Doc-10.qxd 1/21/99 10:24 AM Page 38 ASSESSING RADIATION DOSES ATTRIBUTED TO RESIDUAL RADIOACTIVE MATERIAL POTENTIAL DOSES AT THE ATOLLS BY GORDON LINSLEY AND ANDREW MCEWAN ururoa Atoll has Study, although an estimate of was assessed to be via the been populated such doses in the region was ingestion exposure pathway. Monly occasionally in provided by the United Realistic diets were used for the past, and there is no Nations Scientific Committee populations such as those evidence that Fangataufa has on the Effects of Atomic dwelling on Tureia Atoll, the ever been inhabited. The lack Radiation. (UNSCEAR). (See nearest inhabited atoll, and for of a water supply, and the box, next page.) hypothetical inhabitants of vulnerability of the atolls to the Mururoa and Fangataufa atolls. sea, make it difficult for people CATEGORIES OF For hypothetical populations to live there. EXPOSURE elsewhere, high consumption However, for the purposes of The Study estimated dose rates rates, in particular for seafood, the International Study on the due to exposure to the residual were assumed to ensure that Radiological Situation at the radionuclides from the French upper limit estimates of dose Atolls of Mururoa and nuclear tests for critical groups rates were obtained. Fangataufa, the existence of a of people, for both present and Where possible, the hypothetical population future conditions. Estimates concentrations of radionuclides 38 resident on Mururoa was were made for the following in foodstuffs were obtained by assumed in order to determine categories of groups: direct measurement. If direct potential radiation doses. The ■ present exposure for hypo- measurement was not possible, estimation of doses to more thetical inhabitants of Mururoa as for hypothetical distant communities was also and Fangataufa atolls; populations, concentrations in necessary in order to establish ■ present exposure for inhabi- foodstuffs were estimated. the significance of any releases tants of Tureia Atoll, the nearest of radioactive materials. inhabited atoll in the region; PRESENT DOSES The assessment takes ■ future exposure for inhabi- AT THE ATOLLS account of the dispersion of tants of the region and any A population permanently resi- radionuclides both from the inhabitants of Mururoa and dent on the atolls with a diet of underground and atmospheric Fangataufa atolls as a conse- local produce and seafood from tests, and from accelerated quence of the residual radioac- the lagoons would not gener- releases of material due to tive material now present in ally receive a radiation dose disruptive events of natural or the environment and that part attributable to the residual human origin, such as a of the radioactive material con- radioactive material exceeding landslide, or to changes in tained underground which will climatic conditions. migrate to the accessible envi- Mr. Linsley is Head of the Waste The assessment was ronment in the future; Safety Section in the IAEA concerned with the present and ■ potential exposure of inhabi- Division of Radiation and Waste future radiation doses due to tants of the region and hypo- Safety. Mr. McEwan, Director of residues at Mururoa and thetical inhabitants of Mururoa the National Radiation Fangataufa Atolls. Doses and Fangataufa atolls as a con- Laboratory in New Zealand, received in the past as a result sequence of postulated disrup- served as Chairman of Task Group of the fallout at the time of the tive events. A of the Study on the Radiological French atmospheric testing Pathways of Exposure. The Situation at the Atolls of Mururoa IAEA BULLETIN, 40/4/1998 were not evaluated in the major contribution to doses and Fangataufa. Doc-10.qxd 1/21/99 10:24 AM Page 39 0.01 mSv per year. This is PAST RADIATION DOSES equivalent to a very small frac- FROM FALLOUT tion (less than one part in 200) At the time of the French atmospheric tests between 1966 -74, of the total dose that such a about 5000 people were living within 1000 kilometers of the French resident population would test site, and local exposures did occur, for five tests in particular (see unavoidably receive from nat- table) owing to unusual wind and rainfall conditions. Four tests ural radiation sources. (See caused effective doses of 1to 5 mSv to residents of Tureia (the closest table and box, next page.) inhabited atoll, at a distance of 130 kilometers to the north of The dose estimates are based Mururoa) and the Gambier Islands (400 kilometers southeast of on measured levels of man- Mururoa) in 1966–71. One test caused doses of up to 0.8 mSv to made radionuclides in the residents of Tahiti (1200 kilometers to the northwest) in 1974. environments of the atolls, Only a few individuals on these islands would have received the which will include maximum estimated doses given in the table below. In Tahiti, for contributions from global example, most people would have received external exposures only. fallout (i.e. fallout from all Some internal exposures were estimated on the other islands resulting atmospheric nuclear weapon from the ingestion of green vegetables or lagoon molluscs. testing). Except in the case of Exposures at the time were due largely to the fallout of short- seafoods, it is not possible to lived radionuclides, for example radioactive iodine (especially iodine- determine those contributions 131 with a half-life of eight days). Measurements of iodine-131 to the measured concentrations in milk were made at many locations in the southern environmental levels, and hemisphere during the period of atmospheric nuclear testing at the therefore those fractions of the atolls of Mururoa and Fangataufa. Thyroid equivalent doses received estimated doses that are due to by people as a result of the nuclear tests at the two atolls are believed global fallout. not to have exceeded 10 mSv over the whole period of atmospheric The present average annual testing from 1966–74. dose within the entire 20o to 30o southern latitude band of PAST DOSES FOR MAXIMALLY EXPOSED INDIVIDUALS 39 Mururoa Atoll due to global Date of Location of Annual effective dose fallout is estimated to be of nuclear test exposure (mSv) External Inhalation Ingestion Total the order of 0.002 to 2 July 1966 Gambier Islands 3.4 0.18 1.9 5.5 0.003 mSv. 2 July 1967 Tureia Atoll 0.7 0.023 0.17 0.9 PRESENT DOSES 12 June 1971 Tureia Atoll 0.9 0.003 0.43 1.3 IN THE SOUTH 8 August 1971 Gambier Islands 0.9 0.002 0.24 1.2 PACIFIC OCEAN 17 July 1974 Tahiti (Mahina) 0.6 0.08 0.06 0.8 Present annual doses to inhabitants of other South of around 120), as a result of atolls alone is indeterminate, Pacific islands attributable to releases of radionuclides from since the dose estimates are the residual radioactive mater- Mururoa and Fangataufa. based on measured levels of ial in the accessible environ- Tureia Atoll did receive total man-made radionuclides ment were also estimated. some fallout, however, at the in the environments of Tureia There are some 5000 people time of the atmospheric Atoll, which will include living within 1000 kilometers nuclear tests carried out at some contribution from of Mururoa. The Study esti- Mururoa and Fangataufa global fallout. The dose of mated that only negligible atolls, over and above global 0.005 mSv per year is very doses (of less than 0.0001 fallout. The radiation doses small in comparison with the mSv per year) are being being received by its residents total doses that Tureian received by the residents of as a result of all earlier fallout inhabitants receive from Tureia Atoll, the nearest were estimated to be about natural sources of radiation inhabited land to Mururoa 0.005 mSv per year. Again, and is similar to the dose and Fangataufa atolls (at the fraction of this dose that rate calculated for the about 130 kilometers from is due to fallout from the tests hypothetical population of Mururoa, with a population at Mururoa and Fangataufa Mururoa Atoll. IAEA BULLETIN, 40/4/1998 Doc-10.qxd 1/21/99 10:24 AM Page 40 PRESENT DOSES TO ADULT INHABITANTS DUE TO RESIDUAL RADIOACTIVE MATERIAL & GLOBAL FALLOUT Pathway Annual dose Annual dose at (hypothetical estimates at the Anemone Site on Mururoa Atoll) Tureia Atoll (mSv) (mSv) External irradiation ~0.0011 <0.001 Inhalation <0.0001 — Ingestion: terrestrial foods 0.0009a 0.004a Ingestion: seafood 0.0043b 0.00001b Total ~0.006 ~0.005 aAn indeterminate part of this dose derives from global fallout. bThe contribution to the aquatic ingestion dose from seafood of 0.0004 mSv arising from global fallout is not included in this dose estimate. It should be noted that there COMPARISON OF RADIATION DOSES are differences in the contributions to doses by the Source of dose Dose different exposure pathways for Global natural background doses (mSv per year) ■ Tureia Atoll and Mururoa Typical range 1 to10 ■ Maximum ~ 100 Atoll. At Tureia Atoll, seafood ■ Average 2.4 consumption is high, but the contribution to dose by this Mururoa and Fangataufa atolls pathway is insignificant since ■ Dose due to natural background radiation 1.4 to 3 40 there is virtually no radioactive Estimated current additional doses from remaining residual material due to fallout in the radioactive material at Mururoa and Fangataufa atolls lagoon sediments. The ■ Maximum at Tureia Atoll <0.0001 consumption of terrestrial ■ Average at Mururoa and Fangataufa atolls <0.01 foods is the more important ■ Maximum at Kilo-Empereur region contributor to dose owing to of Fangataufa Atoll ~0.25 the greater deposition on land Maximum additional dose at Tureia Atoll at Tureia of caesium-137 from following a rock slide at Mururoa Atoll 0.007 (initial year) the atmospheric nuclear tests at the time than at Mururoa Atoll.