ORNL-5388 - the Molten Salt Energy Technologies Web Site

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4.4.2. Pebble-Bed High-Temperature Reactors
A second high-temperature gas-cooled thermal reactor that is a possible candidate
for the denatured 233U fuel cycle is the Pebble-Bed Reactor (PBR). Experience with PBRs
began in Augusta 1966, in JGlich, West Germany, with the criticality of the Arbeitgemeinshaft
Versuch Reaktor (AVR), a 46-MGlt reactor that was developed to gain knowledge and experience
in the construction and operation of a high-temperature helium-cooled reactor fueled with
spherical elements comprised of carbon-coated fuel particles. This experience was intended
to serve as a basis for further development of this concept in West Germany.
of electricity with the AVR began in 1967.
Generation
In addition to generating electric power, the AVR is a test facility for investigat-
ing the behavior of spherical fuel elements. It also is a supplier of high-burnup high-
temperature reactor fuel elements for the West German fuel reprocessing development work.
The continuation of the PBR development initiated by the AVR is represented by the THTR
at Schmehausen, a reactor designed for 750 MWt with a net electrical output of 300 MW.
Startup of the THTR is expected about 1980.
Table 4.4-2. PBR Core Design
Power, Qt 3000 MWt
Power density 5 MW/m3
Heating of he1 ium 25b985 OC
He1 ium i nl et pressure 40 atm
P 1 ant ef f i ci ency , Qe/Qt 0.40
Height of ball fill 550 cm
Radius 589 cm
Ball packing 5394 ball s/m3
Inner fueling zone:
Outer radius
Number of ball flow channels
505 cm
4
Relative residence time 9/9/9/9
Outer fueling zone:
Outer Number rarus
o ball flow channels
Re1 ati ve residence time
Top reflector:
589 cm
1
13
Thickness 200
Graphite density 0.32
Bottom reflector:
Thickness 150
Graphite density 1.60
Radial ref lector:
Thickness 100
Graphite density 1.60
The PBR concept offers favorable
conservation of uranium resources due to
its low fissile inventory requirements and
to the high burnup that is achievable in
PBR elements. This has been demonstrated
by the analysis of several once-through
cycles calculated for the PBR by a physics
design group7 at KFA Julich, West Germany,
and summarized here. The reactor core de-
sign used for the study is described in
Table 4.4-2 Various fuel element types
were considered, differing by the coated
particle types used and by the heavy metal
loading. The basic fuel element design is
shown in Table 4.4-3, the coated particle
designs are described in Table 4.4-4, and
the compositions of the various fuel ele-
ment types are given in Table 4.4-5. The
once-through cycles considered are de-
scribed below, with the core compositions
of each given in Table 4.4-6.
Case 1, LEU, Low-enriched uranium
is loaded into the coated fuel particles.
The radial power profile is flattened by
varying the enrichment in the inner and