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People & Events | Cleanup


Enewetak is a circular atoll in the Ralik Chain of the Marshall Islands. Enewetak Atoll is 50 miles in circumference and comprises about 40 islets surrounding a large lagoon.

People and Events on Enewetak Atoll

After an initial series of nuclear tests on Bikini Atoll in 1946, local inhabitants of Enewetak Atoll were relocated to a new home on Ujelang Atoll in December 1947 in preparation for scheduling of the first series of nuclear tests on Enewetak. Operation Sandstone commenced during April of 1948 and included 3 tests atop of 60 m high steel towers located separately on the islands of Enjebi, Aomen, and Runit. An additional 4 near-surface tests were conducted on towers as part of Operation Greenhouse during 1951. Operation Ivy, in 1952, set the stage for the first test of a large thermonuclear device. The Mike thermonuclear blast of 31 October of 1952 had an explosive yield of 10.4 Mt (USDOE, 2000) vaporizing the island of Elugelab and leaving behind a deep crater about 1 km in diameter. Early analysis of Mike fallout debris showed the presence of two new isotopes of plutonium, plutonium-244 (244Pu) and plutonium-246 (246Pu), and lead to the discovery of the new heavy elements, Einsteinum and Fermium. Operation Castle involved a single nuclear test on Enewetak in 1954 and 5 high-yield tests on Bikini. A total of 11 nuclear tests were also conducted on Enewetak in 1956 as part of Operation Redwing including an air burst from a balloon located overwater.

In 1958, the United States anticipated the acceptance of a call for suspension of atmospheric nuclear testing and assembled a large number of devices for testing before the moratorium came into effect. From April through August 1958, 22 near-surface nuclear denotations were conducted on Enewetak Atoll either on platforms, barges, or underwater, 10 tests were conducted at Bikini Atoll, 2 tests near Johnson Atoll, and a high altitude test conducted about 100 kms west of Bikini Atoll. Most nuclear tests conducted on Enewetak Atoll were detonated in the northern reaches of the atoll and produced highly localized fallout contamination of neighboring islands and the atoll lagoon. As a consequence, the northern islands on Enewetak received significantly higher levels of fallout contamination containing a range of fission products, activation products, and unfissioned nuclear fuel. By the time the test moratorium came into effect on 31 October of 1958, the United States had conducted a total of 42 nuclear tests on Enewetak Atoll.

Post Testing Era and Initial Cleanup Activities

Enewetak Atoll continued to be used for defense programs until the start of a cleanup and rehabilitation program in 1977. There were five feasible approaches considered by the Defense Nuclear Agency (NDA, 1981) for cleanup of Enewetak Atoll. The final plan called for (1) removing all radioactive and non-radioactive debris (equipment, concrete, scrap metal, etc.), (2) removing all soil that exceeded 14.8 Bq (400 pCi) of plutonium per gram of soil, (3) removing or amending soil between 1.48 and 14.8 Bq (40 and 400 pCi) of plutonium per gram of soil, determined on a case-by-case basis depending on ultimate land-use, and 4) disposing and stabilizing all this accumulated radioactive waste into a crater on Runit Island and capping it with a concrete dome. Approximately 4,000 U.S. servicemen assisted in the cleanup operations, with 6 lives lost in accidents, in what became known as the Enewetak Radiological Support Project (DOE, 1982). A estimated total of 73,000 cubic meters of surface soil across 6 different islands on Enewetak Atoll was recovered by scapping and deposited in Cactus crater on Runit Island. The Nevada Operations Office of the Department of Energy was responsible for certification of radiological conditions of each island upon completion of the project. The Operations Office also developed several large databases to document radiological conditions before and after the cleanup operations, and to provide data to update available dose assessments. The Enewetak cleanup program was largely focued on the removal and containment of plutonium along with other heavy radioactive elements. However, even during this early period of cleanup and rehabilitation, the adequacy of cleanup of the northern islands on Enewetak was brought into question because predictive dose assessments showed that ingestion of cesium-137 and other fission products from consumption of locally grown terrestrial foods was the most significant route for human exposure to residual fallout contamination on atolls affected by the nuclear test program

The people of Enewetak remained on Ujelang Atoll until resettlement of Enewetak Island in 1980. Between 1980 and 1997, the resettled population was periodically monitored for internally deposited radionuclides by scientists from the Brookhaven National Laboratory using whole body counting and plutonium urinalysis (Sun et al., 1992; 1995; 1997a; 1997b). More recently, the Department of Energy agreed to design and construct a radiological laboratory on Enewetak Island, and help develop the necessary local resources and technical expertise to maintain and operate the facility on a permanent basis. This cooperative effort was formalized in a Memorandum of Understanding signed by the U.S. Department of Energy, the Republic of the Marshall Islands, and the Enewetak/Ujelang Local Atoll Government in August of 2000 (MOU, 2000). Construction on the Enewetak Radiological Laboratory was completed in May of 2001. The laboratory facility incorporates both a permanent whole body counting system, to assess radiation doses from internally deposited cesium-137, and clean living space for collecting in-vitro bioassay samples. Scientists from the Lawrence Livermore National Laboratory continue to support the operation of the facility and are responsible for systems maintenance, training, and quality assurance.


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