Theory 095/Energy & Environment /Nuclear engineering
Waste Heat Follows the Branching
Waste is characterised by activity. The heat that drives the engineering may follow a different isotope.
The heat output of nuclear waste is set by the branching ratio of the decay chains rather than by the total activity, so two wastes with equal activity can differ several-fold in heat and in storage requirements.
01The evidence
Decay heat varies between wastes with similar activity, and the variation tracks the presence of short-lived isotopes with high energy per decay.
02The tension
Waste classification uses activity and half-life, which predict heat by assuming an average energy per decay and miss the branching that concentrates it.
03The mechanism
Heat is energy per decay multiplied by decay rate. Activity measures the rate; the energy per decay varies by orders of magnitude between isotopes and between branches of a chain.
That makes the branching the determinant, and predicts heat should be predictable from isotopic composition rather than from activity.
04What this is not
Activity models assume average energy. This uses composition, which explains heat differences at equal activity.
05Predictions
- P1Heat should track branching composition.
- P2Equal-activity wastes should differ in heat.
- P3Storage needs should follow heat, not activity.
06Refutation
Heat tracking activity at controlled composition would restore the classification.
07What it changes
It would change waste storage planning.