Induced nuclear reactions: processes – systems – and elements – Testing – sensing – measuring – or detecting a fission reactor... – Flux monitoring
Reexamination Certificate
2001-03-19
2002-11-05
Behrend, Harvey E. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Testing, sensing, measuring, or detecting a fission reactor...
Flux monitoring
C376S254000, C376S245000, C376S217000
Reexamination Certificate
active
06477219
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention generally relates to a reactor power distribution monitor system which computes a core power distribution on the basis of a core present data of a reactor with the use of a physical model. In particular, the present invention relates to a reactor nuclear instrumentation system which can accurately compute a reactor core power distribution with the use of plurality of fixed type neutron detectors and fixed type &ggr;-ray heat detector means which are arranged in a core axial direction and has high reliability, to a reactor power distribution monitor system including such reactor instrumentation system and to a reactor power distribution monitoring method.
In a reactor, for example, in a boiling water reactor (BWR), a core performance such as a power distribution and a thermal state of a reactor core are monitored by means of a process control computer included in a reactor power distribution monitor system.
In order to monitor the aforesaid reactor power distribution and thermal state, there is a method of computing a core power distribution with the use of reactor core present data measuring means and a physical model (core three-dimensional nuclear hydrothermal computing code) stored in a process control computer on the basis of the measured reactor core present data and confirming whether a maximum linear heat generation ratio (MLHGR) or a minimum critical power ratio (MCPR) satisfies individual predetermined operation limit value. According to such a method, a reactor operation is carried out.
FIG.
26
and
FIG. 27
show a general reactor power distribution monitor system of a boiling water type reactor. In the boiling water type reactor, a reactor pressure vessel
2
is housed in a reactor container
1
, and a reactor core
3
is housed in the reactor pressure vessel
2
. The reactor core
3
is constructed in a manner that a plurality of fuel assemblies
4
and control rods
5
and the like are mounted. An incore nuclear instrumented fuel assembly
6
is located on a position surrounded by the fuel assemblies
4
of the reactor core
3
.
As shown in
FIG. 27
, a corner gap G formed by four fuel assemblies
4
is provided with an incore nuclear instrumented fuel assembly
6
, and a nuclear instrumentation tube
7
is provided with a neutron detector
8
which is dispersively arranged at a plurality of portions in a core axial direction. The neutron detector
8
has a so-called fixed type (stationary or immovable) structure, and in the boiling water reactor, usually, four neutron detectors are dispersively arranged on an effective portion in a fuel axial direction at equal intervals.
Further, the nuclear instrumentation tube
7
is provided with a TIP (Traversing In-Core Probe: movable incore instrumentation) guide tube
9
. One movable neutron detector (TIP)
10
is located so as to be movable in an axial direction. As shown in
FIG. 26
, there is provided a movable type neutron flux measuring system which continuously measures a neutron flux and is movable in an axial direction by means of a retrieval device (selector)
11
, a TIP drive unit
12
, a TIP drive control device and a TIP neutron flux signal processor
13
or the like. A reference numeral
14
denotes a penetration section,
15
denotes a valve mechanism and
16
denotes a shielding container. These neutron detectors
8
and
10
and their control device such as signal processors
13
and
17
(will be described later) are called as a reactor nuclear instrumentation system
24
.
On the other hand, the fixed type (stationary or immovable) neutron detector (LPRM detector)
8
arranged in the reactor core generates an average signal (APRM signal) for each of some divided groups, and then monitors a power level of a power range of the reactor core
3
. Further, the fixed type neutron detector
8
constitutes a reactor safety guard system which rapidly makes a scram-operation with respect to a reactor stop system (not shown) such as a control rod drive mechanism in order to prevent a breakdown of a fuel and a reactor when there occurs an abnormal transient phenomenon or accident such that a neutron flux rapidly increases.
By the way, in the fixed type neutron detector
8
, a change in sensitivity happens in individual detectors by neutron heat. For this reason, in order to compare and correct the sensitivity of each neutron detector
8
every a predetermined period during operation, the TIP (movable neutron detector)
10
is actuated so as to obtain a continuous power distribution in a core axial direction, and the change in sensitivity of each neutron detector
8
is corrected by a gain adjusting function of a power range detector signal processing unit
17
.
A neutron flux signal obtained by the TIP
10
is processed as a neutron flux signal corresponding to a core axial direction position by means of a TIP neutron flux signal processing unit
13
constituting a reactor nuclear instrumentation system
24
. Further, in a reactor power distribution computing device
18
(which is usually built in one or plural of process control computers for monitoring an operation of an atomic power generation plant as a program), the neutron flux signal is read as a reference power distribution when computing a three-dimensional hydrothermal force. The reactor power distribution computing device
18
includes a power distribution computing module
19
, a power distribution learning module
20
and an input-output unit
21
.
Reading a control rod pattern obtained from a present data measuring device
22
which functions as reactor core present data measuring means, a core flow rate, a reactor doom pressure, a reactor heat power obtained from various core present data, and a process data such as a core inlet coolant temperature or the like, these data are processed by means of a present data processing unit
23
, and then, are supplied to the reactor power distribution computing unit
18
. The present data measuring device
22
is actually composed of a plurality of monitor equipments and is shown as one example of a measuring device for simplification although it is generally named as a device for collecting process data of various operation parameters in the reactor as shown in FIG.
26
. Further, the present data processing unit
23
is composed of a process control computer or a part thereof, and a processed core present process data is supplied to the power distribution computing device
18
. The power distribution computing module
19
computes a reactor core power distribution according to the three-dimensional nuclear hydrothermal computing code stored in the process control computer, and then, supplies the computed result to the power distribution learning module
20
. The power distribution learning module learns on the basis of the reference power distribution, and then, correct the computed result, and thus, accurately computes a reactor power distribution in a power distribution predictive computation after that.
In the conventional incore nuclear instrumented fuel assembly
6
, as shown in a perspective view partly in section of
FIG. 28
, a movable type &ggr;-ray detector
10
A may be used in place of the movable neutron detector
10
. The movable type &ggr;-ray detector
10
A is movable in a core axial direction so as to continuously measure a &ggr;-ray flux in the core axial direction. The &ggr;-ray is generated in proportion to a fission rate in the reactor core
3
, and therefore, by measuring a &ggr;-ray flux, it is possible to measure a fission rate in the vicinity of the reactor core.
By using the movable type neutron detector
10
and the movable type &ggr;-ray detector
10
A, it is possible to compare and correct a dispersion on detection accuracy in each of the plurality of neutron detectors
8
arranged in the core axial direction and to continuously measure a power distribution in the core axial direction.
As described above, in the conventional reactor nuclear instrumentation system, continuous measurement of the axial direction
Hirukawa Koji
Naka Takafumi
Sakurai Shungo
Behrend Harvey E.
Matz Daniel
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