2. Fission and Fusion reactions
2
1) What is a fission reaction? A fusion reaction?
Atomic nucleus composed of nucleons: protons + neutrons
Z which defines the element
e.g. Hydrogen Z = 1
Hydrogen stable element (majority) Z = 1 ; A = 1
but existence of deuterium Z = 1 ; A = 2
tritium Z = 1 ; A = 3
several isotopes (A different) of the same element (same Z)
Remark: masses of isotopes which are different (proportional to A)
3. Fission and Fusion reactions
3
Binding energy
El = (Z * mp + (AZ) mn - m (X)) * c ²
Stability of a nucleus:
The higher the ratio El / A is, the
more stable it is
Aston curve El / A = f (A)
A lower than 20 → fusion reaction
eg:
A higher than 190 → fission reaction
eg:
Conservation of the number of
protons and mass number
nBaKrnU 1
0
140
56
93
36
1
0
235
92 3++→+
nHeHH 1
0
4
2
3
1
2
1 +→+
4. Production of electricity
4
What are main criteria to consider in the production of electricity?
- Access to raw materials
- Radioactivity (and quantity) of the products of reaction
- Energy
Nuclear power plants: thermal
1.Nuclear energy released by the
reaction as heat
2. Heated water. Steam that turns
turbines
Conversion of thermal energy into
mechanical energy
3. Alternator
Conversion into electricity
Now, we use fission.
Why an interest in nuclear fusion?
5. Why an interest in nuclear fusion?
5
Comparative FISSION / FUSION
1st criterion: Access to raw materials
FISSION FUSION
- Limited resources - Unlimited resources: sea water
- Extraction of Uranium in containing large quantities of
unstable countries deuterium (0.015% of hydrogen).
- opportunity to produce tritium
artificially
after, need to enrich by centrifugation
2nd
criterion: Radioactivity of products
FISSION FUSION
- Need to store long-lived - Little or no radioactive products
radioactive waste
6. Why an interest in nuclear fusion?
6
3rd criterion: Energy released
Mass loss → energy release
Mass defect ∆m = mass before (reactants) - mass after (products)
Energy released = ∆m * c ²
FISSION
E = ((234.9935-(93.8945 + 139.8920 + 1.008))*1.66054.10^(-27)) x (3*10^8)² = 2.974*10^(-11) J = 184.7 MeV
For 1g of uranium 235: 7.5.10 ^ 10 J
FUSION
E = ((2.0160+3.0247-4.0015-1.0087)*1.66054.10^(-27)) x (3*10^8)² = 4,5.10*(-12) J = 28.41 MeV
For 1g of mixture D-T: 5.4.10 ^ 11 J
Fusion releases more energy
nHeHH 1
0
4
2
3
1
2
1 +→+
nXeSrnU 1
0
140
54
94
38
1
0
235
92 2++→+
7. ITER project
7
Fusion has great advantages, but problematic experimental and industrial
aspects
Difficulty: Cause fusion of deuterium and
tritium, although they tend to repel
Solution: Mixture at a temperature of 100 million
degrees, plasma having enough energy
to overcome the repulsive forces
Difficulty: No material that resists with this heat
Solution: Confine the plasma at center of the reactor, away from walls in a
virtual magnetic enclosure created by electromagnets
→ Objectives of the ITER project
8. ITER project
8
Country: Russia, China, South Korea,
USA, Japan, European Union, India
Site: CADARACHE, End: 2019
Technical objectives of ITER
-Generate 500MW with 50MW during
6min40s
-Be able to maintain fusion reactions
in plasma for 16min40s
No electricity (thermal only), just check
the feasibility
Futures, REACTOR DEMO - 1500W electric power after losses
Commercial reactors from 2050
