Note: Descriptions are shown in the official language in which they were submitted.
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PRESSURIZED FUEL CHANNEL TYPE NUCLEAR REACTOR
TECHNICAL FIELD OF INVENTION
The present invention relates to nuclear reactors. More specifically, the
present
invention relates to pressurized fuel channel type reactors, for example, the
water-cooled reactors, including pressurized water reactors (PWR) and
pressurized heavy water reactors (PHWR), and, specifically, CANDU reactors for
nuclear power plants.
BACKGROUND OF THE INVENTION AND PRIOR ART
Pressurized fuel channel type reactors are well known. A pressurized fuel
channel type reactor (a reactor in the following text) comprises a group of
fuel
channels. A fuel channel comprises a horizontal or vertical pressure tube
positioned in a moderator and containing fuel assemblies (fuel bundles). The
reactor also comprises a reactor coolant circulation system comprising a group
of
pumps and providing circulation of the reactor coolant through the fuel
channels,
and a fuel handling apparatus (fuelling machine) for insertion of fuel
assemblies
into the pressure tubes and removal of fuel assemblies from the pressure
tubes.
A reactor coolant is usually represented by light water, heavy water (in
latter case
a reactor is also known as a pressurized heavy water reactor (PHWR),
represented by CANDU reactors), but there are many other coolants potentially
available (liquid metal, molten salts, etc.). A reactor coolant circuit
consists of a
reactor, a heat consumer (usually a primary side of boilers in case of nuclear
power plant), and reactor coolant pumps. The reactor coolant is pumped
between fuel elements of fuel assemblies located in the fuel channels
absorbing
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the heat generated by fuel elements and usually through the tube side of
boilers
of the nuclear power plant releasing the heat. The coolant further returns to
the
reactor coolant pump and to the reactor channels. The fuel handling apparatus
(fuelling machine) consists of trolleys, fuelling heads comprising various
mechanical and hydraulic devices to attach the fuelling heads to the both ends
of
the pre-selected pressure tube, remove and re-install the pressure tube plugs,
insert a new fuel assembly into the pressure tube and remove the spent fuel
assembly from another end of the pressure tube, a magazine containing the fuel
assemblies, a heat exchanger and a circulation pump for cooling the removed
fuel assemblies, control and instrumentation.
The pressurized fuel channel type reactors are described in the following
patent
applications or patents granted in Canada:
1066434 Isaac, Peter
2283647 Sollychin, Rayman
The patent No. 2283647 that discloses a pressurized fuel channel type reactor
having fuel channels, containing fuel assemblies (fuel bundles) aligned in
pairs to
reduce a hydraulic resistance of the fuel channel.
The closest prior art is the patent No. 1066434 discloses a pressurized fuel
channel type reactor having horizontally extending fuel channels, a reactor
coolant circulation system, and a fuel handling apparatus (fuelling machine)
for
insertion and removal of fuel assemblies into and from the fuel. The fuel
handling apparatus comprises piston members assisting the process of fuel
removal during on-line refueling.
The prior art does not sufficiently address an issue of on-line refueling that
requires opening both the upstream and the downstream ends of the fuel
channel filled with high temperature reactor coolant being under high pressure
(10 MPa or higher). This operation is performed by a very complex and
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expensive fuelling machine. Any malfunction of the fuelling machine results in
a
forced shut down of the reactor and associated losses in generation in the
range
of $ 1,000,000 per day. There is also a potential for a loss of reactor
coolant in
the form of minor leaks from the connection points or even a complete loss of
the
reactor coolant in case of failure of the fuelling head to re-install
correctly the
pressure tube plug.
In addition, the prior art does not address high operation and maintenance
(O&M) expenses and very high cost of the fuelling machine (fuel handling
apparatus). The fuelling machine maintenance is further complicated by high
radiation fields it is exposed to during on-line refueling thus making all the
parts
of the fuelling machine highly radioactive.
SUMMARY OF THE INVENTION
The present application develops the prior art to simplify the process of
fuelling of
the reactor. A pressurized fuel channel type reactor (a reactor in the
following
text) comprises a group of fuel channels. A fuel channel comprises a
horizontal
or vertical pressure tube positioned in a moderator and containing fuel
assemblies (fuel bundles). The reactor also comprises a reactor coolant
circulation system comprising a group of pumps and providing circulation of
the
reactor coolant through the fuel channels. A reactor coolant can be
represented
by light water or heavy water, but there are many other coolants potentially
available (liquid metal, molten salts, etc.). A reactor coolant circuit
consists of a
reactor, a heat consumer (usually a primary side of boilers in case of nuclear
power plant), and reactor coolant pumps. The reactor coolant is pumped
between fuel elements of fuel assemblies located in the fuel channels
absorbing
the heat generated by fuel elements and usually through the tube side of
boilers
of the nuclear power plant releasing the heat. The coolant further returns to
the
reactor coolant pump and to the reactor channels. Fuel assembly has a
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capability of moving rollably in the pressure tubes and in pipes with the flow
of
the reactor coolant, for example, by having a spherical shape. A fuel assembly
distribution header is connected to the pressure tube inlets and has a
plurality of
hydraulic cylinders controlling movement of fuel assemblies from fuel assembly
distribution header into the pressure tube inlets. Functions of the part of
the
hydraulic cylinders can be performed by nozzles, connected to the source of
the
high-pressure reactor coolant and producing small jets of the reactor coolant
directing each fuel assembly into the predetermined pressure tube. A fuel
assembly collection header is connected to pressure tube outlets and has a
plurality of hydraulic cylinders controlling the movement of fuel assemblies
from
the pressure tube outlets into the fuel assembly distribution header. This
newly
developed reactor completely eliminates the pressure tube plugs (in the range
of
1000 per reactor), fuelling machine trolleys, fuelling heads, thus eliminating
potential leaks of the reactor coolant, simplifying operations, maintenance,
and
greatly reducing the capital and O&M cost of the fuel handling.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of the pressurized fuel channel type
nuclear
reactor having horizontal fuel channels and individual fuel supply and removal
pipes equipped with hydraulic cylinders controlling the movement of the fuel
assemblies according to one embodiment of the present invention and
corresponding to the claims 1, 2, 3, 4, 6, 7.
FIG. 2 is a schematic representation of the pressurized fuel channel type
nuclear
reactor having horizontal fuel channels, a fuel assembly distribution header,
and
a fuel assembly collection header, equipped with hydraulic cylinders
controlling
the movement of the fuel assemblies according to the embodiment of the present
invention and corresponding to the claims 1, 2, 3, 4, 6, 7, 8, and 9.
FIG. 3 is a schematic representation of the pressurized fuel channel type
nuclear
reactor having horizontal fuel channels, a fuel assembly distribution header,
and
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a fuel assembly collection header, equipped with hydraulic cylinders
controlling
the movement of the fuel assemblies according to the embodiment of the present
invention and corresponding to the claims 1, 2, 3, 4, 6, 7, 9, and 10.
FIG. 4 is a schematic representation of a fuel assembly having a capability of
moving rollably in the pressure tubes and in the pipes of the fuel handling
apparatus according to the embodiment of the present invention and
corresponding to the claims 1, 2, 3, 4, and 5. The fuel assembly comprises
cylindrical fuel elements positioned radially within a spherical shell having
a
plurality of holes for circulation of the reactor coolant.
FIG. 5 is a schematic representation of a fuel assembly having a capability of
moving rollably in the pressure tubes and in the pipes of the fuel handling
apparatus according to the embodiment of the present invention and
corresponding to the claims 1, 2, 3, 4, and 5. The fuel assembly comprises
spherical fuel elements positioned within a spherical shell having a plurality
of
holes for circulation of the reactor coolant.
FIG. 6 is a schematic representation of a spherical fuel element.
FIG. 7 is a schematic representation of a part of the fuel assembly
distribution
header with two fuel assemblies shown. The movement of the fuel assemblies
along the header is restricted by stems being a part of the hydraulic cylinder
assembly (not shown).
Parts that are not essential to the invention and well known in power
generation
industry, such as details of the moderator design, end fittings, reactor
coolant
circulation system, boilers, control and instrumentation equipment, etc., are
not
shown.
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DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1 of the drawings, a pressurized fuel channel type reactor
(a
reactor in the following text) comprises a group of fuel channels positioned
in a
moderator 1. A fuel channel comprises a horizontal pressure tube 2 (as shown)
positioned inside the calandria tube 3 providing a thermal insulation layer
between the pressure tube and the moderator. A vertical pressure tube
arrangement is not shown. The pressure tubes contain fuel assemblies (fuel
bundles). The reactor also comprises a reactor coolant circulation system
comprising a group of pumps (not shown) and providing circulation of the
reactor
coolant through the fuel channels. A reactor coolant can be represented by
light
water or heavy water, but there are many other coolants potentially available
(liquid metal, molten salts, etc.). A reactor coolant circuit consists of a
reactor, a
heat consumer (usually a primary side of boilers in case of nuclear power
plant),
and reactor coolant pumps. The reactor coolant is pumped between fuel
elements of fuel assemblies located in the fuel channels absorbing the heat
generated by fuel elements and usually through the tube side of boilers of the
nuclear power plant releasing the heat. The coolant further returns to the
reactor
coolant pump and to the reactor channels.
A hydraulic cylinder is a device comprising a cylindrical hollow body with a
piston.
The piston has an ability to move inside the cylinder along its axis depending
on
a pressure difference applied to the opposite piston surfaces. The stem (rod)
is
attached to the piston in the axial direction and moves with it. The hydraulic
cylinder is attached (welded) to the fuel handling apparatus pipe and,
depending
on its position, either prevents or allows the movement of the fuel assembly
with
the flow of the reactor coolant.
Fuel assembly has a capability of moving rollably in the pressure tubes and in
pipes with the flow of the reactor coolant by having a spherical or close to
spherical shape. Each pressure tube 2 has two connections to the reactor
coolant circulation system. Inlet of the pressure tube 2 is connected to the
pipe
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of the fuel handling apparatus supplying new fuel assemblies 4. The pipe of
the
fuel handling apparatus is connected to the reactor coolant circulation system
having an equal or higher pressure than the pressure of the reactor coolant at
the
inlet of the pressure tube 2 (not shown). The pipe of the fuel handling
apparatus
has two hydraulic cylinders 8, each of them having a piston and attached stem
9
that moves into the pipe of the fuel handling apparatus controlling the
movement
of the fuel assemblies with the flow of the reactor coolant. The piston moves
along the axis inside the cylindrical vessel to and from the pipe of the fuel
handling apparatus depending on the pressure difference on opposite sides of
the piston generated by external source of pressure (not shown). The stem can
be of any form (shape) including being an elongated concave plate having
passages for the reactor coolant (not shown), or having the end of the stem
split
in two rods as shown on Fig. 7.
To remove one used fuel assembly from the pressure tube 2, the stem 9 of the
right (as seen on Fig.1) of two hydraulic cylinders 8, located downstream of
the
outlet of the pressure tube 2, retracts, and the first fuel assembly 4 moves
rollably with the flow from the outlet of the pressure tube 2 and stops when
it
reaches the used fuel storage location outside the reactor (not shown). After
that, the stem 9 returns to previous position (extends into the pipe).
Similarly,
when the stem 9 of the left (as seen on Fig.1) of two hydraulic cylinders 8,
located at the outlet of the pressure tube 2, retracts, all fuel assemblies
positioned upstream of the stem inside the pressure tube 2 move rollably with
the
reactor coolant flow toward the outlet of the pressure tube 2 until the first
of them
reaches the extended stem 9 of the right hydraulic cylinder 8.
To insert one new fuel assembly into the pressure tube 2, the stem 9 of the
lower
(as seen on Fig.1) of two hydraulic cylinders 8, located upstream of the inlet
of
the pressure tube 2, retracts, one new fuel assembly 4 moves rollably with the
flow toward the inlet of the pressure tube 2 and stops when it reaches the
first
(from the left side) fuel assembly positioned in the pressure tube 2. After
that,
the stem 9 returns to previous position (extends into the pipe). Similarly,
when
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the stem 9 of the upper (as seen on Fig.1) of two hydraulic cylinders 8
retracts,
all new fuel assemblies positioned upstream of the stem move rollably with the
reactor coolant flow toward the inlet of the pressure tube 2 until the first
of them
reaches the extended stem 9 of the lower hydraulic cylinder 8.
Referring to FIG. 2 of the drawings, a pressurized fuel channel type reactor
is
provided with a fuel assembly distribution header 10 (a pipe) connected to the
group of the pressure tube 2 inlets and has two hydraulic cylinders 8
controlling a
movement of the fuel assemblies 4 into the fuel assembly distribution header
10,
and a plurality of hydraulic cylinders 8, each of them controlling movement of
fuel
assemblies 4 from fuel assembly distribution header into each pressure tube 2
inlet of the group. When a new fuel assembly 4 is released, it moves with the
flow of the reactor coolant passing all hydraulic cylinders 8 having their
stems 9
retracted until it reaches the hydraulic cylinder having its stem 9 extended
directing the fuel assembly 4 toward the predetermined pressure tube 2. At
that
place, the fuel assembly 4 leaves the fuel assembly distribution header 10 and
moves toward the pressure tube 2 inlet. To ensure that the fuel assembly does
not enter another pressure tube (not predetermined), the fuel assembly
distribution header 10 is slightly curved (not shown). Subsequently, the fuel
assembly moves rollably in the fuel assembly distribution header being in
contact
with the header internal side opposite to the pipe branch leading to the
pressure
tube 2 inlet. This modification requires significantly less hydraulic
cylinders.
The reactor is also provided with a fuel assembly collection header 11 (a
pipe)
connected to the group of the pressure tube outlets. Two hydraulic cylinders 8
control the movement of the fuel assemblies 4 from each of the pressure tubes
2
into the fuel assembly collection header 11.
Referring to FIG. 3 of the drawings, a pressurized fuel channel type reactor
is
provided with a fuel assembly distribution header 10 (a pipe) connected to the
group of the pressure tube inlets and has two hydraulic cylinders 8
controlling a
movement of the fuel assemblies 4 into the fuel assembly distribution header
10,
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and a plurality of hydraulic nozzles 12, each of them controlling movement of
fuel
assemblies 4 from the fuel assembly distribution header 10 into each pressure
tube inlet of the group. Functions of the part of the hydraulic cylinders are
performed by nozzles 12, connected to the source of the high-pressure reactor
coolant and producing small jets of the reactor coolant directing each fuel
assembly into the predetermined pressure tube. When a new fuel assembly 4 is
released, it moves with the flow of the reactor coolant passing all hydraulic
nozzles 12 not producing small jets until it reaches the hydraulic nozzle 12
producing a small jet directing the fuel assembly 4 toward the predetermined
pressure tube 2. At that place, the fuel assembly 4 leaves the fuel assembly
distribution header 10 and moves toward the pressure tube 2 inlet. To ensure
that the fuel assembly does not enter another pressure tube (not
predetermined),
the fuel assembly distribution header 10 is slightly curved (not shown).
Subsequently, the fuel assembly 4 moves rollably in the fuel assembly
distribution header being in contact with the header internal side opposite to
the
pipe branch leading to the pressure tube inlet. This modification requires
significantly less hydraulic cylinders.
Referring to FIG. 4 of the drawings, a fuel assembly has a shell 5 having an
exterior rolling surface by having a circular external axial cross-section and
being
of spherical or close to spherical form. The shell 5 has a plurality of holes
7 for
circulation of the reactor coolant. Fuel elements 6 in the form of rods are
positioned radially in all directions from the centre of the shell 5 (Fig. 4
shows
only the first row of the fuel elements).
Referring to FIG. 5 of the drawings, a fuel assembly has a shell 5 having an
exterior rolling surface. The shell 5 has a plurality of holes 7 for
circulation of the
reactor coolant. Spherical (or quasi-spherical) fuel elements 13 are
positioned in
the internal zone of the shell 5.
Referring to FIG. 6 of the drawings, spherical (or quasi-spherical) fuel
elements
13 comprise a nuclear fuel 14 covered by a metal cladding 15. The cladding 15
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have attached metal pads 16 preventing direct contact between the fuel
elements
and therefore preventing overheating of the fuel elements in the points of
contact.
Referring to FIG. 7 of the drawings, a part of the fuel assembly distribution
header 10 is shown having stems 9 of the hydraulic cylinders 8 preventing the
movement of two fuel assemblies 4 with the flow of the rector coolant. The
stems 9 have the end of each stem split in two rods.
While providing on-power refueling, this newly developed reactor completely
eliminates the pressure tube plugs (in the range of 1000 per reactor),
fuelling
machine trolleys, fuelling ducts, fuelling heads, thus eliminating potential
leaks of
the reactor coolant, reducing the size of the reactor building, simplifying
operations, maintenance, and greatly reducing the capital and O&M cost of the
fuel handling equipment.
Several preferred embodiments of the present invention have been shown and
described. However, it is apparent to those skilled in the art that many
changes
and modifications may be made without departing from the invention as it is
defined in the appended claims.
