In energy sector often we hear about resource depletion, for example in Oil sector but also regarding nuclear energy. Regarding Nuclear energy, how much Uranium do we have? and how long it will last? Let’s try to answer these question.
Index:
- Uranium reserve
- Uranium required for the whole life of a reactor
- World consumption and resource duration
- Final notes
Uranium reserve
The estimated amount of Uranium which is economically viable is 5.5 million tonnes. However another 35 million tonnes can be eventually extracted.
The biggest source of Uranium is in the seawater, we are talking about 4.6 billion tonnes (one thousand time more than on earth crust).
Uranium required for the whole life of a reactor
The amount of Uranium needed in a reactor depends mainly on two things:
- Type of reactor
- Kind of fuel cycle (Recycling or not)
For example, in a Light Water Reactor (LWR) without recycling of spent fuel, we need a total amount of 4260 tonnes of Nautral Uranium. But adopting a recylcing procedure (Saving Uranium and Plutonium in spent fuel) we would need less Natural Uranium: 2665 tonnes.
As I said different kind of reactor have different resources consumption, a LMFBR (liquid metal fast breeder reactor) is able to produce fissile material while it is running, this leads to a strong reduction in terms of Natural Uranium requirements.
In the table below you see a comparison of the Natural Uranium required for a whole life of a reactor using different technologies:
| Reactor type | Amount of Nat U. needed (whole life) |
| LWR – no recycling | 4260 t |
| LWR – with U-Pu recycling | 2665 t |
| LMFBR | 36 t |
World consumption
According to world-nuclear association for a power demands of 400 GWe Uranium consumption is around 67500 tonnes every year. To this correspond a value of terawatt hours equal to:
0.4 [TWe] \cdot 365 [d] \cdot 24 [h/d] = 3504 TWhAnd so the amount of resources normalized to energy production is: 19.26 tonnes/TWh
Lets’s consider varous scenarios in order to understand for how long our Natural Uranium will last.
CASE 1: Nowaday consumption and technology
In this case nuclear power cover just 10% of total energy production, this is approximately nowaday situation.
World nuclear TWh (10% of total 2018 data): 2673 TWh
We can use the reference consumption stated before to derive nowadays requirement making the following proportion:
3504 : 67500 = 2673 : M_{natU,1y}The result is M_{natU,1y} = 51491.8 tonnes/year
Now we have two reasonable option for the total amount of resources, one is consider the amount of resources economically viable today, and the other is consider the total amount of Uranium on earth crust:
- Economically viable resources: \frac{5.5 \cdot 10^6}{51491.8} = 107 years
- Total earth crust resources: \frac{40 \cdot 10^6}{51491.8} = 777 years
One should take in mind that these are just estimation, the real number is probably in between these two values.
CASE 2: Nowaday technology but full nuclear energy production
What happen if tomorrow all electric energy will be produced just by nuclear fission?
Well, since today just 10% of energy is produced by nuclear, moving to 100% mean that we have to multiply by 10 the consumption derived before and so we divide by 10 the time periods that become: 10.7 – 77.7 years
Clearly this is an unrealistic scenario, since it is impossible to move 100% nuclear in a short period. Also relying just on one type of energy source is not a good idea.
CASE 3: Nowaday energy production but gen IV technology
We have seen in the table that a fast breeder reactor requires much less Uranium, this mean that our resources will last for a longer time if we imagine to adopt just this type of reactor. But how long?
To answer this question i need to introduce the so called Utilization factor U. This parameter is the fraction between the amount of fissile material used by the reactor over the total amount of natural Uranium required. In other words high utilization factor means that the reactor can produce the same amount of energy exploiting less Natural Uranium.
Light Water Reactors have a Utilization factor around 0.55% this mean that to burn 1 kg of Uranium – 235 we need approximately 200 kg of Natural Uranium. A typical value of U for a LMFBR is 67%. Making a simple proportion we discover that using only LMFBR our reserve will last for thousands of years (LWR utilization factor is approximated to 1%):
- 107 : 1\% = T_{LMFBR}: 67\% \rightarrow T_{LMFBR} = 7169 years
- 777 : 1\% = T_{LMFBR}: 67\% \rightarrow T_{LMFBR} = 52000 years
With this kind of reactor fuel exploitation is so high that also considering the unrealistic case of 100% Nuclear energy production, Uranium will last for thousand of years.
Final notes
These calculations are just a simplified analysis, more defined studies can be for shure founded in literature. However, my goal was just obtain some order of magnitude so we can understand in which case the issue of limited resources is a real problem.
Before ending this page i want to add just two things.
First i didn’t spoke about sea resources which are an enormous amount, currently the feasibility of extraction from seawater is under study.
Second: Not only Uranium can be exploited as nuclear fuel. Thorium is an element that when irradiated by neutron produce Uranium – 233 (which is better than Uranium – 235 exploited in today reactors) and Thorium is more abundant than Uranium on eath crust.