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ebrh.com Experimental Breeder Reactor-II
Experimental Breeder Reactor-II (EBR-II)is a sodium cooled reactor with a
thermal power rating of 62.5 megawatts (MW), an intermediate closed loop of
secondary sodium, and a steam plant that produces 19 MW of electrical power
through a conventional turbine generator. The original emphasis in the design
and operation of EBR-II was to demonstrate a complete breeder-reactor power
plant with on-site reprocessing of metallic fuel. The demonstration was
successfully carried out from 1964 to 1969. The emphasis was then shifted to
testing fuels and materials for future, larger, liquid metal reactors in the
radiation environment of the EBR-II reactor core. It operated as the Integral
Fast Reactor prototype. Costing more than $32 million, it achieved first
criticality in 1965 and ran for 30 years. It was designed to produce about 62.5
megawatts of heat and 20 megawatts of electricity, which was achieved in
September 1969 and continued for most of its lifetime.
Design
The fuel consists of uranium rods 5 millimeters in diameter and 13 inches long.
Enriched to 67% uranium-235 when fresh, the concentration dropped to
approximately 65% upon removal. The rods also contained 10% zirconium. Each fuel
element is placed inside a thin-walled stainless steel tube along with a small
amount of sodium metal. The tube is welded shut at the top to form a unit 29
inches long. The purpose of the sodium is to function as a heat-transfer agent.
As more and more of the uranium undergoes fission, it develops fissures and the
sodium enters the voids. It extracts an important fission product, cesium-137,
and hence becomes intensely radioactive. The void above the uranium collects
fission gases, mainly krypton-85. Clusters of the pins inside hexagonal
stainless steel jackets 92 inches long are assembled honeycomblike; each unit
has about 10 pounds of uranium. All together, the core contains about 680 pounds
of uranium fuel, and this part is called the driver.
The EBR-II core can accommodate as many as 65 experimental subassemblies for
irradiation and operational reliability tests, fueled with a variety of metallic
and ceramic fuels - the oxides, carbides, or nitrides of uranium and plutonium,
and metallic fuel alloys such as uranium-plutonium-zirconium fuel for the IFR.
Other subassembly positions may contain structural-material experiments.
Safety advantage
The Integral Fast Reactor (IFR) design gains safety advantages through a
combination of metal fuel (an alloy of uranium, plutonium, and zirconium), and
sodium cooling. By providing a fuel which readily conducts heat from the fuel to
the coolant, and which operates at relatively low temperatures, the IFR takes
maximum advantage of expansion of the coolant, fuel, and structure during
off-normal events which increase temperatures. The expansion of the fuel and
structure in an off-normal situation causes the system to shut down even without
human operator intervention. In April of 1986, two special tests were performed
on the EBR-II, in which the main primary cooling pumps were shut off with the
reactor at full power (62.5 megawatts, thermal). By not allowing the normal
shutdown systems to interfere, the reactor power dropped to near zero within
about 300 seconds. No damage to the fuel or the reactor resulted. This test
demonstrated that even with a loss of all electrical power and the capability to
shut down the reactor using the normal systems, the reactor will simply shut
down without danger or damage. The same day, this demonstration was followed by
another important test. With the reactor again at full power, flow in the
secondary cooling system was stopped. This test caused the temperature to
increase, since there was nowhere for the reactor heat to go. As the primary
(reactor) cooling system became hotter, the fuel, sodium coolant, and structure
expanded, and the reactor shut down. This test showed that an IFR type reactor
will shut down using inherent features such as thermal expansion, even if the
ability to remove heat from the primary cooling system is lost.
EBR-II is now defueled. The EBR-II shutdown activity also includes the treatment
of its discharged spent fuel using an electrometallurgical fuel treatment
process in the Fuel Conditioning Facility located next to the EBR-II
The cleanup process for EBR-II includes the removal and processing of the sodium
coolant, cleaning of the EBR-II sodium systems, removal and passivating of other
chemical hazards and placing the deactivated components and structure in a safe
condition.
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