[ RadSafe ] " LLNL research at Marshall Islands could lead to resettlement "

[Jaro Franta]

http://www.physorg.com/news185122428.html 
LLNL research at Marshall Islands could lead to resettlement
February 11, 2010

Through Laboratory soil cleanup methods, residents of Bikini, Enjebi and
Rongelap Islands - where nuclear tests were conducted on the atolls and in
the ocean surrounding them in the 1950s - could have lower radioactive
levels than the average background dose for residents in the United States
and Europe. 

The National Nuclear Security Administration's Lawrence Livermore National
Laboratory scientists Bill Robison and Terry Hamilton calculated the
radiation doses for people resettling Bikini, Enjebi, Rongelap and Utrok
Islands. The two found that when it rains, a portion of the soluble
cesium-137 (137Cs) - an isotope of cesium - is transported to the
groundwater that lies about three meters below the soil surface. The
groundwater eventually gets mixed with the ocean waters so the 137Cs is lost
from the soil and is not available for uptake by growing vegetation on the
island. The rate of this loss process is much faster than the loss by
radiological decay.

In addition, treatment of food crops with potassium reduces the 137Cs
concentration in edible fruits to about 5 percent of pretreatment
concentrations. Potassium treatment and removal of the top 15 centimeters of
soil around houses and community buildings prior to construction of new
buildings to reduce external exposure where people spend most of their time
- referred to as the combined option - could be used as a remediation
strategy before resettlement, Robison said.

"If this approach is taken, the natural background dose plus the
nuclear-test-related dose at Bikini, Enjebi and Rongelap would be less than
the usual background dose in the United States and Europe," Hamilton said.

The United States conducted 24 nuclear tests at Bikini Atoll with a total
yield of 76.8 megatons (MT). The Castle series of tests produced about 60
percent of this total yield and included the 15-megaton Bravo test that was
the primary source of radioactive contamination of Bikini Island and
Rongelap and Utrok Atolls. Pretest estimated yield for the Bravo test was
about five megatons. The much larger yield resulted in vaporization of more
coral reef and island than expected and the debris-cloud reached a much
higher altitude than anticipated.

High-altitude winds were to the east at the time of detonation and carried
the radioactive debris toward Rongelap Atoll. Utrok Atoll also received
fallout from the Bravo test but at much lower air and ground-level
concentrations than at Rongelap Atoll. Other atolls received Bravo fallout
at levels below that of Utrok.

Today, scientists in Lawrence Livermore's Marshall Islands Dose Assessment
and Radioecology Program work to minimize exposure through ingestion and
other pathways for the Marshallese now living on or wishing to return to
their islands. The program continues research begun nearly 30 years ago to
characterize radiological conditions on affected islands and develop
strategies to minimize radiological exposure to a people who want to
resettle. The program also supports Marshallese efforts to implement
radiation protection programs for residents wishing to track their exposure
to radionuclides from fallout contamination that still lingers on the
islands.

Previous assessments showed that 137Cs accounts for about 98 percent of the
total dose for returning resident at the various atolls. About 85 percent to
90 percent of the dose (depending on the atoll) is from consumption of
locally grown foods such as coconut meat and fluid, copra meat and milk,
Pandanus fruit and breadfruit. About 10 percent of the dose is due to
external gamma radiation from 137Cs in the soil. Isotopes of strontium,
plutonium and americium account for less than 5 percent of the estimated
dose.

The research appears as the cover article in the journal, Health Physics.