieverts reported from his place of employment.

A point is made about the risk of acute vs stochastic dose. It is my understanding that the health risk is driven by the total amount of dose received over the time it is received. The risks increase as the dose is increased and/or the time is decreased.

For example a dose that might make someone sick in a day and possibly cause long-term effects has a greater risk than the same dose spread over 5 years. The reason is the human body has the ability to heal and offset some of the health-risks over a longer duration of time so that the radiation contained in the body never reaches the level of an acute exposure to the same dose.

 

[unclesyd]

you will have to redo the math.

One way to resolve the worker's radiation exposure. one question is this an increase in the radiation field or total radiation to the body.

"On Wednesday morning, the Japanese government raised the permitted radiation exposure for plant workers by 2.5 times to allow them to work longer, according to NHK TV".

 

[WoodyPE]

unclesyd,

It's been 15 years since I was pedigreed for nuclear plant access as an engineer.

The radiation dose numbers are measured external to the body. These are the numbers published in th OP. The internal body burden is measured with a chest scan and evaluated differently.

 

[unclesyd]

The latest update from Reuters.

http://www.reuters.com/article/2011/03/16/us-japan-quake-idUSTRE72A0SS20110316

 

[trottiey]

to WoodyPE, regarding acute versus stochastic effects:

Your description is sort of right, but the deterministic and stochastic health effects of radiation are more distinct than you make them out to be. Acute doses of 250,000 µSv or more will cause changes in blood chemistry that can be clinically detected immediately after the exposure. These changes include the production of toxins in the bloodstream that can lead to sickness or death long before cancer would take its course. Acute health effects can be treated with blood transfusions and other techniques to improve survival rates.

Stochastic effects include increased risks of cancer and hereditary defects. These are presumed to be due to genetic changes that are not detectable until the full condition develops, years after the exposure. Someone who survives acute health effects would still be subject to the stochastic effects.

If you look at conventional chemical hazards, you will find that there exists risk-free dose thresholds for many chemicals, because it has been shown that the body can eliminate these quantities and heal their effects. This is what the 250,000 µSv threshold is with respect to acute radiation poisoning. However, no such threshold has been scientifically established for the stochastic health effects of radiation.

Acute radiation effects need to be considered seperately from ordinary cancer-causing doses. I strongly doubt that acute radiation poisoning will be of any concern to anyone outside the Fukushima plant.

 

[WoodyPE]

trottiey,

I should have answered your original point more directly regarding the statistic that says "Lowest clearly carcinogenic level: 100 mSv/year." This statistic comes from a hypothesis test that assumes "INNOCENT until proven GUILTY" where a clear cause-and-effect relationship must be proven to exist between radiation exposure and cancer. Radiation exposure is clearly proven "guilty" at 100 mSv/year or greater.

You said "The science to date does not support any safe threshold of radiation." You are correct, and that's a different kind of hypothesis test that assumes "GUILTY until proven INNOCENT." Radiation exposure has not been proven "innocent" at any level no matter how low it is. Maybe someday the minimum can be found, but there is not enough data. Statistically speaking this implies it must be a very small threshold if it even exists at all.

By the way, the 100 mSV/year benchmark came from the World Nuclear Organization:

http://www.bbc.co.uk/news/health-12722435

They say it a little differently:

"Lowest level at which any increase in cancer is clearly evident."

 

[trottiey]

I figured that our differences would come down to these details. What you say is basically true, and there is some scientific evidence that suggests the linear no-threshold (LNT) theory may be over-conservative, especially for the external gamma exposures that normally dominate occupational doses. However, there is also scientific evidence which suggests the LNT theory may be under-conservative, especially for internal alpha exposures. I am guessing that internal alpha is going to be important in Fukushima. So the global consensus of radiation protection organizations is that it is prudent to stick to LNT until we come up with something better.

The WNO's original article confirms this as the global consensus:

http://www.world-nuclear.org/info/inf05.html

(And by the way, I would point out that their mandate is to promote nuclear power.)

The 100 mSv was quoted from a literature review done by the Electrical Power Research Institute, (EPRI,) whose exact words were as follows:
"From an epidemiological perspective, individual radiation doses of less than 100 mSv in a single exposure are too small to allow detection of any statistically significant excess cancers in the presence of naturally occurring cancers."

So in my mind, 100 mSv is more indicative of the size of epidemiological studies to date than of any safe threshold.

 

[WoodyPE]

trottiey,

I don't see any differences here as far as I can tell. I'm looking at the data from a hypothesis testing point of view. An insurance actuary is probably the best candidate for the mortality analysis.

It appears that the measurement resolution is inadequate to determine a "safe limit." "Background noise" becomes a greater percentage of measurement. How could you prove that someone received 0.01 micro-Sv dose in a year vs. 0.02 micro-Sv of dose which is a 100% increase in dose? It's a lot easier to prove someone received 100 milli-Sv vs 200 milli-Sv which is also a 100% increase in dose.

 

[VEBill]

VIENNA - A U.N. organization has notified member states that radioactive fallout from Japan's crippled nuclear plant has reached Southern California but first readings are far below levels that could pose a health hazard, a diplomat said Friday.

The diplomat, who has access to U.N. radiation tracking of the U.N.'s Comprehensive Test Ban Treaty Organization, was citing readings from a California-based measuring station of the CTBTO.

Initial readings are "about a billion times beneath levels that would be health threatening," the diplomat told The Associated Press. He asked for anonymity because...

http://www.cnbc.com/id/42149446

A billion times beneath level that would be health threatening?

A billion?

What's the ratio between amibient background and the level that would be health threatening? I don't think it's a billion. I though it was only about 1-to-50,000 from typical background to lethal. ?

Parhaps they're doing a more sophiscated measurement than just plain level. ?

 

[msquared48]

I do not think he whole issue here is the allowable dose rate over a short period of time. It's the amount the body absorbs and retains in the long haul, coupled with the the half life statistics of the ingested material, or the material exposed to over time.

For high radiation exposures, such as within 10KM of the plants, immediate OD effects are the short term killer. Over longer periods of time, the amount ingested and retained in the fat and internal organs is the long term, genetic killer. This includes both natural background and fallout radiation. This plume or plumes, will circle the earth for years, continuing to dose above the backround rate for sometime to come, same as Chernoble, increasing the risk of excessive radiation encouraged diseases such as cancer and birth defects. These are multi-generational impacts, very hard to impossible to set a "safe" dose figure for.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[trottiey]

The 50% lethality dose is somewhere just above 3 Sv if it hits you in one burst; higher if it's spread out over a long enough timespan for healing mechanisms to do their work. Average background is a bit below 0.3 mSv/yr. But you cannot compare a dose to a dose rate without making some additional assumptions about timescales; dose rates by themselves are never lethal unless you have some exposure time.

For sure, that report is not based on measuring ambient radiation fields in California. A proper measurement would be based on spectroscopic analysis of airborne contaminant concentrations, and combining this with average rates of inhalation, rates of elimination, decay rate, etc. to arrive at an equivalent dose over the contaminant's lifetime in the human body.

 

[msquared48]

Have there been any articles or information released on the anticipated half-life of the material expelled in the explosions into the atmosphere?

And what about the impact on the future food chain, particularly in California?

Ron asked me to ask if the California wine he purchases three years from now will be glowing in the dark as he imbibes...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[trottiey]

A complex mixture of contaminants would be expelled by these reactors, and it will take some time to characterize it. Concerns so far have focused on the following:
iodine-131, half-life of 8 days
cesium-137, half-life of 30 years
plutonium-239, half life of 24,000 years
A lower half-life means more radioactivity per unit mass, but a longer half-life means we're going to learn to live with it for much longer.

To evaluate the impact on the food chain, you need to look at much more data than just the half-lives. Quantities of contaminants, their solubility in water, how easily they get airborne, residence time in the human body, whether or not any biological mechanisms may concentrate the substance in certain species or particular organs, radiation type, etc. It will take a few years for the scientific community to come to a consensus on the numbers.

The glow of Cherenkov radiation is quite beautiful, but unfortunately it will be too weak to be visible to the naked eye. Only in the core of a nuclear reactor does the radiation get so intense that the glow becomes visible. So no, the wine won't glow, just his nose.

 

[msquared48]

Shall we rename him "Rudolph" then?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[electricpete]

How nasty is plutonium compared to the other stuff. I google a little bit and saw that Ralph Naer had sensationalized the toxicity of plutonium, but I didn't get a feel for how bad it really is.

=====================================
(2B)+(2B)' ?

 

[trottiey]

This is an excellent resource on the health effects of various radioisotopes:

http://www.ead.anl.gov/pub/doc/ANL_ContaminantFactSheets_All_070418.pdf

There probably haven't been any releases of plutonium yet. I've only read about cesium and iodine being measured in the atmosphere. Plutonium is mostly discussed in relation to worst-case scenarios at this point.