Chain Reactions and Nuclear Reactors Flashcards
when does nuclear fission happen
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
what are nuclei that are able to undergo fission called
fissile nucleus/nuclei
most fissile nuceli are ones with high mass - u235 or pu239
how are neutrons released in a fission reaction
nuclear fission reactions release neutrons and are capable of inducing fission in other uranium atoms forming a chain reaction
what is a chain reaction
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
example of controlled and uncontrolled nuclear fission chain reaction
controlled - nuclear power
uncontrolled - nuclear weapons
what happens in nuclear reactors
fission reactors occur under controlled conditions
heat energy released by the reaction is used to generate electricit
common features of nuclear reactors
fuel rods, moderator, control rods, coolant, shielding
what is enrichment process
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
what happens when uranium is mined
99% of it is U-238 and it is not fissile and it has to struck by a neutron to be fissile
what are fuel rods
they are long cylinders in nuclear reactors that contain pellts of enriched uranium
what is a moderator
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
example of moderator materiala
heavy water - H2O with H2 atoms insteaf of H1 is ideal for this as it is less likely to absorb the neutrons
what are control rods used for
they are used to slow the reaction when it is going too fast
what do control rods do
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
what are control rods made out of
material that absorb neutrons easily - boron cardibe, silver and cadmium
what is a coolant
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
what is shielding in a reactor
Reactors are enclosed in a steel case and surrounded by several metres of concrete to prevent radiation from escaping
what is low level radioactive waste
buried underground - protective clothing and tools
what is intermediate level waste
parts of the reactor and fuel casings
they are put in steel drums and encased in concrete for storage background
what is high level waste
it is fused into glass blocks and stored underground
used fuel
characteristics of moderator
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