by Jonathan Tennenbaum
(published in The New Citizen, February 2002, reprinted in April 2006 edition.)
At the beginning of 2001, in the
vicinity of China’s capital,
Beijing, a unique nuclear reactor
was put into operation, which is
destined to play a key role in the
development of the Eurasian infrastructure
corridors. This is the
“pebble-bed” high-temperature
reactor (HTR), first developed in
Germany. After decades-long, highly
successful operation of the first
HTR test reactor AVR in Jülich,
and the construction and operation
of a 500MW HTR power plant at
Hamm-Uentrop, this revolutionary
technology became the victim of
the politically manipulated hysteria
against nuclear energy in Germany.
The pebble-bed reactor subsequently
emigrated—exactly like
the German-developed Transrapid—
to China, and also to South
Africa.
In the Institute for Nuclear Energy
Technology (INET) of the Chinese
Tsinghua University, the HTR
was realised in an especially promising
form for worldwide application.
The 10MW Chinese HTR-10
is the prototype of a standardised
modular reactor of approximately
200MW-thermal capacity, which
can be mass-produced at low cost
in the future. On account of its simple
construction and operation, inherent
safety, small unit-size, flexibility,
and ease of maintenance,
this reactor is eminently suited for
use in developing nations.
Apart from China, these advantages
of the HTR have moved the
large South African electric power
company, ESKOM, to launch an
ambitious program for the development
and assembly-line production
of HTR modules. ESCOM
plans, after the success of a first,
prototype project, to produce 30
modules every year: 10 for internal
consumption and 20 for export
(illustrated in Fig. 1).
The elements of a pebble-bed modular reactor—the future in safe, efficient power production.
The Chinese
HTR-10, already in operation, is
supplying important advance data
and practical experience for the
South African program. In the area
of HTR development, a comprehensive
international cooperation
has emerged in recent years, with
the participation of China, South
Africa, Germany, France, Russia,
and the United States.
The core of the HTR-10 consists
of a graphite-lined cylindrical
chamber of 1.8 meters diameter,
filled with 27,000 spherical fuel
elements (“pebbles”), each the size
of a tennis ball. Each fuel “pebble”
contains about 8,300 tiny particles
of enriched uranium, about
the size of a grain of sand, embedded
in a graphite matrix. Each particle
is encased in concentric layers
of a high-temperature ceramic
(silicon carbide) and carbon material.
The idea of such “coated particles”
is that the radioactive substances
which are generated by
nuclear fission reactions, are permanently
trapped within the particles
themselves, and cannot escape
to the environment. The fuel elements
are so constituted, that they
withstand even extreme temperatures—
up to 1,000 degrees Celsius in normal
operation, and even peak temperatures
of 1,600 degrees Celsius in the event of a
failure of the cooling system—
without any considerable quantities
of radioactivity escaping to the
outside. In addition to this, the fuel
pebbles permit a continuous fueling of the reactor. This eliminates
the need to interrupt power
operation for several weeks for fuel
reloading, as is the case with conventional
reactors. In the HTR, fuel
pebbles are continuously fed in
from the top of the reactor, while
old ones are gradually removed
from the core via its funnel-shaped
bottom.
Through the use of ceramic,
“sealed” fuel pebbles, it is possible
to greatly simplify the entire
construction of the reactor, making
it inherently safe under all conditions.
An accident leading to
dangerous escape of radioactivity
to the environment is precluded in
this reactor, because of its special
physical characteristics—above
all, the “trapping” of radioactive
products in the fuel elements up to
high temperatures and the strong
“negative temperature co-efficient,”
which prevents a “runaway”
power increase in the reactor. The HTR does not need the intricate,
expensive safety systems that are
required for conventional nuclear
power plants. Yet, this is only one
of its many advantages.
A decisive breakthrough over
conventional nuclear technology
lies in the fact, that the HTR has a
much higher operating temperature—
900 degrees Celsius, or more. Therefore,
the HTR can not only reach a higher
thermodynamic efficiency in the
generation of electric power, but
can also serve as an economical
source of process heat for various
chemical and other industrial processes.
Among these are the environmentally
friendly generation of
fuels such as hydrogen and methanol
from natural gas; coal gassification;
process steam generation,
metallurgical processes, and so
forth.
Where conventional nuclear
plants are only suited to, and designed
for, delivering electrical power, the HTR can be employed
in many more sectors of the energy
economy, where energy is needed
directly in the form of heat. HTR
process heat can replace a part of
the costly and environmentally
damaging burning of coal, oil, and
natural gas.
Chinese experts have in mind,
among other things, to use HTRs
for generating high-temperature
steam, whose injection underground
can make it possible to exploit
major heavy oil deposits in
the country.
In a first period, the heat generated
from the Chinese prototype
HTR-10 will only be utilised, with
the help of a conventional steam
generator and a turbine, to generate
electrical power. INET plans
later to install a compact helium
turbine in the primary cooling cycle,
in order to explore the possibilities
for a very much simpler, and
at the same time more efficient conversion
of reactor heat into electricity.
There are also various possibilities
for tapping the HTR’s waste
heat. The helium turbine plays a
large role in the plans of the South
Africans, who hope to be able to
produce electricity at the extremely
advantageous cost of about 1.6
U.S. cents per kilowatt-hour.
The majority of the components
of the HTR-10 were produced in
China itself, including the reactor
vessel, steam generator, and the
helium cycle cooling system. Exceptions
are the graphite structures
for neutron moderation in the nuclear
reactor. The special graphite
was imported from Japan; the precision
machining of the material
was done, however, in China.
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