NUCLEAR REACTORS
G. HETSRONI
Emeritus Danciger Professor of Engineering
Technion – Haifa – Israel
Contents
1. History
2. Fission
3. Nuclear reactor basics
4. Classifications
5. Current technologies
coal
‫גזי שריפה‬
‫ארובה‬
‫טורבינה‬
‫גנראטור‬
‫קיטור‬
‫קיטור מוחלש‬
‫פחם‬
‫מים‬
‫אויר‬
‫חשמל‬
‫מעבה‬
‫דוד‬
Enrico Fermi
Otto Hahn
Lise Meitner
Fritz Strassmann
Nuclear fission was first experimentally achieved by Enrico Fermi in 1934 when his
team bombarded uranium with neutrons. In 1938, German chemists Otto Hahn and
Fritz Strassmann, along with Austrian physicists Lise Meitner and Meitner's nephew,
Otto Robert Frisch, conducted experiments with the products of neutron-bombarded
uranium. They determined that the relatively tiny neutron split the nucleus of the
massive uranium atoms into two roughly equal pieces. Leo Szilard recognized that if
fission reactions released additional neutrons, a self-sustaining nuclear chain reaction
could result. In the United States, where Fermi and Szilard had both emigrated, this led
to the creation of the first man-made reactor, known as Chicago Pile-1, which achieved
criticality on December 2, 1942. This work became part of the Manhattan Project.
NUCLEAR CHAIN REACTION
When a relatively large fissile atomic nucleus (usually uranium-235 or
plutonium-239) absorbs a neutron it is likely to undergo nuclear fission. The
original heavy nucleus splits into two or more lighter nuclei also releasing kinetic
energy, gamma radiation and free neutrons; collectively known as fission products.
A portion of these neutrons may later be absorbed by other fissile atoms and trigger
further fission events, which release more neutrons, and so on.
The nuclear chain reaction can be controlled by using neutron poisons and
neutron moderators to change the portion of neutrons that will go on to cause more
fissions. In nuclear engineering, a neutron moderator is a medium which reduces
the velocity of fast neutrons, thereby turning them into thermal neutrons capable of
sustaining a nuclear chain reaction involving uranium-235.
Nuclear reactor principle
As of 2005, nuclear power provided 6.3% of the world's energy and 15% of the
world's electricity. As of 2007, there are 439 nuclear power reactors in operation
in the world, operating in 31 countries. In 2007, nuclear´s share of global
electricity generation dropped to 14%, because of earthquake in western Japan
on 16 July 2007. The United States produces the most nuclear energy, with
nuclear power providing 19% of the electricity it consumes, while France
produces the highest percentage of its electrical energy from nuclear reactors—
78% as of 2006. In the European Union as a whole, nuclear energy provides 30%
of the electricity.
CLASSIFICATIONS BY TYPE
Boiling water reactor (BWR) is the simplest of all facilities.
Water absorbs heat from the reactions in the core and is
directly driven to the turbines. After condensing the water
is pumped back to the reactor core.
CLASSIFICATIONS BY TYPE
Pressurized water reactor (PWR) uses a sealed system to prevent
water circulating through the core from boiling due to high
pressure. The heat from this system is removed by the water in
pipes to the steam generator.
CLASSIFICATIONS BY TYPE
Gas cooled reactor (GCR) uses CO2 gas to remove heat from the
core. This is then piped through the steam generator where heat
is removed from the gas and it can then be recirculated to the
reactor. As usual steam generated is used to drive the turbine and
generate electricity, condensed then recirculated. Graphite is
used as a moderator to allow energy production by un-enriched
uranium.
BASIC PWR - STEAM CYCLE
I. Primary circuit
II. Secondary circuit
III. Tertiary circuit
A. Reactor
B. Steam generator
C. Turbine
D. Condenser
PWR in Operation
A Primary circuit
B. Secondary circuit
C. Tertiary circuit
1. Reactor
2. Fuel assemblies
3. Control rods
4. Pressurizer
5. Steam generator
6. Primary pump
7. Feedwater primary circuit
8. Feedwater secondary
circuit
9. Steam secondary circuit
10. High pressure turbine
11. Low pressure turbine
12. Condenser
13. Feedwater pump
14. Generator
15. Exciter
16. Transformer
17. High voltage line
18. River
19. Intake cooling water
20. Cold cooling water
21. Warm cooling water
22. Cooling water
23. Upward airflow
24. Steam
25. Outlet cooling water
Diagram of the reactor
REACTOR COOLANT SYSTEM PHYSICAL ARRANGEMENT
The PWR reactor coolant system (RCS) circulates water in a closed cycle, removing
heat from the reactor core and internals and transferring it to a secondary (steam
generating) system. The steam generators provide the interface between the reactor
coolant (primary) system and the main steam (secondary) system. The steam
generators are vertical U-tube heat exchangers with an integral economizer in with
heat is transferred from the reactor coolant to the main steam system. Reactor coolant
is prevented from mixing with the secondary steam by the steam generator tubes and
the steam generator tube sheet, making the RCS a closed system thus forming a
barrier to the release of radioactive materials from the core of the reactor to the
containment building.
Reactor Vessel Assembly Arrangement
Fuel assembly
STEAM GENERATOR
Nuclear Steam Supply System (NSSS) of KNSP uses two steam generators for
transfer of heat from the RCS to the main steam system, One steam generator is
located in each loop. PWR, inverted U-tube steam generator with an integral
economizer which operates with the reactor coolant on the tube side and secondary
coolant on the shell side.
HEAT EXCHANGER
This is a heat exchanger in
which two water circuits meet
each other: hot water under
extremely high pressure in the
primary circuit leaves the
reactor and flows through
thousands of U-shaped heat
conducting tubes.
STEAM TURBINE
Steam turbine consists of a
series of blades mounted on a
shaft. As the steam jet is
inflected, it puts pressure on
these blades, making the shaft
rotate.
Generator
Condenser and cooling towers
CLASSIFICATIONS BY TYPE
Electricity
Nuclear power plants
CANDU at Qinshan