A QUANTITATIVE DETERMINATION OF THE BARRIER
QUALITY OF WASTE PACKAGES FOR THE CASE
OF A MECHANICAL IMPACT
D. Gründler, D. Maric and W. Wurtinger
Institut für Sicherheitstechnologie (ISTec) GmbH
Köln, Germany
J. Migenda
Nationale Genossenschaft für nukleare Entsorgung Wellenberg
Wettingen, Switzerland
ABSTRACT
A model was developed that predicts the amount of airborne aerosols released when solid low level wastes are damaged by a drop or crush. Multiple barriers imposed by, e.g., drums packed in a container are accounted for. The predicted amount of airborne aerosols is a function of the type of waste and the characteristics of the waste package. It is also a continuous function of the impact energy for the common range of energies considered in safety analyses. Consequently, this model can be used to relax the conservative restrictions imposed by older safety analyses and hence to optimize the transport capacity or the capacity of an existing or planned repository.
INTRODUCTION
Solid low level wastes are known to generate airborne aerosols when damaged by a mechanical impact. The amount of the airborne aerosols released into the environment depends on the properties of the waste and those of the package. The latter may consist of multiple barriers, such as those imposed by, e.g., drums packed in a container. These are characterized by their barrier qualities defined via B = 1 – f, where 0 £ f £ 1 is the release factor, i.e. the ratio of aerosol penetrating the barrier.
Hitherto it was not possible to account for the waste package barriers in a safety analysis and consequently the conservative assumption of the lack of any barrier has had to be postulated. This approach is unsatisfactory because it imposes too restrictive limits on the amount of waste which may be safely transported or disposed of in a repository. Therefore, in this work a model was developed which predicts the amount of released airborne aerosols as a function of the type of waste and the characteristics of the waste package. It is applicable to all common types of low level wastes and packages. The mechanical impacts include drop and crush. The predicted amount of airborne aerosols is a continuous function of the impact energy for the common range of energies considered in safety analyses.
BARRIER QUALITY OF 200 L DRUMS
Crush
Shirley [1] has studied the effect of static pressure on 200 L drums. Using his results the barrier quality of 200 L drums for the case of a crush was estimated for several crush energies as shown in Fig. 1.
Figure 1. Barrier Quality of a 200 L Drum for the Case of a Crush.
The estimated values were then interpolated by fitting. The complex shape of the resulting function, cf. Fig. 1, reflects the loss of the lid at a specific energy about 10 J kg-1 followed by the deformation of the drum below 200 J kg-1, above which it finally loses its integrity. The residual barrier quality above 300 J kg-1 was estimated to be 0.5 because the waste possesses some retention properties even after the drum has lost its integrity.
Drop
The available experimental data on the barrier quality of 200 L drums for the case of a drop [2] are shown in Fig.2. They were inter- and extrapolated by fitting to obtain a continuous function of the drop height. However, drop can also be treated as a form of crush, this being a more conservative approach. The barrier quality of 200 L drums obtained in this manner is shown in Fig. 2. Interestingly, the predictions are insensitive to the orientation of the dropped drums as can be seen from the overlap of the curves computed for two different orientations and shown in Fig. 2. The complex shape of the function describing the barrier quality is explicable by the assumed loss of the lid at a drop height of about 2 m followed by the deformation of the drum below 22 m, above which it finally loses its integrity.
Figure 2. Barrier Quality of a 200 L Drum for the Case of a Drop.
BARRIER QUALITY OF A TRANSPORT CONTAINER LOADED
WITH 200 L DRUMS
The barrier quality of a transport container loaded with 200 L drums was estimated using the above results for 200 L drums. The corresponding estimate derived for the cases of drop are shown in Fig. 3.
Figure 3. Barrier Quality of a Transport Container Loaded with 200 L Drums for the Case of a Drop.
BARRIER QUALITY OF A CONCRETE CONTAINER
WITH CEMENTED WASTES
Rämö et al. [3] have measured the damage of small concrete containers (1.3 and 211 L) as a function of the drop height. Their results can be described by
(1)
where D V is the damaged volume of the container, V is the total volume of the container, H is the drop height, and k and V0 are adjustable parameters. The values of the latter can be obtained by fitting. The barrier quality of a concrete container of the usual size containing cemented wastes was obtained by extrapolation using equation (1). The absence of any wastes within the container walling was thereby accounted for. The discrete values of the barrier quality estimated in this manner for several drop heights were interpolated by fitting. The results are shown in Fig. 4. Finally, the barrier quality of the corresponding container for the case of a crush was derived using the above results for the case of a drop.
Figure 4. Barrier Quality of a Concrete Container Containing Cemented Wastes for the Case of a Drop.
CONCLUSION
A model was developed that predicts the amount of airborne aerosols released when solid low level wastes are damaged by a drop or crush. This model can be used to relax the conservative restrictions imposed by older safety analyses and hence to optimize the transport capacity or the capacity of an existing or planned repository. In the latter context, the model was already successfully applied in a safety analysis of a planned repository.
REFERENCES
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