Nuclear PowerMeghna Pancholi, Phi Nguyen, Colin Weinstein

What is Nuclear Power?● Nuclear Power - associated w/energy from nuclear reactions.

o Nuclear reaction releases enormous amount of heat energy which is harnessed in nuclear power.

● 2 kinds of nuclear reactions:o Nuclear fusion - two light nuclei come together to form a

heavy nucleus. Critical Mass - minimum amount of fissile material

needed to sustain nuclear chain reaction

o Nuclear fission - a heavy nucleus breaks apart to form two (or more) lighter nuclei.

Nuclear Fission Power Plants● (Nuclear) Chain Reaction - a nuclear reaction that causes one or

more other nuclear reactions to take place

o Fissionable - material that can undergo nuclear fission

o Fissile - material that can undergo nuclear fission by neutrons with low kinetic energy

● Isotopes - two or more nuclei with the same atomic number but different atomic masses

Chain Reactions● Result of neutrons released in fission

colliding with newly produced nuclei

o Controlled - reaction progresses at a constant, self-sustaining rate

o Uncontrolled - amount of fissions increases exponentially (nuclear weapons)

● Nuclear reactors slow/capture neutrons to keep reaction rate constant

Fuel Enrichment

● Fuel in a nuclear fission power plant must be self-sustainingo U-235 is fissileo U-238 is only fissionable

High energy neutrons cause U-238 fission, but released neutrons too slow to continue chain reaction

● Fuel enrichment - Increasing % of U-235 in fuel by centrifugingo Natural: 0.7% U-235o Low-enriched: 3-4% U-235o High-enriched: 90% U-235

Fission Reactor Components● Control rods - absorb extra neutrons produced by fission to keep

fission rate constanto Materials like boron, cadmium, that absorb neutrons w/out

fissiono Held by electromagnets, if released, reaction becomes

uncontrolled

● Moderators - slow down neutrons through collisions with atoms w/comparable mass (inelastic collisions)o Water, graphite, Beryllium, etc

● Heat Exchanger - creates steam to generate electricity; powered by heat transferred from reactor by water

Sankey Diagram

Plutonium-239

● Pu-239 created in a breeder reactor

● More fissile and creates slightly more energy than U-238

● Longer half-life = more easily stored

● Short production time

● Doesn’t require moderator; saves space and $

Risks of Nuclear Power● Thermal Meltdown - uncontrolled reaction causes extreme heating of reactor core

and reactive fission products; Extreme damageo Caused by component failure, lack of coolant, power surge, failed control

rods

● Radioactive Nuclear Waste - radioactive for several years; health risk exposureo Inappropriate disposal - leakages, abandoned/stolen waste

● Transportation + Mining Dangers - toxic gas emission, pollution

● Inappropriate Use o World’s total nuclear weapons - enough to destroy world/civilizationo Policies for dissipation of nuclear weapons have been considered but difficult

to enforce and too attractive from military perspective.

Chernobyl (Thermal Meltdown)

Nuclear Fusion Power Production Difficulties

● Nuclear fusion energy produces safe products, since fusion reactions between light & nuclei produce another light & radioactively inactive nucleus.

● The problem is that extremely high temps are required to initiate a

fusion reactiono Difficult to maintain & confine high tempo high density plasma would be produced

● Plasma - cloud of charged particles; most common & energetic form of matter; Difficult to confine due to movement & energy

● Even with high temperatures attained, there still must be a critical density of ions required for the reaction to be maintained.

Review Problems1. When a neutron “collides” with a nucleus of uranium-235 ( 235 U)

the following reaction can occur. a. What is this reaction?b. Energy is liberated in this reaction. In what form does this

energy appear?c. Estimate the initial amount of uranium-235 needed to

operate a 600 MW reactor for one year assuming 40% efficiency and that for each fission, 200 MeV is released.

2. The energy released by the chain reactions in a nuclear reactor is equal to 5 GJ each second. a. If the required demand of the power station is 4 GJ per

second, explain why the full demand may not be met. b. Determine the required efficiency of the power station in

order to comply with the demand.

Review Answers

1a. Fission1b. Kinetic energy1c. 578.2 kg

2a. Demand may not be met because the energy must still be transferred and transformed into thermal, mechanical, and electric energy. Energy is degraded in these processes. 2b. The required efficiency is 80%.

Activity

Instructions

There are two teams: the nuclear fission team and the fission reactor team.

Reactor Capacity - 15

The nuclear fission team wins if they achieve thermal meltdown. ● Thermal Meltdown: The reactor overflows.

The fission reactor team wins if they successfully generate electricity for 10 min

● Electricity Generation: The reactor must have at least 8 nuclei in it● If the reactor goes below half full, all accumulated electricity time is

lost

RolesNuclear Fission TeamU-238: Solve problems to perform fission w/out using calculator; may only work w/other U-238; 1 mark = 1 fission

U-235: Solve problems to perform fission; may only work w/other U-235; can use calculator. 1 mark = 1 fission

Fuel Enricher: May convert a U-238 into a U-235 for every 5 marks earned.

Fission Reactor TeamControl Rod: May prevent a fission for every 4 marks earned; can use calculator.

Moderators: May temporarily (1 min) remove a U-238 or U-235 pencil for every 3 marks earned; can use a calculator

Supervisor - Mrs. Jarrett may give help at her discretion.