Post on 08-Jul-2015
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Gas-cooled reactors
By-
Dinesh Chandra Pant
M140207ME
Why gas cooled reactor ?
Single phase behavior.
Optical transparency and electrically non-conducting.
Low power density.
Types of gas cooled reactor
CO2 cooled
reactor
Helium cooled
reactor
Magnox UNGG
GCFR GT-MHR HTGCR AGR
Magnox
Features
Pressurized, CO2 cooled
Graphite moderated
Using natural uranium
MAGNOX alloy for cladding
Boron-steel control rods
Magnox is short for Magnesium non-oxidizing – an alloy used to
clad the fuel rods(covering to contain fission products) inside the
reactor
• This material has the advantage of a low neutron capture cross-
section
• Two major features of MAGNOX:
1. Limits the maximum temperature, and hence the thermal efficiency
2. Reacts with water, preventing long-term storage of spent fuel under
water
• MAGNOX Reactors used as
1. Power plant
2. Producer of Plutonium for nuclear weapons
UNGG (Uranium Natural Graphite Gas)(France)
• UNGG used a horizontal fuel rod orientation
• Requires heavily shielded facilities
Features
Graphite moderated
Cooled by CO2
Fueled with natural uranium metal
Cladding material- Magnesium-zirconium alloy
Later,
• Magnox was replaced by the Advanced Gas-Cooled reactor
(AGR) (an improved Generation II gas cooled reactors)
• And UNGG was replaced by the pressurized water reactor
(PWR)
Thermal, Hydraulic, Neutronic and
Material Considerations-
Mass flow rate of coolant gas.
Pumping power requirement of coolant.
Heat transfer performance of coolant.
Heat transfer area.
Neutronic considerations.
Material/chemical considerations.
Gas-cooled fast reactor
• Helium-cooled system
• Using a direct Brayton cycle gas turbine
• Produce electricity, while at the same time; producing (breeding)
new nuclear fuel.
• Fast-neutron spectrum.
Features
Gas turbine modular helium reactor
Features
Helium as a coolant.
Graphite is used as a moderator.
Cross vessel.
The reactor and power conversion systems are located in a
below grade concrete silo.
It gives an efficiency up to 48% - higher than any other reactor.
Very high temperature reactor
High temperature gas cooled reactor
There are two main types of HTGRs:
1. Pebble bed reactors (PBR)
2. Prismatic block reactors (PMR)
• Uses a graphite-moderated nuclear reactor
• The high temperatures enable applications such as process heat
or hydrogen production via the thermo-chemical sulfur-iodine
cycle.
• The prismatic block reactor refers to a prismatic block core
configuration, in which hexagonal graphite blocks are stacked to
fit in a cylindrical pressure vessel
Pebble bed reactorGraphite-moderated
Gas-cooled
Type of (VHTR)
Contain about 15000
TRISO particles
Each has a mass of
210g, of which 9g is
uranium
Figure : Pebble Bed TRISO Fuel Sphere Cross Section
Advanced gas-cooled reactor(Second generation of British gas-cooled reactors) 1. Charge tubes
2. Control rods
3. Graphite moderator
4. Fuel assemblies
5. Concrete pressure
vessel and radiation
shielding
6. Gas circulator
7. Water
8. Water circulator
9. Heat exchanger
10. Steam
Developed from the MAGNOX reactor
Coolant outlet temperature 650 0C
High thermal efficiency – 42%
Requiring stainless steel fuel cladding
The fuel is uranium dioxide pellets, enriched to 2.5-3.5%, in
stainless steel tubes.
Good quality superheated (and reheated) steam (comparable to
quality from a highly optimised coal plant)
References
en.wikipedia.org/wiki/Gas-cooled reactor
Malcolm P. LaBar General Atomics3550 General Atomics Court San Diego, CA 92121-1122