Depleted Uranium

Proposal for a Research Programme on Depleted Uranium: Health, Safety And Environmental - Source

3.1 Raw Material Characteristics

3.1.1. US KE penetrator material was specified to contain 0.75 wt % titanium (Ti) which produces a heat treatable alloy and the capability to produce KE penetrators with appropriate mechanical properties. The composition of this DU is approximately 0.75 wt % Ti, less than 0.2 wt % ²³⁵U and approximately 0.0008 wt % ²³⁴U, with the remainder being ²³⁸U with some trace impurities (13). For a concise account of DU characteristics see (14). The UK obtained DU for its CHARM ammunition from the US and the material is understood to be identical to that supplied to the US Department of Defense (DoD). In August 1999, the Idaho National Engineering Laboratory advised the US Army that very small amounts of transuranic material and fission products had been identified in some samples of DU. Consequently, UK DU penetrators may contain trace quantities (a few parts per billion) of elements such as neptunium, plutonium, americium and technetium. A recent report published by the European Commission (EC) (1) states that the presence of these elements adds less than 1.0% to the radiation dose from the DU itself. This is insignificant considering the relatively low radiological hazard associated with the DU. The MOD commissioned an independent detailed analysis of CHARM 3 material in Spring 2001, but the analysis has proved to be technically difficult, as the presence of the titanium results in the formation of highly insoluble and intractable precipitates. We will continue to pursue an independent detailed analysis to enhance the data already available from health and safety and environmental monitoring programmes related to DU munitions storage and testing.

3.2 Source Characteristics

3.2.1.1. All the isotopes of U are radioactive and each has its own unique decay process emitting some form of radiation viz. alpha, beta or gamma radiation. The U isotopes of significance in DU munitions (²³⁴U, ²³⁵U, ²³⁶U and ²³⁸U) are alpha particle emitters. Over most of the skin areas that are likely to be in contact with DU, alpha particles do not penetrate the dead external layers and are not generally considered to be an external hazard. However, the hazard is increased if DU is inhaled, ingested or there is absorption into the body through fragment penetration or open wounds. Much has been written on this subject (4,7,9,10,13,14,20-39). Beta particles are emitted during subsequent decay processes and are more penetrating than alpha particles. They can penetrate a few millimetres of skin and have the potential to pose both an internal and an external health risk. Gamma radiation is very penetrating but is only present to a very limited extent and is not considered to represent a significant health risk (13,15-18). DU is categorised by the International Atomic Energy Agency (IAEA) "Regulations on the Safe Transportation of Radioactive Material 1996 Edition" as a low specific activity (LSA 1) material. For DU in equilibrium with its daughter products, the total specific activity and alpha specific activity are dependent on the source and age of the material, but are generally about 39.3 MBq/kg and 14.4 MBq/kg respectively (14,19). For external radiation the beta and gamma emissions are attenuated within the bulk of the DU to such an extent that the only conceivable health risk is from prolonged contact between DU and bare skin. Even in this situation observable medical effects are very unlikely, as the quantity of radiation reaching sensitive cells is not sufficient to cause an appreciable health hazard in any realistic exposure scenario. For internal radiation exposure, account must be taken of the different degrees to which the various radiations (alpha, beta and gamma) damage tissue. Alpha radiation is 20 times more damaging to tissue than is beta or gamma.

3.2.2.1. As with any heavy metal, DU has the potential to be chemically toxic to humans when it enters and is retained by the body. DU fragments, dust and aerosol (in the form of various oxides) are generated to various degrees on penetrator impact with hard (heavily armoured) targets or when penetrators are subjected to intense heat arising from burning vehicles or munitions. DU dust and aerosol can be inhaled directly or re-suspended by personnel working inside damaged vehicles or by wind, personnel and vehicle movements over contaminated ground. Absorption into the body can result from fragment penetration, inhalation, ingestion and through open wounds. DU absorbed by the blood through a wound, the lung or the gastrointestinal tract, will be carried to body tissues and organs. Much has been written on this subject (4,7,9,10,13,14,20-39). The DU hazard assessment information contained in the available source literature should be critically reviewed with the aim of identifying where the available evidence leads to uncertainty in the hazard assessment and what specific new work is needed. An authoritative paper comparing and contrasting past DU hazard assessments, based on the radiological and chemical toxicity properties and extrapolations from U data will be produced.

3.3 Corrosion

3.3.1. UK DU penetrators are shielded with an ion vapour deposit (IVD) coating of aluminium and are further protected by a passivation treatment. This is designed to protect the DU from corrosion for at least 10 to 15 years under normal storage conditions. Research has shown that in moist air the corrosion rate of unprotected DU munitions is low, but in salt fog the corrosion rate increases sharply with about 7% of the total mass being lost in 30 days (40). DU dust, fragments of fired penetrators and penetrators that have impacted soft ground will eventually corrode to form stable oxides. The rate and consequences of such corrosion in a range of soil types and profiles (and in the marine environment since munitions have been fired into the sea) has not been subjected to extensive study and is an area where more research is required. It is proposed that existing information on the corrosion and dissolution of DU should be collected and collated and the results of detailed laboratory studies, involving the use of elevated reaction rates, should be compared and contrasted with the results of in situ monitoring at specific sites. This information can then be fed into the 'pathways' research (i.e. DU transport in the environment) described in Section 4.

3.4 Gun Barrel Contamination

3.4.1. Low levels of DU contamination have been found in some trial gun barrels that have been used to fire DU rounds and this has not been removed or significantly reduced by the subsequent firings of a small number of copper banded (non DU) projectiles. For one barrel, which gave a contamination level above that of the majority of barrels (up to 50 counts per second (cps) as opposed to 2 to 4 cps), it is known that a research round broke up in it. The MOD is funding work on procedures for monitoring and handling contaminated barrels, but there is also a need to determine how some barrels became contaminated. If gun barrel contamination is occurring there is also a need to understand and quantify the nature of any DU being released to the environment by the gun. No DU contamination has been found inside tanks during the test firing of DU munitions at Kirkcudbright, nor has it been detected in the gun barrels of tanks that fired DU during the Gulf conflict.

3.5.1. DU is pyrophoric and during hard target (e.g. armoured vehicle) interactions a series of complex oxides are formed in addition to DU dust and fragments. In such interactions between 10 and 35% of the penetrator may be aerosolised (13). The actual percentage will vary according to the circumstances; the specific area of impact, the hardness of the target; the velocity and angle of impact and the pathway through the target are all factors. The main oxide formed by combustion is U₃O₈ along with UO₂ and UO₃ (14,21). Unburned DU will also eventually oxidise in the environment to produce these oxides (see (13) - TAB M, "Characterising DU Aerosols" for a comprehensive account of KE penetrator encounters with hard targets. See also (41-45)).

3.5.2. Aerosol and dust arising from hard target impacts poses the significant risk as a potential inhalation hazard, particularly for those troops manning the target vehicle and surviving the impact. The nature of the inhaled material, its morphology, its mass, its particle size distribution and its solubility will all be significant factors in assessing any potential risk to health. Extensive test firings have recently been carried out in the US to characterise the aerosol formed during DU impacts with hard targets and the US has advised that an unclassified report of the test and its results will be published. The MOD will evaluate the results of these tests and seek to participate in any future test firings being conducted in the US. Resuspension inside damaged vehicles is an important issue and some work on this topic has already been carried out in the US. Publicly available results are summarised in (46). Information from UK test firings at Eskmeals has been provided to the Royal Society DU Working Group (47).

3.6.1. When a KE munition penetrates a soft target (e.g. lightly armoured or non-armoured vehicles) less of it will be aerosolised. In the Gulf war it is understood that many KE penetrators went straight through their intended targets and buried themselves in the ground (14). This has also been the experience in the Balkans where most of the recovered DU penetrators, including some extracted from brick walls and concrete beams, have been found to be essentially intact. Any dust and aerosol generated during a soft target impact poses a potential inhalation hazard. The factors that are important in assessing the potential risk to health from inhalation of dust or aerosol are the same as those set out in paragraph 3.5.2. The need for additional data on soft target impacts has been recognised and lightly armoured vehicles were used in the recent US tests. The MOD will evaluate the data from these tests and seek to participate in any future US test firings involving soft targets.

3.7.1. DU will corrode slowly in fresh water producing a number of oxides (40). The rate of corrosion will depend on a number of factors that include dissolved oxygen content, pH, conductivity, turbulence, temperature and concentration of dissolved solids. As with any ingestion of DU there can be a health hazard if sufficient quantities are consumed in potable water originating from contaminated fresh water sources. A recent report published by the United Nations Environment Programme (UNEP) (3) failed to find any DU contamination in water sources near sites where DU munitions had been used in Kosovo. However, the report recommended that further water monitoring should be undertaken in the long term.

3.7.2. The rate of corrosion is higher in seawater (40) and will depend on the salinity of the water (estuary to ocean) in addition to those factors identified above. The sea naturally contains about 3ppb of U and the rate of DU solubilization and the diffusion due to sea currents is unlikely to result in any significant environmental alteration (48). Past work aimed at gaining a better understanding of the behaviour of DU in the marine environment has met with limited success. One penetrator has been recovered from the marine environment off Kirkcudbright but an experimental rig used for corrosion studies in the Solway Firth was lost in severe storms recently. Subject to the necessary agreement being received from other government departments with environmental responsibilities, this rig will be replaced. It is not known to what extent the firing of DU munitions strips the penetrator’s protective coating and changes its chemical behaviour. There is some anecdotal evidence from the US that suggests that the rates of corrosion and dissolution of fired DU differ from those of unfired DU. This has not been quantified and it needs to be established if research is required to determine relative and actual corrosion rates of fired and unfired DU to supplement work described in paragraph 4.2.3. Proposed research is described in paragraph 3.3.1.

3.8.1 In bulk form DU will not burn easily however fine DU dust may ignite spontaneously in air at room temperature. Finely divided DU burns very rapidly and can be spontaneously explosive if dust is dispersed in air. In low surface to mass ratios DU is incapable of self-sustaining combustion in air without the continued application of heat from an external source. The temperature for the onset of the self-heating reaction is about 350 degrees centigrade in still air and about 650-750 degrees centigrade in carbon dioxide. Camp Doha (Gulf Conflict) experienced fire and explosion of DU munitions which engulfed the camp (13). See also (49-53) for detailed accounts of work carried out to characterise the effects of fire on DU munitions. In general, less DU aerosol is generated in a fire than in a hard target impact and the fraction of soluble aerosol is very much lower. It has been reported that in three fire tests involving multiple munitions only 10 to 35% of the DU mass was converted to oxide of which less than 1% was in the form of aerosol (4). The size range of the aerosol produced by burning DU has been reported (54). No research is proposed in this area.

Last Updated: 14 Mar 02