The
Nuclear Industry Explained
Uranium is a slightly radioactive metal that occurs
throughout the Earth's crust in most rocks and soils. For example, it is found
in concentrations of about four parts per billion in granite which makes up 60%
of the earth's crust. It is about 500 times more common than gold. However,
there are only a limited number of places in the world where uranium is found
in high enough concentrations for it to be deemed economically viable to
extract it for use as nuclear fuel. Such concentrations are called uranium ore
and they are present in Uganda.
Surveys by the Ugandan Ministry of Energy and Mineral
Development (MEMD) show that the country has about 52,000 square kilometres of
uranium deposits.
In the early 20th century, it was discovered that
radioactive elements such as uranium released huge amounts of energy. A series
of experiments over the following decades culminated in the announcement of
self-sustaining nuclear chain reactions by Frederic Joliot-Curie in 1939. A
nuclear reaction is defined as the process by which two nuclei, or a nucleus
and a sub-atomic particle, collide to produce one or more nuclides that are
different from those that started the process. A nuclear chain reaction occurs
when one single nuclear reaction causes an average of one or more subsequent
nuclear reactions, thus leading to the possibility of a self-propagating series
of these reactions. Most importantly, the nuclear chain reaction releases
several million times more energy per reaction than any chemical reaction - the
potential in terms of power generation is enormous.
Figures
from the World Nuclear Association indicate there are currently 437 operable
civil nuclear power reactors around the world with a further 71 under
construction. Out of the 30 countries currently generating power from nuclear
reactors, the five with the highest number of reactors are:
USA - 99 reactors that generated 790.2
billion kWh in 2013 (19.4 % of total)
France - 58 reactors that generated 405.9
billion kWh in 2013 (73.3% of total)
Japan - 43 reactors that generated 13.9
billion kWh in 2013 (1.7% of total)*
Russia - 34 reactors that generated 161.8
billion kWh in 2013 (17.5% of total)
China - 26 reactors that generated 104.8
billion kWh in 2013 (2.1% of total)
Prior
to the earthquake and tsunami of March 2011 Japan generated 30% of its
electricity from nuclear and planned to increase that share to 40%. However,
all of Japan's nuclear plants have now been closed or their operation suspended
for safety inspections hence the figure of 1.7%.
According
to President Museveni, a developed Uganda requires in excess of 50,000
megawatts of electricity which cannot be generated from the country's limited
hydro and geo-thermal resources. The country therefore is looking at nuclear
energy as a viable option and hopes to begin producing nuclear energy in about
twenty years. Already, Uganda is conducting pre-feasibility studies which
involve assessing the country's energy needs, proposing road maps, developing
expertise and training human resources, establishing policy and regulatory
frameworks and mobilizing funding. When that is completed, Uganda will then
conduct other studies to establish the viability of setting up nuclear plants
in the country.
Developing
nuclear fuel
The
nuclear fuel cycle is the series of industrial processes which lead to the
production of electricity from uranium in nuclear power reactors. It involves
the following stages:
Uranium
mining:
depending
on the nature of the uranium ore and adjoining rock, as well as safety,
environmental and economic considerations, a variety of mining methods can be
used. In the case of excavation it may be underground (for deep deposits) or
open pit (where deposits are close to the surface). In situ leach (ISL) mining
is also now commonly used where oxygenated groundwater is circulated through
very porous rock to dissolve the uranium oxide and bring it to the surface.
Uranium
milling is used to extract the uranium from the ore (or ISL leachate). The ore
is crushed and ground to a fine slurry which is leached in sulphuric acid to
separate the uranium from the waste rock - this waste rock or 'tailings' must
be isolated from the environment. The uranium is then recovered from the
solution and precipitated as uranium oxide (U3O8) concentrate - sometimes known
a 'yellowcake'. This material is then dried and packaged ready for transport
Conversion:
Theuranium
oxide productmust first be refined at a conversion facility into uranium
dioxide (UO2) which can be fabricated into fuel rods for use in some reactors -
notably the Canadian and Indian heavy water type. However, to get more energy
out, most of the uranium dioxide goes through a further process called
enrichment. This is where things get a little complicated.
Enrichment:
The
aim of this process is to increase the proportion of 'fissile' material or
material that is capable of undergoing fission (splitting up of the nucleus).
This is the process by which energy is produced in a nuclear reactor. Only 0.7%
(this is the concentration of the uranium-235 isotope - but we won't go into
that here) of natural uranium is fissile. For most kinds of reactor the concentration
of the fissile material needs to be increased - typically to between 3.5% and
5%. Firstly, the uranium dioxide mentioned above must be converted into gaseous
uranium hexafluoride (UF6) by adding a highly toxic gas called hydrogen
fluoride. The uranium hexafluoride is then passed through a series of rapidly
spinning vertical tubes known as centrifuges to produce low-enriched uranium
hexafluoride. Finally, this is reconverted back to produce enriched uranium
oxide (UO2).
Note
- Uranium enrichment is a critical component for civil nuclear power generation
but also for military nuclear weapons. Weapons grade uranium typically contains
85% or more of 'fissile' uranium-235.
Fuel
fabrication:
The
final stage of the 'front end' is to press and bake the enriched uranium
dioxide into ceramic pellets. The pellets are then encased in metal tubes to
form fuel rods, which are arranged into a fuel assembly ready for introduction
into a reactor. About 27 tonnes of this enriched fuel is required each year by
a 1000 megawatt reactor.
Power
generation:
Several
hundred fuel assemblies make up the core of a reactor. In the reactor core, the
fissile material (uranium-235) fissions or splits producing a huge amount of
heat in a continuous nuclear chain reaction. As in fossil fuel burning plants
such as coal, the heat is used to produce steam which drives a turbine and an
electric generator. To maintain a high level of efficiency in the reactor,
about one third of the spent fuel is replaced with fresh fuel every year or 18
months.
Waste
from the nuclear fuel cycle can be in solid, liquid or gaseous form and is
categorised as either high, medium or low-level depending on the amount of
radiation it is giving off. One of the big issues is that at the present time
there are no disposal facilities in operation in which the very highest level
solid waste i.e. used fuel (not destined for reprocessing) and the waste from
reprocessing can be placed. This highly radioactive waste presents many technical
issues due to the extremely long periods of time that must pass before it stops
being dangerous to humans and the environment. Having said this, the total
volumes of such wastes are relatively small. For example, one year worth of
high level waste from a 1000 megawatt reactor can be contained in five tonnes
of borosilicate (Pyrex) glass, stored in stainless steel containers.
Handling
radiation
One
thing the general public are always concerned about, and rightly so, is the
effect of radiation on people and the environment. Although radiation is
naturally present in our environment, it can have either beneficial or harmful
effects depending on its use and control. Since
the beginning of time all living creatures have been, and are still being,
exposed to radiation. Natural radiation comes from cosmic radiation (i.e. the
sun and stars), terrestrial radiation (i.e. soil, rock, water, food and even
air - all air contains radon which is responsible for most of the dose people
get from background radiation) and internal radiation (i.e. mainly from
radioactive potassium-40 and carbon-14 inside your body from birth). People
who work with or near nuclear materials (i.e. fuel cycle facilities, power
stations, medical radiology departments etc.) will be likely to receive some
additional varying amounts of radiation depending on their specific jobs.
However, note that this occupational exposure is tightly controlled by the
regulatory authority of the country where the operations are taking place. Radiation
can broadly be split into either ionising on non-ionising radiation depending
on how it affects matter. Non-ionising radiation includes light, heat,
microwaves and radio waves and does not have sufficient energy to break
molecular bonds. Ionising radiation on the other hand is more energetic and
when passing through a material it deposits enough energy to break molecular
bonds and remove electrons from atoms causing changes in living cells of
plants, animals and people.
A
common example is the 1986 Chernobyl accident in Ukraine that caused the death
of 30 people due to acute radiation poisoning.
In
the second part of this series, we will explore in more detail the Ugandan
context- how much uranium has been found to date, where it is in the country
and how accessible it is. We shall discuss what this means for Uganda in the
context of wider natural resources management and governance.
By Luke
Williams. He is an Environment, Health and Safety professional.
