Introduction The draft IAEA publication “Generic Post-closure Safety Assessment for the Borehole Disposal of Disused Sealed Sources” (the GSA) (IAEA, 2013) considers the post-closure impacts of the disposal of disused sealed radioactive sources using the Borehole Disposal Concept (BDC). Table 17 of the GSA notes that there is no explicit consideration in the GSA of radiolysis, criticality or thermal effects since such effects are considered to be insignificant for the typical inventories to be disposed. However, there are certain high activity sources, such as the Category 1 and 2 sources, for which it might be necessary to consider such effects. In addition, the calculations undertaken in the GSA are performed for a reference design with fixed dimensions for the capsule and disposal container (Table 5 of the GSA). It is recognised that capsules and disposal containers with alternative dimensions might be used in order to accommodate Category 1 and 2 sources. Changing the dimensions of the capsule/disposal container will impact on steel and concrete thicknesses which in turn will impact failure times. Therefore, it is also necessary to assess the impacts of alternative dimensions. The present project addresses the potential impacts of the disposal of high activity radioactive sources on the post-closure safety of the BDC. The results of this project will be used to determine the need, if any, for additional work. The project relates only to post-closure impacts; operational safety issues associated with the disposal of high activity sources in the BDC and the use of alternative dimensions for capsules and disposal containers is beyond the scope of the present project. This report documents the work undertaken during the project: the collation and documentation of relevant data (Section 2); the undertaking of thermal calculations (Section 3); the undertaking of radiolysis calculations (Section 4); the screening of features, events and processes (FEPs) considered in the GSA (Section 5); the undertaking of post-closure safety assessment calculations (Section 6); and the resulting conclusions (Section 7).
Introduction The draft IAEA publication “Generic Post-closure Safety Assessment for the Borehole Disposal of Disused Sealed Sources” (the GSA) (IAEA, 2013) considers the post-closure impacts of the disposal of disused sealed radioactive sources using the Borehole Disposal Concept (BDC). Table 17 of the GSA notes that there is no explicit consideration in the GSA of radiolysis, criticality or thermal effects since such effects are considered to be insignificant for the typical inventories to be disposed. However, there are certain high activity sources, such as the Category 1 and 2 sources, for which it might be necessary to consider such effects. In addition, the calculations undertaken in the GSA are performed for a reference design with fixed dimensions for the capsule and disposal container (Table 5 of the GSA). It is recognised that capsules and disposal containers with alternative dimensions might be used in order to accommodate Category 1 and 2 sources. Changing the dimensions of the capsule/disposal container will impact on steel and concrete thicknesses which in turn will impact failure times. Therefore, it is also necessary to assess the impacts of alternative dimensions. The present project addresses the potential impacts of the disposal of high activity radioactive sources on the post-closure safety of the BDC. The results of this project will be used to determine the need, if any, for additional work. The project relates only to post-closure impacts; operational safety issues associated with the disposal of high activity sources in the BDC and the use of alternative dimensions for capsules and disposal containers is beyond the scope of the present project. This report documents the work undertaken during the project: the collation and documentation of relevant data (Section 2); the undertaking of thermal calculations (Section 3); the undertaking of radiolysis calculations (Section 4); the screening of features, events and processes (FEPs) considered in the GSA (Section 5); the undertaking of post-closure safety assessment calculations (Section 6); and the resulting conclusions (Section 7).