Generic Operational Safety Assessment GOSA Workshop on the
- Slides: 10
Generic Operational Safety Assessment (GOSA) Workshop on the Application of the IAEA Methodology and Safety Assessment Framework (SAFRAN) Tool for the Safety Case (SC) and Safety Assessment (SA) for Predisposal Management of Disused Sealed Radioactive Sources (DSRS) Athens, GREECE 23 -27 June 2014
Assessment Context • The assessment context of the GOSA should be consistent with the generic safety assessment (GSA) for borehole disposal (IAEA Safety Series Report: Generic Post. Closure Safety Assessment for Borehole Disposal of Disused Sealed Sources)
Purpose • The purpose of the GOSA is to demonstrate that the proposed pre-disposal waste management activities for DSRS are done in a safe manner, as required by the regulatory framework. • The safety of operators (workers) and members of the public will be assessed, both for normal operations and for potential accidental situations.
Scope • The starting point for the GOSA is that the Disused Sealed Sources (DSSs) have arrived at the site • Activities of the original producer [e. g. hospital] and transport to site are beyond the scope of the current project). • The DSRS will be either disposed using the BDC or other disposal options (e. g. disposal in a near-surface or deep facility) and management options (long-term storage) will be used, but this assessment is limited to the pre-disposal phase.
Inventory to be considered • The inventory (Bq) and number of sources to be assessed in the GOSA need to be representative of what is found in practice in different countries. • An initial proposal was to consider two cases: a country (Ghana being an example) with a low to medium inventory of relatively low level activity sources that do not require the use of hot cells, and a country (South Africa being an example) with a medium to large inventory which includes high activity sources that will require the use of hot cells. • Different initial states of the sources are considered, including sources in the original devices, in a transport package, in the working container, and conditioned in cement.
Regulatory Framework • IAEA Safety Standards are used as the basis for the regulatory framework. • This includes normal operation and accidental situations, taking into account dose constraints as well as dose limits. • One issue currently under evaluation is the calculation of doses to the eye, extremities, etc. , in addition to whole body doses.
Typical activities for High activity sources and their duration Operational activities Duration (Minutes) 1) Prepare for Introduction into hot cell 15 2) Lift Original Source Shield into the hot cell 5 3) Close the hot cell 20 4) Remove the source 60 5) Characterise the source 20 6) Encapsulation and test of the capsule 20 7) Place capsule in disposal container and NDT 20 8) Transfer disposal container to the transfer cask 10 9) Disengage and prepare the transport cask for transport 15 10) Emplacement of the disposal container in borehole 15 11) Backfilling of the borehole 15
Examples of accidental scenarios (hot cell) • The situation where the operation team is unaware that the source has an • • activity greater than the value for what the facility was designed for and the team proceeds with standard operations. Error during the determination of the density of the shielding material (sand) in the hot cell and the operation proceeds with a sand density below design requirements. Situation with the Zn. Br 2 window density below design requirements being used by the operation team. Source is dropped after being removed from the original source shield. The source is found to be leaking when removed from the original source shield inside the hot cell. (Could have been damaged during removal). The manipulators malfunction whilst the source is inside the hot cell. The biological shield is damaged while bringing in the original source shield. Power outage in the hot cell. Lights are not operational in the hot cell.
