Toxicity of Plutonium, Americium and Curium (eBook)

A Report Prepared Under Contract for the Commission of the European Communities Within Its Research and Development Programme on Plutonium Recycling in Light Water Reactors

J. C. Nenot, J. W. Stather (Autoren)

eBook Download: PDF | EPUB

2013 | 1. Auflage
238 Seiten
Elsevier Science (Verlag)
978-1-4831-8210-0 (ISBN)

Infos

The Toxicity of Plutonium, Americium and Curium provides a biological basis for an assessment of the radiological health problems resulting from human exposure to americium, curium, and plutonium. This book discusses the method of injection of the chelating agent DTPA for removing soluble forms of americium, curium, and plutonium. Organized into 10 chapters, this book begins with an overview of the biological effects in man that are attributed to exposure to actinides. This text then examines the uses of americium and curium in transmission scanning studies in tissues, in smoke detectors, and in neutron sources. Other chapters consider the metabolism or effects of plutonium in humans that can be employed to predict the potential consequences of human exposure. This book discusses as well routes of entry of radioactive materials into the body by inhalation, by ingestion, through cuts, or by absorption through the intact skin. The final chapter deals with the assessment of the radiological health problems resulting from the use of mixed oxide fuels of uranium and plutonium in light water reactors. This book is a valuable resource for scientists.

Textauszug

Chapter 2

PHYSICAL AND CHEMICAL PROPERTIES OF BIOLOGICAL IMPORTANCE

Publisher Summary

This chapter discusses physical and chemical properties of plutonium, americium, and curium of biological importance. Plutonium, americium, and curium are produced in both thermal and breeder reactors. The main civilian use of plutonium is in breeder reactors and it may also be used as fissionable material in thermal reactors. It has other uses in industry and medicine, such as for power sources and cardiac pacemakers. Americium and curium have a few uses although americium-241 has been used for transmission scanning studies in tissues, in neutron sources, in smoke detectors, and in α-active foils with the applications in static eliminators. The property of plutonium ions in solution to rapidly hydrolyze and form polymers at high concentrations is of particular biological importance. Plutonium is used in fuel mainly in the oxide form. The chemical separation procedures used in the reprocessing of fuel elements involve their dissolution in nitric acid and the subsequent separation of plutonium from uranium and other fission products by extraction in organic solvents. Actinides commonly enter the body by ingestion or inhalation as particles. Depending upon the source of the release, actinides may be taken in either as individual elements or in association with other active or inactive materials.

1 Introduction

Plutonium, americium and curium are produced in both thermal and breeder reactors. The main civilian use of plutonium is in breeder reactors and it may also be used as fissionable material in thermal reactors. It has other uses in industry and medicine such as for power sources and cardiac pacemakers. Americium and curium have few uses although americium-241 has been used for transmission scanning studies in tissues, in neutron sources, in smoke detectors, and in α-active foils with applications in static eliminators.

2 Plutonium

The chemistry of plutonium has been described by Katz and Seaborg (1957), Cleveland (1970) and Taylor (1973a). It is a silvery white metal which melts at 639.5°C and oxidises readily on warming in moist air. In finely divided form the metal may be pyrophoric. When plutonium metal is burnt in oxygen or when oxygen containing compounds such as Pu(IV) oxalate or Pu(IV) peroxide are heated in vacuo to about 1000°C plutonium dioxide is formed. Plutonium dioxide is a highly refractory material which melts at 2200-2400°C and is difficult to dissolve by normal methods.

There are 15 known isotopes of plutonium having atomic weights between 232 and 246. Of these only 236-243 are of any biological interest either as a result of their production in nuclear power programmes or because of other uses. Table 2.1 shows the main physical properties of these isotopes. The isotopes Pu-239 and Pu-241 are fissile and therefore of special interest for fuel in both thermal and breeder reactors. In 1975 the estimated production of plutonium in the Countries of the European Community was 3-0 tons and it was anticipated that this would rise to 5-7 tons by 1980 (Haijtink, 1976). Pu-239 and Pu-240 emit an L X-ray of uranium in 4% and 11% of disintegrations respectively with an energy of about 17 keV. These X-rays can penetrate a few centimetres of tissue thus allowing Pu-239 (+Pu-240)* to be detected in the lung or a wound site. The other α emitting isotopes of plutonium also emit L X-rays in varying amounts. Pu-238 is used as a heat source in thermo-electric power generators such as cardiac pacemakers and Pu-236 and Pu-237 are used in tracer studies. Because of its short half-life (5 hrs) and low β energy (0.6 MeV) plutonium-243 is of little radiological importance.

Table 2.1

Physical properties of the manor isotopes of Plutonium, Americium and Curium

E.C. – Electron capture

Reference:

a– In comparison with 1 μCi of plutonium-239 which is taken as 1

A– Harte (1976)

Plutonium can exist in solution mainly in four valence states: Pu(III), Pu(IV), Pu(V) and Pu(VI) and in some conditions as Pu(VII). The individual oxidation states can be stabilised by appropriate oxidising, reducing or complexing agents. In concentrated acidic solutions a number of oxidation-reduction reactions can occur leading to the formation of an equilibrium in which the different oxidation states can co-exist.

There is little information on the oxidation state of plutonium in biological systems. In neutral solutions the formation of the Pu(IV) state is favoured and biological fluids contain ligands and complexing entities that tend to stabilise the Pu(IV) state. Stable plutonium complexes can be formed with citrate, ascorbate, amino acids and proteins. The stability of these complexes decreases in the order Pu(IV) > Pu(III) > Pu(VI) > Pu(V). It is, therefore, probable that most if not all plutonium in biological systems is in the Pu(IV) state.

Of particular biological importance is the property of plutonium ions in solution to rapidly hydrolyse and form polymers at high concentrations. The tendency to hydrolyse decreases in the order Pu(IV) > Pu(VI) > Pu(III) > Pu(v). Hydrolysis of Pu(IV) can result in the formation of relatively insoluble polymers, a process which is only slowly reversible. The formation of plutonium polymers in the body leads to their phagocytic uptake by macrophages and other cells that can accumulate particulate material. Compounds of Pu(III) and Pu(VI) hydrolyse less rapidly at physiological pH and can potentially be more readily absorbed from the gastrointestinal tract, lung or other sites.

3 Americium and Curium

The chemistry of the transplutonium elements americium and curium has been reviewed by Katz and Seaborg (1957), Pascal (1970) and Taylor (1973b).

Americium metal is silvery white, malleable and ductile and melts at 994 ± 7°C. It oxidises slowly in the air. Curium is a silvery, hard, brittle metal with a melting point of 1350 ± 60°C. It oxidises rapidly in the presence of oxygen. The oxides of both americium and curium are more soluble than plutonium dioxide.

There are 13 known isotopes of americium (232, 234, 237–247). Am-241 is the most abundant isotope and is produced from Pu-241 by β decay. It subsequently decays by α emission also giving rise to a γ-ray with an energy of 60 keV (40% of disintegrations) and if incorporated in the body can be readily detected outside. Am-243 is the only other isotope of americium produced in any quantity. Of the 12 known isotopes of curium only Cm-242 and Cm-244 are produced in significant amounts.

The main physical properties of these isotopes of americium and curium are shown in Table 2.1. In solution the trivalent state is the most stable oxidation state and the only one of importance in biological systems. The general features of hydrolysis and complex ion formation are similar to those found for plutonium. The trivalent transplutonics are however less readily hydrolysed because of their lower ionic charge and larger ionic radii (Am III = 99 pm, Cm III = 98 pm, Pu IV = 90 pm; Durbin, 1962). The most important feature of their solution chemistry is that they form only weak complexes with serum proteins and other ligands (Taylor, 1973b).

4 General data relevant to problems in Radiological Protection

The relative amounts of the most important isotopes of plutonium, americium and curium produced either in a thermal reactor (PWR) or in a breeder reactor fuelled with plutonium from an SGHWR reactor are given in Table 2.2. Both inventories show that high levels of both americium and curium isotopes are produced as well as plutonium. This is in contrast to the fuel inventory after low burn-up times of say 1000 MWD/Te when Pu-239 + 240 are the main isotopes produced (Dolphin, et al., 1974). Although the Cm-242 isotope accounts for most of the alpha activity in fuel rods at the end of long irradiation times it decays rapidly with a half-life of 163 days to Pu-238.

Table 2.2

Relative activities of the major isotopes of plutonium, americium and curium in irradiated fuel

Reference:

aIn comparison with plutonium-239 taken as 1

bPressurised Water Reactor (PWR)

cCommercial Fast Reactor (CPR)

dSteam Generating Heavy Water Reactor (SGHWR)

A.Bell (1973)

B.Kelly et al, (1977)

Plutonium is used in fuel mainly in the oxide form. The chemical separation procedures used in the reprocessing of fuel elements involve their dissolution in nitric acid and subsequent separation of plutonium from uranium and other fission products by extraction in organic solvents. Plutonium is precipitated as the oxalate and then converted to the oxide. In the preparation of plutonium metal an intermediate stage is the formation of the fluoride compound. Accidental releases from chemical separation plants may therefore involve numerous chemical forms of plutonium which appear in various process streams during the separation procedures. The higher actinides are normally removed during reprocessing but...

Produkt-Details

• Erscheint lt. Verlag: 22.10.2013
• Sprache: englisch
• Themenwelt: Medizin / Pharmazie ► Gesundheitsfachberufe
• Themenwelt: Medizin / Pharmazie ► Medizinische Fachgebiete ► Pharmakologie / Pharmakotherapie
• Themenwelt: Naturwissenschaften ► Chemie ► Technische Chemie
• Themenwelt: Technik ► Bauwesen
• ISBN-10: 1-4831-8210-X / 148318210X
• ISBN-13: 978-1-4831-8210-0 / 9781483182100