Lecture 5.

Topics
1. Elements of Nuclear Physics
2. History of Nuclear Physics; beginning of nuclear
energetics
3. Detecting nuclear radiations, radiation detectors
4. A nuclear power plant
5. Types of nuclear reactors based on usage of the
reactors
6. Generations of nuclear power plants
7. Nuclear reactors in Hungary
8. Mini or small nuclear power plants
9. Reactor safety, radiation safety
10. Nuclear accidents, abnormal operations
11. Nuclear power plants and environmental protection
12. Fusion, fusion devices, fusion power plants
13. Natural nuclear reactors or nuclear reactors in nature
Lecture #5.
Types of Nuclear Reactors
Based on Usage of the
Reactors
Chapter 5.
Lecture #5.
Classification Criteria
of Nuclear Reactors
Lecture #5.
Classification of Nuclear Reactors
1.
According to energy range of neutrons
2.
According to their nuclear fuel types
•
Reactors with uranium, thorium, plutonium
3.
According to enrichment factor of the nuclear fuel
•
Enrichment: The percentage ratio of the uranium-235 isotope in the
natural uranium ore is 0,7 %. Enriching uranium increases the proportion
of uranium-235 isotope in the uranium material. Huge part of the nuclear
reactors can work only with enriched uranium. This is a difficult, complex
and energy-intensive project.
4.
According to the medium of the moderator
•
Water, Heavy water, graphite –moderated reactors
5.
According to the medium of the coolant/cooling material
•
Water, gas, metal –cooled reactors
6.
According to use/usage of the reactors
Lecture #5.
Classification of Nuclear Reactors
1.
According to energy range of neutrons
•
It means: It is the kinetic energy range of the moving neutrons cause
nuclear fissions in uranium fuel.
a) Thermal/thermic: Most of the fissions occur with thermal neutrons
(slow neutrons, neutrons with thermal energy)
o
Cross-section of the fission using thermal neutrons is hundred-times
higher, than using energetic neutrons.
o
High energy neutrons (MeV) must be slowed down. Moderator can
slow down the energetic neutrons.
o
It is not good if the nuclear fuel absorbs the neutrons without any
effects. It is good, if the absorbed neutron can generate fission in the
nuclear fuel. Slow neutron can generate fissions; fast neutrons
cannot generate fission in the uranium-235.
o
Good nuclear fuel:
o
Natural uranium, if the moderator is graphite or heavy water
(uranium fuel + graphite moderator + cooling works by nitrogen
or carbon-dioxide gas – gas-graphite nuclear power plants, in
France, England, Russia (Tsernobyl)).
o
Enriched uranium-235, if the moderator and coolant is water
Lecture #5.
Classification of Nuclear Reactors
b)
Intermedier reactors: Most of the fissions occur with neutrons with kinetic
energy fells between 100 eV and thermal energy range
o
Enriched uranium
o
Nuclear fuel rods are set very close to each other  thermalization
of neutrons cannot work on the very short free path
c)
Fast reactors: Most of the fissions occur with neutrons with kinetic energy
range under 100 eV energy range
o
There is a new type nuclear fuel used: 239Pu breeding for reactors
o
Cooling: liquid metals (liquid Sodium, liquid Potassium )
Lecture #5.
Classification of Nuclear Reactors
• Plutonium breeding process for fast reactors:
238
𝑈+𝑛 →
92
239
∗+𝛾
𝑈
92
239𝑈 ∗
92
239
→ 93
𝑁𝑝∗ + 𝛽− + 𝜐෤
239
93
(𝑁𝑝: neptunium)
239
𝑁𝑝∗ → 94
𝑃𝑢∗ + 𝛽− + 𝜐෤
Comment: The * means unstable nucleus, which can
decay easily
Lecture #5.
Classification of Nuclear Reactors
6. According the use/usage of the reactors:
a) Nuclear reactors for producing energy
i.
Light water reactors (LWR)
1. Pressurized water reactors (PWR)
2. Boiling water reactors (BWR)
ii. Heavy water reactors
iii. Graphite-moderated reactors, Reactors with graphite
moderator
b) Breeder reactors
c) Experimental reactors
d) Critical systems or reactors with zero power
e) Training reactors
f) Reactors with high neutron flux
g) Pulsed reactors
Lecture #5.
a) Nuclear reactors for producing energy
•
Definition (nuclear reactors for energy generation):
•
Definition (reactivity in a nuclear status):
This is the metric of the neutron balance in a given reactor state. In other words reactivity is a value shows the
numerical expression of the distance from the critical status of the reactor.
Determinative factors of reactivity:
In general, reactivity decreases during the normal operation of a nuclear reactor. Speed of the decreasing is
determined by:
o
Reactivity depends on the temperature
•
Increasing temperature helps the safety operation of the reactor
•
If the temperature increases in the reactor, than the reactivity decreases.
•
Increasing the reactivity the number of fission decreases.
•
In case of very high medium temperature the operation of the reactor stops itself – physics.
o
Fragments from nuclear fission
•
In order to start a nuclear reactor additional reactivity is needed.
•
In a working nuclear reactor additional reactivity is needed to keep the power level constant (due
to the fragments have relatively high capability for absorbing neutrons from the system)
•
Definition (poisoning of a nuclear reactor):
Accumulation of neutron absorbing nuclear fragments in a nuclear reactor usually calls as
poisoning of nuclear reactor.
135Xe is the most typical nuclear poisoning isotope in a nuclear reactor. Absorbing cross-section of
•
xenon-135 is very high, it means the capability for absorbing neutrons is very high. After stoping the
nuclear reactor, the device an go to „xenon-pit”. If a reactors goes into xenon-pit, it cannot be
restarted. Long time needs to be waited to start the reactor again. „Reactor comes out from xenonpit.”
•
Burn-out effect:
•
Definition (burn-out of a nuclear fuel):
The quantity of the nuclear fuel continuously decreases during the normal operation of a nuclear
reactor. This natural process calls as burn-out of nuclear fuel. During burn-out effect of the nuclear
fuel, the percentage of uranium-235 decreases under a given limit.
•
Speed of burn-out depends on the type of reactor.
•
In breeder reactors the amount of nuclear fuel increases during the normal operation. It would
mean that, reactivity would increase during the operation in breeder reactors. Continually
increasing reactivity can be/must be controlled by use of control rods.
•
It is a type of nuclear reactor. In this reactor the energy generated by nuclear chain reactions is used for
energy production at industrial level.
Lecture #5.
Most types of nuclear reactors used for energy
production (according to moderator mediums)
1.
Lecture #5.
Light Water Reactor – LWR
o
Definition (Light Water Reactor):
This is a nuclear reactor which is mainly used for energy production. In light water reactor
the moderator and the coolant is normal light water.
o
Worldwide there is 438 working reactors. From 438 reactors 347 pieces are light water
reactor.
o
This type has the highest safety
o
8000 operational hours / year (approximately. 333 days)
o
Usage approximately 90%
o
Energy efficiency 25-30%
o
Types of:
•
Pressurized Water Reactor – PWR
(Water medium in the primary water loop system stays under high pressure, it means
the water stays in liquid state in the whole primary water loop. Water vapor
generation is made only in the secondary loop. Water vapor is used to operate
turbines.
o
Water temperature is 300-400 °C in the primary loop;
water is liquid on this temperature due to high pressure
o
Wall thickness of the reactor is very thick (10-20 cm)
o
Water in the secondary loop is warmed/boiled up by heat exchanger
•
Boiling Water reactor – BWR
(it has only one water loop; it means there is no high pressure in the water loop)
o
Water can be boiled up (due to the pressure is not so high)
o
Water vapor generated is driven to the turbines directly
Pressurized Water Reactor scheme - PWR
Source: https://www.clpgroup.com/nuclearenergy/Eng/power/power4_1_2.aspx
Lecture #5.
Boiling Water Reactor - BWR
Lecture #5.
Source: http://www.nrc.gov/reading-rm/basic-ref/students/what-is-nuclear-energy.html
Most types of nuclear reactors used for energy
production (according to moderator mediums)
2.
Heavy Water Reactor (D2O) – CANDU (CANada Deuterium Uranium)
o Reactor chamber holds hundreds of tubes. Fuel rods are installed in these
tubes. Using this technique the fuel rods are available to change them
separately from reactor moderator. Change of uranium rods are easier
process.
o Fuel rods can be moved easily
o Reactor chamber does not holds high pressure. In other words, reactor
chambers does not operate under high pressure. Only tubes are under
high pressure!
o Due to low or lower pressure inside the reactor, processes inside the
reactors can be monitored by sensors easily.
o This type of reactor can work by neutral uranium as well
o This type of reactor needs huge amount of clean heavy water for its
operation, but heavy water is very expensive!
Lecture #5.
Heavy Water Reactor – CANDU
Source: http://www.nuclearfaq.ca/cnf_sectionA.htm
Lecture #5.
Most types of nuclear reactors used for energy
production (according to moderator mediums)
3. Graphite-moderated Reactor
o RBMK - Reaktor Bolsoj Mosnosztyi Kanalnij, jelentése „Canal-type reactor
with high energy output", in Russian language: Реактор Большой
Мощности Канальный
• Very old reactor type, but there is RBMK reactors in operation in the
area of the old Soviet Union.
• Operation of RBMK is same as the operation of the boiling water
reactor, but only the moderator is graphite and not water
• Its huge disadvantage is (against BWR): Runaway of RBMK reactors
can be controlled very hardly. Not easy to control the RBMKs.
• Tsernobyl is/was installed with RBMK type reactors
o Cooling is made by gas flowing gas
Lecture #5.
Graphite moderated RBMK scheme - RBMK
Forrás:
wikipedia
Lecture #5.
Breeder reactors
•
Dual purpose:
o Energy production + fuel production !!!
•
Definition (breeder reactor):
A breeder reactor is a nuclear reactor that generates more fissile
material than it consumes. These devices achieve this because
their neutron economy is high enough to breed more fissile fuel than
they use from fertile material, such as uranium-238 or thorium-232.
Breeders were at first found attractive because their fuel economy
was better than light water reactors, but interest declined after the
1960s as more uranium reserves were found, and new methods
of uranium enrichment reduced fuel costs.
•
It is operated by fast neutrons.
Lecture #5.
Breeder reactors
Lecture #5.
Experimental reactors for scientific purposes
• Definition (experimental reactors):
Nuclear reactor which is used for experiments in Physics, in
Biology and Chemistry for isotope-experiments, material
processing etc.
Nuclear reactor uses high neutron intensity or high neutron flux
for experiments.
• Heat generated cannot be used at the experiments!
• Power of them is in general 10 kW – 50 MW.
• Experimental reactors at KFKI Campus, Budapest, Hungary is
installed.
Lecture #5.
Critical systems
• Definition (critical systems or reactors with zero power):
Nuclear reactors or neutron multiplier systems which are used
in experiments at the field of reactor physics or reactor
technology, we use to call as critical systems or reactors with
zero power.
• Power (heating power) of this type of reactors is very small,
power of the system is equal to several watts only, or nearly
zero.
• During the normal operation of these reactors, there is no
need for any cooling capability.
• During the normal operation of these reactors, there is no
need for any radiation safety. (due to very low power)
• Designing, planning and building new type of nuclear reactor
can be done after running experiments on given type of
critical systems.
• Reactor installed in KFKI Campus, Budapest, Hungary can be
used as a critical system.
Lecture #5.
Training Reactors
• Definition (Training reactor):
The nuclear reactor used for teaching and training reactor
specialists and experts can be called as training reactor.
• There is training reactors in Hungary at the Technical University
Budapest (BME)
• Reactor safety systems on this type of reactor is „stupid-safe”.
It is impossible to destroy the reactor with incorrect operation.
Lecture #5.
Nuclear Reactor with High Neutron Flux
• Definition (nuclear reactor with high neutron flux):
The nuclear reactor, in which the neutron flux is high, very high
or extremely high (huge), we use to call it as nuclear reactor
with high neutron flux.
• Example: ILL – Institute Laue – Langevin, Grenoble, France
o Development of France, England and Germany (cooperation)
o 1971
o Nuclear fuel: enriched 235U. Enriched on 93% of U-235 (!)
(in general enrichment works on 3-4% of U-235 from 0,7%)
o Moderator and coolant: heavy water (D2O: D: deuterium)
o Special fuel rods
o Dimension of reactor zone: 40 cm (diameter) + 80 cm (height)
o Power: 57 MW (heating power)
o Reactor flux: 𝟏, 𝟓 ∙ 𝟏𝟎𝟏𝟓
Lecture #5.
𝒏𝒆𝒖𝒕𝒓𝒐𝒏
𝒄𝒎𝟐 ∙𝒔
(huge!)
Pulsed-reactors
• Definition (pulsed-reactors):
If the nuclear reactor does not generate neutrons
continuously, but it generates neutrons
discontinuously, then we call the reactor as pulsedreactor.
• Example: IBR – Joint Institute for Nuclear Research,
The Frank Laboratory of Neutron Physics, Dubna
o
o
o
o
o
o
The very first pulsed-nuclear reactor on the Earth
The only one pulsed-reactor on the Earth
Since 1960
Amazingly easy operational principle
The reactor is very useful for Physics experiments
Background radiation is much smaller in the break period. It is very
good for time-of-flight (TOF) measurements
Lecture #5.
IBR1 scheme - Dubna
•
•
•
•
•
•
•
•
•
•
•
•
•
Two rotating disks
reflector
Disk contains 235UDuring the rotation of the disks
uranium can move close to the rods
in given time windows.
If the uranium moves close to the
rods, the reactor operates Secondary rotating disk
in supercritical phase.
Moving
nuclear fuel
If the uranium on the disk
moves far away from the stable rods,
the supercritical operation ends.
4-50 pulses per second
Disk: d = 112 cm
f = 3000 1/s
Number of rotations of the secondary disk
can be controlled
Air-cooling
Power level:
in 1960: 6 kW
in 1968-69: 30 kW
peak: 150 MW (during supercritical operation)
Width of one pulse: 50 s
IBR-2 – redesigned and rebuilt version:
Power: 4 MW, in peak: 7700 MW
𝑛𝑒𝑢𝑡𝑟𝑜𝑛
Neutron flux: 1,5 ∙ 1018
2
Lecture #5.
𝑐𝑚 ∙𝑠
active zone
Stable nuclear fuel (not moving!)
Moving nuclear fuel
Main rotating disk
IBR2 scheme - Dubna
Lecture #5.