Chain Reactions and Nuclear Reactors

Question 1

when does nuclear fission happen

Answer 1

when an atomic nucleus splits into two or more smaller nuclei

triggered by the absorption of a neutron

random proccess and many combinations of fission products are possible

Question 2

what are nuclei that are able to undergo fission called

Answer 2

fissile nucleus/nuclei

most fissile nuceli are ones with high mass - u235 or pu239

Question 3

how are neutrons released in a fission reaction

Answer 3

nuclear fission reactions release neutrons and are capable of inducing fission in other uranium atoms forming a chain reaction

Question 4

what is a chain reaction

Answer 4

refers to a process in which neutrons released in fission produce an additional fissoin in at least one further nucleus

nucleus produces neutrons and process repeats

Question 5

example of controlled and uncontrolled nuclear fission chain reaction

Answer 5

controlled - nuclear power
uncontrolled - nuclear weapons

Question 6

what happens in nuclear reactors

Answer 6

fission reactors occur under controlled conditions

heat energy released by the reaction is used to generate electricit

Question 7

common features of nuclear reactors

Answer 7

fuel rods, moderator, control rods, coolant, shielding

Question 8

what is enrichment process

Answer 8

it is the process of refining uranium ore to raise the concentration of U-235 in the fuel rods/reactor

about 0.7% of the mined uranium is U-235 and most reactors require fuel that is 3.5% U-235

Question 9

what happens when uranium is mined

Answer 9

99% of it is U-238 and it is not fissile and it has to struck by a neutron to be fissile

Question 10

what are fuel rods

Answer 10

they are long cylinders in nuclear reactors that contain pellts of enriched uranium

Question 11

what is a moderator

Answer 11

when free neutrons are released by fission, they moving much too fast to cause fission reactions in other atoms

to slow them down, the space between the fuel rods is filled with a material called the moderator (graphit or water )

free neutrons slow downa s they bounce of the moderators atoms

Question 12

example of moderator materiala

Answer 12

heavy water - H2O with H2 atoms insteaf of H1 is ideal for this as it is less likely to absorb the neutrons

Question 13

what are control rods used for

Answer 13

they are used to slow the reaction when it is going too fast

Question 14

what do control rods do

Answer 14

when they are lowered into the reactor vessel with the fuel rods, they absorb some of the neutrons that are being releasedd from fuel rods

this slows teh reaction down and can stop it entirely

Question 15

what are control rods made out of

Answer 15

material that absorb neutrons easily - boron cardibe, silver and cadmium

Question 16

what is a coolant

Answer 16

a coolant (usually water) is ciruclated through a nuclear reactor to transfer heat from the core to the generators

in some reactors, the coolant is isolated from the rest of the system because the reactor makes it temporarily radioactive

Question 17

what is shielding in a reactor

Answer 17

Reactors are enclosed in a steel case and surrounded by several metres of concrete to prevent radiation from escaping

Question 18

what is low level radioactive waste

Answer 18

buried underground - protective clothing and tools

Question 19

what is intermediate level waste

Answer 19

parts of the reactor and fuel casings

they are put in steel drums and encased in concrete for storage background

Question 20

what is high level waste

Answer 20

it is fused into glass blocks and stored underground

used fuel

Question 21

characteristics of moderator

Answer 21

nuclei size must be small, around the size of neutron for it to collide with the neutron and bounce off and it doesnt pass through it