Induced nuclear reactions: processes – systems – and elements – With control of reactor – By coolant flow
Reexamination Certificate
2001-02-27
2003-11-04
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
With control of reactor
By coolant flow
C376S211000, C060S660000
Reexamination Certificate
active
06643348
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to steam supply in a nuclear power plant. Steam moves from a nuclear reactor to a steam turbine through a main steam system with main steam isolation valves for isolating the nuclear reactor.
2. Description of the Related Art
Japanese Non-examined Patent Publication No. 9-80195 discloses a steam turbine control device for a nuclear power plant.
FIG. 8
is a basic block diagram of the main steam system and a turbine by-pass system of a nuclear power plant.
Steam generated in a nuclear reactor
1
is supplied to a steam turbine
8
through a main steam system
61
. There are a plurality of, for example ten, main steam isolation valves (MSIV)
2
settled inside and outside of a primary containment vessel (PCV)
3
containing a nuclear reactor
1
, and a main steam header
4
, a main steam stop valve
5
, and a main steam control valve (CV)
6
, in the main steam system
61
.
The main steam isolation valves
2
operate independently from other pressure control valves to isolate the nuclear reactor
1
. The main steam isolation valves
2
are open in the usual state of operation, and close to automatically seal the inside and outside of the primary containment vessel
3
when there is possibility that reactor coolant may flow out of the primary containment vessel
3
. The main steam isolation valves
2
thus close, for example, if an accident internal or external of the primary containment vessel
3
arises.
The main steam stop valve
5
blocks the steam from reaching a steam turbine
8
when suspending the steam turbine
8
. The main steam control valve
6
adjusts the discharge of steam that is generated in the nuclear reactor
1
and that flows into the steam turbine
8
. The steam then rotates the steam turbine
8
, and a generator
9
, directly linked with the steam turbine
8
, generates an electric output A turbine by-pass system
62
, independent of the main steam system
61
, branches from the main steam system
61
at the main steam header
4
and connects to a condenser
10
via the turbine by-pass valve
7
.
A steam system supplies drive steam for a turbine gland steam evaporator
12
, a reactor feed water pump turbine
13
, and a steam jet air ejector
14
, from the main steam system
61
. The turbine gland steam evaporator
12
supplies a little steam to the space of a gland sealing part of the steam turbine
8
, i.e., the boundary portion with the open air, in order to seal the gland part of a turbine
8
. The steam jet air ejector
14
continuously extracts noncondensing gases, such as hydrogen and oxygen, from air in a condenser
10
or in exhaust gas of the steam turbine
8
. The steam jet air ejector performs an action like spraying the steam supplied from the turbine by-pass system
62
and sends the noncondensing gas to an off-gas system and thereby maintains the vacuum of the condenser
10
.
During normal operation, the main steam control valve
6
adjusts the reactor dome pressure, when a reactor dome pressure detector
11
, installed in the nuclear reactor
1
, detects the reactor dome pressure. A turbine by-pass valve
7
is kept completely closed then.
If an accident occurs at a startup or a shutdown of the nuclear power plant, or a electric transmission system, the position of the main steam control valve
6
is restricted, and the turbine by-pass valve
7
adjusts the pressure of the nuclear reactor
1
.
FIG. 9
is a block diagram for explaining the conventional example of the steam turbine control device of the nuclear power plant of FIG.
8
.
The steam turbine control device described below controls the positions of the main steam control valve
6
and the turbine by-pass valve
7
.
A reactor dome pressure signal from the reactor dome pressure detector
11
is inputted into the steam turbine control device
19
and is compared with the pressure setting of the reactor dome pressure setter
23
. A first pressure deviation calculating unit
24
then calculates the pressure deviation. A reactor dome pressure control calculating unit
25
receives the pressure deviation calculated by the first pressure deviation calculating unit
24
and sends a signal proportional to the deviation as a pressure control signal
29
to a first low value selector
18
.
The first low value selector
18
compares the pressure control signal
29
to a speed/load control signal from a speed/load control calculating unit
15
, a load restriction signal of a load limiter
16
, and a maximum discharge restriction signal from a maximum discharge restriction unit
17
. The speed/load control signal from the speed/load control calculating unit
15
controls the speed, i.e., the rotational number of the steam turbine
8
, and the load of the generator
9
, i.e., the electric output. The first low value selector
18
then chooses the lowest value signal among these signals and outputs it as a position demand of the main steam control valve
6
.
Moreover, a first deviation calculating unit
20
generates the deviation signal between the pressure control signal
29
calculated by the reactor dome pressure control calculating unit
25
and the position demand signal to the main steam control valve
6
. A second deviation calculating unit
21
generates the deviation signal between the maximum discharge restriction signal calculated by the maximum discharge restriction unit
17
and the position demand of the main steam control valve
6
. The two deviation signals from the first and second deviation calculating units
20
,
21
are inputted into the second low value selector
22
, which outputs the lower value of the two deviation signals as a position demand signal of the turbine by-pass valve
7
.
In addition, the reactor dome pressure detectors
11
are generally multiplexed to improve reliability, and in
FIG. 9
, a first medium value selector
27
selects a medium value of the triplex reactor dome pressure detectors
11
as a signal to be used for control.
In the conventional steam turbine control device of the nuclear power plant described above, in a usual operating state, the main steam control valve
6
is adjusted, based on the pressure signal from the reactor dome pressure detectors
11
installed in the nuclear reactor
1
, to control and fix the pressure of the nuclear reactor
1
. But in that case, if an accident detected by, for example, a reactor isolation signal detector (not shown) inside or outside of the primary containment vessel
3
occurs, and if the main steam isolation valves
2
are automatically in a fully closed position at the time of the accident, the pressure of the nuclear reactor
1
, i.e., the reactor dome pressure, will rise abruptly.
In this case, the main steam control valve
6
and the turbine by-pass valve
7
open, and the drive steam of the turbine gland steam evaporator
12
, the reactor feed water pump turbine
13
, and the steam jet air ejector
14
decrease abruptly.
FIGS. 10
a
-
10
c
are signal time charts for explaining this situation.
If the main steam isolation valves
2
in
FIG. 8
are fully closed, the pressure signal from the reactor dome pressure detectors
11
installed in the nuclear reactor
1
goes up as shown in
FIG. 10
a
. In
FIG. 10
a
, the ordinate axis shows pressure and the abscissa axis shows time.
Since at that time the pressure deviation which is the output of the first pressure deviation calculating unit
24
of the steam turbine control device
19
rises, the pressure control signal
29
calculated by the reactor dome pressure control calculating unit
25
goes up as shown in
FIG. 10
c
In
FIG. 10
c
, the ordinate axis shows an output of the signal and the abscissa axis shows time. The output of the first low value selector
18
goes up until it is restricted by either the speed/loadcontrol signal, the load restriction signal, or the maximum discharge restriction signal. Then, the main steam control valve
6
will open according to an increase of the pressure control signal
29
.
On the other hand, if the first low value selector
18
Nakajima Masayuki
Yokota Yutaka
Carone Michael J.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Palabrica Rick
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