College of Engineering
University of Wisconsin - Madison
University of Wisconsin Nuclear Reactor Tour
The University of Wisconsin Nuclear Reactor (UWNR)
Most nuclear reactors
use the energy (heat) of the fission
fragments to produce steam which is then used to spin a turbine and
produce electricity. The UWNR is a research reactor primarily used to instruct
students, train operators and perform scientific studies using the
in the reactor
core. A major difference between the UWNR and the nuclear power reactors
is the UWNR is not a pressurized system and it does not produce electricity.
It is also about one tenth the size of an average commercial reactor.
The reactor core is covered by water in an open pool. Because our reactor
operates at power levels significantly below that of power producing reactors,
the water does not boil. The reactor core (fuel
elements) resides in a 27 foot deep pool of water. Because of the large
amount of water between the reactor core and the top of the pool and also
because the water serves as a shield against radiation,
personnel can go to the top of the pool during operation of the reactor.
As mentioned before, the radiation coming from the reactor core
is shielded by concrete and water. The shield, which also serves as a vessel
for the pool water, is made of ordinary concrete. The shield ranges from about 18
inches to 8 feet thick from top to bottom. It stands approximately 24 feet tall
from floor level and is shaped roughly octagonally
if viewed from the top.
Reactor Bridge and Core
The core is suspended from an all-aluminum frame which extends from
the grid box at the bottom of the pool to the top of the pool surface. The grid box
at the pool bottom is the structure that holds the individual fuel bundles and shrouds for the control
blades. The reactor bridge (mounted over the pool) supports the core suspension
frame. A locating plate spans the upper end of the suspension frame. It
is bolted to the bridge and aligns the four control blade drive mechanisms
and the transient rod drive with the core in the pool below. A
diffuser pump and jet above the core but within the reactor pool also help
to keep water circulating throughout the reactor pool.
The core elements, such as the fuel and control elements, are supported
and enclosed on four sides by the grid box. The bottom is an aluminum grid
plate spaced to conform with the reactor's fuel bundles. The sides of the grid box help
to maintain a current of cooling water through the core. The grid box does
not rest directly on the bottom of the pool, but is suspended from above.
Four corner posts attached to the lower end of the suspension frame, which
is part of the bridge, support the grid box.
A neutron source is provided to always maintain a neutron population
in the reactor, because in order to start a chain
reaction you need to have neutrons. The neutron source has been
to give an out at least 10 million neutrons per second.
Safety Blade Drives
The first structures noticed at the top of the pool are the control
blade drives. The drive mechanism for the safety blades includes a reversible electric motor. Each blade is
coupled to its mechanism through an electromagnet that allows the blades to undergo a free fall by gravity
when it loses electricity to ensure the reactor turns off, also known as a SCRAM. Instrumentation in the
drive mechanism gives the operator indication of the height of the
drive and therefore the height of the blade and whether or not the drive
is attached to the blade by the magnet. The safety blade drive mechanism operates under a range of only 16 inches.
Transient Rod Drive
The transient rod drive can be used to control the reactor as the safety blade
drives are used. In order to perform certain experiments, a control element which can be quickly
withdrawn from the core is necessary. The transient rod can be
used as such an element. The transient rod has a piston within a cylinder
that is attached to the transient rod by means of a connecting rod. When
the transient rod is ejected from the core, compressed air is to drive the piston upward. As the piston
rises, the air being compressed above the piston is forced out through
vents at the upper end of the cylinder. When the transient rod needs to
be lowered, the compressed air is allowed out of the cylinder and the rod falls back down.
Fission Counter Drive
The fission counter is a nitrogen filled instrument with a
lining. The purpose of the fission counter is to show the number of neutrons
in the core while the reactor is being started. The fission counter counts
the number of fissions
that occur from the neutrons in a shut down or
reactor striking the U-235 in the counter, which gives an idea of how many
neutrons are present in the core.
Power Reactors Work.
the fission process.
Read more about Radiation.
our irradiation experiments.
5. Go to
to the control elements.
7. Go to
to the cooling system.
the reactor sharing program (not part of the virtual tour)
a real tour of the UWNR