Matter consumption in a nuclear reactor
In general, the nuclear fission results in the release of enormous quantities of energy. This energy comes from the nuclear binding energy which holds nuclei together. The binding energy per nucleon is higher for fission fragments than for uranium nuclei. It was found the sum of the rest masses of products of fission is measurably smaller than the rest mass of uranium nucleus.
It is due to the fact during the nuclear fission some of the mass of the nucleus gets converted into these huge amounts of energy and thus this mass is removed from the total mass of the original particle, and the mass is missing in the resulting nuclei.
According to the Einstein relationship (E = mc2) this binding energy is proportional to this mass difference and it is known as the mass defect.
Δm = ΔE/c2
Δm = 3000×106 (W = J/s) x 31.5×106 (seconds in year) / (2.9979 x 108)2 = 1.051 kg
Consumption of a 3000MWth (~1000MWe) reactor (12-months fuel cycle)
It is an illustrative example, following data do not correspond to any reactor design.
- Typical reactor may contain about 165 tonnes of fuel (including structural material)
- Typical reactor may contain about 100 tonnes of enriched uranium (i.e. about 113 tonnes of uranium dioxide).
- This fuel is loaded within, for example, 157 fuel assemblies composed of over 45,000 fuel rods.
- A common fuel assembly contain energy for approximately 4 years of operation at full power.
- Therefore about one quarter of the core is yearly removed to spent fuel pool (i.e. about 40 fuel assemblies), while the remainder is rearranged to a location in the core better suited to its remaining level of enrichment (see Power Distribution).
- The removed fuel (spent nuclear fuel) still contains about 96% of reusable material (it must be removed due to decreasing kinf of an assembly).
- Annual natural uranium consumption of this reactor is about 250 tonnes of natural uranium (to produce of about 25 tonnes of enriched uranium).
- Annual enriched uranium consumption of this reactor is about 25 tonnes of enriched uranium.
- Annual fissile material consumption of this reactor is about 1 005 kg.
- Annual matter consumption of this reactor is about 1.051 kg.
- But it corresponds to about 3 200 000 tons of coal burned in coal-fired power plant per year.