Internal structure of nuclear reactor with coolant flow...

Details Internal structure of nuclear reactor with coolant flow... Internal structure of nuclear reactor with coolant flow...

1999-10-13

2002-09-03

Poon, Peter M. (Department: 3641)

Induced nuclear reactions: processes, systems, and elements

Reactor structures

Circulating fluid within reactor

C376S352000, C376S361000, C376S373000, C376S377000, C376S385000, C376S389000, C376S390000, C376S395000

Reexamination Certificate

active

06445758

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to the shape and disposition of an internal structural member constituting part of an internal structure and disposed within a pressurized water reactor in which heat exchange takes place between heating members and a coolant. More particularly, the invention is concerned with the shape and disposition of coolant flow stabilizing members disposed within an upper plenum in the vicinity of outlet nozzles for stabilizing the coolant flow in regions located close to the outlet nozzles.
2. Description of the Related Art
In a pressurized water reactor for a power plant, light water serving as a coolant is fed to a reactor core to be heated to a high temperature by heat generated through nuclear fission. The heated light water is taken out and supplied to a steam generator for generating steam which is then fed to a steam system provided separately from a core cooling system to be utilized for rotationally driving a steam turbine and a rotor of an electric generator operatively coupled to the turbine to thereby generate electric energy.
For a better understanding of the invention, background techniques thereof will be reviewed below.
FIG. 8
of the accompanying drawings shows an internal structure of a pressurized water reactor typical of nuclear reactors. Referring to the figure, accommodated within a nuclear reactor vessel
10
are reactor core internals, nuclear fuel assemblies, control rods, control rod cluster guide tubes, support members and others. Described in brief, the nuclear reactor vessel
10
is integrally provided with inlet nozzles
11
and outlet nozzles
12
for the reactor coolant which is light water, and a core barrel
30
is suspended vertically within the nuclear reactor vessel
10
. The number of the inlet nozzles
11
and the outlet nozzles
12
, respectively, coincide with the number of coolant circulation loops which in turn depends on the output power rating of the reactor. Ordinarily, the number of the inlet nozzles
11
and outlet nozzles
12
ranges from two to four each.
By way of example, in a power plant with a large power generation capacity, there are ordinarily provided a plurality of coolant circulation loops in consideration of the capacities of pumps and the steam generator employed in the cooling system as well as restrictions imposed with respect to the disposition thereof within a containment vessel. In other words, the a number of coolant circulation loops installed is determined depending on the output capacity. Since a reactor power plant with a large output capacity is provided with four coolant circulation loops, the number of the inlet nozzles
11
and the outlet nozzles
12
is also four, respectively. The inlet nozzles
11
and the outlet nozzles
12
are installed in the nuclear reactor vessel at predetermined intervals in the circumferential direction thereof. Further, a lower core support plate
32
and a lower core plate
31
are horizontally disposed within the core barrel
30
at a lower portion thereof, respectively. A bottom or lower plenum
41
is defined beneath the lower core support plate
32
.
Mounted on the lower core plate
31
are a large number of loaded fuel assemblies
33
which are disposed adjacent to one another to thereby constitute a reactor core. Disposed above the fuel assemblies
33
is an upper core plate
21
which is supported by an upper core support plate
20
by way of upper core support columns
23
. The fuel assemblies
33
are pressed downwards by means of the upper core plate
21
so that the fuel assemblies
33
are prevented from being displaced upwards under the influence of buoyancy exerted by the flowing coolant. A plurality of control rod cluster guide tubes
22
are supported at lower ends thereof on the upper surface of the upper core plate
21
by means of supporting pins or the like (not shown). The control rod cluster guide tubes
22
extend upwardly through and beyond the upper core support plate
20
. By withdrawing the control rod clusters (not shown either) from the reactor core through the medium of the control rod cluster guide tubes
22
or inserting the control rod clusters into the fuel assemblies
33
of the reactor core through the control rod cluster guide tubes
22
, the thermal output of-the reactor core can be adjusted.
The upper core plate
21
and the upper core support plate
20
are interconnected by means of the upper core support columns
23
in order to ensure structurally high strength or robustness. Further, the control rod cluster guide tubes
22
extending through the upper core support plate
20
are fixedly secured to the upper core support plate
20
. Thus, the control rod cluster guide tubes
22
are protected against displacement or dislocation in a lateral or transverse direction. Defined between the upper core plate
21
and the upper core support plate
20
interconnected as mentioned above is an upper plenum
40
.
Next, description will be directed to the flow or streams of light water employed as the coolant within the nuclear reactor vessel
10
realized in the structure described above. Referring to
FIG. 8
, light water of low temperature fed to the nuclear reactor vessel
10
by way of the inlet nozzles
11
flows as indicated by the arrows in FIG.
8
. More specifically, light water fed to the nuclear reactor vessel
10
through the inlet nozzle
11
flows at first downwardly through an annular space defined between the outer surface of the core barrel
30
and the inner wall of the nuclear reactor vessel
10
. The light water is forced to turn upwards within the lower plenum
41
. Thereafter, the light water flows into the reactor core after passing through the lower core support plate
32
and the lower core plate
31
. Within the reactor core, light water flows upwardly substantially in parallel. In the course of flowing through the reactor core, heat generated by the fuel rods of the fuel assemblies is absorbed by the light water, which results in a temperature increase thereof. After passing through the upper core plate
21
, the flowing direction of light water changes to a horizontal or transverse direction. Finally, light water leaves the nuclear reactor vessel
10
through the outlet nozzle
12
to be supplied to a steam generator (not shown) by way of an outlet pipe
42
.
More specifically, within the upper plenum
40
defined above the upper core plate
21
, light water flows radially outward from a central region of the core to reach the inner wall of the core barrel
30
whereupon the light water flows toward the outlet nozzle
12
along the inner wall of the core barrel
30
in a space surrounding the outer periphery of the core. A portion of the light water flows in one direction along the inner wall of the core barrel
30
while another portion of the light water flows in the other direction opposite to the previous direction along the inner wall of the core barrel
30
. Thus, in a space located within the upper plenum near but bellow the outlet nozzle
12
, between the streams of light water flowing in opposite directions collide. After the collision, the flow directions of the light water are changed so as to flow upward toward the outlet nozzle
12
. Such being the case, the flow of light water in the space located in the vicinity of the outlet nozzle
12
is made unstable due to the above mentioned collision as well as occurrence of turbulence such as swirls or vortexes.
Also, the nuclear reactor vessel
10
of the four-loop reactor plant mentioned previously is implemented in a structure such that two outlet nozzles
12
are disposed adjacent to each other because of the restrictions imposed in view of the requirement for realizing the structure of the primary coolant loop and the reactor containment vessel in a reduced size and the like, as can be seen in
FIGS. 9 and 10
of the accompanying drawings. Consequently, some of the light water flowing along the inner wall of the core barrel
30
tends to flow transversely beneath the o

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