Woods Hole scientists return to site of 1946-58 nuclear bomb testing in Pacific
By CHRISTINE LEGERE | Cape Cod Times, Hyannis, Mass. | Published: November 6, 2017
WOODS HOLE, Mass. (Tribune News Service) — Even though the last nuclear test bomb detonated by the U.S. military on two remote Pacific Ocean atolls was 60 years ago, Woods Hole Oceanographic Institution scientists found radioactivity continues to linger in the lagoons there.
The crew of scientists just completed analysis of sediment and water samples they gathered in January 2015.
The Bikini and Enewetak atolls, each a ring of low-lying coral reef islands surrounding lagoons and part of the Marshall Islands system, were used as post-World War II nuclear weapons test sites and became known as the western part of the "U.S. Pacific Proving Grounds."
Following an evacuation of the inhabitants, 66 nuclear bomb tests were conducted there, above and below the water surface, between 1946 and 1958: 23 on Bikini Atoll and 43 on Enewetak Atoll.
The weapons tested were many times more powerful than the bombs dropped on Nagasaki and Hiroshima. In fact, three of the Enewetak islands were bombed out of existence during testing.
While radiation monitoring was extensive in the decades following the test program, it has been less frequent in recent years.
Woods Hole ocean scientist Ken Buesseler, a leader of the team, said he jumped at the chance to participate in the water and sediment sampling venture.
"I have been studying radioactivity for 30 years," Buesseler said. "I couldn't pass up an opportunity to go to Ground Zero for nuclear testing."
The Woods Hole team gathered samples of groundwater on the islands, as well as sediment from the sea floor and lagoon, during their 10-day stay in the region in January 2015.
The scientists then returned to Woods Hole to conduct their analysis.
Findings revealed levels of plutonium are 100 times higher in the lagoon water than in the neighboring Pacific Ocean, and radioactive cesium levels about two times higher.
"Put in comparison to Fukushima Daiichi, cesium is the most abundant radionuclide of concern," Buesseler said. "In the Atolls, the radionuclide of concern is plutonium."
Plutonium 239 and 240 are both used in making nuclear weapons and both remain present.
"They're not going to go away because of radioactive decay," Buesseler said.
Plutonium has a half-life of 24,000 years.
The scientists found the two main sources of radioactivity are the massive craters created by the bombs and the sediments on the floor of the lagoons.
Groundwater test results were a surprise.
"We measured the groundwater seeping from the islands into the ocean and found that wasn't a significant source of radioactivity," Buesseler said.
That proved to be the case even on Runit Island in the Enewetak Atoll, where a massive concrete cap, stretching 350 feet in diameter and called the Runit Dome, covers 111,000 cubic yards of radioactive soil and debris that U.S. workers bulldozed into a bomb crater in an effort to clean up the site in the late 1970s.
There is no liner in the crater's bottom, which sits in seawater, and the top of the dome, which has multiple cracks, is only about 10 feet above sea level.
While radioactive groundwater has not leaked much from beneath the dome area to date, rising seas and the porous coral foundation of the island atolls are a cause for concern, said groundwater specialist and fellow Woods Hole team leader Matthew Charette.
Other team members included scientists Steven Pike, Paul Henderson and Lauren Kipp.
The group sailed to the test sites from Majuro, the Marshall Islands capital, on the 185-foot research vessel Alucia. The venture was funded by the Dalio Explore Fund.
The scientists collected sediment samples from the lagoon in three-foot tubes, which divers pushed into the muddy sea floor and then capped. Back in the lab, the scientists sliced the samples to get an historic picture of the contaminants, with the deepest sediments representing the oldest.
"In some cases we couldn't do it because there had been further test blasts mixing everything up," Buesseler said.
Water samples were taken at selected sites in the lagoons, and collected from wells, cisterns, beaches and other locations on land.
Buesseler said the water was "super clear" and radioactive levels in the water low.
"The danger from the radioactivity is through ingested dust and food products," he said.
Inhabitants of the two island atolls, three generations after the bomb testing, are still not allowed to return to their ancestral homes. A brief return to the Bikini Atoll by a small group of inhabitants in the 1970s proved unsuccessful. They were once again evacuated from their homes after body scans revealed high levels of radioactive cesium.
"The concern was the cesium in the 1970s," Buesseler said. "It gets into the coconuts and the inhabitants would eat 10 to 12 coconuts each day."
None of the 26 islands that make up the Bikini Atoll are currently inhabited. Of the 40 that make up Enewetak, only one island has been resettled by about 300 inhabitants.
The U.S. nuclear bomb testing program in the atolls had a component of Cold War muscle-flexing, with camera crews and reporters accompanying the military to the Bikini Atoll for the initial test bombs, known as Able and Baker, and detonated in July 1946.
They witnessed the explosions from 10 miles away.
More than 90 surplus U.S. and captured Japanese ships — some with goats, pigs and rats aboard to help determine what the effect would be on humans and animals — were scattered throughout the lagoon.
The stated aim was to see whether naval fleets could weather a nuclear blast.
Able was detonated in the atmosphere about a half mile off the planned target. It proved to be not nearly as devastating as Baker, detonated 90 feet below water a few weeks later.
That second bomb created a crater in the lagoon floor 30 feet deep and 2,000 feet wide, based on historical records, and caused a gigantic tower of radioactive water 2,000-feet-wide to shoot 6,000 feet into the sky, raining radioactivity onto all the test ships in the lagoon, sinking one and rolling over the others.
Tests continued in the two atolls for more than a decade. The most devastating was a thermonuclear bomb called Bravo, detonated in the Bikini Atoll in 1954. It had an explosive yield of 15 megatons, according to the Marshall Islands government website.
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