10.1 - Radioactivity

Question 1

How has radiation been important to our evolution

Answer 1

Human beings can survive small doses of nuclear radiation relatively unscathed. This has been important in our evolution, as the natural environment incorporates low levels of radiation from natural sources. This is called background radiation.

Question 2

In the uk what is background radiation like

Answer 2

In the uk it averages to less than one radioactive particle every two seconds in any given place.

Question 3

How could we measure background radiation, what result would you expect

Answer 3

If we measure background radiation using a Geiger-Müller (G-M) tube, the number of counts per second usually ranges from 0.2 - 0.5 depending on the exact location.

Question 4

How are radiation levels often reported

Answer 4

Radiation levels are often reported in counts per second, and the unit is called the becquerel (Bq) after Henri Becquerel, the frêńçh physicist credited with the discovery of spontaneous radiation in 1896.

Question 5

Levels of background radiation dose in Great Britain is measured in Bq….

Answer 5

A unit for measuring radiation energy delivered to the body.

Question 6

What are the sources of background radiation

Answer 6

Radon gas (50%)
Ground and buildings (14%)
Medical (14%)
Food and drink (11.5%)
Cosmic rays (10%)
Nuclear power and weapons (0.3%)
Other (0.2%)

Question 7

Tell me about the background radiation sources in WORDS

Answer 7

The actual exposure to nuclear radiation that any individual will receive from their environment will depend on where they are and for how long, as different environmental factors contribute to the local level of background radiation. On earth, approximately half of the background radiation is from naturally radioactive gases in the atmosphere, particularly radon.

Question 8

Where is radon produced

Answer 8

Radon is produced in the decay of uranium ore present in certain rocks (especially granite) and thus is more prevalent in certain parts of the world than others. In Cornwall in the uk, some houses are fitted with radon detectors and special ventilation systems to flush out excess radon gas from the household atmosphere.

Question 9

Where is the most naturally radioactive place on earth? Fun fact

Answer 9

Ramsar, in Iran, where the dosage can be more than 200 times the natural dose rate in the uk.

Question 10

How can we investigate background radiation

Answer 10

It is easy to determine the average background radiation in your area using a Geiger muller tube and counter. As radioactive decay is a random and spontaneous process, the activity in your lab must be measured over a long period of time (30 minutes or more) and then an average calculated. Otherwise, you may find that the measurement is, by chance, particularly high or particularly low and thus does not truly indicate the average over time. For example, if the G-M tube and counter are set to counting for two hours, and the final count is then divided by 7200(seconds), this will give a good approximation to the average over time as the count time is long compared with the average count of about 0.5 Bq. Measurements of radioactivity that have had the background radiation deducted, so that they only represent activity by a radioactive source under test, are known as corrected counts.

Question 11

What are corrected counts

Answer 11

Measurements of radioactivity that have had the background radiation deducted, so that they only represent activity by a radioactive source under test, are known as corrected counts.

Question 12

The background count will skew the results of investigations into nuclear radiations what must we do

Answer 12

Whenever such an investigation is undertaken, the background radiation must also be measured separately and then deducted from each count measured in the main part of the investigation.

Question 13

Many nuclei are slightly unstable and there is a slight probability that, each second they may …..

Answer 13

Decay

Question 14

What does decay mean

Answer 14

With a nuclei, this means that a nucleon may change from one type to another, or the composition or energy state of the nucleus as a whole may change.

Question 15

When a nuclear decay occurs, what happens

Answer 15

The radiation particle emitted will leave the nucleus carrying a certain amount of kinetic energy.

As the particle travels, it will ionise particles in its path, losing a small amount of that kinetic energy at each ionisation. When all the kinetic energy is transferred, the radiation particle stops and is absorbed by the substance it is in at that moment.

Question 16

What are the three main types of nuclear radiation

Answer 16

Alpha (a symbol ish)
Beta (B)
Gamma (y) radiation.

Each one comes about through a different process within the nucleus, each one is composed of different particles, and each one has different properties.

Question 17

How can we investigate radiation penetration

Answer 17

You can investigate the penetrating power of alpha, beta and gamma radiation using a Geiger-Müller tube to detect them. Between the source and the GM tube, place absorber sheets that progressively increase in density, and measure the average count rate. This investigation is often simulated using computer software. This removes all risk of exposure to radiological hazards.
The absorber sheets will be made from paper, lead and aluminium. Use a data logging computer to record counts.

Question 18

What are alpha particles

Answer 18

Alpha particles are composed of two protons and two neutrons, the same as a helium nucleus.

Question 19

How ionising are alpha particles

Answer 19

This is a relatively large particle with a significant positive charge (+2e), so it is highly ionising.

An alpha particle moving through air typically causes 10,000 ionisations per millimetre. As it ionises so much, it quickly loses its kinetic energy and is easily absorbed. A few centimetres travel in air is enough to absorb an alpha particle, and they are also blocked by paper or skin.

Question 20

Tell me an example of an alpha decay equation

Answer 20

241,95 Am —> 237,93 Np + 4,2 a

Question 21

What is the decay constant symbol

Answer 21

Lamder symbol

Question 22

What is the decay constant

Answer 22

Since radioactive decay is a spontaneous and random process, any radioactive nucleus may decay at any moment. For each second that it exists, there is a certain probability that the nucleus will decay. This probability is called the decay constant.

Question 23

Can we predict when a nucleus will decay

Answer 23

Just like guessing which number will come up next in a lottery, it is not possible to predict when any given nucleus will decay. The likelihood that a particular nucleus will decay is not affected by factors outside the nucleus, such as temperature or pressure, or by the behaviour of neighbouring nuclei - each nucleus decays entirely independently.

Question 24

If we have a large sample of the nuclei, what will the probability of decay determine

Answer 24

The fraction of these nuclei that will decay each second. Naturally, if the sample is larger, then the number that decay in a second will be greater.

Question 25

The number decaying per second is called

Answer 25

The activity

Question 26

What is the symbol for activity

Answer 26

A (or dN/dt)

Question 27

What is activity proportional to

Answer 27

The number of nuclei in the sample,N.

Question 28

Mathematically how is activity expressed

Answer 28

A = -lamder x N

dN/dt = -lamder x N

The minus sign in this formula occurs because the number of nuclei in the sample, N, decreases with time. In practice we ignore the negative sign when using the formula.

Question 29

What’s the unit for the decay constant

Answer 29

s^-1

Question 30

What activity, A measured in

Answer 30

Bq

Question 31

How is the formula for the rate of decay of nuclei in a sample formed

Answer 31

It’s a differential equation. We have previously met this type of equation when studying the discharge of a capacitor. The equation

dN/dt = -lamder x N can be solved to give a formula for the number of nuclei remaining in a sample, N, after a certain time, t:

N = N(subscript 0) x e(^-lamder x t)

Where N(subscript 0) is the initial number of nuclei within a sample.

The exponential mathematics that govern radioactive decay is identical in structure to those for the discharge of capacitors.

Question 32

N is the number of nuclei…

Answer 32

REMAINING in a sample.

Question 33

Tell me about half life as a measure of activity

Answer 33

As we have seen, the activity of a radioactive sample decreases over time as the radioactive nuclei decay, leaving fewer radioactive nuclei available to decay. While the activity of a sample depends on the number of nuclei present, the rate at which the activity decreases depends only on the particular isotope. A measure of this rate of decrease of activity is the half life, t(subscript 1/2)

Question 34

The rate at which the activity decreases depends only on the…

Answer 34

Particular isotope

Question 35

Half life is a measure of

Answer 35

Rate of decrease of activity

Question 36

What is half life ?

Answer 36

This is the TIME taken for half of the atoms of that nuclide (type of atom/isotope) within a sample to decay.

Question 37

Mathematically, how can the half life equation be found

Answer 37

By putting N = 1/2N(subscript 0) into the decay equation

N = N(subscript 0) x e(^-lamder x t)

N(subscript 0)/2 = N(subscript 0) x e(^-lamder x t(subscript 1/2)

N(subscript 0) cancels out on both sides

1/2 = e(^-lamder x t(subscript1/2)

Take natural logs

ln(1/2) = -lamder x t(subscript 1/2)

-ln(2) = -lamder x t(subscript 1/2)

t(subscript 1/2) = ln(2)/lamder

Rearranging this also gives us an equation for the decay constant

Lamder = ln(2)/t(subscript 1/2)

Question 38

How can we investigate radioactive decay rates

Answer 38

You may have the equipment to measure the half life for a radioactive sample, such as protactinium-234m. If you do not, a simulation in which dice represent the radioactive nuclei can demonstrate the exponential decay of a sample.

Question 39

Tell me about an equation for activity to do with exponential decay

Answer 39

An experiment to determine the half life of a substance will usually measure its activity over time. As activity is proportional to the number of nuclei present, when the activity is plotted against time, the shape of the curve is exponential decay. The activity, A, follows the equation:

A = A(subscript 0) x e(^-lamder x t)

Question 40

What graph can we use to determine the half life of a substance

Answer 40

We can use the graph of activity(y axis) against time(x axis) to determine the half life of the substance by finding the time taken for the activity to half.

Question 41

How would we actually calculate half-life from an activity (y axis) time (x axis) graph

Answer 41

To find the half life from such a graph, find a useful start point on the curve. Eg when activity is 800Bq. As the half life is defined as the time taken for the activity to fall to half of its original value, we use the graph to find the time taken for the count to drop to 400Bq, which, let’s say is 70 seconds.

Doing this a second time, from a count rate of 400Bq to a count rate of 200Bq, gives a time of 80 seconds. Notice that the time interval is not identical each time. This is due to the random nature of radioactive decay, plus experimental and graphing errors. The best fit curve will be a matter of the drawers judgment. Thus, to get the best answer for half life, we must undertake the analysis on the graph several times in different parts of the graph and average the results. For, the two half lives calculated, the average half life for protactinium-234m would be 75 seconds.

Question 42

How can we improve from calculating half life from a activity/time graph

Answer 42

There are numerous graphical uncertainties which could lead to unreliabilities in our conclusion of the half life for a sample under test. To improve on the curving graph, we can analyse the experimental date to generate a straight line graph so our best fit line will be less uncertain.

Question 43

How can we produce a straight line graph from activity and time

Answer 43

Using either of our decay equations, taking the logarithm of the equation will give us a new equation for the data that is in the form y = mx + c

Considering data from measuring the activity of a sample over time:
A = A(subscript 0) x e^-lamder x t)

Ln A = -lamder x t + ln(A subscript 0)

So a plot of lnA on the y axis against t on the x axis will be a straight line with a negative gradient equal to the magnitude of the decay constant, lamder. The y intercept will be the natural logarithm value of the initial activity.

Alternatively, if the experimental data is measuring number of nuclei (often actually measured as mass):

N = N(subscript 0) x e^-lamder x t

Ln N = -lamder x t + lnN(subscript 0)

Here a plot of Ln N on the y axis against t on the x axis will also be a straight line with a negative gradient, which is equal in magnitude to the decay constant, lamder. The y intercept in this case will be the natural logarithm value of the initial number of nuclei.

In either case, the gradient gives the decay constant, from which we can find the half life from:

t(subscript 1/2) = ln2/lamder

Question 44

Define decay constant

Answer 44

A decay constant is the probability, per second, that a given nucleus will decay.

Question 45

Define activity

Answer 45

Activity is the number of radioactive decays in unit time.

Question 46

Define half life

Answer 46

Half life is the time taken for half of the atoms of a nuclide within a sample to decay. Alternatively, the time taken for the activity of a sample of a radioactive nuclide to reduce to half its initial value.

Question 47

What is 1 unified atomic mass, u

Answer 47

We have previously seen that a nucleon has a mass which is approximately equal to 1 unified atomic mass unit, u = 1.67 x 10^-27 kg.

Question 48

What’s the exact mass of a proton

Answer 48

1.007276 mass/atomic mass units/u

Question 49

What’s the exact mass of a neutron

Answer 49

1.008665 mass/atomic mass unit/u

Question 50

What’s the exact mass of an electron

Answer 50

0.00054858 mass/atomic mass units/u

Question 51

What is the mass deficit also known as

Answer 51

Mass defect

Question 52

What is mass deficit/defect

Answer 52

We might expect that if we know the constituent parts of any nucleus, we can calculate its mass by finding the total mass of its nucleons. However, in practice we find that the actual, measured mass of a nucleus is always LESS than the total mass of its constituent nucleons. This difference is called the mass deficit or sometimes the mass defect.

Question 53

Tell me about calculating mass deficit

Answer 53

Subtract the electron mass from the atom to get the mass of the nucleus together

Then find the individual sums of what we would expect the mass of the nucleus to be by adding total mass of neutrons and protons together.

Then subtract the sum of constituent masses from what the actual mass of the nucleus is.

Question 54

Why does the mass deficit come about

Answer 54

The mass deficit comes about because a small amount of the mass of the nucleons is converted into the energy needed to hold the nucleus together. This is called binding energy.

Question 55

How is binding energy calculated

Answer 55

Using Einstein’s mass-energy relationship

Triangle E = c^2 x triangle m

Question 56

What are the two common systems of units for calculating binding energy

Answer 56

If you have calculated the mass deficit in kilograms (SI units) then using c = 3.00 x 10^8 m/s will give the binding energy in joules.

Alternatively, if you have calculated the mass deficit in atomic mass units, u, turn you convert this into binding energy in mega electron volts (MeV) using:

1u = 931.5 MeV

Question 57

How can we convert binding energy to MeV

Answer 57

Calculate it in joules then divide by 1.6 x 10^-13 to get to MeV, or use 1u = 931.5 MeV.

Note that in calculations of both mass deficit and binding energy, you need to use as many significant figures as possible, only rounding off at the very end of the calculation.

Question 58

What do we need to calculate binding energy per nucleon

Answer 58

How much energy would be needed to remove one nucleon from a nucleus? To work this out we need to know both the binding energy of a nucleus, and the number of nucleons within it. This gives us the binding energy per nucleon in a nucleus in MeV, and from this we can determine how strongly different nuclei are held together.

Question 59

Tell me about a graph of binding energy per nucleon, MeV (y axis) against mass number, A (x axis)

Answer 59

Drawing a graph of binding energy per nucleon against mass number for the nuclei gives us a useful measure means of comparing how tightly different nuclides are bound together. Any nuclear reaction which increases the binding energy per nucleon will give out energy.

The graph shows us that small nuclides can combine together to make larger nuclei (up to Fe-56) with a greater binding energy per nucleon. This process is called nuclear fusion.

Similarly, larger nuclei can break up into smaller pieces which have a greater binding energy per nucleon than the original nucleus. Reactions like this are called nuclear fission. Both of these types of nuclear reaction will give out energy, and could be used as power sources.

Question 60

Tell me what the process of nuclear fusion is like

Answer 60

If we take some light nuclei and force them to join together, the mass of the new heavier nucleus will be less than the mass of the constituent parts, as some mass is converted into energy. However, not all of this energy is used as binding energy for the new larger nucleus, so energy will be released from this reaction. The binding energy per nucleon afterwards is higher than the start. This is the process of nuclear fusion and is what provides the energy to make starts shine. 💫🤺

Question 61

Tell me the steps in a proton-proton nuclear fusion reaction

Answer 61

This is typical in small cool stars such as our sun, where the core temperature is about 15 x 10^6 K

Stage 1: two protons fuse

Stage 2: one proton changes into a neutron, as in beta plus decay, to leave a deuterium nucleus.

Stage 3: another proton joins making a nucleus of He-3

Stage 4: two He-3 nuclei fuse

Stage 5: two protons break off leaving an He-4 nucleus.

The proton-proton chain nuclear fusion reaction effectively takes four protons and converts them into helium-4 nucleus and two positrons (which have the same mass as electrons)

The energy released is equal to the mass of the 4 individual protons subtract the mass of a He-4 nucleus + 2 positrons (nucleus - 2 electrons + 2 positrons)

Subtract the constituent mass from the nucleus mass to get mass deficit and convert to MeV to get the energy released.

Question 62

Tell me about nuclear fusion and proton proton reactions releasing energy

Answer 62

These reactions occurring in enormous numbers provide the energy which causes the sun to emit heat and light in all directions in great quantities.

Question 63

Tell me about nuclear fusion on the earth

Answer 63

Converting hydrogen into helium with the release of energy would appear to be a fantastic way of supplying the planets energy needs. The seas are full of hydrogen in water molecules, and the helium produced would be an inert gas which could simply be allowed to float off into the upper atmosphere. However, scientists have not yet successfully maintained a controlled nuclear fusion reaction. The problem lies in forcing two positively charged, mutually repelling, protons to fuse together. The kinetic energy they need to have to collide forcefully enough to overcome this electrostatic repulsion requires temperatures of many million kelvin. Moreover, to ensure enough colliding protons for the reaction to be sustained requires a very high density of them. Comparing the energy output with nuclear fission, 235 grammes of hydrogen undergoing nuclear fusion would produce an energy output of 1.40 x 10^14 J.

Question 64

Tell me about man made fusion reactions

Answer 64

Nuclear fusion as an energy source for us to generate electricity is currently only at a research stage. The Joint European Torus (JET) experiment in Oxfordshire is a research facility which investigated sustained nuclear fusion reactions. After 25 extremely expensive years of tests on confining and controlling ‘burning plasmas’, the main JET experiment was recently upgraded to provide demonstration and development support for the ITER project (international thermonuclear experimental reactor), which is JETs successor. This is a truly international project, whereas JET was a European funded experiment. The costs were becoming too much for the European Union to bear alone, and although the ITER will be sited in France, six other large nations (India, China, Russia, USA, Korea and Japan) will also contribute towards the 15 billion euros construction cost. An estimated 10 years of construction began in 2010, and when ITER is complete, the aim is to generate temperatures of 150 million kelvin in a plasma volume of 840 cubic metres, nearly ten times larger then JET was.

Question 65

Tell me about the process of nuclear fission

Answer 65

We have seen that nuclear fusion is not yet an option for electricity generation, as we have not been able to create the high densities and temperatures needed to sustain a fusion reaction. However, another process which releases binding energy from nuclei Is called nuclear fission. In this process a large nucleus breaks up into two smaller nuclei, with the release of some neutrons and energy. Fission reactions can be triggered when the nucleus absorbs another particle making it unstable.

Eg Uranium-235 can absorb slow moving neutrons to become the unstable isotope Uranium-236 which may split into Kr-92 and Ba-142 and some fast neutrons.

Question 66

How can the energy released from fission be calculated

Answer 66

Add up masses before (eg uranium + neutron) and subtract from masses after (eg Ba and Kr and 3 neutrons)

Turn the mass defect into energy released, this is the energy per fission. If one mole of these were to occur, using 235g of uranium 235, then the total energy produced would be:

E = 6.02 x 10^23 x energy per fission
Idk why?

However, U-235 is a small proportion, around 0.7% of all the uranium found, and thus a larger amount of uranium fuel would be needed in order to provide enough U-235 atoms to produce this much energy.

To find the changes in binding energy per nucleon, find total binding energy of uranium 235 and divide this by number of nucleons.
Then find binding energy of products, Ba and Kr and divide these each by the number of nucleons they have. The two products should have a higher binding energy per nucleon than the original uranium nuclide.

Question 67

Tell me about the concept behind nuclear bombs

Answer 67

The neutrons in controlled nuclear fission reactions are slowed to speeds needed to sustain fission using a moderator. However, some nuclear fission reactions, such as those using plutonium, will progress by reacting with high speed neutrons, meaning that a moderator is not required. If such a reaction were allowed to run uncontrolled, it would produce energy continuously, at an ever increasing rate, until all the fuel were used up. This is the essential concept behind the design of nuclear bombs. A lump of plutonium-239 about the size of a cricket ball can completely react in less than a microsecond, releasing the energy equivalent to 20 Kilotonnes of TNT.

This type of bomb was dropped on the city of Nagasaki in Japan during the Second World War. It killed 40,000 people immediately, and a similar number had died from after effects by the end of 1945. The atomic bombings in japan were so devastating that the country surrendered to the allies just 6 days after the Nagasaki bomb, and since the 1960s the Japanese government has resolved never to allow Japan to hold nuclear weapons.

Question 68

Define mass deficit

Answer 68

A mass deficit is the difference between the measured mass of a nucleus and the sum total of the masses of its constituent nucleons.

Question 69

Define mass defect

Answer 69

It’s an alternative phrase for mass deficit

Question 70

Define binding energy

Answer 70

Binding energy is the energy used to hold the nucleus together, converted from the mass deficit, following E=mc^2

Question 71

Define fusion

Answer 71

Fusion happens when small nuclides combine together to make larger nuclei, releasing energy.

Question 72

Define fission

Answer 72

Fission happens when larger nuclei are broken up into smaller nuclides, releasing energy.

Question 73

The most common nuclear fission reaction used in power stations is that of…

Answer 73

Uranium-235

Question 74

Tell me about the nuclear fission of uranium-235

Answer 74

If a nucleus of this uranium isotope is hit by a slow moving neutron, often called a thermal neutron, it may absorb the neutron to form U-236, which is unstable and quickly breaks up.

The products of this disintegration will be two medium sized (and radioactive) nuclei with roughly half the nucleons each, plus a number of high speed neutrons. The actual composition of the two main products varies - the vast majority of these fissions will produce a heavier daughter nucleus with mass numbers in the range 130-50, whilst the lighter product usually has a mass number in the range 85-105.

Question 75

How is energy released by fission (with U-236)

Answer 75

There is a difference in the amount of binding energy in the U-236 and the daughter products. This is given off as the kinetic energy of various particles harnessed by the nuclear reactor to drive an electricity generating system(eg an advanced gas cooled reactor).

Question 76

How is the nuclear fission reaction controlled

Answer 76

A moderator, such as water or graphite, is used to slow down the emitted neutrons, so that they arrive at the next uranium fuel rod at the slow speed needed to allow them to be absorbed by further U-235 nuclei, to cause further fissions and continue the reaction.

As each reaction requires only one neutron but produces two or three, this chain reaction could run out of control, as is the case in a nuclear bomb. To control the reaction in a nuclear reactor, control rods typically made of cadmium or boron absorb excess neutrons. These control rods are lowered into the reactor on an electromagnetic support. If there is a failure in the control rods system, gravity will pull them completely down into the reactor core, where they will absorb all neutrons and shut down the reaction.

Question 77

What’s an advanced gas cooled reactor like

Answer 77

It’s a typical nuclear reactor design in the uk

In the middle are graphite moderators with control rods in between. When control rods and removed from moderators, energy/heat moves up the chamber to heat water and turn it back into steam.

I think that how it work - check page 155

Question 78

Control rods do what

Answer 78

Boron-steel control rods absorb excess emitted neutrons to control the rate of reaction.

Question 79

What do graphite moderators do

Answer 79

Slows neutrons

Question 80

Is nuclear power the way forward

Answer 80

In the UK, nuclear power went through periods of popularity in the 1950s and 1980s, and our current fleet of 16 reactors produce approximately 18% of UK electricity. Most of these power stations are reaching the end of their lives, and few will be able to continue operation after 2023. The increasing costs of fossil fuels, and the need to reduce carbon emissions, has brought nuclear power back into popularity with the government as an option for our future production of electricity. Modern reactor design is far superior to those early power stations, so they are much safer, but there are still some important environmental concerns to be considered.

Question 81

Tell me how nuclear power is a better alternative to non renewable energy

Answer 81

Radioactive materials which can supply energy through a controlled nuclear fission reaction are not uncommon in the earth’s crust - uranium is about 500 times more abundant than gold. And in order to supply a standard size power station, such fuels are only needed in very small quantities. 3kg of uranium-235 per day will run a 1000 MW nuclear power station. Compare this with the 9000 tonnes of coal per day which would be needed in a coal fired power station of the same output.

Indeed, a million tonnes of uranium-235 could supply the energy equivalent to all the fossil fuels on earth. There is estimated to be about 6 times that quantity of uranium available. However, it is principally located in only a handful of countries, with Australia, Russia and Kazakhstan having over 50% of global reserves. This raises some serious issues about the security of fuel supply for countries which choose to use nuclear power.

Question 82

Tell me how recent global increased interest in nuclear power has caused issues with nuclear power usage

Answer 82

Recent global increased interest in nuclear power has caused the potential longevity of reserves to be called into question. Considering only the reserves that could be mined at a reasonable cost, and with current usage (66,000 tonnes per year), reserves could run out in as little as 90 years. As investment in uranium exploration has increased significantly recently, new reserves have been discovered and the time estimates improved.

However, should there be any unexpected supply problem (for example, the McArthur river mine in Canada, which produces 13% of world supply, was flooded in 2003, which took it out of action for three months), the precarious balance between supply and demand would be highlighted.

Question 83

Tell me about nuclear power use in the UK, how does society choose to use nuclear power

Answer 83

The first generation of nuclear power stations in the UK were built and run by the government. Many of them have now been sold to private energy companies, and politicians are currently keen to have all future nuclear installations built and run privately. There is an economic argument that this will increase efficiency within the operation, and in the end this should make the electricity cheaper for the consumer, even after allowing for the company’s profits. Few energy companies have been willing to risk the enormous capital investment needed.

In recent years, public opinions in the UK, along with the viewpoint of British industry (as represented by the Confederation of British Industries (CBI)) and that of MPs, have all moved towards a more positive stance on nuclear power.

The health and safety executive has a department covering nuclear installations and they implement various acts of parliament governing the required safety procedures in such power stations.

Question 84

Tell me about nuclear disasters in general

Answer 84

All industries have a risk of accidents occurring, and the potential hazards must be balanced by the likelihood of their occurrence, and the checks put in place to minimise this likelihood or limit the potential damage. In the nuclear industry the hazards are extreme, so the probability of accidents must be virtually eliminated. Only two events have been classified as level 7 on the international nuclear event scale. Whilst reading about the nuclear disasters later, consider the fact that in the USA, in 2014 alone, 16 coal miners died in mining accidents.

Question 85

Tell me about the Chernobyl explosion

Answer 85

Nuclear power poses an extreme potential hazard to health and safety, as a major incident can destroy an entire landscape. In 1986, a reactor explosion at Chernobyl in the Ukraine released about 5% of the reactor core material into the atmosphere. Up to 2004, there had been 56 fatalities which could be directly attributed to this disaster, 28 of these occurring within a few weeks from acute radiation exposure. Large areas of Russia, Ukraine and Belarus were contaminated, and 336000 people have been resettled elsewhere. There will be an ongoing (small) increased incidence of cancer amongst the ‘liquidators’ - the half million people from all over the Soviet Union who worked on the clean up operation in the two years after the explosion.

However, the world health organisation, international atomic energy agency and United Nations have all undertaken investigations and their reports on the regions population are in agreement that the actual harmful effects have been considerably overestimated. The most harmful isotopes released decayed quite quickly, leaving the area with a background radiation which is at present about 50% higher than normal. There were four reactors at Chernobyl, and the other three continued to operate for many years afterwards. Reactor number 4 was encased in a concrete shield very soon afterwards, and this is to be enhanced by a more permanent shelter to be completed in 2017.

Question 86

Tell me about Fukushima Daiichi nuclear accident

Answer 86

On 11 March 2011, Japan was hit by a massive earthquake (magnitude 9.0). This generated a 14 metre tsunami wave that hit the Fukushima nuclear power plant on Japan’s east coast. This destroyed the cooling system for three of the plants 6 reactors. These suffered meltdown and released significant amounts of radioactive material over three days shortly afterwards. No fatalities were directly attributable to this accident, but as a result of the evacuation of over 100,000 people, more than 1000 deaths occurred. The world health organisation estimated very small increased risk of cancers in later life if the population had remained in the affected areas. Whilst the clean up process will take decades, the safety procedures in place significantly limited the hazards generated by this incident.

Question 87

Tell me about radioactive waste and there waste levels

Answer 87

High - heavy metals, fuel rods
Intermediate - resins, chemical sludges, reactor components
Low - paper, rags, tools, clothing, filters

Question 88

What are the sources and treatments of different types of radioactive waste

Answer 88

Heavy metals, fuel rods - spent fuel, fuel reprocessing products. Treatment: cooled in a water pool for 1-20 years, then buried in a deep underground repository.

Resins, chemical sludges, reactor components - reactor decommissioning. Treatment: solidified in concrete or bitumen and buried.

Paper, rags, tools, clothing, filters - hospitals, laboratories, industry. Treatment: incinerated and buried.

Question 89

Tell me about nuclear power legacies

Answer 89

Nuclear fission of uranium produces a variety of daughter nuclei which are also radioactive, with varying half lives. This spent fuel is the most dangerous of the radioactive wastes generated in the process. The material of the reactor cores construction will also become slightly radioactive during the course of its lifetime, mostly through exposure to free neutrons which can be absorbed by a nucleus, turning it into an unstable, radioactive isotope. This means that the production of radioactive waste from a nuclear power station occurs throughout its lifetime and then the decommissioning process at the end of the useful lifetime will generate about the same amount of waste again. The projected cost for decommissioning all of the nuclear power stations in Britain is over £70 billion.

Question 90

Define thermal neutron

Answer 90

A thermal neutron is a relatively slow moving neutron

Question 91

Define moderator

Answer 91

A moderator is a material used in a nuclear reactor to slow fast moving neutrons to thermal speeds.

Question 92

Define fuel rod

Answer 92

A fuel rod within a nuclear reactor is a rod containing the fissionable material, eg uranium-235

Question 93

Define chain reaction

Answer 93

A chain reaction is a self sustaining nuclear reaction in which the products from one individual fission reaction go on to trigger one or more further fissions.

Question 94

Define control rods

Answer 94

Control rods within a nuclear reactor are made of materials that can absorb neutrons to stop the triggering of further fission reactions, eg boron.