We can't pretend to be nuclear physicists, but this piqued our interest, too, so we've given it our best shot.
Originally named the Nevada Proving Ground, then, until recently, the Nevada Test Site, and now the Nevada National Security Site, is a 1,360-square-mile United States Department of Energy reservation located in southeastern Nye County (about 65 miles northwest of Las Vegas), which was established on 11 January 1951 for the testing of nuclear devices. Between 1951 and 1992 there were a total of 928 announced nuclear tests at Nevada Test Site, of which the majority (828) were underground, at depths of up to 5,000 feet.
Back in the early days of the atomic era, there was little or no understanding of the risks of exposure to radiation (or, more cynically, official denial), and the frequent explosions at the NTS were a popular Las Vegas tourist attraction, with groups of VIPs being taken out to the desert to watch in close proximity, and even a Miss Atom Bomb contest (see QoD 5/20/2006).
While researching this answer, we came across this document, dated 1955 and full of jolly cartoons of happy desert dwellers. It's from the Test Manager of the site, addressed to those living in proximity, emphasizing that they were not at risk, even if accidentally exposed to nuclear fall-out:
"If you are in an area exposed to fall-out, you will be so advised by our radiation monitors. If there is any probability that exposure to fall-out will approach our very conservative exposure guides, you will be advised what to do. As has happened at St. George and Lincoln Mine, you might be advised to stay indoors for a few hours until the fall-out loses its strength. If you have been outdoors during the fall-out you might be advised to bathe, wash your hair, dust your clothes, shake off your shoes, etc. If the fall-out is across a highway, traffic might be halted temporarily."
So, the reassuring official message from the Atomic Energy Commission was that any dangers arising from their frequent nuclear tests were nothing that a quick shakedown and shower couldn't cure, with the possible additional inconvenience of the odd minor traffic delay.
The report goes on to further allay any fears about the dangers of exposure to radiation:
"Fixed recording stations, mobile teams with recording instruments, low-flying aircraft which measure ground-level radiation, and planes which track the atomic air mass are all used. Thousands of reports are made.
"These reports have shown that, under the controls used in Nevada, there has been no significant fall-out anywhere in the nearby region as a result of aerial bursts in which the fireball did not touch the ground. Fall-out levels have been very low--only slightly more than normal radiation which you experience day in and day out wherever you may live.
"The reports have shown that with low tower, surface, or underground shots--where the fireball touches the ground--there has been heavier fall-out. As the AEC has reported, no person in the nearby region has been exposed to hazardous amounts of radiation, even from this heavier fall-out, and no crops or water supplies have been made hazardous to health. Fall-out of significance to animals has been experienced only close to the site of the detonation."
Subsequent developments would call into question what could most charitably be described as this naive optimism, however.
In 1979, a study reported in the New England Journal of Medicine concluded that a significant excess of leukemia deaths occurred in children born between 1951 and 1958 and residing in counties receiving high fallout from the NTS.
Three years later, a lawsuit brought by nearly 1,200 people accused the government of negligence in atomic and/or nuclear weapons testing at the Nevada Test Site in the 1950s and that radiation protection measures in the tests were substandard. In a subsequent report by the National Cancer Institute, it was determined that ninety of the atmospheric tests at the NTS had deposited levels of radioactive iodine-131 high enough to produce 10,000 to 75,000 cases of thyroid cancer. To date, well over 10,000 claims have been approved, with settlements totalling over half a billion dollars paid out in compensation to cancer victims who lived downwind of the NTS during the early testing years.
In terms of the long-term environmental impact of the tests in the Nevada dessert, when testing ended in 1992, the Energy Department estimated that more than 300 million curies (1,110,000,000 Bqu) of radiation remained. If accurate, this makes the site one of the most radioactively contaminated places in the United States, with radioactivity levels in the worst-affected zones reaching millions of picocuries per liter. The federal standard for drinking water is 20 pCI per liter. (1 curie or Ci = 1000 mCi; 1 mCi = 1000 µCi; 1 µCi = 1000 nCi; 1 nCi = 1000 pCi.)
Although radiation levels in the water continue to decline over time, it's estimated that the longer-lived isotopes will continue to pose risks for tens of thousands of years to come. However, as the contaminated water is generally at depths of hundreds or even thousands of feet, in a remote area of the desert, it's not considered an immediate health risk.
As to how these levels compare with those in Japan, it's difficult to conclude, since data is sketchy for the 1950s NTS area and the preferred units of measurement for radiactivity and exposure doses have changed over the years, so it's hard to compare like with like (and, as we prefaced this article, we're not nuclear physicists).
However, according to data we do have, leaked water sampled from one unit at the Fukushima Daiichi nuclear plant recently had 100,000 times the radioactivity of normal background levels. This is less radioactive than the worst samples in Nevada; however, the latter are generally buried underground and the NTS is considered safe enough for monthly tours these days, whereas in Japan nuclear workers and local residents are being directly exposed to elevated radiation levels.
To put that in perspective, the occupational Threshold Limit Values (TLVs) for workers in the nuclear environment is an average annual dose of 0.05 Sieverts (50 mSv), while for the general public it's 1 mSv. With radiation being released at a rate measured at 1,000 millisieverts per hour, a worker at the Fukushima plant would reach his yearly occupational exposure limit in 15 minutes. A dose of 4,000 to 5,000 millisieverts absorbed fairly rapidly will eventually kill about half of those exposed. With a dose of 10 Sv, you risk death within days or weeks.
For daily updates on radiation levels across Japan, in microsieverts, and what the implications of those levels are health-wise, click here.
In terms of the level of radiation being detected in various U.S. states that is being attributed to fall-out from the Japanese nuclear reactor, obviously there is a spectrum of opinion as to its severity and significance and we're not qualified to comment. Radiation from Japan has turned up in either rainwater or air in Alaska, Alabama, California, Hawaii, Idaho, Nevada, Pennsylvania, Ohio, Vermont, South Carolina, and Washington, with levels of radioactive iodine-131 that exceeded drinking water standards by 181 times found recently in a rainwater sample outside San Franciso.
The agency maintains that the radiation poses no risk to human health, however, and that drinking-water levels are set for long-term exposure, while rainwater exposure is of short duration. This makes sense and we're not unduly concerned about any local impact, although we realize that similar sweeping statements have been made in the past and turned out to be less than 100-percent accurate...
If you're interested in Nevada's nuclear past and haven't yet paid a visit to the Atomic Testing Museum, we strongly recommend that you do. It's a surprisingly engaging, fun, and interactive educational experience. Give yourself at least a couple of hours to explore, or you'll find you miss out.
