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FIRE TESTING OF FULLY ACTIVE MEDIUM LEVEL WASTE FORMS

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THE BEHAVIOUR OF MEDIUM LEVEL WASTE FORMS IS BEING STUDIED AT TEMPERATURES THAT MIGHT BE ENCOUNTERED IN ACCIDENTS INVOLVING FIRES. THE INFORMATION OBTAINED WILL BE USEFUL IN SAFETY ASSESSMENTS IN THE TRANSPORT AND DISPOSAL OF THESE PACKAGED RADIOACTIVE WASTES.

THERE ARE TWO PARTS TO THE PROGRAMME:

(A) AN EXPERIMENTAL PART IN WHICH SAMPLES OF WASTE FORM ARE HEATED TO OBTAIN DATA ON THE RADIONUCLIDES RELEASED, THE GASES EVOLVED AND THE PHYSICAL EFFECTS ON THE WASTE FORM,

(B) A THEORETICAL AND INTERPRETIVE PART IN WHICH EXPERIMENTAL DATA IS USED TO DESCRIBE THE BEHAVIOUR OF THE WASTE FORM IN A FIRE. INFORMATION FROM A CONCURRENT PROGRAMME AT WINFRITH ON HEATING FULL SCALE INACTIVE DRUMS WILL BE INCLUDED.
The effect of heat on packaged Intermediate Level Waste (ILW) has been studied. This was done in order to be able to predict the behaviour of the ILW under accident conditions involving fire during transport or at the repository. In the study experimental data were obtained and used in the development and validation of theoretical models to describe aspects of the behaviour of the waste form when subjected to heat. The prime objective was to be able to predict the amounts of radioactive materials released from a given incident.

4 ILW streams were selected for experimental study. These 4 were chosen as the minimum that could be studied to provide a set of data that could be used in the prediction of the behaviour of the majority of ILW produced in the United Kingdom. Heating experiments were carried out at small scale using packaged ILW samples made from active wastes or inactive simulants. Data were obtained on temperatures in the waste form, production of volatile materials, carry forward of solid particulate materials and carry forward of radionuclides. The results were used, together with data from full scale experiments with inactive simulant ILW as a function of the applied heating conditions. The temperature of the waste form is used to predict the release of radioactive materials from the package.

The results obtained showed that under the conditions studied (exposure to external temperatures of up to 1000 C) there was no significant release of solid particles of waste form. The total fractional releases of radionuclides were generally very low. The release of radionuclides below waste form temperatures of 500 C was postulated to result mainly from the rapid evaporation of pore waters in the waste form matrix. A small fraction (typically 0.0001) of radionuclides dissolved in the pore water was carried forward with the steam produced.

Temperatures within a 500 litre drum of packaged ILW can be calculated provided that the thermal conductivity and ther mal capacity data for the waste form are available. The calculations show that, even for extreme accident conditions with a boundary temperature of 1000 C held for 2 hours, less than 25% of the waste form exceeds 100 C. The calculated release fractions for radionuclides from such severe conditions are less than 10{-7} for actinides and less than 0.01 for caesium, strontium and cobalt.
1. PROCUREMENT OF SAMPLES OF FULLY ACTIVE WASTES FOR STUDY.
2. MANUFACTURE OF SMALL-SCALE SAMPLES OF WASTE FORM TO REFERENCE SPECIFICATIONS FOR EACH WASTE.
3. HEATING THE SAMPLES OF PACKAGED WASTE FORM UNDER CONDITIONS TO SIMULATE A FIRE ACCIDENT DURING TRANSPORT (IN WHICH CASE THE FULL SIZE DRUMS WOULD BE IN A TRANSPORT FLASK) OR IN A REPOSITORY.
4. MEASUREMENT OF THE RADIOACTIVE MATERIAL RELEASED FROM THE HEATED PACKAGED WASTE FORM AS A FUNCTION OF TEMPERATURE.
5. MEASUREMENT OF THE INACTIVE MATERIALS PRODUCED WHEN THE WASTE FORM IS HEATED, INCLUDING SOLID PARTICULATES, STEAM AND OTHER CONDENSABLE MATERIALS AND GASES.
6. EXAMINATION OF THE RESIDUES FROM HEATING THE WASTE FORM.
7. EXAMINATION OF THE RESIDUES FROM HEATING THE WASTE FORM.
8. INFORMATION DERIVED FROM THE EXPERIMENTAL PROGRAMME IS TO BE ASSESSED AND USED AS AN INPUT TO THE DEVELOPMENT OF A MATHEMATICAL MODEL.

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CSC - Cost-sharing contracts

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United Kingdom Atomic Energy Authority
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Letzte Aktualisierung: 23 Januar 1994

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Permalink: https://cordis.europa.eu/project/id/FI1W0176/de

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