Physics 380 Nuclear (Hw #4)
1. Why does a fusion reactor produce less waste than a fission reactor? (20%)
A fusion reactor does not produce nuclear waste because the only product of the fusion reaction is Helium which is not radioactive. It will only produce large quantities of high energy neutrons. In contrast the fission reactor produce large quantities of unfissioned Uranium and Plutonium which are very radioactive and hence very dangerous materials.
2. How many grams of 235U must undergo fission to operate a 1 GW power plant for one day if it is 30% efficient? Assume each fission releases 208 MeV.
($1 MeV = 1.6*10^{-13} J$) ($1 g 235U = 2.5*10^{21} atoms$). (20%)
$Energy = power*time =10^9*24*60*60 =8,64*10^{13} J$
$Uranium mass =total energy/1 atom energy =$
$=8.64*10^{13}/2.5*10^{21}/(208*1.6*10^{-13}) =1000 g =1Kg$
Because there is only 30% efficiency the total mass is 3 kg
3. Describe the purpose of the following nuclear reactor components. (20%)
a. Fuel
The fuel is the fissionable material . it gives out the energy in a fission nuclear reaction
b. Moderator
The moderator is holding back the chain nuclear reaction to happens. It is necessary in order to prevent a nuclear explosion.
c. Coolant
The coolant takes the energy released by the fuel and convert is to electric energy. It is necessary in order to cool down the reactor and prevent a nuclear melting of the core fuel.
d. Containment
The containment is necessary to stop the dangerous nuclear radiations (high speed neutrons and gamma rays) to affect the outside of the reactor.
4. Describe each of the following radioactivity terms. (20%)
a. Alpha decay
An alpha decay is the break down of a nucleus of an atom into an alpha particle (He nucleus) and a smaller nucleus (with mass M-2)
b. Beta decay
Beta decay is the emission of a high energy electron from a nucleus (a high energy neutron) . by this way the nucleus that emitted the beta ray has one proton in addition.
c. Gamma decay
Gamma decay is the emission of a high energy electromagnetic quanta. By this way the nucleus becomes more stable having a lower total energy.
d. Fission
The process of fission is the process in which two smaller nuclei fission together into a larger mass nucleus and a certain quantity of electromagnetic energy.
e. Half-life
Half life is the time needed for a radioactive compound to attain half of its initial mass by nuclear decomposition.
