Radioactive decay is always exoergic since the mass of the parent nuclide is greater than the total mass of the daughter nuclide(s) and the emitted… [625377]

CHAPTER 7
Nuclear Energy Production
Radioactive decay is always exoergic since the mass of the parent nuclide is greater than
the total mass of the daughter nuclide(s) and the emitted particle(s). The equation
expressing the release of energy contains an expression describing the kinetic energy of the
particles. When interacting with the environment, the particles slow down and become
thermalized, and most of the kinetic energy transforms into thermal energy. The decay of
the natural radioactive isotopes plays an important role in the heat balance of the Earth. The
decay of 1 mol238Ut o206Pb releases about 4.3 31012J of energy. The half-life of238Ui s
4.53109years, meaning that the release of this energy is a very long process.
Energy can be produced by nuclear reactions as well. This procedure has a very important
practical role since energy can be released in a fairly short time this way. The binding
energy per nucleon can be calculated by means of the liquid-drop model of nuclei by
Weizsa ¨cker formula (see Eq. (2.17)). As seen in Fig. 2.4, energy can be produced by two
ways: by fusion of light nuclei (as discussed in Section 6.2.4) or by fission of heavy nuclei
(see Eq. (6.21)).
In the fission reaction, two lighter nuclei and some neutrons are formed. The neutrons can
initiate additional fission reactions if their energy is relatively low (thermal or slow
neutrons). This process can be repeated, producing more and more neutrons. If the quantity
of the fissile material reaches critical mass, a continuous fission, chain reaction takes place.
The principle of the nuclear chain reaction was formulated and patented by Leo Szila ´rd in
1934, and it was experimentally proved by Otto Hahn in 1938. For this discovery, Hahn
received the Nobel Prize in Chemistry in 1944.
When the number of fissions increases very rapidly and there are enormously high energy
releases, the chain reaction becomes unregulated, as in the nuclear bombs (such as the ones
used on Hiroshima on August 6, 1945 (U-235), and Nagasaki on August 9, 1945 (Pu-239),
discussed in more detail in Section 7.5 ). The number of fissions, however, can be
controlled. Controlled, sustained chain reactions occur in nuclear power plants.
The first nuclear reactor began to operate in the University of Chicago at 3:45 on December
2, 1942. This was the first artificial nuclear chain reaction. The first nuclear reactor
constructed directly for energy production was opened in Obninsk, in the Soviet Union, in
1954. According to the International Atomic Energy Agency (IAEA), 450 nuclear reactors
159Nuclear and Radiochemistry.
DOI: http://dx.doi.org/10.1016/B978-0-12-813643-0.00007-X
©2018 Elsevier Inc. All rights reserved.

were operational as of November 2016, and their number increases continuously; 60 nuclear
reactors are under construction ( Fig. 7.1 ). The net electric power of the operating nuclear
reactors is 391,915 MW and that of the reactors under construction will be 59,917 MW.
7.1 Nuclear Power Plants
In most cases, the controlled and uncontrolled chain reaction of the fission of235U is used
in nuclear power plants and weapons, respectively. The neutron balance is quantitatively
determined using the effective neutron multiplication factor ( k), which is the average
number of neutrons produced from one fission that cause an additional fission:
k5ns
np(7.1)
where npand nsare the number of primary and secondary neutrons, respectively.
One of the most important properties of the fission is that two to three neutrons per fission are
released (see Eq. (6.21)), which can initiate new fission steps. The condition of theUSA
FranceJapanRussia
Korea, RepublicIndia
United KingdomCanadaUkraineChina
SwedenGermanySpain
BelgiumTaiwan
Czech RepublicSwitzerlandFinlandHungarySlovakiaPakistanArgentinaBrazil
BulgariaMexico
Romania
South AfricaArmenia
NetherlandsSlovenia020406080100120
Under construction
In operation
Figure 7.1
Nuclear reactors in operation and under construction worldwide.160 Chapter 7

sustainable chain reaction is that at least one of the released neutrons should initiate an
additional fission. If the average number of the neutrons initiating new fission ( k) is one, the
released energy becomes constant. In a stationary state, this is the case in nuclear reactors.
When the number of neutrons initiating additional fission is more than one, the released
energy exponentially increases. This is the case, for example, at the startup of nuclear
reactors, or when the power produced by nuclear reactors is to be increased. Nuclear
weapons are designed to operate in this way.
In fission reactions, the energy of the released neutrons is usually high (1 /C02 MeV); the
additional fission, however, can be initiated only by slow or thermal neutrons ( ,0.1 eV). For
this reason, the velocity or energy of the neutrons has to decrease, which significantly
influences the neutron multiplication factor. When the fissile material is assumed to be in
an infinite quantity, the multiplication factor ( kN) is given by the four-factor formula as
follows:
kN5εpfη (7.2)
In this equation, εis the fast fission factor, which ta kes into consideration that the fast
neutron can initiate another fission to a small degree (by 1% /C03%); pis the resonance
escape probability, the fraction of neutrons escaping capture while slowing down. The
value of pusually ranges from 0.6 to 0.9 and is increased by all factors assisting the
slowing down of the neutrons (e.g., by the improvement of the moderators), by
decreasing the size of the fuel and by increa sing its distance from the fuel rods. The
thermal utilization factor, f, is the ratio of the thermal neutrons initiating additional
fission to the number of thermal neutrons captured by another reaction (e.g., by nuclides
other than fissile ones), and ηis the thermal neutron yield, that is, the number released in
the fission process.
If the size of the fuel is finite, the effective multiplication factor ( keffin Eq. (7.1) ) is used;
keff,kN.A t keff,1, the chain reaction stops because of the continuous decrease of the
neutrons. The reactor is subcritical . When keff51, the rate of the chain reaction is constant,
and the reactor is critical. When keff.1, the number of the neutrons, and, as a
consequence, the number of fission reactions, increases and the reactor is supercritical.
A characteristic property of the reactor is the reactivity ( ρ):
ρ5keff21
keff(7.3)
The value of ρcan be negative, zero, or positive, depending on whether the reactor is
subcritical, critical, or supercritical, respectively. Since the fissile material is continuously
used up by fission, the fission products can also capture neutrons, and a certain excess of
reactivity is required for the critical operation.Nuclear Energy Production 161

7.1.1 The Main Parts of Nuclear Reactors
The very simple scheme of a nuclear reactor and the connecting energetic units are shown
inFig. 7.2 . The arrangement of the fuel and control rods in the reactor vessel is shown in
Fig. 7.3 .
Reactor vessel
Electric curren tModerator and
coolant
Fuel and
control rods
Heat exchanger
and evaporatorTurbine,
generator
Secondary circuit Primary circuit
Figure 7.2
A very simple scheme of a nuclear reactor and the connecting energetic units.
Coolant to heat
exchanger
Control rod Fuel rod
Figure 7.3
The arrangement of the fuel and control rods in the reactor vessel.162 Chapter 7

The most important parts of the nuclear reactors are the fuel elements, moderator, reflector,
cooling system, control rods, and shielding. In the following sections, the material,
properties, and operation of these parts will be discussed.
7.1.1.1 Fuels of Nuclear Power Plants
Most nuclear power plants use uranium-235 as fuel. Under geological conditions, the
thermodynamically stable species of uranium is the uranyl cation (UO21
2), which is fairly
soluble in water. As a result, uranium is present everywhere in the Earth’s crust; its
concentration is relatively low, and the average concentration is about 3 /C05 ppm. Uranium
can be extracted economically from rocks that have a concentration of uranium that is at
least a couple of thousand parts per million. The most important of uranium ore is the
uranium pitchblende, with mean uranium content about 0.5% /C00.8%. About 40% of the
Earth’s uranium is in Australia.
The uranium is produced from the ore by crashing the ore into smaller pieces, and then
concentrating the uranium containing ores by flotation. If uranium is present as U(IV), it is
oxidized to U(VI) by air, or sometimes in a microbiological way. Then, the substance is
leached by sulfuric acid. The formed uranyl sulfate complex, [UO 2(SO 4)2]22, is separated
by ion exchange resins or by extraction using an organic solvent. Since natural uranium
contains 99.3%238U and only 0.7%235U, and because235U-enriched uranium compound is
needed as fuel for nuclear reactors, the uranyl sulfate must be converted into a species that
is appropriate for isotope enrichment. This species of uranium is UF 6, the gas diffusion of
which can be used for isotope enrichment. However, even uranium with a natural isotopic
ratio can initiate fission chain reaction.
In addition to uranium, artificial fissile material such as239Pu,241Pu, and233U
(see Eq. (6.22) and Eq. (6.23)) can be used as fuels. The fuel has to have a high cross
section for thermal neutrons. Since the released energy is huge, the heat resistance of
the compound of the fissile isotope is also i mportant. The activation of the other atoms
in the compound has to be avoided. These con ditions are fulfilled by oxides. Usually,
uranium dioxide (UO 2), plutonium dioxide (PuO 2), and thorium dioxide (ThO 2)a r e
used. In some reactors, uranium carbide (UC) has been tested. Mixed oxides (MOXs)
are also produced from plutonium oxide and uranium oxide. For homogeneity, the
oxides are co-precipitated from oxalate an d then calcinated to oxide. MOX is used in
light water reactors (as discussed in Section 7.1.1.2 ). One advantage of MOX fuel is
that it provides a way to dispose of the surplus of weapons-grade plutonium, which
otherwise would have to be disposed of as nuclear waste and would remain a nuclear
proliferation risk. The characteristic properties of the most important fuels are shown
inFig. 7.4 .Nuclear Energy Production 163

Uranium dioxide is prepared as pellets and placed into rods made of zircon, zircalloy
(zirconium with 1% niobium), or another metal. The rods are hermetically sealed and
placed into the active zone of the reactor with the moderator. The seal should ideally be
hermetic, but in reality, the fuel rods often have micro- and macro-ruptures through which
the gaseous and soluble fission products can escape. A part of the gaseous fission products
(Kr-85, Xe-133, and Xe-135 isotopes) is emitted into the atmosphere. The gaseous
molecules and compounds of iodine are filtered, usually by coal filters. The relative
activities of the iodine isotopes with different half-lives give information on the size of the
ruptures. The presence of iodine isotopes with short and long half-lives indicates the
existence of macro- or micro-ruptures, respectively. Besides the gaseous fission products,
the gaseous compounds of tritium and C-14 (see Section 7.3 ) are also released into the
atmosphere. To decrease the emitted radioactivity, the gas emission is delayed or ignited
and the products are condensed.1000
100
10
1
3.5
3
2.5
2
1.5
1
0.5
0
233U235U Natural U239Pu241Pu233U235U Natural U239Pu238UThermal neutron
absorption
Thermal neutron yieldNumber of neutrons per
fissionFission for thermal
neutronsCross section, barnNeutron yield
Figure 7.4
The characteristic properties of the most important fuels.164 Chapter 7

If the moderator ( Section 7.1.1.2 ) and/or the coolant ( Section 7.1.1.5 ) is water or heavy
water, the soluble fission products (e.g., Cs-137, Cs-134, strontium, and iodine ions) can
dissolve in them. For this reason, water is continuously purified by ion exchangers.
During the operation of nuclear reactors, the quantity of235U continuously decreases; the
fissile material is burning up. Most of the235U present in the reactor undergoes fission
reaction; however, a small part converts to236Ui na n( n,γ) reaction. Similarly, the ( n,γ)
reaction of238U produces transuranium elements, including239Pu and241Pu (Eq. (6.23)),
which also undergo fission reaction, increasing the power of the nuclear reactors. There are
nuclear reactors specifically made to produce fissile plutonium isotopes, which are called
“breeder reactors.”
The operation of the nuclear reactors is influenced by the fission products. Some of them
(e.g.,135Xe and149Sm) strongly absorb neutrons, decreasing the number of the neutrons and
the reactivity. These fission products are called “reactor poisons.”
7.1.1.2 The Moderator of Nuclear Power Plants
Another important part of nuclear reactors is the moderator. Its function is to slow down the
fast neutrons emitted in the fission reaction by reducing the energy of neutrons to the level
of thermal neutrons. Light elements are suitable moderators because they can effectively
decrease the energy of the fast neutrons through inelastic collisions with neutrons.
According to its atomic mass, hydrogen (1H) is expected to be the most effective
moderator; however, a suitable moderator must also have a small cross section for neutron
captures, which hydrogen does not have. Hydrogen can capture neutrons easily,
transforming to deuterium. Deuterium is the most effective moderator, but it is rather
expensive. The ratio of the moderator effect and the neutron capture can be expressed by
the moderation ratio (given in Table 7.1 ).
Frequently used moderators are the following:
 Water (H 2O), which is an effective moderator, absorbs part of the neutrons. A water-
moderated reactor is shown in Fig. 7.2 .
Table 7.1: The number of collisions to thermalize and the moderation ratio of
different substances.
Substance Number of Collisions to Thermalize Moderation Ratio
H2O1 9 6 2
D2O 35 4830
He 42 51
Be 86 126
B 105 0.00086
C 114 216Nuclear Energy Production 165

 Heavy water (D 2O), which is an effective moderator, absorbs only a few neutrons, but
it is expensive.
 Graphite, which is a less-effective moderator than water, absorbs only a few neutrons.
Its disadvantage is that it is flammable. In the first nuclear reactor, graphite was applied
as the moderator.
 Beryllium and organic solvents are also suitable as moderators.
7.1.1.3 Moderator/Fuel Ratio
The moderator decreases the velocity of the neutrons, as discussed in Section 7.1.1.2 .I n
addition, the moderator acts as a passive controller of the operation of the nuclear reactors.
All substances, including moderators, more or less absorb neutrons, inhibiting the fission
chain reaction. Thus, if the reactor contains too much moderator, the degree of neutron
absorption increases. However, if the quantity of the moderator is too low, the velocity of
the neutrons does not decrease enough. As a result, the effective neutron multiplication
factor versus the moderator/fuel plot function has maximum. Those reactors in which the
moderator/fuel ratio is below the maximum are under-moderated, and those in which this
ratio is above the maximum are over-moderated ( Fig. 7.5 ).
Under- and over-moderation play an important role in the safety operation of the reactors.
The under-moderated reactors are safer because the decrease of the quantity of the
moderator results in the decrease of the effective neutron multiplication factor, stopping the
reactor from entering a subcritical state. In over-moderated reactors, however, the decrease
of the quantity of the moderator can increase the effective multiplication factor, and then
the reactor can become supercritical (as happened in the Chernobyl accident, discussed in
detail in Section 7.2 ).
Under-moderatedkeff
Over-moderated
Moderator/fuel ratio
Figure 7.5
The effect of the moderator/fuel ratio on the effective neutron multiplication factor.166 Chapter 7

7.1.1.4 Reflection of Neutrons
The active zone of the reactors is usually surrounded by a mantle consisting of the
moderator (water, graphite, or another substance as previously mentioned). Thus, the
number of the escaping neutrons can decrease because this mantle reflects a part of the
escaping neutrons. The escaping neutrons influence the effective neutron multiplication
factor. The application of the reflector can decrease the size of the reactor, and the fuel can
be utilized more economically.
7.1.1.5 Coolants
The greatest part of the energy released in the fission is the kinetic energy of the fission
products ( Table 7.2 ). While the fission products are slowing down, the fuel rods are heated.
In operation, the temperature of the fuel rods may rise above 1000/C14C, and then they have to
be cooled permanently. Therefore, the active zone always contains coolant.
Because of the strong neutron radiation in the active zone, the coolant becomes radioactive.
For this reason, the coolant must be circulated in a closed system, which is called a
“primary circuit.” The primary coolant is pumped into a heat exchanger full of tubes. Heat
is transferred through the walls of these tubes to the lower-pressure secondary coolant
located on the sheet side of the heat exchanger, where it evaporates to pressurized steam (a
steam generator). In this way, the coolants in the primary and secondary circuits do not
touch each other directly, so the secondary coolant remains inactive.
The pressurized steam formed in the steam generator is fed through a steam turbine, which
drives the electric generator. In the meantime, the secondary coolant (a mixture of water
and steam) is cooled down and condensed in a condenser. Then the condensed steam is
pumped back into the steam generator ( Fig. 7.2 ).
In reactors moderated by light or heavy water, the moderator acts as a coolant too. In
graphite-moderated reactors, the coolant is a gas (CO 2or He) or water. In some reactors,
molten metals (e.g., sodium), salts, organic solvent, He, or steam are applied as the coolant.
Table 7.2: Distribution of the energy released in the ( n,f) reaction of235U.
Energy (MeV)
Kinetic energy of the fission products 167
Kinetic energy of neutrons 5
Prompt gamma radiation 6
Neutrinos 12
Beta radiation of fission products 8
Gamma radiation of fission products 6Nuclear Energy Production 167

In the water reactors, the coolant is continuously purified by ion exchangers to remove the
dissolved radioactive ions (e.g., cesium and iodide ions). The colloidal or greater solid
particles are filtered.
7.1.1.6 Regulation of Chain Reactions
In the fission process, two or three neutrons are formed ( Fig. 7.4 ), 99% of which are
emitted within a very short time. These are called “prompt neutrons,” and their mean
half-life is about 1024seconds. Some fission products also emit neutrons (via neutron
decay, as discussed in Section 4.4.4), and these are delayed neutrons. The amount of the
delayed neutrons is less than 1% of the total numbers of the neutrons. Delayed neutrons
play a role in the neutron balance of the reactor. If all the neutrons were produced as
prompt neutrons, the whole fission products would be complete within a very short time
and could not be controlled. Therefore, the nuclear reactors are planned in such a way that
the controlled chain reaction can be initiated in the same time as the delayed neutrons.
The reactors are controlled by control rods. They are fabricated from very good neutron
absorbers, such as boron as boron carbide (or cadmium in the old reactors). The control
rods are inserted among the fuel rods ( Fig. 7.3 ). The reactivity is controlled by the
movement of the control rods. When the reactor starts, the control rods are raised. The
power is measured by neutron detectors. When the power reaches the desired value, the
control rods are stopped. So, the power does not continue to increase, the reactor becomes
critical.
There are three different types of control rods:
1. Safety rods, whose function is the fast stop of the reactor in an emergency. In normal
operation, they are totally raised.
2. Shim rods, which are used for coarse control and/or to change reactivity in relatively
large amounts. They equalize the changes of the reactivity resulting in burn-up,
poisoning, or breeding. Another tool for the equalization of reactivity is that neutron
absorbers (usually boric acid) are dissolved in the coolant, whose concentration can be
varied as required. Of course, this method can be applied only in the water reactors.
3. Regulating rods, which are used for fine adjustments and to maintain the desired power
or temperature.
7.1.1.7 Shielding
In nuclear reactors, shielding against neutron and gamma radiation is essential. When
planning the shielding for neutron radiation, it is important to take into consideration that
the cross section for the fast neutron is rather small (see Fig. 6.4). So, for shielding
material, those substances should be chosen that efficiently slow down the neutrons and
then efficiently absorb the thermal neutrons. The same moderators discussed in168 Chapter 7

Section 7.1.1.4 are suitable for this purpose; therefore, the active zone of the reactors is
usually surrounded by a mantle consisting of the moderator (water, graphite, etc.).
In nuclear reactors, the gamma radiation is very intense. The intensity of the gamma
radiation continuously increases because of the increase of the quantity of the fission
products. For protection against the gamma radiation, substances with a high atomic
number and density are suitable. The stainless steel reactor vessel itself provides some
shielding against gamma radiation. The nuclear reactors are surrounded by a thick concrete
wall.
7.1.1.8 Containment of Nuclear Reactors
The containment building is a gas-tight cover around the nuclear reactor and the primary
circuit. Its role is to confine the release of the fission products into the atmosphere in the
event of an accident. Moreover, the containment protects the nuclear reactor against
external effects, including natural and human attacks. It contributes to the radiation
shielding too.
Such enclosures are usually dome-shaped and made of steel-reinforced concrete or lead
structures. It can stand free or attach to the concrete shielding.
Practically, all nuclear power plants in the last few decades have been built equipped with
containment.
7.1.2 Natural Nuclear Reactors
The analysis of uranium ores shows that the ratio of238U:235U isotopes in the natural
uranium is constant (139:1), and the concentration of235U is about 0.7%. There is just one
uranium pitchblende, in Oklo (Gabon), in which the ratio of238U:235U is higher than the
usual value, and the concentration of235U is below 0.5% (238U:235U.200:1). Studies of
this uranium mine have shown that the isotope ratios of the rare earth elements show
similar isotope ratios to the fission products of235U. For example, natural neodymium
contains 27%142Nd, while the Oklo ores contain less than 5%142Nd. The143Nd content,
however, typically is 12%, while its concentration in the Oklo samples is 24%. Neodymium
formed in the fission of235U contains 29%143Nd and no142Nd isotope.
These values indicate that the fission of235U could have taken place a very long time ago;
that is, a natural nuclear reactor could have been present long ago. Natural water probably
acted as the moderator. Based on the composition of the fission products and the uranium
content, the properties of the natural reactors are estimated to be as follows: the neutron
flux was ,109neutron/cm2per second in the core of the reactor, and its power was less
than 10 kW about 2 billion years ago. It consumed about 6 tons of235U, and produced
about 1 ton of239Pu.Nuclear Energy Production 169

It is interesting to mention that the half-life of235Ui s73108years; its relative isotope
ratio could be about seven times higher than the recent value (0.5 %). This means that the
235U concentration could be as high as (3%) which is similar to the235U of the recent
artificial reactors.
7.1.3 The First Artificial Nuclear Reactor
The first artificial reactor was built in Chicago in the early 1940s as part of the Manhattan
Project. The project supervisor was Enrico Fermi, in collaboration with Leo Szila ´rd, the
discoverer of the chain reaction. The first self-sustaining chain reaction was started on
December 2, 1942. The fuel was enriched uranium, and the moderator was graphite. The
controls consisted of cadmium-coated rods that absorbed neutrons. The withdrawal of the
rods increased neutron activity, leading to a self-sustaining chain reaction ( keff51). The
reactor had no radiation shielding and no cooling system. Fermi himself described the
apparatus as “a crude pile of black bricks and wooden timbers.”
The construction of nuclear reactors for energy production started in the 1950s. As
mentioned previously in this chapter, the first nuclear reactor built specifically for energy
production opened in Obninsk in 1954.
7.1.4 Types of Nuclear Reactors
Nuclear reactors may be built for many different purposes, such as energy production,
breeding of new fissile materials, production of radioactive isotopes, and for research and
education. The nuclear reactors are classified based on factors that include the following:
1. energy of the neutrons: thermal neutrons for energy production or fast neutrons for the
breeding of new fissile material;
2. fuel: natural uranium, enriched uranium, plutonium, or MOX;
3. moderator: light water, heavy water, graphite, and so on;
4. the distribution of the fuel and moderator: homogeneous, quasi-homogenous, or
heterogeneous;
5. coolant: gas, heavy and light water (boiling or pressurized), molten metals and salt, or
organic compounds.
Nuclear power is used in many naval vessels (e.g., submarines and icebreakers), both for
military and civil (including scientific) purposes. As an example, the main technical
parameters of a frequently used pressurized light-water-moderated and -cooled reactor
(PWR) are summarized in Table 7.3 . This reactor type was designed in the Soviet Union
and referred to as VVER (the Russian translation of “pressurized light-water-moderated and
-cooled energy producing reactor”).170 Chapter 7

7.1.5 Environmental Impacts of Nuclear Reactors
7.1.5.1 Positive Impacts
Nuclear power plants have many positive environmental and economical effects. The specific
energy production (energy per mass of fuel) is much higher than that of other types of power
plants. For example, the electric energy produced from 10 g uranium dioxide is equivalent tothe energy obtained from about 1100 m
3gas, 900 dm3oil, or 5 tons of coal. Conventional
thermal power plants emit many pollutants such as sulfur dioxide, nitrogen oxide, and carbonTable 7.3: The main technical parameters of a VVER (PWR).
Electric power 440 MW
Heat power 1375 MW
Fuel
Enriched uranium,235U content 1.6 /C02.4/C03.6%
Quantity of fuel 42 tonsChemical species UO
2
Number of fuel rods 44,000
Number of fuel assemblies 312
Number of control rod assemblies 37
Sizes of UO 2Pellets
Diameter 7.65 mm
Height 30 mm
Pellets per rod /C2580
Density of UO 2 10.6/C010.97 kg/dm3
Sizes of Fuel Rods
External diameter 9.1 mm
Length 2570 mmThickness of wall 0.65 mm
Filling gas He
Cladding Zr with 1% Nb
Data of fuel assembliesNumber of fuel rods per assembly 126
Hexagonal size 144 mm
Cladding Zr with 2.5% NbMean burn-up after 3 years 28,600 MWday/t U
Maximal surface contamination 10
29g235U/cm2
Moderator and coolant Light water
Mass of coolant in primary circuit 1.93 3105kg
Pressure at the outlet 12.26 MPa
Concentration of boric acid in primary circuit 0 /C012 g/kg
Concentration of potassium hydroxide 2 /C016 mg/kg
Concentration of ammonia 0 /C05 mg/kgNuclear Energy Production 171

dioxide, increasing the greenhouse effect and damaging the ozone layer of the Earth’s
atmosphere. Moreover, the ash produced by coal-based thermal power plants can contain
radioactive isotopes; in addition, they emit radon, which is also radioactive, along with its
daughter elements. Nuclear power plants, however, do not increase the greenhouse effect and
do not damage the ozone layer. In addition, the emission of the radioactive isotopes can be
much lower in nuclear power plants than in thermal power plants. For example, a PWR
nuclear reactor can emit about 0.01 Bq/second radioactivity, while a coal-based thermal
power plant can emit 2700 Bq/second, supposing that coal is rather radioactive.
This is true even if we compare nuclear energy to renewable energy. For example, the
production of 2000 MW of electricity by solar energy requires solar elements with 600 km2
surface area, supposing sunshine over 24 hour/day (a condition not existing in real life). In
addition, the production of the solar elements and the accumulators use gallium, arsenic,
selenium, and other elements which become heavy pollutants when disposed.
7.1.5.2 Negative Impacts
Under normal operation, nuclear power plants emit few radioactive gases. This emission is
regularly checked. In accidents, however, the emission of the radioactive isotopes can
increase. Because of the very strict safety regulation, accidents are very rare, and they are
always caused by human faults or natural catastrophes, such as earthquakes (see Section 7.2
for more). A very important problem of nuclear energy production is the safety treatment
and storage of the nuclear wastes (discussed in Section 7.3 ).
InFig. 7.6 , the environmental impacts of different energy sources related to the nuclear
energy are illustrated. The plot was constructed using standard Eco-Indicator 99 data,
Figure 7.6
The environmental impacts of different energy sources related to the nuclear energy constructed
using standard eco-indicator 99 data.172 Chapter 7

namely numbers that express the total environmental load of a product or a process for the
whole life cycle that is from the design to the dismantle and the reconstruction of the
original environmental conditions. As seen in Fig. 7.6 , the nuclear energy having lowest
impact is the most desirable way of energy production.
7.2 Accidents in Nuclear Power Plants
The safe operation of nuclear power plants is very important. People are very sensitive to
all events, both usual and unusual, relating to the nuclear power plants, including their
construction, operation, and radioactive wastes. The safe operation is controlled by the
IAEA. In 1990, an International Nuclear Event Scale was introduced, which evaluates
events other than normal operations. The scale is as follows:
 Level One: Anomaly
Overexposure of a member of the public to radiation in excess of statutory annual
limits.
Minor problems with safety components with significant defense-in-depth remaining.
Low-activity lost or stolen radioactive source, device, or transport package.
 Level Two: Incident
Exposure of a member of the public to radiation in excess of 10 mSv. (The units of
radioactive doses will be discussed in Section 13.4.1.)
Exposure of a worker to radiation in excess of the statutory annual limits.
Radiation levels in an operating area of more than 50 mSv/hour.
Significant contamination within the facility into an area not designed for such.
Significant failures in safety provisions but with no actual consequences.
Found highly radioactive sealed orphan source, device, or transport package with
safety provisions intact.
Inadequate packaging of a highly radioactive sealed source.
 Level Three: Serious Incident
Exposure to radiation in excess of ten times the statutory annual limit for workers.
Nonlethal deterministic health effect (e.g., burns) from radiation.
Exposure rates of more than 1 Sv/hour in an operating area.
Severe contamination in an area not designed to handle it, with a low probability of
significant public exposure.
Near accident at a nuclear power plant with no safety provisions.
Lost or stolen highly radioactive sealed source.
Misdelivered highly radioactive sealed source without adequate procedures in place
to handle it.
 Level Four: Accident with Local Consequences
Minor release of radioactive material unlikely to result in implementation of
planned countermeasures other than local food controls.Nuclear Energy Production 173

At least one death from radiation.
Fuel melt or damage to fuel resulting in more than 0.1% release of core inventory.
Release of significant quantities of radioactive material within an installation with a
high probability of significant public exposure.
 Level Five: Accident with Wider Consequences
Limited release of radioactive material likely to require implementation of someplanned countermeasures.
Several deaths from radiation.
Severe damage to the reactor core.
Release of large quantities of radioactive material within an installation, with a highprobability of significant public exposure. This could arise from a major accident orfire.
 Level Six: Serious Accident
Significant release of radioactive material likely to require implementation ofplanned countermeasures.
 Level Seven: Main Accident
Major release of radioactive material with widespread health and environmentaleffects requiring implementation of planned and extended countermeasures.
The most important nuclear accidents and their impacts are briefly presented here.1957, Windscale (Great Britain): In a plutonium breeding reactor, graphite heated up. As a
result, some fuel rods filled with natural uranium were melted and radioactive isotopes(
131I,132Te,137Cs,89Sr,90Sr, and noble gases) were emitted into the environment. About
700 km2were contaminated. The effect on human populations could not be detected. The
emitted radioactivity was 4 31016Bq. The average effective dose in the area of the power
plant was 0.8 Sv. This event was categorized as a Level Five accident on the InternationalNuclear Event Scale.
1979, Three Mile Island (USA, Pennsylvania): Because of the coincidence of some
technical, mechanical problems and human mistakes, the reactor got out of control, and theactive zone melted.
131I and radioactive noble gases were emitted into the environment. The
polluted coolant was emitted into the Susquehanna River. The effect on human populationscould not be detected. The dose evaluation showed that one more instance of cancer wasexpected for the 2 million inhabitants within 20 years (the usual number of cancer is350,000). The emitted radioactivity was about 10
15Bq. The average effective dose in the
area of the power plant is not known. This event was treated as a Level Five accident onthe International Nuclear Event Scale.
1986, Chernobyl (Soviet Union, today Ukraine): This accident took place during a test to
determine how long turbines would spin and supply power to the main circulating pumps174 Chapter 7

following a loss of the main electrical power supply. The automatic shutdown mechanisms
did not permit some of the operations. For this reason, the operators, who were not well
trained in this type of reactor, switched them off, and a sudden power increase boiled up the
coolant water. Water vapor is less able to absorb the neutrons than liquid water, so the
neutron flux increased. This resulted in an increase of power. By the time the operator
attempted to shut down the reactor, the control rods were too high to stop the chain
reaction. In addition, the control rods were made of boron carbide with graphite tips. The
graphite tips initially displaced coolant before neutron-absorbing material (boron) was
inserted and the reaction slowed. As a result, the power continued to increase, and the total
volume of coolant boiled up. At the same time, the reactor prompt became critical. The
interaction of very hot fuel with the cooling water led to fuel fragmentation, along with
rapid steam production and an increase in pressure. The overpressure caused a steam
explosion that released fission products into the atmosphere. Seconds later, a second
explosion occurred, in which the hydrogen produced from the reaction of the graphite
moderator and zirconium cladding with water blew up. In this process, the graphite
moderator could react with the oxygen of the air, graphite ignited. Since the reactor was
over-moderated ( Fig. 7.5 ) and the moderator/fuel ratio decreased, the multiplication factor
continued to increase.
In the Chernobyl accident, about 5% of the f uels were emitted into the atmosphere. This
contained the fission products (e.g.,131I and other iodine isotopes,134Cs and137Cs,
Sr isotopes, noble gases), uranium, and transu ranium elements. A significant number of
the radioactive isotopes were bounded to aerosols. The aerosols and the gaseous isotopes
were spread over several thousand kilometers, at first in a northwest direction, then
toward the south. The emitted radioactivity was about 2 31018Bq. The average effective
dose in the area of the power plant was 6 /C016 Sv, in Chernobyl, 0.2 /C01 Sv, in Kyiv. This
incident was categorized as a Level Seven accident on the International Nuclear Event
Scale.
2011, Fukushima (Japan): The fourth strongest earthquake in history, followed by a
tsunami, occurred in Japan. As a result, the power supply of the nuclear reactors was
destroyed. The emergency instruments stopped the reactors; however, the decay of fission
products that had already been produced continued and overheated the reactors. About
75% of the fuel melted. The operators tried to cool the melted fuel by adding sea water,
which caused hydrogen explosions in four reactors (three operational and one
nonoperational). The activity measurements of the radioactive isotopes (iodine-131 and
cesium-137) showed the released radioactivity was about 15% of the released radioactivity
in the Chernobyl accident. At first, the accident was assigned to Level Four of the
International Nuclear Event Scale, and then raised to Level Five and then raised again to
Level Seven.Nuclear Energy Production 175

7.3 Storage and Treatment of Spent Fuel and Other Radioactive Waste
One of the very important aspects of nuclear energy production is the safe treatment and
storage of nuclear waste. The sources of nuclear waste are as follows:
 the fission products of the ( n,f) nuclear reactions,
 transuranium elements produced in the ( n,γ) reactions of uranium, and
 radioactive nuclides produced in the ( n,γ) reactions of the structural material and the
environment.
As seen in Section 6.2.1, the fission reaction of235U (Eq. (6.21)) produces about 300
fission products, many of which are radioactive because the ratio of neutrons to protons is
too high for stability (Fig.6.5). The fission products emit negative beta radiation, which are
frequently accompanied by gamma radiation. As seen in the last two rows of Table 7.2 , the
energy of the beta and gamma radiation of the fission products is about 14 MeV, which is
about 7% of the total energy released in the fission reaction. The radioactivity of the fission
products as a function of time is shown in Fig.7.7 .
As seen in Fig. 7.7 , the two most important fission products are137Cs and its daughter
nuclide,137mBa, as well as90Sr and its daughter nuclide,90Y. Their fission yield is
relatively high, and they have relatively long half-lives. Twenty years after the irradiation,
the radioactivity of the fission products is almost exclusively due to the presence of these
isotopes. About 60% originates from the137Cs/C0137mBa pairing, and about 40% originates
from90Sr/C090Y pairing. It should be noted, that cesium and strontium can substitute
potassium and calcium in the living organism. Thus, the two isotopes are considered to be
the most dangerous fission products.
The transuranium elements are formed in the ( n,γ) reaction of238U (Fig. 6.22), which
composes the main part ( .95%) of the fuel elements. Similar reactions produce additional
isotopes of the transuranium elements up to246Pu,244Am, and some curium isotopes,
respectively.
(n,γ) nuclear reactions take place with the structural material and the elements in the
environment; for example, with the coolant, the air, and so on. Besides ( n,γ), other nuclear
reactions can also produce radioactive isotopes. For example, C-14 isotope can be formed
by the ( n,p) reaction of the nitrogen in the air:14N(n,p)14C. Tritium is also formed from the
nitrogen by14N(n,34He)Tand14N(n,T)12C reactions. The most important radioactive
isotopes produced in these reactions are T, C-14, N-16, O-19, F-18, Ar-41, Cr-51, Mn-54,
Fe-55, Fe-59, Co-58, Co-60, Ni-63, Zn-65, and Ag-110.
Nuclear wastes are formed during the mining and refining of uranium ores, the production
and reprocessing (see Section 7.3.2 ) of the fuel element, or in the industrial, medical, or
research isotope laboratories and any applications of sealed and unsealed radioactive sources.176 Chapter 7

The radioactive wastes are classified based on their activities. The classification is different
in different countries; the IAEA also has radioactive waste safety standards. The radioactive
wastes can be classified as follows:
 Low-level wastes; for example, the wastes of radioactive workplaces, such as
contaminated tools, clothes, and laboratory vessels.
 Intermediate-level wastes have higher activity and often require shielding. The ion
exchange resins, filters, chemical sludge, and other technological wastes of nuclear12 3 4 5 7 1 4 2 1 12 3 4 5 12 3 4 5 10 20 50
Days Months Y ears10–310–210–110102103104
g FP
1
10–310–210–110102103104
1Curies1 2 3 4 5 10 50 100 1000 days 10.000
CePrJNbZrXeYLaBa Y
JX e
BdLa
YSrZr
NbSrMoTeRuPm
Pm
Rh
Cs
Eu
Cs
Sm
Sb
Kr
Eu
Ag
Sn
Pd
Rb
Cd
As
Ge
Jn
GdTcTb
Tc
RbGbGe
JnPdAsTb
MoAgXe
Cd Nd LaBa
AgTeJ Ru
RhPr
Sn ZrNb CeSmSb
EuTcSmEuSmKrPm
Ce
PrRhRuSr
YCsFPNd
SmFPT= 2 years
Figure 7.7: Radioactivities of fission products formed in the thermal fission of235U
after an irradiation time of 2 years
The neutron flux is denoted as: …1012n/cm2per s,—1013n/cm2per s, and — 1014n/cm2per s.
Reprinted from Prawitz, J., Rydberg, J., 1958. Composition of products formed by thermal neutron fission of
235U. Acta Chim. Scand. 12, 369 /C0377 Prawitz and Rydberg (1958) , with permission from the
Swedish Chemical Society.Nuclear Energy Production 177

power plants belong to this group. Under normal operating conditions, these wastes
contain fission products, and the radioactive isotopes produced by the nuclear reactions
of the structural material and the nuclides of the environment. The quantity of the
transuranium elements is very low. The radioactivity of the isotopes in a container filled
with typical intermediate-level waste is shown in Fig. 7.8 . Low- and intermediate-level
wastes are frequently handled together.
 High-level waste, such as the wastes formed in the core of the nuclear reactors; namely,
the spent fuel elements. In addition, the reprocessing of the spent fuel elements (see
Section 7.3.2 ) produces high-level radioactive waste. Their radioactivity and heat
emission is high; thus, they require shielding and cooling by air or in basins filled with
water. High-level nuclear waste is stored under these conditions up to approximately
50 years.
In the United States, the transuranium nuclear wastes are also differentiated and treated
separately, independent of their alpha activity.
The annual quantities of the nuclear wastes in the European Union compared to the other
toxic and industrial wastes are illustrated in Fig. 7.9 .
7.3.1 Storage of Low- and Intermediate-Level Nuclear Waste
Low- and intermediate-level radioactive wastes are buried in geological repositories. These
repositories must isolate the nuclear waste from the biosphere for as long as 100,000 years.
Figure 7.8
Radioactivity of the isotopes in a container filled with typical intermediate-level waste.178 Chapter 7

For the storage of radioactive waste, the geological formations were used where
water-soluble compounds have been accumulated for millions of years, such as salt mines,
clay rocks, granite, and tuff. In these geological formations, further engineering barriers are
constructed. The nuclear waste is placed into sta inless steel or reinforced concrete containers
and deposited inside the engineering barrier syst em. Only solid wastes are stored; liquid wastes
are solidified by cementation or bitumen. Th e holes among the containers are filled with
cement too. In the geological repositories, there are several barrier systems (rocks, engineering
barriers) which one by one must isolate the radioactive waste from the environment.
There are some very important aspects to take into account when selecting a
suitable environment for waste disposal. These are, for example, the hydrological properties
of the geological environment, the corrosion and erosion of the engineering barrier system,
leaching, and migration of the radionuclide in the geological environment. In addition, the
microbiological activity and the effects of radiolysis have to be considered.
Low- and intermediate-level radioactive wastes contain the technological wastes of nuclear
energy production (clothing, paper, wood, ion exchange resins, plastics, contaminated tools,
instruments, etc.). In the corrosion and microbiological degradation of these substances,
gaseous compounds are released. The corrosion produces hydrogen, while the
microbiological processes transform the organic substances of the nuclear wastes into carbon
dioxide or methane, depending on the redox conditions. The formation of carbon dioxide is
less important because the anaerobic conditions are dominant in underground disposal. The
gases can have unfavorable effects during storage. For example, the increasing pressure can
push the radioactive gases and solutions into the environment. As a result of the
cementation, the pH of the pore solution is set above 12. This pH inhibits the corrosion of
the containers and the microbiological activity, decreasing the rate of gas release.
The leaching and migration of radionuclides is the net effect of hydrological, interfacial
(adsorption, ion exchange), and chemical processes (hydrolysis, precipitation, redox
Figure 7.9
The annual quantities of the nuclear wastes in the european union compared to the other toxic
and industrial wastes. Reprinted from Hegyha ´ti, J., 2007. Radioaktı ´v hullade ´kok kezele ´se e´sv e´gleges
elhelyeze ´se (Treatment and final disposal of nuclear waste). http://www.matud.iif.hu/07jan/07.html (accessed
15.01.17.) Hegyha ´ti (2007) , with permission from Magyar Tudoma ´ny (Hungarian Science).Nuclear Energy Production 179

reactions). The interactions are determined by the surface charge of minerals and rocks, and
the chemical species of radioactive isotopes as discussed in Sections 9.3.2.2 and 13.3.3.
The radiolysis of water (discussed in Section 13.4.2) also releases gases; however, this
reaction can be disregarded for the disposal of low- and intermediate-level nuclear waste.
7.3.2 Treatment and Storage of High-Level Nuclear Waste
As mentioned previously in this chapter, high-level nuclear waste (namely, the spent fuel
elements) are stored under shielding and cooling in transitional disposals for about 50 years, and
then they are deposited in geological repositories for final storage. The spent fuel elements
contain the fission products and the transuranium elements. Before final storage, the spent fuel
elements have to be treated in different ways. The aims of these treatments are as follows:
 to utilize the energy of beta and gamma decays,
 to produce additional fuel material (e.g., plutonium),
 to decrease the risk and cost associated with the storage of high-level nuclear waste,
 to decrease the cost of the fuel cycle of nuclear energy production, and
 to gain valuable by-products, e.g., fission products that can be used in other areas.
One possibility of treating the high-level nuclear waste is reprocessing. This is a chemical
procedure in which the spent fuel elements are dissolved, and then the fission products,
uranium, and transuranium elements are separated. In this way, about 97% of the high-level
nuclear waste can be recycled. The steps of reprocessing are as follows:
 The spent fuel elements are cut into pieces and dissolved in 6 /C011 mol/dm3HNO 3
solution. If the cladding is zirconium or zircalloy, fluoride is also added to the solution.
To avoid the chain reaction, neutron absorber (Cd, Gd) is also added.
 The gases released during the dissolution (Kr, Xe, I, T compounds, CO 2, etc.) are
treated as they would in the normal operation of the nuclear power plant (see
Section 7.1.1.1 ).
 By flowing oxygen gas; if there is any uranium in an oxidation state lower than six, it is
oxidized to uranyl cation (UO21
2). As a result of the nitric acidic dissolution, all cations
present in the solution are nitrates. The oxidation state of uranium and plutonium is 16
and14, respectively.
 The uranium and plutonium is extracted by tri-butyl-phosphate dissolved in kerosene.
This procedure is called the “PUREX procedure.” The fission products remain
dissolved in the aqueous phase.
 The uranium and plutonium are separated by using the reduction of plutonium. For this
reason, ferrous(II) sulfamate or U(IV) are added to the kerosene solution. Plutonium is
reduced to Pu(III), then extracted by water. The uranium remains in the organic phase
(kerosene). If required, this process can be repeated for additional purification.180 Chapter 7

 The fission products are separated from the aqueous phase using different techniques
(precipitation, extraction, ion exchange, etc.). At first, the chemically similar fissionproducts are separated, and then the individual isotopes are separated from the groups
of the chemically similar elements. An example will be shown in Section 8.5.2
(Eq. (8.17)) and Section 8.7.1.4 (Eq. (8.24)).
 The liquid residue of the procedure is solidified in the form of ceramics by the addition
of Al(NO
3)3and SiO 2, or vitrificated by Al(NO 3)3, SiO 2, borax, or phosphates.
Besides recycling, isotopes with shorter and longer half-lives may also be separated during
the reprocessing. In this way, both the quantity and the radioactivity of the high-level wastecan be significantly reduced, and less-disposal capacity is required.
Another possibility for the treatment of high-level nuclear waste may be the transmutation
of the fission products of the spent fuel elements to isotopes with shorter half-lives. Duringthis treatment, the fission products are dissolved in melted salts and bombarded withneutrons with high flux. The neutrons are produced by the spallation reaction of an elementwith a high atomic number (such as Pb, Bi, or Hg) induced by the bombardment of protonswith very high energy ( .800 MeV). High-energy protons are generated in linear
accelerators. The neutrons react with the nuclei of the fission products: fission, neutroncapture, and then beta decay take place. Finally, radioactive isotopes with shorter half-lives,or even stable isotopes, can be produced. This process is exoergic; about 20% of thereleased energy is used for the operation of the linear accelerator, and the rest can beutilized for other purposes. Thus, the nuclear energy production becomes more economical.The development of transmutation of spent fuel elements is in the experimental phase at themoment; we may have to wait a long time for the implementation of this process.
Independent of the treatment of spent fuel elements, some amount of high-level nuclear
waste is always formed; so final disposal of this waste is always required. Today, the onlyreal option for final disposal is storage in geological repositories; however, presently thereis no operating geological repository for high-level radioactive waste. Some countries areresearching the construction of such waste repositories, and they are expected to beoperational by about 2040. In these repositories, high-level wastes are placed in stainlesssteel containers surrounded by a bentonite layer and natural geological formations.Recently, an Implementing Geological Disposal of Radioactive Waste Technology Platformwas created by EURATOM, and their “vision is that by 2025, the first geological disposalfacilities for spent fuel, high-level waste and other long-lived radioactive waste will beoperating safely in Europe.”
7.4 New Trends in Nuclear Energy Production
7.4.1 Improvement of the Fission in Nuclear Power Plants
On the basis of their history and technical condition, nuclear power plants are classified intofour groups. The first-generation (Generation I) nuclear power plants were developed in theNuclear Energy Production 181

1950s/C01960s in the Soviet Union, the United States, Great Britain, and France. Most of
them have been dismantled now; only a few of these reactors are still operating. They do
not fulfill today’s safety, technical, and environmental requirements.
The second-generation (Generation II) nuclear power plants were the improved version of
the first-generation plants; they are more safe, economical, and reliable. Most of the power
plants in operation today belong to this type. PWRs are the most widespread; they provide
about 65% of the total production of nuclear power plants today. The very important
difference between first-generation reactors and the PWRs is that in PWR reactors, the total
primary circuit (namely, all the contaminated parts of the reactor) is placed in containment
(Section 7.1.1.8 ), which is a high-volume, pressure-proof, hermetically sealed building. This
creates a new safety barrier in case of an accident.
The third-generation (Generation III) nuclear power plants are improvements over the
second-generation plants. For this reason, they are called “evolution nuclear power plants.”
The number of evolution power plants is relatively low; there are some third-generation
nuclear power plants, for example, in Japan, at this time, but they are being planned and
constructed all over the world. Their typical features are as follows:
 They will be built using standard plans, so they can be up and running in a relatively
short time (a few years); the operation time, however, is longer.
 Their structure is simpler and more robust than the previous reactors.
 They are safer because of the application of passive protection techniques.
 Their environmental impact is very low.
 The fuel is burned up better, so the fuel cycle is more economical and produces less waste.
The fourth-generation nuclear power plants are called “innovative plants” because they
apply new technical solutions and have new safety requirements. The most important trends
are as follows:
 In addition to235U,238U, and232Th will be utilized for energy production.
 Besides electric energy production, hydrogen will be produced by the electrolysis of
water. This in itself should have a significant positive environmental impact because
right now, hydrogen is produced from natural gas, which also produces carbon dioxide,
increasing the greenhouse effect.
 To decrease the quantity of high-level nuclear waste produced, the facilities for the
transmutation of the long-life radioactive isotopes (see Section 7.3.2 ) will be included
in the nuclear reactor itself.
 The possibility of the production of the nuclear weapons from the spent fuel elements
will be significantly reduced.
These aims may be achieved by different reactor types, such as thermal reactors, including
the very-high-temperature reactor, the supercritical-water-cooled reactor, and the molten salt
reactor; fast reactors, including the gas-cooled fast reactor; and molten metal (sodium, lead,
lead/C0bismuth)-cooled reactors.182 Chapter 7

7.4.2 Experiments with Fusion Energy Production
As seen in Fig. 2.2, the fusion of light elements also can be used for energy production.
These thermonuclear processes provide the energy in stars (see Sections 6.2.4 and 6.2.5)
and in the hydrogen bomb (see Section 7.5 ).
The potential of controlled thermonuclear reactions has been studied for several decades.
These processes should provide the energy requirements of the Earth for a million years
by the fusion of deuterium in the oceans. In addition, the fusion reactions produce no
nuclear waste.
The thermonuclear reactions have two basic requirements. First, the temperature must be
about 108K because the ignition temperature of the2H/C02H reaction and the2H/C03H
reaction are 3 3108and 33107K, respectively (Section 6.2.4). Second, the nτvalue, the
Lawson limit, must be higher than 1021particles s/m3for the2H/C02H reaction and 1020
particles second/m3for the2H/C03H reaction, where nis the particle density and τis the
confinement time. The Lawson limit indicates the ability of the plasma to retain heat. The
two conditions depend on each other; that is, a given temperature needs a certain nτvalue.
There are two approaches to achieving a controlled thermonuclear reaction. A part of the
reactors is based on the magnetic confinement of the hot ( .108K) plasma containing the
isotopes of hydrogen (deuterium and tritium). The most successful results with this method
have been obtained in the Tokamak instrument, in Moscow. In this instrument, the plasma
is toroid shaped. The other type of controlled thermonuclear reactor operates in pulsed
mode (inertia confinements) when small pellets of solid deuterium and/or tritium are
injected into a chamber and irradiated by an intense beam of photons from lasers. Recently,
there are experiments with the combination of the magnetic and inertia confinement.
The controlled thermonuclear reactors are in the experimental stage. Some examples of
important experimental fusion reactors are JET (Joint European Torus, United Kingdom),
DIII-D (USA, San Diego), EAST (Experimental Advanced Superconducting Tokamak,
China), TFTR (Tokamak Fusion Test Reactor, USA, Princeton), K-Star (Korea
Superconducting Tokamak Advanced Research, South Korea), JT-60 (Japan Torus 60,
Japan), TCV (Tokamak a `configuration variable, Switzerland), T-15 (Russia), and Tore
Supra (France). The International Thermonuclear Experimental Reactor (ITER) in France is
under construction. This reactor is scheduled to be operational in 2020. Its objectives are to
demonstrate the feasibility of fusion power and to prove that it can work without negative
impact. This includes to ignite self-sustaining plasma for at least 8 minutes, and to produce
more than enough energy to ignite the fusion. Commercial reactors may be produced in the
second part of the 21st century at the earliest. There are still many technical problems to be
solved. For example, when heating to a suitably high temperature, the fuel separates from
the walls of the vessels (no substances are able to withstand this temperature). In addition,Nuclear Energy Production 183

the injection of fuel (deuterium and tritium) and the withdrawal of the product (helium),
and the control of the fusion are problematic at this time.
Some popular scientific papers state that fusion plasma was operated for 102 seconds in
China in February, 2016.
7.5 Nuclear Weapons
The nuclear reactions that are used for energy production are also used for militarypurposes. Nuclear weapons utilize both the fusion reaction and the combination of thefusion and fission reactions.
In the fission bomb (better known as the atomic bomb), the unregulated fission of
235U
(Eq. (6.21)) or another fissile, plutonium, takes place. The fissile is placed in pieces, eachcontaining less fissile than the critical mass. The chain reaction is ignited by a chemicalexplosion, which causes the addition of the pieces so that the mass will become more thanthe critical mass. During the unregulated chain reaction, the very high energy of the fissionreaction releases in a very short time, causing another explosion. As mentioned inChapter 1, Introduction, the first two nuclear bombs were exploded at the end of WorldWar II in Japan. On August 6, 1945, a bomb known as “Little Boy” was exploded inHiroshima; the fission of
235U took place in the bomb. On August 9, 1945, the “Fat Man”
bomb was detonated in Nagasaki; the fissile in this bomb was plutonium.
The combination of the fusion and fission reactions is the thermonuclear or hydrogen bomb.
The first hydrogen bomb was developed in 1952. The high temperature needed for the ignitionof the fusion reaction of hydrogen isotopes (deuterium and tritium; see Eq. (6.47) throughEq. (6.50)) is provided by a fission reaction; that is, by an atomic bomb. The fusion fuel istritium, deuterium, or lithium deuteride. As mentioned in Section 6.2.4, the ignitiontemperature is the lowest for the
2H/C03H reaction; so the most favorable fusion reaction is the
2H/C03H reaction. The production of tritium, however, is expensive, and in addition, its half-life
is 12.4 years. For this reason, lithium deuteride is frequently used. From lithium, tritium isproduced in the reaction Eq. (6.17) under the effect of neutrons formed in the fission reaction.
Recently, fission /C0fusion/C0fission bombs have been developed. In these bombs, there is an
outer mantle, and the fission reaction takes place. In the salted bombs, the nuclear weaponis surrounded by a substance such as cobalt or gold, from which radioactive isotopes are
formed via the nuclear reactions initiated by neutrons that are produced in the fission
reactions. These bombs can be considered “dirty bombs” because of their high radioactivecontamination.
A special type of thermonuclear weapon is the neutron bomb, in which the fissile has low
critical mass (e.g., californium). The fusion fuel is the mixture of deuterium and tritium.184 Chapter 7

The bomb is surrounded by a substance that has a very low level of neutron absorption. In
this way, the main destructive impact is caused by the escaping neutrons. The mass of the
neutron bombs is only a few kilograms, and therefore it can be transported very easily.
Because of the small quantity of fissile, the radioactive contamination is relatively low.
Further Reading
Choppin, G.R., Rydberg, J., 1980. Nuclear Chemistry, Theory and Applications. Pergamon Press, Oxford, ISBN:
0-08-023826-2.
Choppin, G.R., Liljenzin, J.-O., Rydberg, J., Ekberg, C., 2013. Radiochemistry and Nuclear Chemistry. fourth ed.
Elsevier, Amsterdam, ISBN-13: 978-0124058972, ISBN-10: 0124058973.
European Nuclear Society, 2003. European Nuclear Society, 2003. Nuclear power plants, world-wide. ,www.
euronuclear.org/info/encyclopedia/n/nuclear-power-plant-world-wide.htm .(IAEA, November 28 2016)
(accessed 13.01.17.).
Friedlander, G., Kennedy, J.W., Macias, E.S., Miller, J.M., 1981. Nuclear and Radiochemistry. Wiley,
New York, NY, ISBN: 978-0-471-86255-0.
Hegyha ´ti, J., 2007. Radioaktı ´v hullade ´kok kezele ´se e´sv e´gleges elhelyeze ´se (Treatment and final disposal of
nuclear waste). ,http://www.matud.iif.hu/07jan/07.html .(accessed 15.01.17.).
Green Capital, 2009. A magyar energiaszektor villamosenergia-termele ´se´nek e´letciklus-, e ´s “carbon footprint”
elemze ´se (Life Cycle and “Carbon Footprint” Analyses of Hungarian Electric Energy Production). ,http://
www.greencapital.hu/dokumentumok/LCA_villeneregia_GreenCapital_osszefoglalas.pdf .(accessed
17.01.17.).
http://www.cebc.hu/ppt/energetika2011/hamvas_istvan.ppt (accessed 17.01.17.).
https://www.pre-sustainability.com/download/EI99_Manual.pdf (accessed 17.01.17.).
Implementing Geological Disposal of Radioactive Waste Technology Platform, ,http://igdtp.eu/ .(accessed
09.10.17.).
Kratz, J.-V., Lieser, K.H., 2013. Nuclear and Radiochemistry: Fundamentals and Applications. third ed. Wiley-
VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, ISBN: 3527329013.
Lehto, J. Basic of Nuclear Physics and of Radiation Detection Measurement. ,https://nucwik.wikispaces.com/
Nuclear 1and1Radiochemistry 1Textbook 1and1Compendia .(accessed 02.12.16.).
Lieser, K.H., 1997. Nuclear and Radiochemistry. Wiley-VCH, Berlin, ISBN: 978-3-527-30317-5.
McKay, H.A.C., 1971. Principles of Radiochemistry. Butterworths, London, ISBN: 0 408 70161 7.
Prawitz, J., Rydberg, J., 1958. Composition of products formed by thermal neutron fission of235U. Acta Chim.
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