Induced nuclear reactions: processes – systems – and elements – Reactor structures – Circulating fluid within reactor
Reexamination Certificate
1999-02-26
2001-01-09
Jordan, Charles T. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Reactor structures
Circulating fluid within reactor
C376S373000, C376S352000
Reexamination Certificate
active
06173028
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus or structure for promoting intermixing of heated coolant streams within a upper plenum of a nuclear reactor, which plenum is disposed above a reactor core in which heat exchange takes place between fuel rods and a coolant such as light water and which has high and low temperature regions where the coolant is heated to high and low temperatures, respectively. More particularly, the invention is concerned with a structural configuration and disposition of internal component members disposed within the upper plenum at locations substantially corresponding to an outer periphery of a fuel region.
2. Description of Related Art
In a power reactor, heat generated internally of fuel rods is transferred to a coolant such as light water or the like for utilization as energy. In other words, heat exchange is carried out between the nuclear fuel and the coolant. For a better understanding of the invention, background techniques thereof will be reviewed below.
FIG. 3
of the accompanying drawings shows an internal structure of a pressurized water reactor, a typical nuclear reactor. Referring to the figure, there are accommodated within a nuclear reactor vessel
10
core internals inclusive of nuclear fuel assemblies, control rods, control rod cluster guide tubes, a coolant and others. In general, the nuclear reactor vessel
10
is integrally provided with inlet nozzles
11
and outlet nozzles
12
for the reactor coolant which is light water, wherein 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 is determined in dependence on the output power rating of the reactor. Ordinarily, the number of the inlet nozzles
11
as well as that of the outlet nozzles
12
is in a range of two to four. The inlet nozzles
11
as well as the outlet nozzles
12
are installed in the nuclear reactor vessel in a circumferential direction with predetermined distance therebetween. Disposed within the core barrel
30
at a lower portion thereof are a lower core support plate
32
and a lower core plate
31
, each extending in a horizontal direction. A bottom plenum
41
is defined beneath the lower core support plate
32
.
Mounted on the lower core plate
31
are a large number of fuel assemblies
33
which are disposed adjacent to one another to thereby constitute a reactor core. Further disposed above the fuel assembly
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 displacing 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.
FIG. 4
is a fragmentary enlarged view showing a structure above the fuel assembly
33
. As can be seen in this figure, the upper core plate
21
and the upper core support plate
20
are interconnected by the upper core support columns
23
in order to ensure structurally high strength or robustness. Furthermore, 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 a upper plenum
40
.
Next, description will be directed to the flows or streams of light water employed as the coolant within the nuclear reactor vessel
10
realized in the structure described above. Referring to
FIGS. 3 and 4
, light water of low temperature fed to the nuclear reactor vessel
10
by way of the inlet nozzles
11
follows flow paths of such patterns as indicated by arrows in these figures. 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 flowing direction of the light water is forced to turn upwards within the bottom plenum
41
. Thereafter, 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 deprived of by light water, which results in temperature rise thereof. After passing through the upper core plate
21
, the flowing direction of light water changes to a horizontal or transverse direction, being deflected under the stop action of the upper core support plate
20
. 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
.
At this juncture, it should be mentioned that the reactor core which is constituted by a plurality of fuel assemblies
33
ordinarily undergoes periodical maintenance for fuel exchange such that about one third of the fuel is exchanged at the end of every operation cycle. Consequently, the core is constituted by three groups of fuel assemblies in correspondence to three cycles which differ from one another in respect to the degree of burn-up (hereinafter referred to as the burn-up degree). Thus, the output powers of the fuel assemblies
33
differ from one to another assembly in dependence on the burn-up degrees. Besides, in the core region where the control rods have been loaded for controlling the output power of the reactor as well as in the outer peripheral region of the core where leakage of neutron fluxes externally of the reactor occurs, there prevails neutron flux distribution of low density when compared with that in a center region of the core. As a consequence, power outputted from the outer peripheral portion or region of the reactor core is low when compared with that of the center region of the core.
Such being the circumstances, the flow behavior of light water within the reactor core will now be analyzed in more detail. Under the influence of the different neutron flux distributions within the reactor core such as described above, a stream (indicated by an arrow d in
FIG. 4
) of light water flowing through the center region of the core where the nuclear fission is vigorous is heated up to a relatively high temperature, whereon the light water heated to a high temperature leaves the core to flow into the upper plenum
40
. In succession, high temperature light water flows along and through the control rod cluster guide tubes
22
disposed within the upper plenum
40
to impinge on the lower surface of the upper core support plate
20
, whereby the flowing direction of the light water is deflected so that it flows substantially transversely through the upper plenum
40
. Finally, light water flows out from the reactor through the outlet nozzle
12
, as indicated by arrows e, f and g in FIG.
4
.
On the other hand, a stream (indicated by an arrow a in
FIG. 4
) of light water flowing through the outer per
Ichikawa Toshio
Izumi Hajime
Kurimura Chikara
Matsushima Yoko
Tsutsui Takehiko
Gottlieb Rackman & Reisman P.C.
Jordan Charles T.
Keith Jack
Mitsubishi Heavy Industries Ltd.
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