JPS6134498A - Detecting system of damage of fuel and position of damage offuel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to fuel failure and fuel failure location detection systems.

[Background of the invention]

) In IJ-cooled fast breeder reactors, various in-core abnormality monitoring/abnormality diagnosis systems are installed for early abnormality detection and early abnormality diagnosis, from the perspective of preventing serious accidents caused by abnormalities occurring in the reactor core. ing. The following devices are considered to be used in actual equipment: (1) assembly outlet temperature meter, (2) assembly outlet flow meter, (8) fuel failure detector, (4) fuel failure position detector, and (5) acoustic detection. vessel, (6) reaction meter, (7)
Such as sodium fluoroscopy equipment.

Among these, those using an assembly outlet thermometer and an assembly outlet flow meter are installed in the upper core mechanism as shown in FIG. That is, as shown in the figure, at a position approximately 50 wm away from subassembly 1 at the core outlet,
A flow guide 2 corresponding to each subassembly 1 is installed, and a thermometer 3 and a flow meter 4 are inserted into the flow guide 2. Two thermometers 3 are installed in each assembly 1, and one flowmeter 4 is installed in each area where the fuel assembly is divided into several areas, to monitor temperature rises and flow rate abnormalities associated with various accident events. . In addition, if the fuel bundle 5 floats up, the floating fuel nodule 5 may hit the flow guide 2 when rotating the rotary plug during fuel exchange, causing rotation failure. In order to monitor the floating of the fuel bundle 5 before rotating the plug, it is considered to install an IJum fluoroscopy device on the vertical plate.

FIG. 3 shows a conventional example of a fuel damage/fuel damage position detection system. When fuel failure occurs in the reactor core 6, fission products leak into the IJium 7, and a portion is released as a gas into the cover gas 8. The fission products in the sodium 7 are transported through the core outlet pipe 9 together with the sodium 7, but a detector 10 attached to the core outlet pipe 9 detects late emission from the fission products. Detects fuel damage by detecting neutrons. This method is called the delayed neutron method. On the other hand, the gaseous fission products released into the cover gas 8 are sampled through the sampling pipe 11, and the vapor trap 12 produces sodium mist and
After removing the steam, it is transported to the cover gas detection system (fuel damage detector) 15. The cover gas detection system 15 detects fuel damage using two detectors: a precivitator 13 for detecting a minute amount and an N, I detector 14 for detecting a relatively large amount of fission products. Further, the fuel damage position detection system 16 employs the low-degree gas method.

In this method, tracers X, , with different composition ratios are sealed in each fuel bottle, and what is released into the cover gas 8 due to fuel failure is sampled.
By measuring the concentration (0.1 to several PPb) of υ, the location of fuel damage can be detected from its composition ratio. That is, the sampled gas is cooled and adsorbed in the recovery section 17, de-Ared in the concentration section 18, and further desorbed with X, . Each of these stages is controlled by a system controller '-20, and the delayed neutron system 22, cover gas detection system 15, and fuel failure position detection system 16 are connected to a computer 21, respectively. In the figure, 23 is a rotating plug, 24 is a reactor vessel, and 25 is a coolant inlet pipe.

In addition, acoustic detectors can be used to detect local boiling sounds caused by flow channel blockages (in combination with flow meters) and as loose parts monitors.

As described above, in the current design, various types of in-core abnormality monitoring/diagnosis systems are installed from the viewpoint of safety design.

However, various measures are being considered to make fast breeder reactors competitive with light water reactors on a commercial basis. One of these is the need to reduce and eliminate excessive safety equipment.
There is a need for a system that has the same level of reliability or higher than the current system for the in-core abnormality monitoring/abnormality diagnosis system, and is low cost and easy to configure (easy maintenance). The same goes for the fuel damage location detection system.
= Also, when detecting the fuel damage location using the conventional tag gas method,
It is difficult to detect the location of fuel damage by analysis of , , , , especially when fuel damage occurs in two or more locations at the same time. It took about 2 hours for #1 to complete the analysis. □ [Object of the Invention] The present invention has been made in view of the above points, and provides a fuel damage and fuel damage position detection system that can easily detect fuel damage and its location and improve detection reliability. The purpose is to provide

[Summary of the invention]

That is, the present invention provides an in-core abnormality detection system having a temperature detecting means for detecting the temperature of each subassembly at the core exit and an ultrasonic wave transmitting/receiving means for transmitting and receiving ultrasonic waves. An end plug is provided, and the propagation time of the ultrasonic wave between the ultrasonic transmitting/receiving means and the upper end plug, the amplitude intensity, and the sound velocity corrected by the temperature detected by the temperature detecting means are used to detect air bubbles due to fuel damage. The present invention is characterized by detecting the presence or absence and location of fuel damage from the change in the sound speed caused by the generation of bubbles. will be detected.

We considered how we could achieve our desired objectives. It is sufficient to be able to measure temperature and ultrasonic waves in each subcannel, but information on flow velocity is also required as described above for core exit instrumentation. However, as shown in Figure 2 above, the space for installing the sensor is limited, and the number of signal lines increases when measuring these three types of information individually. A multi-functional sensor that can measure three types of information will simplify the plant (cost reduction).
desirable from this point of view. As a prior art related to such a multifunctional sensor, Japanese Patent Laid-Open No. 59-37495 discloses a structure as shown in FIG. 4.

This is because, as shown in the figure, when the primary coil 26 is excited, an eddy current is generated.
6 and detected by an fc secondary coil 27. The waveform of this detected eddy current is f, )'J wa. Like-
electric body. flows. , c vary depending on the temperature and flow velocity, so by extracting the component in which the AC component is superimposed on the DC component of the signal from the two gray coils 27, and taking the two sum signals and the difference signal, each Temperature and flow velocity are determined. Furthermore, the magnetic field generated by exciting the primary coil 26 causes the magnetostrictive vibrator (for example, nickel) to vibrate and transmit ultrasonic waves. The reflected wave is received by the magnetostrictive vibrator 28, and the primary coil 26
Detect with. A permanent magnet 29 in the center of the shaft is installed to improve the ultrasonic transmission and reception sensitivity. By the way, although this prior art shows that it is possible to detect fuel bundle floating using acoustic means, it is not recognized that fuel damage detection and fuel damage location detection using acoustic methods is possible. do not have. Therefore, in the present invention, such a sensor is used for the temperature detection means and the ultrasonic wave transmission/reception means. It has been confirmed that the intended purpose can be achieved using such a multifunctional sensor.

[Embodiments of the Invention] Hereinafter, the present invention will be explained based on illustrated embodiments. FIG. 1 shows an embodiment of the invention. The same parts as before are given the same reference numerals, so explanations will be omitted. In this embodiment, an upper end plug 3° having a reflective surface is provided at the top of the fuel in each subassembly 1, and an ultrasonic wave between the ultrasonic transmitting/receiving means (for example, the multifunctional sensor 31 as described above) and the upper end plug 3o is provided. Sound wave propagation time, amplitude intensity and temperature detection means (
Using the sound speed corrected with the temperature detected by the multifunctional sensor 31) described above, the presence or absence and location of fuel damage is detected from the change in sound speed due to the generation of bubbles due to fuel damage. By doing this, the existence and location of fuel damage can be detected from the change in sound speed due to the generation of bubbles due to fuel damage, making it easy to detect fuel damage and the location of damage, and increasing the reliability of detection. An improved fuel damage and fuel damage location detection system can be obtained.

That is, a multifunctional sensor 31 capable of measuring temperature, flow velocity, and ultrasonic waves is installed inside each flow guide 2 corresponding to each subassembly 1 at the core outlet. The ultrasonic waves were transmitted downward through the multifunctional sensor 31, and the reflected waves from the upper surface of the upper end plug 3o provided at the upper part of the fuel bundle 5 in the subassembly 1 were received by the multifunctional sensor 31 again.

Then, at a certain arbitrary time t detected by the multifunctional sensor 31
Temperature signal Tt(t
), ultrasonic propagation time τ1(t), reflected wave amplitude intensity P
+(t) was used to detect damage and location of multiple fuels based on these three types of information.

In the figure, 32 is a control rod guide tube. By doing this, it becomes possible to obtain a fuel damage and fuel damage location detection system that can easily detect fuel damage and damage location and improve detection reliability. I will explain.

The speed of sound in a medium (1 m/s) can be expressed by the following equation.

v=, redundancy 5 ・・・・・・・・・(1) Here K
is the bulk modulus (N7m”), and ρ is the density of the medium (Kf/
m3). From equation (1), the sound speed V changes with the density ρ, and the density ρ changes with the temperature, so the sound speed V in the medium is a function of the temperature of the medium. Therefore, the speed of sound v(t) at a certain time t needs to be corrected based on the temperature. The change in sound speed due to temperature in sodium has been determined experimentally.
V) la””2577 0.5238 'TNa
This relationship is expressed as (2), where the vertical axis represents the speed of sound in sodium (m/S), and the horizontal axis represents the sodium temperature (tll). It is also shown in FIG. 5, where the change in is shown.

When the propagation time τ'I' (t, ) of the ultrasonic wave at the distance t between the multifunctional sensor 31 and the upper end plug 30 is calculated using the sound velocity V Na corrected at this temperature, τ< (t
)=2 t/ VN-(t) −・”・・・(
8). Therefore, the temperature signal Tt (t) is converted by the temperature-propagation time converter 33 into the ultrasonic propagation time τ'+(t) by calculating equations (2) and (8), and is input to the subtracter 34. Ru. The subtracter 34 calculates the difference (Δτ(t
)=τl (t)−τ′I(t)). This relationship is also shown in FIG. 6, where the amplitude of the reflected ultrasonic wave is plotted on the vertical axis and the propagation time is plotted on the horizontal axis, showing the change characteristics of the amplitude of the reflected ultrasonic wave depending on the propagation time.

Note that the dotted line in the figure is the calculated value. In the performance section 35, Δτ, (t
) After taking the absolute value of ), the comparator 36 calculates the set tolerance E1.
If it is within E1, a signal 81 indicating no abnormality is issued.
If E1 or higher, an abnormality signal is issued, but let us consider a case where a fuel failure accident occurs in the first subassembly 1.

When a fuel failure occurs, the gas enclosed within the fuel pin leaks into the sodium and flows upwardly within the subassembly 1 together with the sodium. When bubbles exist in the liquid, the sound speed decreases, so the propagation time difference signal Δτ+(i) becomes positive, and the set tolerance El becomes larger, so the comparator 36 activates the abnormality diagnosis circuit 37, and the signal becomes The signal is input to the calculation unit 38. The calculation unit 38 calculates the propagation time τI(1
) to find the change in sound speed, calculate the void ratio, and estimate the scale of fuel damage. By the way, since one multifunction sensor 31 is installed in each subassembly 1, it is possible to detect the presence or absence of fuel damage, the scale of the damage, and the location of the damage at the same time. An alarm signal S2 is generated when the fuel is damaged, and the location and scale of the damage are simultaneously recorded in the recorder 39. Arithmetic unit 38
The calculation will be specifically explained below.

As shown in equation (1), the sound velocity in a liquid is based on the relationship between the bulk modulus and the density ρ, and ρ changes from 9 to 9 depending on the presence or absence of bubbles. The bulk modulus of the liquid is Kl, and the density is ρ1.
If the bulk elastic modulus of the gas is 2° and the density is ρ2, then
In the bulk modulus of the synthesized medium, the density ρ can be expressed as a function of the void ratio γ by the following equations.

1 1-γ γ 1=□+-・・・・・・・・・(4) Km KI Km ρ=(1-γ)ρ1 + r・ρ2 ・・・・・・
...(5) (4), By substituting equation (5) into equation (1), the speed of sound V can be found as follows.

(6) Assuming that the gas sealed in the fuel pin is A, find the effect of bubbles on the sound velocity in sodium.

In the case of gas, the bulk modulus can be expressed as follows.

K-γ1・Pa・・・・・・・・・
・(7) Here, γ is the specific heat ratio (= constant pressure specific heat/constant volume specific heat)
, po is static pressure (dyn/cm2). # A for Su,
Then, γ, = 1.7. Since ρAy = 0.4877TC', 'll (g/crr1''), under the conditions of temperature = 500U and pressure = 1.0'1X10'(N/m''),l'
A y =6.3X10-4 (g/cm3) = 0
．． 63 (klI/m”), KA, = 1.72X
10' (N/m2). On the other hand, for sodium, under the same conditions, pH = 830 (kg7 = 3) *K
M,: 5.65 x 10'(N/m"). Therefore, Kl" =? J-, Km = Nim1
By substituting ρl = ρl'l a 1 ρ2 = ρm 1 into equation (6), the sound speed V can be found.

As can be seen from equation (6), the sound velocity V is a quadratic function of the void ratio γ ($J) and has an extreme value at the point dv/dr=Q, and the value of the void ratio γ in that case is given by the following equation. It will be done.

r=-H+! Q-m) 2 Klp, °-°--(8) Therefore, the sound velocity V is at its minimum value at the point where γ is approximately 0.5.If the liquid is sodium and the gas is argon, then v j, II
= 28.7 (m/S).

In FIG. 7, the vertical axis shows the sound speed in sodium, and the horizontal axis shows the void ratio, and shows changes in the sound speed in sodium depending on the void ratio. As is clear from the figure, the sound velocity in sodium decreases as the void ratio increases, and is lowest when the void ratio is 0.5. FIG. 8, like FIG. 7, shows the change characteristics of the sound velocity in sodium depending on the void ratio, but shows an enlarged region where the void ratio is relatively small. As is clear from the figure, the sound velocity V is drastically reduced due to the presence of voids, so even if a minute fuel damage occurs, it can be sufficiently detected.

On the other hand, if the scale of fuel damage is relatively large, large bubbles will occur, and the ultrasonic waves will be diffusely reflected at the interface between the bubbles and the sodium, and may not be reflected back to the multifunctional sensor. However, it must be possible to detect fuel damage and the location of the damage.

For this reason, the amplitude intensity signal P+(t) of the reflected wave is used as shown in FIG. 1 mentioned above. In other words, the input amplitude strength signal P+(t) is used by a subtracter 40 to obtain a difference signal between Δ and the amplitude strength signal pt(t−Δt) of the previous data, and is compared with a set value E2 by a comparator 41. .

If the deviation is larger than the allowable deviation, it is recorded in the recorder 42 and an alarm signal S3 is issued. Further, if the deviation is within the tolerance, a normal signal S4 is generated. By doing this, when large bubbles are generated, even if the reflected waves are diffusely reflected at the air-liquid interface, the amplitude intensity of the ultrasonic waves received by the multifunctional sensor 31 is reduced, so that damage to the fuel and the location of the damage can be reduced. Can be detected.

Furthermore, if floating of the fuel bundle and fuel damage occur at the same time, there is a possibility that the propagation time τI(1) will not change even if an abnormality occurs. However, even in such a case, since the reflected waveform changes, an abnormality can be determined using the amplitude intensity signal P+(t) of the reflected wave.

In this way, by using temperature information at the core exit and the acoustic method, it not only simplifies equipment and detection compared to the conventional tag gas method, but also makes it possible to locate the damage even if multiple fuel failures occur simultaneously. can be detected reliably, the reliability of detection can be improved, and the detection time can be significantly shortened (several seconds/channel).

〔Effect of the invention〕

As described above, according to the present invention, it is easy to detect fuel damage and the location of damage, and the reliability of detection is improved. A fuel damage and fuel damage location detection system can be obtained.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a system diagram of an embodiment of the fuel failure detection system and fuel failure position detection system of the present invention, and Fig. 2 is a system diagram of an embodiment of the fuel failure detection system and fuel failure position detection system of the present invention. 3 is a system diagram of a conventional fuel failure and fuel failure position detection system, FIG. 4 is a vertical side view of a multifunctional sensor of the fuel failure and fuel failure position detection system, and FIG. 5 is a system diagram of a conventional fuel failure and fuel failure position detection system. Characteristic diagram showing the relationship between the sodium temperature and the sound velocity in sodium in one embodiment of the fuel damage and fuel damage position detection system. FIG. 6 also shows the relationship between the amplitude of reflected ultrasonic waves and propagation time in one example. The characteristic diagram, FIG. 7 is a characteristic diagram showing the relationship between the void fraction and the sound velocity in sodium in one example, and the characteristic diagram in FIG. 8 is the void fraction in a relatively small region in one example. FIG. 3 is a characteristic diagram showing an enlarged view of the relationship with the speed of sound. 1...Subassembly, 2...Flow guide, 5.
...Fuel handle, 26...Primary coil, 27...
Secondary coil, 28... Magnetostrictive vibrator, 29... Permanent magnet, 30... Upper end plug, 31... Multifunctional sensor (
temperature detection means and ultrasonic transmission/reception means), 33... temperature-propagation time converter, 34... subtractor, 35... calculation unit, 36... comparator, 37... abnormality diagnosis circuit, 3
8... Arithmetic unit, 39... Recorder, 40... Subtractor, 41... Comparator, 42... Recorder.

Claims (1)

[Claims] 1. An in-core abnormality detection system having a temperature detection means for detecting the temperature of each subassembly at the reactor core exit and an ultrasonic wave transmitting/receiving means for transmitting and receiving ultrasonic waves, an upper end having a reflective surface at the top of the fuel in each of the subassemblies. Provide a stopper,
Using the propagation time of the ultrasonic waves between the ultrasonic transmitting/receiving means and the upper end plug, the amplitude intensity, and the sound speed corrected by the temperature detected by the temperature detecting means, it is possible to determine the speed of sound due to the generation of bubbles due to fuel damage. A system for detecting fuel damage and fuel damage location, characterized in that the presence and location of fuel damage is detected from changes in the fuel.