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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 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 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 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. For Mururoa Atoll, and to individuals consuming lagoons is relatively large; some where there is plutonium in similar quantities of seafood five kilograms at Mururoa Atoll the lagoon sediments, seafood from areas neighbouring South and three kilograms at consumption is the more America are all negligible; Fangataufa Atoll. However, this important pathway. typical doses are many orders plutonium will deliver only very Doses to individuals of magnitude below average small doses owing to its low rate consuming seafood caught in doses due to natural of transfer via feasible pathways Pacific fishing areas further background radiation. to people. The availability of afield were also estimated. The plutonium is also decreasing dose rates are, in all cases, very PARTICULAR owing to the removal of the much lower even than the dose SITUATIONS lagoon sediments over time to rates calculated for Mururoa The Study in addition consid- the ocean, and the gradual and Fangataufa atolls. Present ered four particular situations burial and dilution of lagoon annual doses to high at Mururoa and Fangataufa. sediments by the accumulation consumers of seafood caught ■ Plutonium in the lagoons. of fresh sediments. from areas neighbouring The inventory of plutonium in ■ Tritium in the lagoons. The IAEA BULLETIN, 40/4/1998 Australia and New Zealand the sediments of the two concentration of tritium in the Doc-10.qxd 1/21/99 10:24 AM Page 41

lagoons is at present some ten coral bedrock collected on about ten times the average times higher than the very low Colette and in sand from a sand dose accumulated in 50 years levels in the open ocean (of the bank in the lagoon adjacent to from natural radiation sources. order of 1000 Bq/m3 the Colette area. The lifetime dose would respectively), as a consequence These particles provide depend on the age of the of releases from underground another pathway for potential individual and on the solubility sources. However, tritium is exposure in the Colette area. If of the particle in body fluids. one of the least radiotoxic of an individual were to go to For a child, the lifetime dose radionuclides. Continuous Colette motu or the smaller could be higher by up to a drinking of fresh water motus of Ariel and Vesta (which factor of two. Given the containing 1.6 x 108 Bq/m3 are on a remote part of the atoll protracted (chronic) nature of would be required to lead to a rim and barely above sea level), the exposure, it is unlikely that dose of 2.4 mSv per year, the there is a risk, albeit very small, any immediately apparent average annual dose received that such a particle could be health effect, apart from the from naturally occurring incorporated into the body via a production of a small nodule sources of radiation. The cut and retained. The of dead tissue around the radiation doses which would consequent exposure would particle, would be experienced result from the tritium in the persist unless the particle were as a result of such an intake, lagoon are therefore negligible. removed (by natural process or even by highly active particles. ■ Potential exposure due to human action) and a significant The chance of such an particulates containing radiation dose could be exposure actually occurring plutonium. The atmospheric accumulated. The assumption is was estimated to be very safety trials that were conducted that while the particle remained remote, however. The on the motus of Colette, Ariel in the body it would be a probability of an individual and Vesta on Mururoa Atoll continuous source of living on Mururoa incurring resulted in the explosive plutonium; the plutonium fatal cancer in this way is dispersion of plutonium would slowly dissolve in body estimated to be less than one in 41 (together with small quantities fluids and would be transported one million per year. of americium). The Study to critical organs and tissues (in ■ Doses to a hypothetical found that the general surface particular bone) which would critical group on Fangataufa. activity of residual plutonium in be continuously irradiated. The Study indicates that the the area was perhaps three times Information obtained from highest doses that could be the French criterion for clean- the Study’s own survey and received as a result of residues up operations of 106 Bq/m2 examination of collected from the French nuclear tests which was established to limit particles was sufficient for an would be doses to a potential exposures via estimate of the overall hypothetical and very small inhalation of finely divided radiological risk to be made. group of people consuming coral containing plutonium. Data from experimental studies only local produce from a This enhanced level of general of the incorporation of similar limited area of the Kilo- surface activity would, however, active particles from the Empereur region of Fangataufa lead only to low doses; for Maralinga nuclear test site in Atoll. This region is windward example, less than 0.001 mSv Australia were used. For a of the site where a 125 kiloton per year to people such as retained plutonium oxide atmospheric barge test was fishermen who might spend particle, the estimated carried out on 24 September 120 hours per year in the area. potential effective dose to an 1966. The barge test left a Some of the dispersed adult could range between 9 x narrow strip of land along radioactive material is in the 10-8 and 9 x 10-6 Sv/Bq. three kilometers of the atoll form of discrete particles, If one of the most active rim with elevated levels of however, ranging in size from particles of plutonium, of caesium-137 and other the order of 0.1 millimeter up around 100,000 Bq, were to be radionuclides in the soil, to perhaps 1 millimeter. retained in the body, doses over though the distribution is very Plutonium particles were found a lifetime of up to around patchy. The dose would be due in samples of sand, coral and 1000 mSv could result. This is mainly to the supposed IAEA BULLETIN, 40/4/1998 Doc-10.qxd 1/21/99 10:24 AM Page 42

consumption of coconuts and According to the Study’s from underground radioactiv- other produce containing predictions, the rate of ity at Mururoa and Fangataufa caesium-137, all grown in areas leaching of the caesium-137, are predicted to be less than of the strip where the levels of strontium-90 and plutonium- those very low values from this radionuclide are highest. 239,240 in the lagoon radionuclides currently present The consequent effective dose sediments, which are in the accessible environment. rate would be less than 0.25 mSv responsible for present levels of ■ Potential exposure of inhab- per year. This is equivalent to these radionuclides in lagoon itants of the region as a conse- about 10% of the annual water, will continue to decrease quence of postulated disrup- background radiation dose that with time, as will the estimated tive events. The Study investi- such a resident population radiation doses associated with gated the radiological conse- would unavoidably receive from these radionuclides. Estimated quences of postulated disruptive natural sources alone. However, hypothetical future doses from events. These included glaciation this hypothetical scenario is the existing sources at Mururoa and a slide of carbonate rock considered highly unlikely to if the atolls were actually to be leading to a release of radionu- occur in practice, since inhabited would initially clides into the ocean. In the case Fangataufa Atoll is virtually decline over 100 years from the of a rock slide, the highest hypo- uninhabitable by people present maximum of no more thetical annual doses would be adopting a traditional semi- than 0.01 mSv per year to received by residents of nearby subsistence lifestyle; the Atoll is about 0.001 mSv per year as atolls, since any radionuclides so on occasions inundated by the residual radioactive released would be carried away seawater and has no fresh water material at the surface decays by ocean currents. For the resi- and edible crops other than and disperses. (It should be dents of Tureia Atoll, the dose in some coconuts. noted that these doses will rise the first year following such a in the long-term future as rock slide would not be more ESTIMATED DOSES plutonium migrating from than a few thousandths of a mil- 42 IN THE FUTURE underground reaches the lisievert, even if it were pes- Three cases were considered in lagoons; however, they will simistically assumed that all the the estimation of doses to popu- never exceed present doses.) plutonium involved in the slide lations in the future. ■ Potential exposure due to went into solution. This dose ■ Doses in the future due to underground radionuclides. would only occur in the one year residual radioactive material The assessment of the likely following the rock slide; subse- presently in the accessible envi- future releases due to the quent doses would be progres- ronment. The estimated annual migration of radionuclides sively lower as the radioactive radiation doses to any possible from underground sources material was dispersed. future inhabitants of Mururoa shows that the releases of cae- and Fangataufa due to the gen- sium-137 and strontium-90 to CONCLUSION eral dispersion of radionuclides the lagoon will decrease with Overall, the Study analyzed from nuclear tests in the envi- time but that, after an initial potential radiation doses to pre- ronment are all small in absolute decline, the plutonium release sent and future hypothetical terms and insignificant on the rate will increase to a maxi- population groups at the atolls. basis of any existing criterion or mum after 5000 to 6000 years. It found that — except in the comparison. Radiation doses However, even at the time of hypothetical case on the Kilo- due to radioactive material this maximum, the associated Empereur rim of Fangataufa — already in the accessible environ- estimated doses to hypothetical no group is likely to receive at ment — principally arising from Mururoa residents would be any time a dose attributable to caesium-137 and plutonium- less than those estimated to be the residual radioactive material 239,240 — will persist. But they received today by the same at Mururoa and Fangataufa will decline in magnitude owing hypothetical residents, that is, which exceeds approximately to both radioactive decay and less than 0.01 mSv per year. 1% of the background radiation other processes that reduce the Similarly, exposures at other dose that the group will availability of these radionuclides locations in the South Pacific unavoidably receive from nat- IAEA BULLETIN, 40/4/1998 in the environment. in the future due to releases ural radiation sources. ❐