ARPANSA - Australian Radiation Protection and Nuclear Safety Agency

The Russians launched the Mars 96 probe from Kazakhstan on 16 November, 1996. The launch failed and left portions of the probe in a low earth orbit. The remaining portions of the probe eventually plummeted to earth and landed in the Pacific ocean between Easter Island and Chile on 18 November, 1996.

In the period leading up to the re-entry of the debris the potential crash locations included part of northern Australia. At the time the debris was reputed to contain about 200 grams of plutonium 238 (²³⁸Pu) as part of a radioisotope thermoelectric generator (RTG). Since ARPANSA has radiation protection expertise and specialized radiation monitoring equipment, this laboratory would be involved in the monitoring and cleanup of any radioactive contamination as part of the Commonwealth plan for the re-entry of radioactive space debris.

Emergency Management Australia (EMA) is the organization responsible for coordinating the emergency response for the re-entry of space debris under a plan entitled Australian Contingency Plan for Space Re-entry Debris (AUSCONPLAN-SPRED). This involves the Australian Defence Forces, the Australian Nuclear Science and Technology Organization (ANSTO) and a number of Commonwealth Departments, including the Department of Health and Family Services of which ARPANSA forms a part. The preliminary stages of this plan were implemented on the morning of 18 November.

Subsequently it has been claimed that the part of the probe containing radioactive material had separated and landed in the ocean earlier. The debris tracked on 18 November was claimed to be only the 10 tonne fourth stage booster rocket.

The RTG

Space missions near and beyond Mars are unable to use photovoltaic cells for electrical power because there is insufficient sunlight and the missions are too long for chemical cells (batteries).

²³⁸Pu is an alpha emitter with a half life of 86.7 years and should not be confused with ²³⁹Pu which has a half life of 25,000 years and is the isotope used for manufacturing weapons. The alpha emissions from ²³⁸Pu are used as a heat source which is then converted into electricity.

Toxicity of plutonium

The media has made much of the toxicity of plutonium (they are referring to ²³⁹Pu) often claiming it to be the most toxic substance known to man. This is not the case however.

Plutonium's toxicity is due to the alpha emissions which are capable of altering or killing cells with which they come into contact. If the plutonium is of the correct particle size it can be inhaled and deposited in the lungs or it may be ingested and migrate to the bones. Long term exposures to alpha particles can induce cancer. Since the Russians claim that the RTG is expected to survive re-entry and since it is encapsulated no health hazard would be expected. Alpha particles can be stopped with a piece of paper or the external layer of the skin. Even if the RTG did break up it is unlikely to form particles of the correct size for inhalation and since, as the oxide it is insoluble, ingested plutonium would pass straight through the gut.

Related Page

ARPANSA and the Australian Contingency Plan for Space Re-Entry Debris

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