What are the roles of the moderator and the control rods in a nuclear reactor?

The moderator, such as water or graphite, slows neutrons so they cause fission more readily. Control rods absorb neutrons and are raised or lowered to control the reaction rate.

Outline how a nuclear power station generates electricity.

Fission in the reactor core releases heat, which a coolant carries to a steam generator. The steam drives a turbine coupled to a generator, as in a fossil fuel station.

What is meant by the energy density of a fuel?

Energy density is the energy released per unit mass or volume of a fuel. Nuclear fuel has an energy density millions of times greater than any fossil fuel.

Complete fission of 1 kg of uranium-235 releases about 8.2 × 10¹³ J. Coal releases about 24 MJ/kg. How many times more energy does the uranium release?

The uranium releases about 3.4 million times as much energy as the same mass of coal. The working is 8.2 × 10¹³ J ÷ 2.4 × 10⁷ J = 3.4 × 10⁶.

CCEA A-Level Environmental Technology 3930

Fossil Fuels

Topic overview Coal, oil and gas in modern society Reserves, lifespan and accessibility Fossil fuel combustion and the IPCC evidence Carbon trading schemes Fossil fuel demand, emerging economies and fuel security Environmental impacts of fossil fuel use

Global Action on Energy Conservation and Climate Change

Topic overview Sustainable development and climate agreements Emissions and energy efficiency targets for 2020 Renewable energy and demand reduction in policy Nuclear power as an alternative

Macrogeneration

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Microgeneration

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Energy From Wind

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Energy From the Sun

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Global Action on Energy Conservation and Climate Change

Nuclear power as an alternative

3 things to know
AS 1

Overview

Fission and the chain reaction, moderators and control rods, energy density calculations, lifecycle emissions compared with gas, baseload supply, radioactive waste, Chernobyl and Fukushima, cost and small modular reactors.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Discuss whether nuclear power is a viable alternative to fossil fuels and renewable energy sources.

Key term

What is nuclear fission?

Key term

How does a fission chain reaction keep a reactor running?

Questions from this subtopic

Each one with the model answer underneath.

1
What is nuclear fission?
Model answer
Nuclear fission is the splitting of a heavy nucleus, such as uranium-235, after it absorbs a neutron. The split releases a large amount of energy and two or three further neutrons.
2
How does a fission chain reaction keep a reactor running?
Model answer
Neutrons released by one fission go on to split further uranium nuclei. A steady chain reaction occurs when on average one neutron from each fission causes another.
3
What are the roles of the moderator and the control rods in a nuclear reactor?
Model answer
The moderator, such as water or graphite, slows neutrons so they cause fission more readily. Control rods absorb neutrons and are raised or lowered to control the reaction rate.
4
Outline how a nuclear power station generates electricity.
Model answer
Fission in the reactor core releases heat, which a coolant carries to a steam generator. The steam drives a turbine coupled to a generator, as in a fossil fuel station.
5
What is meant by the energy density of a fuel?
Model answer
Energy density is the energy released per unit mass or volume of a fuel. Nuclear fuel has an energy density millions of times greater than any fossil fuel.
6
Complete fission of 1 kg of uranium-235 releases about 8.2 × 10¹³ J. Coal releases about 24 MJ/kg. How many times more energy does the uranium release?
Model answer
The uranium releases about 3.4 million times as much energy as the same mass of coal. The working is 8.2 × 10¹³ J ÷ 2.4 × 10⁷ J = 3.4 × 10⁶.

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Fossil Fuels

Global Action on Energy Conservation and Climate Change

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