Fission And Fusion

Question 1

Nuclear fusion

Answer 1

the fusing together of two small nuclei at a very high temperature and pressure, releasing a lot of energy (from the small amount of the particles mass)

Question 2

Where does nuclear fusion occur

Answer 2

Stars

Question 3

Nuclear fusion reaction

Answer 3

Deuterium + tritium -> (fusion) helium + energy + neutron

Question 4

Nuclear fission

Answer 4

The splitting of a large unstable nucleus into two smaller nuclei

Question 5

What is the nucleus that is split and the nuclei that are formed called

Answer 5

-parent nuclei
-daughter nuclei

Question 6

What is fissile material and what are examples of them

Answer 6

-material that can undergo fission under the right conditions, often used as fuels in nuclear power stations
-some isotopes of uranium and plutonium are fissile materials

Question 7

Spontaneous fission

Answer 7

When a nuclei undergoes fission without additional energy being put into the nucleus

Question 8

Induced fission

Answer 8

-when an unstable nucleus absorbs a neutron, making it more unstable then it decays almost immediately

Question 9

Half life Uranium-235

Answer 9

700 million years
-means fission has to be induced

Question 10

Half life Uranium-235

Answer 10

700 million years
-means fission has to be induced

Question 11

How is uranium 235 induced fission

Answer 11

-It absorbs a neutron and becomes uranium 236
-it is unstable and plots almost immediately to produce two smaller daughter nuclei and 2-3 neutrons

Question 12

What are the products of fission

Answer 12

-two smaller nuclei
-2 or 3 neutrons
-gamma rays are also emitted

Question 13

What happens immediately after fission

Answer 13

-the products of the fission reaction move away very quickly
-the energy is transferred from the nuclear potential energy stored in the ordinal nucleus into the kinetic energy of the products
-in a nuclear power station, this energy can be harnessed and inverted into electrical energy

Question 14

Chain reaction

Answer 14

A neutron emitted from the splitting of a nucleus causes further nuclei to split and the neutron emitted from these cause further fission reactions

Question 15

Critical mass

Answer 15

The minimum amount of fissile material to maintain a chain reaction e.g if the fissile material is greater than the critical mass, the rate of reaction accelerates (can cause uncontrollable release of energy; explosion)

Question 16

Factors that must be controlled in a nuclear reactor

Answer 16

1. The number of free neutrons in the reactor
2. The energy of the free neutrons

Question 17

What are control rods and how do they work

Answer 17

-they are made of a material which absorbs neutrons in a nuclear reactor to control the rate of reaction without becoming dangerously unstable themselves

Question 18

How are control rods controlled

Answer 18

(to absorb neutrons)
-the depth of control rods in the core is changed to control the rate of reaction (lower rods decreases the rate of fission, more neutrons absorbed)
-adjusted to the point that each fission event produces one fission neutron that causes another fission
-if the nuclear reactor needs to shut down, the control rods can be lowered all the way so no reactions can take place

Question 19

what are moderators and how do they work

Answer 19

(slow down neutrons)
-a material that surrounds the fuel rods and control rods inside the reactor core
-fast-moving neutrons produced by the fission reactions slow down by colliding with the molecules of the moderator
-neutrons are slowed down so they are in thermal equilibrium with the moderator
(these neutrons are called thermal neutrons)
(ensures neutrons can react efficiently with the uranium fuel)

Question 20

what is shielding and how does it work

Answer 20

(to absorb hazardous radiation)
-nuclear reactor is surrounded by shielding materials
-daughter nuclei formed and the neutrons emitted are radioactive
-this ensures the environment is safe for workers

Question 21

differences between nuclear fusion and fission

Answer 21

-nuclei joins together vs nuclei splitting
-nuclei are small ie hydrogen vs large ie uranium
-occurs in stars vs nuclear reactors
-produces large energy and large nuclei vs less energy and smaller daughter nuclei
-requires high temperature and pressures vs thermal neutrons to induce fission

Question 22

advantages of nuclear fusion reactors

Answer 22

-capable of generating more energy than fission reactions
-nuclear fuel for fusion is more abundant than fuel required for fission
-nuclear fusion produces no long-lived nuclear waste products

Question 23

disadvantages of fusion reactors

Answer 23

-conditions for nuclear fusion are much harder to achieve and maintain Earth than fission

Question 24

equation for possible fusion reaction

Answer 24

deuterium + tritium -> helium + a neutron

Question 25

what are stars made of

Answer 25

they balls of mostly hydrogen

Question 26

conditions required for nuclear fusion

Answer 26

extremely high temperature and pressures (these temperatures are only on stars

Question 27

why are extreme conditions needed for fusion

Answer 27

-protons have a positive charge and repel each other -to overcome this repulsion, protons must have very high kinetic energies to allow them to get close enough to fuse -high pressure increases the number of collisions (and fusions) that occur between nuclei