JPH03274495A - Local power range monitor - Google Patents

Abstract

PURPOSE:To find out a neutron vibration phenomenon very early and to make it use for keeping stability of a reactor core and a channel by providing a pulse height discriminater, a level setting circuit for pulse height discrimination, and a trip circuit. CONSTITUTION:An electrical signal 3 being input to an LPRM 1 (a local power range monitor) is amplified and then is output as LPRM signal 6a to 6c to the first trip circuit 7, an APRM (an average power range monitor), a pulse height discriminater 11 and a level setting circuit 12 for pulse height discrimination. When a neutron vibration phenomenon occurs, the LPRM signal finally reaches an LPRM high level. The discriminater 11 counts the number of peaks which exceed a counting level before the LPRM high level is reached. The number of the pulses is carried by pulse number signal 14 and sent to the second trip circuit 15. In the circuit 15, a pulse number which is a stanard for judging occurrence of the neutron vibration phenomenon, is stored and is compared with the number sent from the discriminater 11. When the measured pulse number is larger than the standard one, the circuit 15 sends a connection point signal 16 to dispatch an alarm.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention can detect neutron flux oscillation phenomena in a nuclear reactor core at an early stage, and can be used to ensure the stability of the reactor core and channels. This relates to local area monitoring.

(Prior art) The power level of a nuclear reactor core is monitored based on the neutron flux value measured by a neutron detector. A plurality of control rods are arranged while taking into consideration the symmetry of the control rod insertion position. Each neutron detector includes a local power range monitor (hereinafter referred to as rLPRM), and the LPRM outputs an LPRM signal representing a neutron flux value in an analog format.

At this time, the LPR and M signals are assigned one of several levels depending on their magnitude, and the average power range monitor (rAPR
(denoted as MJ). APRM calculates the average mesoton flux value based on each level-divided LPRM signal, and adjusts the gain of the APRM signal that sends the obtained average power of the core metal body to the output monitor panel in the main control room. Output.

In such a neutron flux monitoring system, operators in the central control room mainly monitor whether the APRM signal displayed on the output monitor panel is at an abnormal level, and rarely pay attention to the LPRM signal.

Note that the LPRM normally has a trip circuit into which the LPRM signal is input, and when the LPRM signal in this trip circuit exceeds a set value determined based on the health of the fuel, a contact signal is sent to the central control room to notify that fact. Sent. When the central control room receives this contact signal, it issues an alarm stating that the rLPRM signal is high.

(Problems to be Solved by the Invention) By the way, in a boiling water nuclear power plant, the stability of the core and channels deteriorates in a region of high power, low reactor flow rate, due to core characteristics. For example, when a reactor coolant recirculation pump trips, the core flow rate of coolant locally decreases significantly, and an abnormal neutron flux oscillation phenomenon (the LPRM signal gradually oscillates greatly) occurs. There is.

Appropriate countermeasures must be taken to deal with this, but in conventional systems, the amplitude of the LPRM signal gradually increases and the rLP
The neutron flux oscillation phenomenon cannot be discovered until an alarm indicating "RM signal level is high" is issued or a clear increase in output appears in the APRM signal.

Even if there is a locally large neutron flux value in the LPRM signal, the APRM signal is emitted after being smoothed out with the LPRM signal showing a low neutron flux value elsewhere. Locally occurring neutron oscillation phenomena cannot be captured by the APRM signal until the neutron flux value that gradually increases at that location becomes very large. Therefore, regardless of whether the alarm or the APRM signal is used, it takes time to discover the neutron flux oscillation phenomenon, and there is a possibility that prompt countermeasures cannot be taken.

The present invention was made in view of the above circumstances, and it is an object of the present invention to provide a local power range monitor that can detect neutron flux oscillation phenomena in the reactor core at an early stage and can be used to ensure the stability of the reactor core and channels. shall be.

[Structure of the invention]

(Means for Solving the Problems) The present invention has been made in view of the above circumstances, and includes inputting a local output region signal representing a neutron flux value in a nuclear reactor core and setting a counting level for this local output signal. , a pulse height discriminator that counts the number of peaks in the local output area signal that exceeds this counting level, a pulse height discrimination level setting circuit that outputs the counting level to this pulse height discriminator, and the pulse height discriminator. A local output area monitor comprising a trip circuit into which the number of peaks of the counted local a-power area signal is input and outputs a contact signal to notify the occurrence of a neutron flux oscillation phenomenon when the number of peaks exceeds a predetermined value. I will provide a.

(Function) According to the present invention, the pulse height discrimination level setting circuit sets the analog local a-area signal to the pulse height discriminator at a level lower than the set value at which an alarm to the effect that the rLPRM signal level is high is issued. Set counting level in value. In the pulse height discriminator, the peak of local output region signals that exceed this count level in a certain time width ("
It can also be seen as a "pulse". ) is counted and sent to the trip circuit. In the trip circuit, when a neutron flux oscillation phenomenon occurs and the number of peaks increases, a contact signal is output to notify the occurrence when the number of peaks exceeds a predetermined value.

(Example) The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a local output area monitor (
LPRM) 1 is a configuration diagram. Sensitive part 2 of neutral pre-detector a
is inserted into the core of a nuclear reactor, captures incoming neutrons, and outputs an electrical signal 3 representing the neutron flux density. In addition,
A constant voltage is always applied to the sensitive section 2 from the power source 4 of the LPRM1.

The electrical signal 3 is input to the DC amplifier 5 of the LPRMI,
After being amplified by the DC amplifier 5, the LPRM signals 6a, 6b,
6c and the first trip circuit 7, APR, respectively.
M, a pulse height discriminator 8 and a pulse height discrimination level setting circuit 9.

In the first trip circuit 7, a predetermined value is set for the level of the LPRM signal, and when the LPRM signal 6a exceeds this predetermined value, a contact signal 10 is outputted to the alarm circuit. When the alarm circuit receives this signal,
An alarm indicating "PRM signal level is high" is issued in the central control room.

On the other hand, the LPRM signal 6b is sent to the APRM, where A
It is converted into a PRM signal.

Further, the LPRM signal 6c is input to a pulse height discriminator 11 and a pulse height discrimination level setting circuit 12. The pulse height discrimination level setting circuit 12 averages each fluctuating LPRM signal 6c in a predetermined time width,
The count level is calculated by adding a certain boundary value α to the count level signal 13, and is constantly outputted to the pulse height discriminator 11 as a count level signal 13.

When the pulse height discriminator 11 receives the count level signal, the count level is set as shown in FIG.
LPR exceeding this count level for each LPRM signal
The number of peaks in the M signal 6c is counted.

In FIG. 2, the dashed line 21 is the level at which the contact signal is generated in the first trip circuit 7 (referred to as "OLPRM high level"), and the dashed lines 22 and 23 are the count level and the average value of the LPRM signal, respectively. If you are trying to discover the neutron flux oscillation phenomenon before the alarm that "rLPRM signal level is high" is issued through the first trip circuit 7,
The counting level is lower than the LPRM high level.

When the neutron flux oscillation phenomenon occurs, L
The PRM signal gradually increases in amplitude while swinging up and down, and eventually reaches the LPRM high level.

However, in this embodiment, the LPRM signal is
Before reaching the M high level, the pulse height discriminator 11 counts the number of peaks (pulses) of the LPRM signal that exceed the counting level at regular time intervals.

This number of pulses is then sent on the pulse number signal 14 to the second trip circuit 15 shown in FIG. In the second trip circuit 15, the number of pulses per predetermined time serving as a guide for the occurrence of a neutron flux oscillation phenomenon is stored in advance. compared to numbers. The second trip circuit 13 sends a contact signal 16 to the alarm circuit if the measured number of pulses is greater than the reference number of pulses.

When the alarm circuit receives this contact signal 16, it issues an alarm in the central control room to notify the occurrence of the neutron flux oscillation phenomenon.

Therefore, according to this embodiment, the operator in the central control room is alerted to the LPR by the alarm based on the LPRM signal 6c.
Abnormality of APRM signal where M signal 6b is averaged or LPR
Based on the M signal 6a, it is possible to know the occurrence of a neutron flux oscillation phenomenon before issuing an alarm stating that the rLPRM signal level is high.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to know the occurrence of a neutron flux oscillation phenomenon earlier than by receiving an alarm indicating that the APRM signal is abnormal or the LPRM signal level is high, and to take appropriate countermeasures.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a local output area monitor according to an embodiment of the present invention, and FIG. 2 is a diagram of the LP when a neutron flux oscillation phenomenon occurs.
FIG. 3 is a graph diagram showing an RM signal. 2...Sensitive part of neutron pressure detector, 6a, 6b,
6C... LPRM signal, 11... Pulse height discriminator, 12... Pulse height discrimination level setter, 13...
Counting level signal, 14...Pulse number signal, 15...
Second trip circuit, 16... contact signal.

Claims (1)

[Claims] A pulse height discriminator receives a local power region signal representing the neutron flux value of the reactor core, sets a counting level for this local output signal, and counts the number of peaks in the local power region signal exceeding this counting level. A pulse height discrimination level setting circuit outputs the counting level to this pulse height discriminator, and the number of peaks of the local output area signal counted by the pulse height discriminator is input, and this number of peaks is set to a predetermined value. A local output area monitor equipped with a trip circuit that outputs a contact signal that notifies the occurrence of a neutron flux oscillation phenomenon when the value exceeds the value.