Chain Reactions and Nuclear Reactors Flashcards

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1
Q

when does nuclear fission happen

A

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

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2
Q

what are nuclei that are able to undergo fission called

A

fissile nucleus/nuclei

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

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3
Q

how are neutrons released in a fission reaction

A

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

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4
Q

what is a chain reaction

A

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

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5
Q

example of controlled and uncontrolled nuclear fission chain reaction

A

controlled - nuclear power
uncontrolled - nuclear weapons

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6
Q

what happens in nuclear reactors

A

fission reactors occur under controlled conditions

heat energy released by the reaction is used to generate electricit

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7
Q

common features of nuclear reactors

A

fuel rods, moderator, control rods, coolant, shielding

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8
Q

what is enrichment process

A

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

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9
Q

what happens when uranium is mined

A

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

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10
Q

what are fuel rods

A

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

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11
Q

what is a moderator

A

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

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12
Q

example of moderator materiala

A

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

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13
Q

what are control rods used for

A

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

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14
Q

what do control rods do

A

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

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15
Q

what are control rods made out of

A

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

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16
Q

what is a coolant

A

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

17
Q

what is shielding in a reactor

A

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

18
Q

what is low level radioactive waste

A

buried underground - protective clothing and tools

19
Q

what is intermediate level waste

A

parts of the reactor and fuel casings

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

20
Q

what is high level waste

A

it is fused into glass blocks and stored underground

used fuel

21
Q

characteristics of moderator

A

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