The first man-made chain reaction occurred under the grandstand of the University of Chicago football field on December 2, 1942, in what was known as an atomic "pile." It was so named because it was constructed of a "pile" of 45,000 high-purity graphite bricks (250 tons), with 19,000 drilled holes to contain the approximately 93,000 pounds of uranium metal and uranium oxide along with the cadmium control rods. When operating at its design point, it generated a half watt of power - enough to almost power a pencil sharpener. (Fortunately, it was not designed as a power reactor, but as an experiment to prove the "chain reaction" hypothesis.)
Why the "high-purity graphite bricks?" It has to do with the statement a few paragraphs back about "... if the energy of the neutron is within a certain range." When we want to make little rocks out of big rocks, we are accustomed to using a bigger hammer and swinging hard. Not so in the nuclear world. In order for a neutron to have a decent chance at fissioning a U235 nucleus, it must be slowed down by the action of a moderator. Carbon - as long as it is of high enough purity to avoid absorbing the neutrons - is a good moderator, although, as Chernobyl demonstrated, it has a few potential problems - which is why U.S. power reactors never use this material... or this type of "graphite reactor." It is typically used in military reactors for the production of plutonium - which reportedly was one of Chernobyl's functions, in addition to generating power. [Other uses would be in research reactors, as well as in reactors for use in creating medical radionuclides.]
Footnote to chapter: There is much evidence that a natural reactor "happened" in Western Africa in the Republic of Gabon at Oklo some 1.7 billion years ago when the ratio of U235 to U238 was considerably higher. It appears to have operated in accordance with the Nuclear Regulatory Commission rules of that time and was safely shut down after several hundred thousand years of operation. See Oklo Reactor, Scientific American, August 1976.
Showing posts with label nuclear regulatory commission. Show all posts
Showing posts with label nuclear regulatory commission. Show all posts
Monday, March 28, 2016
Monday, March 14, 2016
Keeping Abreast of the Evidence
Breast cancer is a pretty depressing matter. An estimated 44,300 women (and several thousand men) will die of breast cancer this year. It is second only to lung cancer as a cause of cancer death among women. Increased use of mammography is one of the reasons for the decline in death rates. In 1992 (the most recent statistics I could find), 67% of women over forty reported having at least one screening - up from only 22% in 1979.
But sadly, many women are still hesitant to have regular mammography examinations, often because they fear that X-rays from the mammograms will increase their chances of cancer. Doing their own risk assessment, they conclude the risk from "late detection" is less than that from radiation. And who is to blame them, in light of the commonly accepted dictum that all radiation is dangerous and cumulatively so? Besides, it costs time and money to have a mammogram - at least worrying about cancer is cheap.
"So," you say, " they should just consult a professional and ask about the dose they will receive from the mammogram and make the decision on that basis." Not as simple as that may sound. In researching this chapter I called four local mammography clinics with what I thought was a pretty simple question: "What is the dose of radiation received by a woman in the process of having a mammogram?" I had seen a figure before, but it seemed high to me.
I spoke with two mammography technicians and one nurse who relayed messages from their radiologists. The unanimous answer: "We don't know." One of them, however, was kind enough to put me in touch with a local health physicist, who said the dose was "negligible" - but, even better, offered to lend me some of his reference books. In one, I was able to find the range of exposures to a "gland" (their quotation marks) at a dept of 3 cm to be 0.04 to 0.49 cGy (40 to 490 mrem), which was consistent with the 0.15 cGy figure I had found earlier and was trying to confirm.
But the information I had was perplexing, as it mentioned the dose as 150 mrem per breast. It was much like the confusion I had when learning that radon gave an exposure of 24,000 mrem/year to the bronchial epithelium (which, of course, you now know is the windpipe). The borrowed volumes were quite illuminating, I found there is an official weighting factor that, when multiplied by the local dose gives the effective dose equivalent. And what does this tell you? It tells you the increase in your chances of contracting cancer if the Linear No-Threshold theory were true!
Using a weighting factor of 0.15 for each breast, a 150 mrem per breast exposure would be an equivalent "whole body" exposure totaling 45 mrem (0.045 cSv). [Exposure of the U.S. Population from Diagnostic Medical Radiation, NCRP Report #100, National Council on Radiation Protection and Measurements, Bethesda, Md.]
The figure - in my opinion - means nothing, but if we pretend it is accurate we can use it as a starting point for a "conventional" analysis.
Published in the New England Journal of Medicine in 1989, an investigation by A.B. Miller and associates charted the doses received by 31,710 women who were irradiated in the course of repeated fluoroscopic examinations between 1930 and 1952. [Miller, A.B., et al. Mortality from breast cancer after irradiation during fluoroscopic examination in patients being treated for tuberculosis. New England Journal of Medicine, 321, 1285, 1989.]
In this Canadian study, one group - in Nova Scotia - was fluoroscoped facing the X-ray source. This results in a dose to the breast approximately twenty-five times that when faced away. The women facing the source had a significant increase in cancer risk - it tripled for each 100 cGy (100,000 mrad) of radiation absorbed.
The balance of the study was for all other provinces, with the results presented in Figure 28. Before going on, please remember that a normal annual U.S. background dose is 0.3 cGy, with the first data point on the graph at 5 cGy - about thirteen times this amount. The minimum mortality rate is at a value fifty times the annual background dose or the equivalent (using their figures) of 100 mammography exams.
On the basis of this evidence - which is almost certainly conservative, since the dose rate for fluoroscopy is much higher and, therefore, considered more traumatic to the breasts than present mammography techniques - women should have four or five mammograms per year.
Does that sound strange? That's nothing compared with the most unusual aspect of the study, namely its conclusion: The authors completely ignored the most statistically significant data points in the entire investigation, namely the 34% reduction in relative risk at 15 cGy and the 15% reduction at 24 cGy. Myron Pollycove, M.D., remarked regarding this omission:
"The decreased RR [risk rate] of breast cancer produced by low dose, low level radiation were rejected a priori by the choice of mathematical models that extrapolate the dose-risk relation from high dose exposures to low dose exposures."
[We met Dr. Pollycover back in Chapter 2. But since he is such an important player in the LNT controversy, allow me to remind you that he is professor emeritus in Laboratory Medicine and Radiology at the University of California at San Francisco, head of Nuclear Medicine at San Francisco General Hospital, as well as a visiting medical fellow on the Nuclear Regulatory Commission.]
To most of us that simply means the researchers, for whatever reason, chose to "spike" all results that indicated hormesis. Why? Probably because they were not even considering bio-positive data; they were looking for harmful effects... period. Pollycove continues:
"Nine hundred excess deaths from breast cancer are predicted theoretically from the exposure of one million women to 0.15 Gy. However, the quantified low dose data predicts with better than 99% confidence limits that instead of causing 900 deaths, a dose of 0.15 Gy would prevent 10,000 deaths in these million women."
Pardon me, but do you understand what this man - who has possibly the most impressive credentials in this entire debate - is saying? He is proclaiming that there is unmistakable evidence of hormesis in this study, which, if acted upon, might be developed into an effective weapon against breast cancer in millions of women, thousands of whom will die needlessly because of a theory that was never intended to apply to low-level radiation! It is a pity, a shame, a disgrace that the current ingrained reliance by regulators on the Linear No-Threshold hypothesis makes even a consideration of studying the hormesis phenomen extremely difficult, if not impossible.
But sadly, many women are still hesitant to have regular mammography examinations, often because they fear that X-rays from the mammograms will increase their chances of cancer. Doing their own risk assessment, they conclude the risk from "late detection" is less than that from radiation. And who is to blame them, in light of the commonly accepted dictum that all radiation is dangerous and cumulatively so? Besides, it costs time and money to have a mammogram - at least worrying about cancer is cheap.
"So," you say, " they should just consult a professional and ask about the dose they will receive from the mammogram and make the decision on that basis." Not as simple as that may sound. In researching this chapter I called four local mammography clinics with what I thought was a pretty simple question: "What is the dose of radiation received by a woman in the process of having a mammogram?" I had seen a figure before, but it seemed high to me.
I spoke with two mammography technicians and one nurse who relayed messages from their radiologists. The unanimous answer: "We don't know." One of them, however, was kind enough to put me in touch with a local health physicist, who said the dose was "negligible" - but, even better, offered to lend me some of his reference books. In one, I was able to find the range of exposures to a "gland" (their quotation marks) at a dept of 3 cm to be 0.04 to 0.49 cGy (40 to 490 mrem), which was consistent with the 0.15 cGy figure I had found earlier and was trying to confirm.
But the information I had was perplexing, as it mentioned the dose as 150 mrem per breast. It was much like the confusion I had when learning that radon gave an exposure of 24,000 mrem/year to the bronchial epithelium (which, of course, you now know is the windpipe). The borrowed volumes were quite illuminating, I found there is an official weighting factor that, when multiplied by the local dose gives the effective dose equivalent. And what does this tell you? It tells you the increase in your chances of contracting cancer if the Linear No-Threshold theory were true!
Using a weighting factor of 0.15 for each breast, a 150 mrem per breast exposure would be an equivalent "whole body" exposure totaling 45 mrem (0.045 cSv). [Exposure of the U.S. Population from Diagnostic Medical Radiation, NCRP Report #100, National Council on Radiation Protection and Measurements, Bethesda, Md.]
The figure - in my opinion - means nothing, but if we pretend it is accurate we can use it as a starting point for a "conventional" analysis.
Published in the New England Journal of Medicine in 1989, an investigation by A.B. Miller and associates charted the doses received by 31,710 women who were irradiated in the course of repeated fluoroscopic examinations between 1930 and 1952. [Miller, A.B., et al. Mortality from breast cancer after irradiation during fluoroscopic examination in patients being treated for tuberculosis. New England Journal of Medicine, 321, 1285, 1989.]
In this Canadian study, one group - in Nova Scotia - was fluoroscoped facing the X-ray source. This results in a dose to the breast approximately twenty-five times that when faced away. The women facing the source had a significant increase in cancer risk - it tripled for each 100 cGy (100,000 mrad) of radiation absorbed.
Source for Figure 28 Incidence of Breast Cancer Death Following Fluoroscopic Examination: Miller, A.B., Howe, G.R., Sherman, G.J., Lindsay, J.P., Yaffe, M.J., Dinner, P.J., Risch, H.A., and Preston, D.L. Mortality from breast cancer after irradiation during fluoroscopic examination in patients being treated for tuberculosis. New England Journal of Medicine, 321:1285, 1989.
The balance of the study was for all other provinces, with the results presented in Figure 28. Before going on, please remember that a normal annual U.S. background dose is 0.3 cGy, with the first data point on the graph at 5 cGy - about thirteen times this amount. The minimum mortality rate is at a value fifty times the annual background dose or the equivalent (using their figures) of 100 mammography exams.
On the basis of this evidence - which is almost certainly conservative, since the dose rate for fluoroscopy is much higher and, therefore, considered more traumatic to the breasts than present mammography techniques - women should have four or five mammograms per year.
Does that sound strange? That's nothing compared with the most unusual aspect of the study, namely its conclusion: The authors completely ignored the most statistically significant data points in the entire investigation, namely the 34% reduction in relative risk at 15 cGy and the 15% reduction at 24 cGy. Myron Pollycove, M.D., remarked regarding this omission:
"The decreased RR [risk rate] of breast cancer produced by low dose, low level radiation were rejected a priori by the choice of mathematical models that extrapolate the dose-risk relation from high dose exposures to low dose exposures."
[We met Dr. Pollycover back in Chapter 2. But since he is such an important player in the LNT controversy, allow me to remind you that he is professor emeritus in Laboratory Medicine and Radiology at the University of California at San Francisco, head of Nuclear Medicine at San Francisco General Hospital, as well as a visiting medical fellow on the Nuclear Regulatory Commission.]
To most of us that simply means the researchers, for whatever reason, chose to "spike" all results that indicated hormesis. Why? Probably because they were not even considering bio-positive data; they were looking for harmful effects... period. Pollycove continues:
"Nine hundred excess deaths from breast cancer are predicted theoretically from the exposure of one million women to 0.15 Gy. However, the quantified low dose data predicts with better than 99% confidence limits that instead of causing 900 deaths, a dose of 0.15 Gy would prevent 10,000 deaths in these million women."
Pardon me, but do you understand what this man - who has possibly the most impressive credentials in this entire debate - is saying? He is proclaiming that there is unmistakable evidence of hormesis in this study, which, if acted upon, might be developed into an effective weapon against breast cancer in millions of women, thousands of whom will die needlessly because of a theory that was never intended to apply to low-level radiation! It is a pity, a shame, a disgrace that the current ingrained reliance by regulators on the Linear No-Threshold hypothesis makes even a consideration of studying the hormesis phenomen extremely difficult, if not impossible.
Friday, January 1, 2016
I Still Have My Toes
We have got to stop science and scientific progress... Facts separate people. - Abby Hoffman
Dateline: Memphis, Tennessee; circa 1950: When my mother would take me to buy shoes in my pre-teen years, we would use the shoe store's fluoroscope to check the fit of shoes on my rapidly growing feet. I thoroughly enjoyed my chance to be like Superman with X-ray vision, seeing my toe bones wiggle through layers of rubber and canvas. Of course I would have to check several pairs of shoes each visit. And there were three or four visits every year.
Dateline: Europe; May 1986: After the Chernobyl accident, there was, according to the International Atomic Energy Agency in Vienna, and increase of between 100,000 to 200,000 European babies who were intentionally aborted by their mothers. These were not unwanted fetuses. The babies' mothers had been convinced they might be carrying "nuclear monsters."
* * *
What is the significance of these two events, separated as they are in time and distance? In my opinion, they show the sea change in our attitude toward radiation dangers - and provide a good example of the widespread ignorance of the means and units by which dangers can be quantified.
While we'll get around to using proper units to describe radiation and its biological effects a little later, for now let's just call the radiation I got from inspecting my toes through the fluoroscope as one SXR (Shoe X-ray). We'll compare this dose to the doses received by the Europeans after Chernobyl.
Obviously the amount of radiation received from the accident at Chernobyl would be strongly dependent on geography. In Greece, where abortions were epidemic, the dose from Chernobyl was about 1.4 SXR units. This is the equivalent of the additional radiation received from background sources in nineteen months of living in Colorado instead of Texas. In Italy it was 0.8 SXR; in France less than 0.5 SXR. The increase over background radiation in Spain and Portugal was not really measurable, as the tiny theoretical increases disappeared below the slightest variations in natural background radiation.
So, what has changed in the forty-odd years since we didn't give a thought to using the shoe fluoroscope, and today, when mothers abort their children because of a mind-distorting fear that trivial amounts of radiation would cause genetic dangers to their in utero children? And we should remember, all of this occurred long after data were widely available showing no genetic damage or excessive mutations (over the approximately 6% rate of naturally occurring genetic defects) reported in extensive investigations of Japanese mothers exposed to 100,000 times the radiation received by women downwind of the Chernobyl fire.
Before going on, though, let's look at the radiation on the borders of U.S. nuclear power plants, and also review the Three Mile Island "disaster" that anti-nuclear activists want so badly for us to consider as being on the same order of magnitude as Chernobyl.
Under U.S. law, it is the Nuclear Regulatory Commission (NRC) that regulates the amount of radiation that a nuclear power plant can emit annually at its boundary. In practice, the plants seldom approach this limit, but it amounts to just under 3% of a SXR. So, if you lived next to a power plant emitting its maximum for thirty-five years, you'd get the same amount of radiation I did each time I pushed the button to see if my Keds were large enough to be worn out before my toes pushed through.
"But what about accidents," you might ask, "such as the catastrophe at Three Mile Island?"
In our worst nuclear plant accident, the "survivors" living within a few miles of the "disaster" at TMI were subjected to a withering 0.6% of an SXR - but only if they had remained unclothed, outside, during the entire incident. Those who remained "on site" for the duration would have been exposed to just under one-half of an SXR.
But were't there injuries at TMI? Only if you consider anxiety an injury. All the reported afflictions consisted of people who were either mentally or physiologically harmed by the media's sensationalistic mishandling of the incident. Ironically, those who evacuated to the homes of relatives in Denver would have received more additional radiation in a one-day stay than had they lain naked in the front yard of their Harrisburg homes during the week of media frenzy.
[The main concern of the politicians and bureaucrats was a hydrogen bubble they feared would explode and spew radioactive materials across the state. Fortunately, there was a high-school chemistry student who reminded them that oxygen is needed for hydrogen combustion. The hydrogen was vented to the atmosphere, and the danger evaporated.]
Dateline: Memphis, Tennessee; circa 1950: When my mother would take me to buy shoes in my pre-teen years, we would use the shoe store's fluoroscope to check the fit of shoes on my rapidly growing feet. I thoroughly enjoyed my chance to be like Superman with X-ray vision, seeing my toe bones wiggle through layers of rubber and canvas. Of course I would have to check several pairs of shoes each visit. And there were three or four visits every year.
Dateline: Europe; May 1986: After the Chernobyl accident, there was, according to the International Atomic Energy Agency in Vienna, and increase of between 100,000 to 200,000 European babies who were intentionally aborted by their mothers. These were not unwanted fetuses. The babies' mothers had been convinced they might be carrying "nuclear monsters."
* * *
What is the significance of these two events, separated as they are in time and distance? In my opinion, they show the sea change in our attitude toward radiation dangers - and provide a good example of the widespread ignorance of the means and units by which dangers can be quantified.
While we'll get around to using proper units to describe radiation and its biological effects a little later, for now let's just call the radiation I got from inspecting my toes through the fluoroscope as one SXR (Shoe X-ray). We'll compare this dose to the doses received by the Europeans after Chernobyl.
Obviously the amount of radiation received from the accident at Chernobyl would be strongly dependent on geography. In Greece, where abortions were epidemic, the dose from Chernobyl was about 1.4 SXR units. This is the equivalent of the additional radiation received from background sources in nineteen months of living in Colorado instead of Texas. In Italy it was 0.8 SXR; in France less than 0.5 SXR. The increase over background radiation in Spain and Portugal was not really measurable, as the tiny theoretical increases disappeared below the slightest variations in natural background radiation.
So, what has changed in the forty-odd years since we didn't give a thought to using the shoe fluoroscope, and today, when mothers abort their children because of a mind-distorting fear that trivial amounts of radiation would cause genetic dangers to their in utero children? And we should remember, all of this occurred long after data were widely available showing no genetic damage or excessive mutations (over the approximately 6% rate of naturally occurring genetic defects) reported in extensive investigations of Japanese mothers exposed to 100,000 times the radiation received by women downwind of the Chernobyl fire.
Before going on, though, let's look at the radiation on the borders of U.S. nuclear power plants, and also review the Three Mile Island "disaster" that anti-nuclear activists want so badly for us to consider as being on the same order of magnitude as Chernobyl.
Under U.S. law, it is the Nuclear Regulatory Commission (NRC) that regulates the amount of radiation that a nuclear power plant can emit annually at its boundary. In practice, the plants seldom approach this limit, but it amounts to just under 3% of a SXR. So, if you lived next to a power plant emitting its maximum for thirty-five years, you'd get the same amount of radiation I did each time I pushed the button to see if my Keds were large enough to be worn out before my toes pushed through.
"But what about accidents," you might ask, "such as the catastrophe at Three Mile Island?"
In our worst nuclear plant accident, the "survivors" living within a few miles of the "disaster" at TMI were subjected to a withering 0.6% of an SXR - but only if they had remained unclothed, outside, during the entire incident. Those who remained "on site" for the duration would have been exposed to just under one-half of an SXR.
But were't there injuries at TMI? Only if you consider anxiety an injury. All the reported afflictions consisted of people who were either mentally or physiologically harmed by the media's sensationalistic mishandling of the incident. Ironically, those who evacuated to the homes of relatives in Denver would have received more additional radiation in a one-day stay than had they lain naked in the front yard of their Harrisburg homes during the week of media frenzy.
[The main concern of the politicians and bureaucrats was a hydrogen bubble they feared would explode and spew radioactive materials across the state. Fortunately, there was a high-school chemistry student who reminded them that oxygen is needed for hydrogen combustion. The hydrogen was vented to the atmosphere, and the danger evaporated.]
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