International Advisory Committee (IAC) Working Group 4 (1998), The Radiological Situation in the Atolls of Mururoa and Fangataufa, Technical Report, Volume 4, Releases to the Biosphere of Radionuclides from Underground Nuclear Weapon Tests at the Atolls, International Atomic Energy Agency (IAEA), Vienna, 270 pp. [The Members of Working Group 4 (Geosphere radionuclide transport) of Task Group B (Evaluation of potential long term radiological situation) were Fairhurst, C., de Marsily, G., Hadermann, J., Nitsche, H., Sastratenaya, A.S., and Townley, L.]
INTRODUCTION
(1) In April 1996, following a request from the Government of France, the International Atomic Energy Agency (IAEA) embarked on a Study of the Radiological Situation at the Atolls of Mururoa and Fangataufa, in French Polynesia, where France conducted 193 'expériences nucléaires' (nuclear experiments) above and beneath the atolls between July 1966 and January 1996.
(2) Mururoa and Fangataufa Atolls are situated at 21¡ã50' S, 138¡ã54' W and 22¡ã14' S, 138¡ã45' W, respectively, in the middle of the South Pacific Ocean, halfway between Australia and South America, they belong to the Pitcairn-Gambier Island chain at the southeastern extremity of the Tuamotu Archipelago. An atoll is a ring shaped coral reef enclosing a lagoon. The reef is a narrow rim - jutting a few metres at most above the surrounding ocean - which may be cut in many places by irregular channels, termed 'hogs', with the resulting formation of a string of islets, termed 'motus'. Mururoa and Fangataufa Atolls have evolved from extinct submarine volcanoes, and each rests upon a massive volcanic substratum capped by a coral reef platform and surrounded by ocean water thousands of metres deep. Therefore, in vertical structure each atoll consists essentially of two rock sequences: an igneous volcanic basalt basement and, capping it, sedimentary carbonate formations hundreds of metres thick. (Each coral platform consists of carbonate rocks of organic origin - limestones and dolomites. For the purpose of the study, the classification of the carbonate rocks is not important and they will therefore be simply referred to as 'carbonate formations'.) The carbonate formations are heterogeneous and fairly porous and the basalt basements are of lower permeability, but all are saturated with sea water. There is slow migration of water from the ocean inwards, rising through the basalt basements and carbonate formations towards the lagoons.
(3) The expériences nucléaires were of two types: 178 were nuclear tests, in which nuclear devices were exploded with large releases of fission energy, and 15 were safety trials, in which more or less fully developed nuclear devices were subjected to simulated accident conditions and the nuclear weapon cores were destroyed by means of conventional explosives, with no or - on a few occasions - very small releases of fission energy. Forty-one of the nuclear tests were atmospheric nuclear tests which took place - 37 at Mururoa Atoll and 4 at Fangataufa Atoll - between July 1966 and September 1974, and 137 were underground nuclear tests which took place - 127 at Mururoa Atoll and 10 at Fangataufa Atoll - between June 1975 and January 1996. Of the 15 safety trials, all of which were carried out at Mururoa Atoll, 5 were atmospheric safety trials and 10 were underground safety trials. Three underground safety trials had small releases of fission energy associated with them.
(4) The expériences nucléaires were carried out as follows:
The French programme of expériences nucléaires ceased on 27 January 1996.
OBJECTIVE
(5) The Study was designed to assess the residual radiological conditions at the atolls after the end of all the exp¨¦riences nucl¨¦aires and covered both the present radiological situation and the potential long term radiological situation. Specifically, the aims of the Study were as follows:
FRAMEWORK
(6) The Study used as its principal international authority on radiation protection matters the International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, which are jointly sponsored by the Food and Agriculture Organization of the United Nations (FAO), the IAEA, the International Labour Organisation, the Nuclear Energy Agency of the Organisation for Economic Co-operation and Development, the Pan American Health Organization and the World Health Organization (WHO) and were published by the IAEA in 1996 (Safety Series No. 115).
ORGANIZATION AND SUPPORT
(7) The organizational basis for the Study consisted of: an International Advisory Committee (IAC) (The IAC was chaired by Dr E Gail de Planque of the United States of America and comprised ten prominent scientists from ten IAEA Member States plus experts representing ex officio WHO, UNSCEAR, the South Pacific Forum and the European Commission.); two task groups and five working groups set up by the IAC; a Project Management Office set up by the IAEA; and a Liaison Office set up by the French Government (see the following diagram and the annexed list of participants). The first meeting of the IAC took place in Vienna on 13 and 14 April 1996, marking the commencement of the Study. (The Government of France covered most of the of the direct costs of the Study. Significant in-kind contributions were made by Argentina, Australia, Austria, Belarus, Belgium, Cuba, Denmark, Fiji, Germany, Indonesia, Japan, the Republic of Korea, New Zealand, Norway, the Russian Federation, Slovenia, Spain, Sweden, Switzerland, the United Kingdom, the United States of America, the European Commission, the South Pacific Forum, the South Pacific Regional Environment Programme, the Office of the FAO Sub-Regional Representative for the Pacific, WHO and UNSCEAR. In addition, substantial in-kind contributions were made by the various laboratories involved in the Study The Government of France provided invaluable logistic assistance throughout the Study.)
The Working Groups of Task Group A were supported by a network of laboratories and other institutions co-ordinated by the Agency's Laboratories at Seibersdorf, Austria, and another co-ordinated by the IAEA Marine Environment Laboratory, Monaco The network of laboratories and other institutions co-ordinated by the Agency's Laboratories at Seibersdorf, Austria, consisted of the Institute for Inorganic Chemistry and the Federal Institute for Food Control and Research, Vienna, Austria, the Institute of Radiobiology, Minsk, Belarus, the Centro de Is¨®topos, Havana, Cuba, the Physikahsch-Technische Bundesanstalt, Braunschweig, Germany, the Norwegian Radiation Protection Authority, ?ster?s, Norway, the Jo?ef Stefan Institute, Ljubljana, Slovenia, the Institute del Medio Ambiente, CIEMAT, Madrid, Spain; the Radiochemistry Group, Central Veterinary Laboratory, Addlestone, Surrey, United Kingdom, and the Environmental Measurements Laboratory, US Department of Energy, New York, N.Y., United States of America The network of laboratories and other institutions co-ordinated by the IAEA Marine Environment Laboratory, Monaco, consisted of the Australian Nuclear Science and Technology Organisation (ANSTO), Sydney, and the Australian Radiation Laboratory, Melbourne, Australia, the Ris? National Laboratory, Roskilde, Denmark; the Federal Fisheries Research Centre, Hamburg, Germany, the National Radiation Laboratory, Christchurch, and the Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand, the Centre for Environment, Fisheries and Aquaculture Science, Lowestoft, United Kingdom, and the Lawrence Livermore National Laboratory, Livermore, California, United States of America.
CONDUCT OF THE STUDY
General approach
(8) The Study activities were divided between two Task Groups (see the diagram):
Environmental sampling and surveillance campaign
(9) The Study involved an environmental sampling and surveillance campaign at Mururoa and Fangataufa Atolls, which provided the basis for evaluating a large amount of available data (mostly from French sources). The campaign was split into a terrestrial part, covering the surface soils and corals and the flora of the atolls, and an aquatic part, covering the atoll lagoons, the surrounding ocean and their biota. The terrestrial part involved the collection of about 300 samples (vegetation, coconuts, sand, soil, corals, cores of coral bedrock and aerosols), a large analytical effort (over 1000 radioanalytical determinations) and more than 100 in situ gamma spectrometry measurements. The aquatic part involved gamma spectrometric surveys of the seabed, in order to optimize sampling, and the collecting of over 300 samples of lagoon water, ocean water, sediment pore water, sediment, corals and biota. Some 13 000 litres of water and about 1000 kilograms of solid samples were analysed, also representing a large analytical effort. No restrictions were placed by the French authorities on the sampling and surveillance campaign.
The present radiological situation
(10) The aim of the assessment of the present situation was to estimate the radiation doses that people would receive from the radionuclides in the residual radioactive material that is already present in the accessible environment of Mururoa and Fangataufa Atolls and their surrounding waters. The values used for the present activity levels of radionuclides were based on the available data evaluated and supplemented through the sampling and surveillance campaign carried out at the atolls.
(11) There are no records of previous permanent indigenous habitation of Mururoa and Fangataufa Atolls, although there has been some intermittent habitation of Mururoa Atoll in addition to the habitation of both atolls by personnel involved in the programme of expériences nucléaires. However, the Study postulated hypothetical dwellers on the atolls and assessed the radiation doses that might be received by them. The hypothetical dwellers were presumed to eat largely local seafood and locally grown produce. By making conservative assumptions about diet and mode of living, the Study estimated an upper limit to the doses that might be experienced if the atolls were actually to be inhabited. Also, the Study provided a conservative estimate of the doses being received by the present population of Tureia Atoll, the nearest inhabited land to Mururoa and Fangataufa Atolls, located at about 130 km from them.
The potential future radiological situation
(12) The aim of the long term assessment was to estimate the hypothetical doses that people anywhere in the South Pacific region might receive (in addition to the doses attributable to the residual radioactive material that is now already present in the accessible environment of the atolls) as a result of the release of residual radioactive material presently underground at Mururoa and Fangataufa Atolls into the atoll lagoons or directly into the surrounding ocean. Such a release could be caused by the normal migration of the residual radioactive material through the geosphere (modified by the hydrogeological effects of the nuclear testing) or by the occurrence of disruptive events. The assessment involved four steps.
(13) The initial step was an assessment of the yield of each nuclear test using seismic monitoring information from various sources ¡ª mainly from New Zealand. The specific characteristics of each nuclear device and each nuclear test were not provided by the French Government for the Study, but it was possible to assess independently the total 'inventory source term', i.e., the activity presently underground at Mururoa and Fangataufa Atolls of all radionuclides in the residual radioactive material generated by each nuclear test, by making assumptions about the design of the nuclear devices on the basis of their yields and the materials used in their assembly.
(14) The second step was to assess the 'effective source term' to be used in calculating the dispersion of the released residual radioactive material into the ocean, i.e., the rate at which the radionuclides in each nuclear test cavity-chimney might escape into the lagoons or directly to the ocean. This was a two stage process: first, the concentration of each radionuclide dissolved in the saline water filling each cavity-chimney was estimated; second, the rate of migration of the dissolved material through the surrounding basalt basement and through the carbonate formations was modelled. An independent check on the validity of the assumptions made in the Study's calculation of nuclear test cavity-chimney water concentrations was carried out by comparing the Study's estimates with independently measured concentrations in water samples collected from two nuclear test cavity-chimneys.
(15) Modelling of the migration of radionuclides through the basalt basements into the carbonate formations was carried out using a dual porosity model developed for the assessment of underground waste repositories. The modelling calculations took account of flow in the fractures and of the retention of some radionuclides on surfaces within the basalt rock matrix. (The effects of the underground nuclear tests on the geological structures and on the stability of Mururoa and Fangataufa Atolls were not within the terms of reference of the Study, except insofar as geological pathways for radionuclide transport to the biosphere may have been affected by the explosions. The possibility that migration may have been enhanced by the explosions was examined. The geological consequences of the nuclear test programme for Mururoa and Fangataufa Atolls, including the issue of geological stability, were the subject of a detailed investigation carried out at the request of the French Government by a group of earth scientists (an ad hoc International Geomechanical Commission, IGC) The IGC investigation was independent of the Study, although three scientists participated in both.) The velocity of water flow, assumed constant, was determined by hydrological modelling calculations were carried out for 32 radionuclides, but particular attention was paid to 3 radionuclides of potential radiological significance - 239Pu, 137Cs and 90Sr - and to 3H, which was a useful tracer for model validation The predicted inventory in the carbonate formations was compared with estimates based on concentrations of radionuclides in the underground waters of the carbonate formations as determined by French scientists, supplemented by the Study's independent measurements. Future rates of radionuclide release from the carbonate formations, either upwards to the lagoons or laterally to the ocean at depth, were estimated using a semiempirical mixing model.
(16) In order to simplify the assessment of the total effective source term, i.e., the releases as a function of time from all underground nuclear tests, the Study divided the nuclear tests into categories and then determined the integrated release rate for each category. Three categories of nuclear test were the most important contributors to the overall release rates 12 nuclear tests (carried out at Mururoa Atoll early in the nuclear test progamme) in which the top of the cavity-chimney penetrated into the carbonate formations; four nuclear tests (three at Mururoa Atoll and one at Fangataufa Atoll) in which the basalt basement surrounding the cavity, though apparently thick enough, was inadequate to ensure complete confinement; and four safety trials (carried out in the carbonate formations at Mururoa Atoll - with no release of fission energy) which were found to be the major sources for the long term release of plutonium.
(17) The Study also examined a number of hypothetical disruptive events, including extreme events and events due to climatic changes, that could lead to enhanced rates of release of the material presently in the cavity-chimneys or to enhanced rates of exposure to material in the environment (e.g., to the plutonium in the sediments). The consequences of only one disruptive event were considered worth investigating further: a hypothetical extreme event consisting of a major breakaway and slide of the carbonate formations in the northern zone of Mururoa Atoll, in the area where the underground safety trials and some of the nuclear tests that produced cavity-chimneys penetrating into the carbonate formations were carried out. It was assumed that this slide would intersect a safety trial cavity and also a nuclear test cavity-chimney which had penetrated into the carbonate formations, and pessimistic assumptions were made about the fraction of the exposed material that might be released instantaneously.
(18) The third step was to use the effective source term at different times in modelling the dispersion of the released material through the South Pacific Ocean and in calculating the future concentrations of the radiologically significant radionuclides at a number of selected sites in the South Pacific Ocean at various times.
(19) The final step in the evaluation was to estimate the dose rates to which critical groups of people would be exposed at those places and times for which future concentrations of radionuclides had been calculated. It was through consideration of the implications of the present and future estimated dose rates that the IAC came to its findings about the radiological situation at the atolls and to its conclusions and recommendation about remedial and other actions.
REPORTS RESULTING FROM THE STUDY
(20) In March 1998, the IAC approved its reports on the Study of the Radiological Situation at the Atolls of Mururoa and Fangataufa, which are being issued by the IAEA in its Radiological Assessment Reports Series. These reports are: the Main Report, which incorporates this Executive Summary, a Technical Report in six volumes ("Radionuclide Concentrations Measured in the Terrestrial Environment of the Atolls", "Radionuclide Concentrations Measured in the Aquatic Environment of the Atolls", "Inventory of Radionuclides Underground at the Atolls", "Releases to the Biosphere of Radionuclides from Underground Nuclear Weapon Tests at the Atolls", "Transport of Radioactive Material within the Marine Environment" and "Doses due to Radioactive Materials Present in the Environment or Released from the Atolls"); and a Summary Report for the benefit ¡ª in particular ¡ª of persons with executive, managerial and administrative responsibilities The IAEA is also issuing a public information booklet and ¡®at a glance¡¯ poster relating to the Study.
FINDINGS
Residual radioactive material already present in the accessibly environment of the atolls
(21) The Study found that the terrestrial and aquatic environments of Mururoa and Fangataufa Atolls that are accessible to people contain residual radioactive material attributable to the expériences nucléaires, but at generally very low concentrations which the Study concluded were of no radiological significance. There are, however, some features of note whose radiological implications are examined in paragraph (24):
(a) Several kilograms of plutonium resulting from the atmospheric nuclear tests carried out at the atolls remain in sediments under the lagoon of each atoll. Some of the plutonium in the sediments of the Mururoa Atoll lagoon came from the atmospheric safety trials.
(b) The concentration of tritium in each lagoon was found to be higher than in the open ocean, as the result of leakages from a number of the cavity-chimneys created by underground nuclear tests.
(c) Particles containing plutonium and small amounts of americium resulting from atmospheric safety trials remain in the area of the trial sites ¡ª the motus of Colette, Ariel and Vesta on Mururoa Atoll. The Study analysed these types of particles, found in samples of sand and coral collected from the surface of the motu of Colette and in sand taken from a sandbank adjacent to it.
(d) Elevated levels of 137Cs were found over small areas totalling several hectares on the Kilo-Empereur rim of Fangataufa Atoll.
Residual radioactive material underground at the atolls
(22) The Study found that the results of the assessments of the nuclear explosive yields of all underground nuclear tests and of the resulting inventories of residual radioactive material contained underground at the atolls are in good agreement with information made available for the Study from French sources. (The Study estimated the total yields, calculated from the sum of the yields of individual nuclear tests, to be 2400 kilotons (one kiloton being equivalent to one thousand tons of trim-trotoluene (TNT)) for Mururoa Atoll and 770 kilotons for Fangataufa Atoll; the values provided by the French Liaison Office were 2400 and 800 kilotons. (Most experimental and theoretical values for the explosive energy released by TNT range from 900 to 1100 calories per gram. At one time, there was uncertainty as to whether 'kiloton' of TNT referred to a 'short' kiloton, a 'metric' kiloton or a 'long' kiloton. In order to avoid ambiguity, it was agreed that the term 'kiloton' should refer to the release of 1012 calories of explosive energy.))
(23) From the measurements of the activity in underground water samples taken from the two cavity-chimneys selected for the in situ sampling, the Study found that the concentrations of highly refractory radionuclides, in particular of 239+240Pu, are extremely low, indicating a high level of retention of such radionuclides in the glasslike lava formed in the cavities by basalt rock melted in the underground explosions. Potential radiation doses due to residual radioactive material already present in the accessible environment of the atolls.
(24) Although it is doubtful whether Mururoa Atoll - still less Fangataufa Atoll - could sustain a permanent population dependent solely on local resources for food, the Study assessed the radiation doses to hypothetical inhabitants that could result from the residual radioactive material at present in the terrestrial and aquatic environments of the two atolls. The Study found that a population permanently resident on the atolls, and living on a diet of local produce and seafood, would not generally receive a radiation dose attributable to the residual radioactive material exceeding 0.01 mSv per year, which is equivalent to a very small fraction (less than one part in 200) of the annual background radiation dose that such a resident population would unavoidably receive from natural radiation sources. The Study found it necessary, however, to examine specifically the four features of note identified in paragraph (21).
(a) Plutonium in the lagoons. The Study found that the inventory of plutonium in the sediments of the two lagoons, while large, is of little radiological significance, mainly because of the low rate of transfer of plutonium to people via feasible pathways. Also, the Study noted that the availability of the plutonium will decrease over time owing to (i) the removal of the lagoon sediments to the ocean and (ii) the gradual burial and dilution of lagoon sediments by the accumulation of fresh sediment.
(b) Tritium in the lagoons: Similarly, the Study found that concentrations of tritium in the lagoons are of no radiological significance even though they are at present higher than in the open ocean.
(c) Plutonium-containing particles: The Study noted that, if an individual were to visit the motus of Colette, Anel or Vesta at Mururoa Atoll, there is a possibility that a particle containing plutonium with small amounts of americium could be incorporated into that individual's body - for example, through a cut caused by a fall. The Study assessed the probability of the incorporation of such a particle and its long term retention within the body. It also assessed the associated radiation dose and the probability of harm as a result of the dose received. On this basis, the Study found that the probability that a hypothetical individual visiting and spending some time on any of the three motus would ultimately incur a fatal cancer attributable to the incorporation of a particle containing plutonium is less than one in one million per year.
(d) Caesium-137 on the Kilo-Empereur rim. The Study found that, if any population were to subsist entirely on produce grown on small areas of the Kilo-Empereur rim of Fangataufa Atoll, the estimated maximum radiation dose attributable to the 137Cs in the rim would be about 0.25 mSv per year, equivalent to about one tenth of the total radiation dose which that population would unavoidably receive as a result of natural radiation sources. The Study considers, however, that this hypothetical situation is highly unlikely to arise, since - interalia - the Kilo-Empereur rim is almost barren and virtually uninhabitable by people adopting a traditional semisubsistence lifestyle.
(25) The Study found that the highest dose attributable to the residual radioactive material already present in the accessible environment of Mururoa and Fangataufa Atolls, which is estimated to be currently received by residents of Tureia Atoll, is less than 0.0001 mSv per year, which is a completely insignificant fraction (about one part in 10,000) of the annual background radiation dose that these residents will unavoidably receive from natural radiation sources. It should be noted, however, that Tureia Atoll did receive some immediate fallout from the atmospheric nuclear tests carried out at Mururoa and Fangataufa Atolls, in addition to the fallout globally experienced as a result of all atmospheric nuclear testing. The radiation doses currently being received by residents of Tureia Atoll as a result of residues from earlier fallout and due to the nuclear testing at Mururoa and Fangataufa Atolls were assessed and found to be about 0.005 mSv per year, which is an extremely small fraction (about two parts in 1000) of the annual background radiation doses that the residents will unavoidably receive from natural radiation sources.
(26) The radiation doses due to the residual radioactive material already present in the accessible environment ¡ª principally arising from 137Cs and plutonium isotopes - will persist, but they will decline owing to both radioactive decay and other processes that reduce the availability of these radionuclides in the environment. According to the Study estimates, the rate of leaching of the 137Cs and the plutonium isotopes present in the lagoon sediments will continue to decrease with time, as will the estimated radiation doses associated with these radionuclides. The Study found that the highest estimated potential annual doses attributable to the residual radioactive material already present in the accessible environment of Mururoa and Fangataufa Atolls and their surrounding waters will decline from the present hypothetical maximum of no more than 0.01 mSv per year to about 0.001 mSv per year within 100 years. Migration of residual radioactive material from underground.
(27) The Study estimated the rate of migration of the radionuclides in the radioactive material produced by the underground nuclear tests from the cavity-chimneys, through the geological media, into the lagoons and directly into the ocean over periods of more than 100,000 years. The Study found that, over the first few decades, most of the released radionuclides would come from the small number of underground nuclear test sites where the basalt basement above the nuclear test point provided inadequate confinement of the nuclear tests. (This inadequate confinement is caused by fractures in the basalt basement which reach from the cavity-chimneys to the carbonate formations above.) In terms of amounts of activity, tritium would dominate the early releases, but with activity concentrations that are of no radiological significance. Other radionuclides, including 137Cs and 90Sr, would be effectively retained underground within the basalt basement, most of their activity decaying and only small amounts of activity being released. Plutonium would continue to be released over long periods of time but at very low rates. The modelling predicts that concentrations of 137Cs and 239+240Pu in the lagoon water are unlikely to exceed present levels at any time in the future. The concentrations of 90Sr and 3H could rise marginally above current levels, but only during the next few decades. Dispersion of residual radioactive material throughout the ocean.
(28) The Study used regional and far field oceanographic models to estimate the concentrations in sea water at various locations and times of radionuclides released into the ocean from Mururoa and Fangataufa Atolls The Study found that, except as a consequence of a hypothetical extreme disruptive event (see paragraph(29)), the predicted long term concentrations of radionuclides decrease to background oceanic levels beyond about 100 km from the atolls; thus, at Tureia Atoll the predicted concentrations will be around background levels and of no radiological significance.
Consequences of postulated disruptive events
(29) The only disruptive event that was found by the Study to warrant a thorough assessment was the hypothetical major breakaway and slide of the carbonate formations in the northern zone of Mururoa Atoll, in the area where the underground safety trials and some of the nuclear tests producing cavity-chimneys which penetrated into the carbonate formations were carried out. If such a hypothetical extreme event were to occur, ocean currents would carry the released radioactive material away from Mururoa Atoll and the highest potential annual dose would therefore be received by residents of nearby atolls For the residents of Tureia Atoll, the dose in the first year following such a slide would not be more than a few thousandths of a millisievert - which is an extremely small fraction (a few parts in 1000) of the annual background radiation dose that the residents will unavoidably receive from natural radiation sources ¡ª even pessimistically assuming that all the plutonium involved in the slide went into solution. Potential doses in the future.
(30) The Study found that - except in the hypothetical situation discussed in paragraph (24) - no population group is likely to receive at any time in the future a dose attributable to the residual radioactive material at Mururoa and Fangataufa Atolls which exceeds approximately 1% of the background radiation dose that the group will unavoidably receive from natural radiation sources.
CONCLUSIONS
Implications for human health
(31) The Study concluded that there will be no radiation health effects which could be either medically diagnosed in an individual or epidemiologically discerned in a group of people and which would be attributable to the estimated radiation doses that are now being received or that would be received in the future by people as a result of the residual radioactive material at Mururoa and Fangataufa Atolls.
(32) Nevertheless, the Study noted that the reported cancer incidence in populations in the South Pacific region and throughout the world is changing for a number of reasons, including: the improved diagnosis and registration of cancer cases; modifications in environmental exposure to cancer causing agents and in personal habits (such as dietary and smoking habits); population migrations that alter baseline cancer incidence rates; and changes in the incidence of other diseases. The Study emphasized, however, that at the very low levels of dose estimated in the Study there will be no changes in cancer incidence rates in the region attributable to radiation exposure caused by the residual radioactive material at Mururoa and Fangataufa Atolls.
Implications for biota
(33) The Study assessed the dose rates to native biota resulting from the residual radioactive material at Mururoa and Fangataufa Atolls and, in the great majority of cases, found them to be similar to or lower than dose rates due to natural radiation sources. An exception is the potentially high dose rates that could be experienced by individual members of some species owing to plutonium contained in particulates - for example, from the sediment of the sandbank adjacent to the Colette motu in the northern part of Mururoa Atoll. Overall, the Study concluded that the expected radiation dose rates and modes of exposure are such that no effects on biota population groups could arise, although occasionally individual members of species might be harmed, but not to the extent of endangering the whole species or creating imbalances between species.
Remedial actions
(34) Given the measured and predicted radionuclide activity levels, and the low dose levels estimated for the present and for the future, and with account taken of international guidance, the Study concluded that no remedial action at Mururoa and Fangataufa Atolls is needed on radiological protection grounds, either now or in the future.
Monitoring
(35) Similarly, the Study concluded that no further environmental monitoring at Mururoa and Fangataufa Atolls is needed for purposes of radiological protection.
Robustness of the conclusions
(36) Although many assumptions were made in the modelling of systems, the findings are robust: i.e., the Study concluded the expected extent of changes in the conclusions due to uncertainties in the parameters used in the modelling is slight. Furthermore, the predicted doses are so low that large errors (even of an order of magnitude) would not affect the conclusions.
RECOMMENDATION
(37) The Study noted that a scientific programme of monitoring of the radionuclide concentrations in the carbonate formations and in the nuclear test cavity-chimneys is under way at Mururoa and Fangataufa Atolls. Should this programme continue, the Study recommends that emphasis be placed on monitoring the migration behaviour of long lived and relatively mobile radionuclides and radiocolloids because of its particular scientific interest. The scientific programme, supplemented by some monitoring of radionuclide levels in the biosphere, may also be useful in assuring the public about the continuing radiological safety of the atolls.
Note: Ciguatera
Ciguatera is a type of food poisoning brought about by eating fish contaminated by a neurotoxin generated by a marine microorganism often found in association with disturbed coral reefs. There have been some reports in news media that outbreaks of ciguatera may be linked to exposure to radiation from the residual radioactive material at Mururoa and Fangataufa Atolls The symptoms of ciguatera poisoning have been recognized for over a century and a range of anthropogenic and natural disturbances may contribute to ciguatera outbreaks. However, there is no evidence in the scientific literature of radiation exposure being a causal factor.
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Copyright © 2022 by Lloyd Townley |