Annual Report 1999-2000
Brief Outline
of the Nuclear Fuel Cycle
Currently there are more than 430 nuclear power reactors in
operation in over 30 countries worldwide.
In many cases they supply a substantial proportion of national
electricity requirementssee Table 8 on
page 83.
Reactor types
The majority of the worlds power reactors
are of the light water type (LWRslight water reactors), where ordinary water
acts as both moderator, slowing down neutrons to efficient speeds for nuclear
fission to occur, and coolant, transferring heat from the nuclear reaction to
steam generators for producing electricity.
Because ordinary water is an inefficient
moderator, LWRs must be operated on enriched uranium, that is, uranium in which
the proportion of the fissile isotope U-235 has been increased from the level in
natural uranium, 0.71%, usually to between 3 and 5%. Some reactor types can be operated on natural uranium, by using
more efficient moderators, such as heavy water, which has a proportion of the
heavier hydrogen isotope deuterium, and graphite. Typical examples of this type of reactor are the Canadian CANDU,
which is moderated and cooled by heavy water, and gas-cooled graphite-moderated
reactors such as the UK Magnox.
Fuel
cycle stages
Following mining and
milling of uranium and production of uranium ore concentrates (yellowcake), the
stages of the light water fuel cycle are as follows (see Figure 4 page 82):
-
Conversion: natural uranium is formed into a gaseous compound,
uranium hexafluoride (UF6), prior to enrichment; -
Enrichment: a process by which the proportion of the U-235 content is
increased. The main technologies in use
are gaseous diffusion and centrifuge.
The product is described as low enriched uranium (LEU), containing
between 3 and 5% U-235; -
Fabrication: manufacture of LEU into uranium oxide fuel pellets, which
are assembled into fuel rods and then fuel elements for use in a reactor; -
Reactors: a power reactor uses the heat from a controlled nuclear chain
reaction to drive a turbine to generate electricity. Typically the turbine(s) is driven by steam. In the case of pressurised water reactors as
well as liquid metal-cooled reactors and some gas-cooled reactors, steam for
the turbines is produced in a secondary circuit. There are some high-temperature gas-cooled reactors where the
generating turbine is gas-driven.
In a typical LWR fuel elements are used
over 3-4 operating cycles each of 12-18 months (i.e. the reactor might be
unloaded every 12 months, with a third of the core being replaced each time);
-
Reprocessing: spent fuel is dissolved for the separation of highly
radioactive fission products, and for the recovery of plutonium and
uranium. Uranium can be re-enriched for
further reactor use. Plutonium is mixed
with uranium to produce MOX (mixed oxide) fuel and used both in LWRs and
potentially in fast breeder or fast neutron reactors.
Partly because depressed uranium prices are
impacting on the economics of reprocessing, a number of countries have
committed to, or are considering, the once-through cycle, where spent fuel will
be disposed of without reprocessing.
Military
fuel cycle
There are five acknowledged nuclear-weapon
States (US, Russia, UK, France and China) and three threshold States, two of
which have conducted nuclear explosive tests (India and Pakistan) and one which
is suspected of having a nuclear weapon capability (Israel). In all cases the military nuclear programs
developed ahead of civil power programs.
Military programs involve the production of special grades of nuclear
material, substantially different to the material used in civil programs.
Nuclear weapons are based on the following
nuclear materials:
Plutonium: Plutonium is formed
through the irradiation of uranium in a reactor. The uranium-238 isotope absorbs a neutron, leading to the
formation of plutonium-239. Longer
irradiation times lead to the formation of higher plutonium isotopes, Pu-240,
Pu‑241 and Pu-242.
Weapons-grade plutonium predominantly comprises the isotope Pu-239 and contains no more than
7% of the isotope Pu-240. Pu-240 (and
the higher isotope Pu-242) are undesirable for weapons purposes because their
rate of spontaneous fission causes pre-initiation (a premature chain reaction). By contrast, reactor-grade plutoniumfrom the normal operation of a LWR contains
high levels of Pu-240, typically around 25%.
Because of the need to minimise the Pu-240
content, weapons-grade plutonium is produced in dedicated plutonium production
reactors, usually natural uranium-fuelled, graphite-moderated, where irradiated
fuel can be removed after short irradiation times (i.e. at low burn-up levels).
Uranium: Uranium used in
nuclear weapons is very highly enrichedweapons-grade uranium is 93% U-235. This compares with normal civil enrichment
levels of around 3-5% U-235. High
enrichment levels are produced in enrichment plants specially designed and
operated for this purpose.
in Civil and Military Nuclear Fuel Cycles. Figures are approximate
Material
Military
Plutonium
60% Pu-239
93% Pu-239
Uranium
4% U-235
93% U-235
The US, Russia, UK and France have
announced that they have ceased production of fissile material for nuclear
weapons purposes, and China is believed to have done so. Australia is a strong supporter of a Fissile
Material Cut-off Treaty (FMCT) under which this situation will be formalised,
and extended to India, Israel and Pakistan.
The FMCT will prohibit production of fissile material for weapons
purposes, and will provide for verification on relevant facilities and
material.
Figure 4 Civil
Nuclear Fuel Cycle-Outline
Some countries choose to dispose of their spent fuel in
repositories instead of recycling it.
Nuclear Electricity Generation at 31 December 1999
Country
Operating
Capacity
% of Total
Reactors under construction
Reactors
(GWe)
Electricity in 1999
Number
(GWe)
World total
433
349.0
(est) 16.0
41
34.4
*USA
104
97.1
19.8
*France
59
63.1
75.0
*Japan
53
43.7
35.9
4
4.5
*Germany
19
21.1
31.2
Russia
29
19.8
14.4
3
2.8
*ROK
16
13.0
42.8
*UK
35
13.0
28.9
Ukraine
14
12.2
43.8
4
3.8
*Canada
14
10.0
12.4
*Sweden
11
9.4
46.8
*Spain
9
7.5
31.0
*Belgium
7
5.7
57.7
Taiwan, China
6
4.9
24.8
2
2.7
Bulgaria
6
3.5
47.1
*Switzerland
5
3.1
36.0
*Finland
4
2.7
33.0
Lithuania
2
2.4
73.1
4
4.5
China
3
2.2
1.2
7
5.4
Slovak Republic
6
2.4
47.0
2
0.8
South Africa
2
1.8
7.1
2
0.8
India
11
1.9
2.7
3
0.6
Hungary
4
1.7
38.3
Czech Republic
4
1.6
20.8
2
1.8
*Mexico
2
1.3
5.2
4
3.8
Argentina
2
0.9
9.0
1
0.7
Romania
1
0.7
10.7
1
0.7
Slovenia
1
0.6
37.2
Brazil
1
0.6
1.1
1
1.2
*Netherlands
1
0.4
4.0
Armenia
1
0.4
36.4
Pakistan
1
0.1
0.1
1
0.3
* Eligible
to use Australian uranium. Countries
eligible to use Australian uranium operate 339 power reactors, accounting for
around 83% of world nuclear generating capacity.
Source: IAEA Press Release 00/9, 6 March 2000
(http://www.iaea.org/worldatom/Press/P_release/2000/99npptable.shtml)
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