Radioactive Waste Management and Decommissioning
This domain tests waste classification, conditioning, storage, disposal and the planning of decommissioning.
Core rules
- Waste is classified by activity concentration, half-life and heat output: exempt or clearance, very low-level, low-level, intermediate-level and high-level waste. High-level waste is heat-generating and requires deep geological disposal.
- The waste hierarchy is avoid, reduce, reuse, recycle, recover and dispose. Volume reduction and decay storage are common before disposal.
- Conditioning includes cementation, bituminisation and vitrification. High-level liquid waste is typically vitrified and stored in engineered canisters before geological disposal.
- Near-surface disposal is suitable for short-lived low- and intermediate-level waste; geological disposal is used for long-lived and high-level waste.
- Decommissioning strategies include immediate dismantling, deferred dismantling and entombment. Planning should begin at design stage and include waste routes, dose optimisation and site release criteria.
Worked example
A metallic component has Co-60 contamination at 100 Bq/g. Co-60 has a half-life of 5.27 years. If the clearance level is 0.1 Bq/g, how long must it be decay-stored, ignoring other nuclides?
The required reduction factor is 100/0.1 = 1000, close to 2^10 = 1024. Therefore about 10 half-lives are needed: 10 × 5.27 = 52.7 years. The reasoning is exponential decay. In practice, other nuclides may be present, and the limiting nuclide may not be Co-60, so the storage period must be based on the full radionuclide inventory.
Traps
Do not classify waste by mass or volume alone; activity concentration and half-life matter. Do not assume decay storage solves long-lived waste. Do not ignore the heat output of high-level waste. Do not treat clearance as unconditional disposal; it requires verified compliance. Do not leave decommissioning planning until shutdown.
Key points
- Waste classes range from exempt to high-level.
- High-level waste is heat-generating and needs geological disposal.
- Vitrification immobilises high-level liquid waste.
- Near-surface disposal suits short-lived low- and intermediate-level waste.
- Decommissioning options include immediate and deferred dismantling.
- Decay storage depends on the limiting radionuclide.