Nuclear testing

DEFINITION: Explosion of nuclear devices to evaluate their utility as weapons

Since 1945, hundreds of nuclear devices have been exploded in the atmosphere and underground as part of the testing of nuclear weapons systems. Such testing has raised concerns about nuclear fallout and its effects on human health and the environment.

The United States began nuclear testing with the shot code-named Trinity on July 16, 1945, at Alamogordo, New Mexico. The United States has tested 219 nuclear devices in the atmosphere, with the last atmospheric test occurring in 1963. Most of these tests were conducted at the Nevada Test Site, but the most powerful tests were done in the South Pacific at Christmas Island and in the Marshall Islands at Bikini Atoll and Enewetak Atoll.

The former Soviet Union conducted 219 atmospheric tests, the last one in 1962. Nearly all these tests were at the Semipalatinsk Test Site in Kazakhstan or at the Northern Test Site, Novaya Zemlya. The higher-yield weapons were tested at the Northern Test Site, including a 50-megaton bomb on October 30, 1961, the largest weapon ever exploded. The last of China’s twenty-three atmospheric tests occurred in 1980. These were conducted at the Lop Nur Test Site in northwest China. Britain conducted twenty-one atmospheric tests off Christmas Island, near Monte Bello Island off Australia, and at sites in South Australia. Britain ended atmospheric testing in 1965. France, which continued atmospheric testing into 1974, conducted fifty-six such tests at Reggane in Algeria and at Fangataufa and Moruroa in the South Pacific.

The United States ended underground testing in 1992, the former Soviet Union in 1990, Britain in 1991, France in 1996, and China in 1996. Pakistan and India both conducted underground tests in 1998. In 2006, North Korea announced that it had conducted its first underground nuclear test, confirming years of suspicion that the relatively politically isolated country had been developing nuclear weaponry. Though this activity was denounced by Western nations including the United States, North Korea continued to conduct further nuclear tests in 2009, 2013, 2016, and 2017. The 2016 test, North Korea claimed, was its first successful test of a hydrogen bomb, and with the 2017 test (causing a 6.3 magnitude earthquake), the country asserted that it had developed the capability to attach the nuclear weapon to an intercontinental ballistic missile. With some notable exceptions, little in the atmosphere has resulted from the underground tests by the United States, Britain, and France. The chief adverse environmental effect of most of these underground tests is that the radioactive subterranean rubble might someday pollute groundwater. The former Soviet Union was less successful in containing the radioactivity of underground tests. As of July 2024, North Korea’s test in 2017 was the last confirmed nuclear test on Earth.

Testing at Bikini

The global effect of atmospheric nuclear tests is judged to be small, since the dose that individuals received from global fallout was less than they received from natural background radiation. In contrast, local fallout from atmospheric tests has had serious consequences. The most notorious case of injury from radioactive fallout occurred with the Bravo shot of March 1, 1954, at Bikini Atoll in the South Pacific. The weapon’s yield of about 15 megatons was three to four times what was expected. Twelve hours before the test, the wind direction changed, and it was understood that the fallout would no longer be carried safely out to sea. The decision to proceed despite the wind change shows that scientists vastly underestimated the problems that could result from to radioactive fallout.

The nine-man firing team crouched in a bunker only 32 kilometers (20 miles) from ground zero. As their radiation meters began to show unexpectedly high amounts of fallout, they sealed their bunker. Navy ships that were arriving to pick up the firing team and recover scientific data encountered such heavy fallout 50 kilometers (31 miles) out that they retreated at top speed. The fallout ceased after three hours. The ships were washed and returned to rescue the firing party. Covered with bedsheets sealed with masking tape to keep out fallout particles, the members of the firing party drove 1 kilometer (0.6 miles) to the landing site and were taken to the rescue ship by helicopter.

Radiation doses are measured in grays (Gy). (The old unit for an absorbed dose was the rad; 1 gray equals 100 rads.) Normal background radiation results in a dose of around 0.002 Gy per year. Acute doses are doses received over several days instead of over months or years. Acute doses of 0.25 Gy or less generally result in no obvious injuries. Radiation sickness and some obvious injuries begin to occur with acute doses between 0.5 and 1.0 Gy. An acute dose of 6.0 Gy is generally fatal. The men of the firing party received only 0.005 Gy. Had they been outside their bunker, they would have received more than a fatal dose during the first few hours.

Groups farther from Bikini were evacuated as the magnitude of their peril became clear. It was not until two days after the blast that eighty-two people were taken from Rongelap Atoll, 200 kilometers (124 miles) east of Bikini. They received an estimated 1.0 Gy, and some were already showing signs of radiation sickness. A survey flight failed to detect significant radiation over Rongerik Atoll, 240 kilometers (149 miles) east of Bikini, but sensors on the ground did. Again, the magnitude of the problem was unclear, and the twenty-eight men at the weather station on Rongerik were not evacuated before they received an estimated 0.3 to 0.5 Gy. The final evacuation was a group of 158 inhabitants on Utirik Atoll, 500 kilometers (310 miles) from Bikini. They received an estimated 0.15 Gy.

The greatest radiation dose was received by twenty-three Japanese fishermen who unwittingly sailed their vessel, the Lucky Dragon, into the fallout cloud only 160 kilometers (100 miles) from Bikini. Not realizing that they should wash the fallout from their ship, their dose continued to increase during their two-week voyage to port. By then, their estimated dose was between 1.3 and 4.5 Gy. The ship’s radioman, Aikichi Kuboyama, died seven months later of hepatitis, a complication brought on by his treatment for radiation sickness.

After Effects of the Bikini Tests

Further weapons tests were conducted at Bikini Atoll in 1956 and 1958. By 1967, most of the radioactivity had been swept away by nature or had decayed, and pressure mounted to return the refugees to their home. Radioactive debris from the tests, some plants, and some topsoil were removed from Bikini. New trees were planted, and new houses were built. The first group was resettled on Bikini in 1969. However, some water wells and some local foods were mildly radioactive. Two radioactive elements, strontium 90 and cesium 137, accumulated in the inhabitants’ bodies to worrisome levels. They were evacuated again in 1978.

By the mid-1990s, lush vegetation made Bikini seem like paradise, and the atoll’s former inhabitants were again anxious to return. In 1997, however, the International Atomic Energy Agency recommended against resettlement of the island because of the risks of radiation from locally grown food. Bikinians argued that the coconut trees would take potassium from the soil instead of the radioactive cesium; therefore, if the food trees were given a heavy dose of potassium fertilizer, and if a few centimeters of topsoil around the living areas were scraped away, it should be safe for the inhabitants to return. Critics of the plan argued that devastating environmental damage would be caused by scraping away so much topsoil. Arguments concerning resettlement of the native extended into the twenty-first century. Responding to considerable pressure, the US Congress eventually set aside over $600 million by 2021 for health care and other needs of the Marshall Islanders affected by nuclear tests. As of early 2024, Bikini residents had still not been able to return to their homes due to tested levels of radiation remaining a concern for safety.

Following World War II, five nuclear tests were carried out at the Bikini and Enewetak Atolls. However, logistic and security problems made it attractive for the US government to seek a test site in the continental United States. The Nevada Test Site was chosen because the government already owned the land, its surroundings were only sparsely populated, and it was close to the Los Alamos weapons laboratory. The best evidence available showed that off-site fallout from devices with yields less than 50 kilotons would be minimal. This estimate proved to be too optimistic, however. Although the contamination was light, teams occasionally closed sections of state highways for a few hours or a day and had vehicles washed off. More seriously, on May 19, 1953, fallout near St. George, Utah, amounted to 0.05 Gy for people in the open.

The legacy of the United States’ testing of nuclear weapons remained a concern in the early twenty-first century, with many groups pushing for compensation for those affected by nuclear testing and contamination. Although the Radiation Exposure Compensation Act (RECA) was passed in 1990 and provided compensation for certain groups affected by radiation exposure caused by the US government, it was set to expire in 2022 before being extended by President Joe Biden to June 2024. After its expiration, Congress struggled to reach a consensus on whether it should be renewed.

Iodine 131

Years of careful study have shown that iodine 131 is probably the most dangerous element of nuclear fallout. It accounts for 30 percent of the radioactivity produced by a nuclear bomb, but it rapidly decays. Its activity decreases by one-half every eight days, so that after one or two months, it has virtually disappeared. Two factors make iodine 131 dangerous: Cows and goats that graze on plants dusted with fallout concentrate iodine in their milk, and iodine ingested by humans concentrates in their thyroids. This two-step process means that significant doses to the thyroid might result from fallout levels previously considered harmless. US scientists also learned that rainstorms or snowstorms could wash enough fallout from the air to create fallout hot spots as far away from the Nevada Test Site as the East Coast.

Scientists at the National Cancer Institute estimated a per capita thyroid dose in the United States caused by iodine 131 from all the nuclear tests. They accomplished this by using available fallout measurements, the predictions of mathematical models, weather data, and information on patterns of milk consumption. During testing periods, children between the ages of three months and five years received thyroid doses three to seven times the average per capita because they drank more milk and because their thyroids were smaller. The estimated twenty thousand individuals who drank goats’ milk were at greater risk, because goats’ milk concentrates iodine ten to twenty times more than does cows’ milk. Much smaller doses of radioactivity may have come from eating other dairy products or leafy vegetables.

Thyroid cancer is rare, occurring in only 3 or 4 people out of 100,000. Officials at the National Cancer Institute have estimated that nationwide, fallout might have caused 10,000 to 75,000 cases of thyroid abnormalities. It has been pointed out that individuals who were born in the 1950s, drank a lot of milk as children, and lived in areas that received the most fallout would be prudent to seek medical examination of their thyroids.

This fallout was probably allowed to occur because of ignorance of its effects and because of the Cold War mentality. At the time, it was believed that some risk to the public was justified by the needs of the national defense. It also took some years for scientists to collect convincing data that dangerous levels of iodine 131 from fallout could concentrate in the thyroid. Even those doses were no higher than those given by fluoroscopy examinations and some X-ray procedures in the early 1950s.

Scientists at the University of Exeter in the United Kingdom pioneered an ingenious use of radioactive tracers: the estimation of rates of soil and deposition on agricultural land through the measurement of amounts of radioactive cesium at different locations. Tiny amounts of radioactive cesium were deposited worldwide during the years when nuclear weapons were tested in the atmosphere. In undisturbed permanent pastureland or rangeland, the cesium remains near the surface, and scientists need only compare the cesium concentrations from various locations with that of an undisturbed site to determine the amount of erosion.

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