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INTROUCTION
The development of the nuclear
power industry has been nearly stagnant in the past few decades. In fact there
have been no new nuclear power plant construction in the United States since the
late 1970s. What many thought was a promising technology during the "Cold
War" days of this nation; they now frown upon, despite the fact that nuclear
power currently provides the world with 17% of its energy needs. Nuclear technology's
lack of popularity is not difficult to understand since the fear of it has been
promoted by the entertainment industry, news media, and extremists. There is public
fear because movies portray radiation as the cause of every biological mutation
and now; terrorist threats against nuclear installations have been hypothesized.
Also, the lack of understanding of nuclear science has kept news media and extremists
on the offensive. The accidents at Three Mile Island (TMI) and Chernobyl were
real and their effects were dangerous and, in the latter case, lethal. However,
many prefer to give up the technology rather than learn from these mistakes. Recently,
there has been a resurgence of interest in nuclear power development by several
governments, despite the resistance. The value of nuclear power as an alternative
fuel source is still present and public fears have only served to make the process
of obtaining approval more difficult. This resurgence is due to the real threat
that global warming, caused by the burning of fossil fuels, is destroying the
environment. Moreover, these limited resources are quickly being depleted because
of their increased usage from a growing population. The
estimation is that developing countries will expand their energy consumption to
3.9 times that of today by the mid-21st century and global consumption is expected
to grow by 2.2 times. Development has been slow since deregulation of the power
industry has forced companies to look for short term return, inexpensive solutions
to our energy needs rather than investment in long term return, expensive solutions.
Short-term solutions, such as the burning of natural gas in combined cycle gas
turbines (CCGT), have been the most cost effective but remain resource limited.
Therefore, a few companies and universities, subsidized by governments, are examining
new ways to provide nuclear power. An
acceptable nuclear power solution for energy producers and consumers would depend
upon safety and cost effectiveness. Many solutions have been proposed including
the retrofit of the current light water reactors (LWR). At present, it seems the
most popular solution is a High Temperature Gas Cooled Reactor (HTGR) called the
Pebble Bed Modular Reactor (PBMR). HISTORY
OF PBMR The
history of gas-cooled reactors (GCR) began in November of 1943 with the graphite-moderated,
air-cooled, 3.5-MW, X-10 reactor in Oak Ridge, Tennessee. Gas-cooled reactors
use graphite as a moderator and a circulation of gas as a coolant. A moderator
like graphite is used to slow the prompt neutrons created from the reaction such
that a nuclear reaction can be sustained. Reactors used commercially in the United
States are generally LWRs, which use light water as a moderator and coolant. Development
of the more advanced HTGRs began in the 1950s to improve upon the performance
of the GCRs. HTGRs use helium as a gas coolant to increase operating temperatures.
Initial HTGRs were the Dragon reactor in the U.K., developed in 1959 and almost
simultaneously, the Arbeitsgemeinshaft Versuchsreaktor (AVR) reactor in Germany. Dr
Rudolf Schulten (considered "father" of the pebble bed concept) decided
to do something different for the AVR reactor. His idea was to compact silicon
carbide coated uranium granules into hard billiard-ball-like graphite spheres
(pebbles) and use them as fuel for the helium cooled reactor. The
first HTGR prototype in the United States was the Peach Bottom Unit 1 in the late
1960s. Following the success of these reactors included construction of the Fort
S. Vrain (FSV) in Colorado and the Thorium High Temperature Reactor (THTR-300)
in Germany. These reactors used primary systems enclosed in prestressed concrete
reactor vessels rather than steel vessels of previous designs. The FSV incorporated
ceramic-coated fuel particles imbedded within rods placed in large hexagonal shaped
graphite elements and the THTR-300 used spherical fuel elements (pebble bed).
These test reactors provided valuable information for future design
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