JPS593294A - Off-gas monitor system for detecting failure of nuclear fuel cladding tube - 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 [Technical Field of the Invention 1 The present invention relates to a nuclear fuel cladding tube that monitors radioactive residue contained in off-gas discharged at a nuclear power plant and quickly and accurately detects damage to the nuclear fuel cladding tube.・Related to an off-gas monitoring system for detecting damage to nuclear fuel cladding tubes that quickly and accurately detects pipe failures.

[Technical Background of the Invention] Generally, in a nuclear power plant, steam generated in a nuclear reactor is sent to a turbine to perform mechanical work, and this mechanical work is further converted into electric power. The steam that has done work in the turbine is deprived of C heat in the condenser, becomes condensation, and is sent to the reactor again. When it is condensed in the condenser, the gases contained in the steam are extracted by the air extractor. It is separated and released into the atmosphere through chimneys. Therefore, the off-gas extracted from the hot well of the condenser by the air extractor usually contains radioactive scum, which is a nuclear fission product.

The radioactive rare gas nuclides contained in such off-gases have half-lives of minutes, and are in the A-der short-lived group (Kr-89, Kr-89,
Kr-90, Xe-135m, Xe-137, Xe-1
38) and a long-lived group (Kr-86m, 1(r-(37, Kr-88, Xo
-133, ) (e -135), and the content of these radioactive rare gases in the off-gas is considered to be a measure of the soundness of the nuclear fuel cladding.

In other words, if there is a high content of radioactive noble gases, the nuclear fuel cladding may be damaged, so the amount of radioactive noble gas contained is important to know the extent of the damage. This is an essential requirement.

In addition, by approximate reduction of the diffusion from the nuclear fuel pellets to the plenum and the release from the brenum through the damaged hole, in the release of radiation↑IF noble gas, recoil and diffusion (Dirrt + 5 ions) are calculated depending on the presence or absence of damage.
>Equilibrium release models are known, and the proportions (composition ratios) of these release models also serve as an indicator of the soundness of the nuclear fuel cladding.

In other words, if a nuclear fuel cladding tube breaks, the composition ratio (R) of the recoil model will rapidly decrease, and the composition ratios (D and E) of the diffusion J and equilibrium models will increase, so the monitor should also This is necessary to immediately detect damage to nuclear fuel cladding and ensure the safety of FCA nuclear power plants.

``Problem in the Background Art 1 However, conventional off-gas monitoring systems (Koi C) are equipped with a pipe that bypasses a portion of the off-gas in the middle of the main off-gas pipe that connects the air extractor and the chimney. The off-gas flowing through the bypass pipe is Na ((1
Since a method of measuring the cross-count rate of gamma rays with a -1,-) detector is used, there is a problem in that information regarding the composition of the radioactive rare gas stack and the composition ratio of the emission model cannot be obtained.

[Purpose of the Invention] The present invention divides radioactive rare gases in off-gas emitted from nuclear power plants into Chimanmei group and long-life group, and evaluates the release rate of each nuclide and the recoil of the radioactive rare gases as a whole. It is an object of the present invention to provide an off-gas monitoring system for detecting damage to nuclear fuel cladding, which can measure and calculate the composition ratio of each emission model of , diffusion, and equilibrium.

[Summary of the Invention] The present invention provides an off-gas mixer that mixes off-gas and water, and a radioactive rare gas nuclide contained in the off-gas discharged from the off-gas mixer into a short-life group and a long-life group. A detection unit that performs measurement and detection, a pulse height analyzer that analyzes the data detected by the detection unit to identify and quantify the radioactive rare gas nuclide, and a pulse height analyzer that analyzes the data detected by the detection unit to identify and quantify radioactive rare gas nuclides. This off-gas monitoring system for detecting damage to nuclear fuel cladding is characterized by comprising a process calculator that calculates the composition ratios of recoil, diffusion, and equilibrium release models.

[Embodiment of the Invention] An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a longitudinal cross-sectional view of a gamma ray detection unit for radioactive rare gas nuclides in off-gas according to the present invention. As shown in the figure, the gamma ray detection section, which is designated as a whole by reference numeral 1, has a short-life group nuclide measuring section 4 and a long-life group nuclide measuring section 5 located outside the shield in a space 3 surrounded by a lead shield 2. It is shaped like a +-1 structure with 6 in between. It is preferable that the measuring section 4.5 and the delay tube 6 have a spiral tube structure as shown in the figure.

Note that a Ge (germanium) detector 7 is installed in the space 3.
is provided.

FIG. 2 is a block diagram of an off-gas monitoring system according to an embodiment of the present invention. As shown in the figure, a portion of the off-gas discharged from the air extractor (not shown) is transferred to the off-gas transfer pump 8.
The off-gas is sucked into the bypass pipe 10 provided in the middle of the off-gas main piping 9, reacts with the valve 11, and is sent to the off-gas mixer 13 through the valve 12, which is opened and closed by a signal from the medium-heat process unit 18, which will be described later. It will be done.

In addition, the off-gas mixer 13 is connected to a water pump 14 with one τ
Clean water sucked up from a water tank 15 is supplied, and off-gas is mixed at a constant rate with a constant stream of clean water inside this off-gas mixer 13. That is, the valve 1
2, a water flow in which off-gas bubbles are arranged in a grid pattern is created at the exit vibe of the off-gas mixer 13, and this water flow is sent to the gamma ray detection section 1 described above.

Note that the valves 11 and 12 are operated so as to repeat opening and closing in opposite directions. In other words, when off-gas is supplied to the off-gas mixer 13, the valve 11 is closed for a predetermined period of time and the C valve 12 is opened.On the other hand, when the supply is to be stopped, the valve 11 is opened at the same time as the valve 12 is closed, and the off-gas is sucked into the off-gas transfer pump 8. The off-gas that has entered the bypass pipe 10 is prevented from returning to the off-gas main pipe 9 through the valve 11.

Next, the off-gas-water mixture sent through the exit vibe of the off-gas mixer 13 passes through the measurement section 4 of the gamma ray detection section 1 shown in FIG. Here, the Ge detector 7 measures and detects the short-lived radioactive rare gas in the off-gas.

The off-gas-water then passes through a delay tube 6 for 1 to 5 hours to attenuate the radioactivity of the short-lived radioactive noble gas. Thereafter, the gas enters the measuring section 5, and the long-lived radioactive rare gas in the off-gas is measured and detected by the Ge detector 7.

The off-gas-water exiting the measuring section 5 is separated in the bubble separator 16, and the water is discharged as drain, -7= On the other hand, the off-gas is returned to the off-gas main pipe 9 and is dissipated into the atmosphere through a chimney (not shown) through a shuttle C. .

The gamma ray spectrum measured by the Ge detector 7 is first input into the pulse height analyzer 17, and from there it is roughly sent to the central prolesconit 18, where spectrum analysis is performed in the pulse height analyzer 17 and the central process unit 18. The radioactive rare gas nuclides are identified and quantified, and the release rate of each nuclide is calculated.

The release rate is calculated based on the flow rate data sent from an off-gas flow meter (not shown) installed in the middle of the main off-gas pipe 9. In addition, in this central process unit 18, the above-mentioned The composition ratio of the recoil, diffusion, and equilibrium release models for the entire radioactive noble gas is calculated based on the release rate of each nuclide. That is, it is known that each release model described below corresponds to the damage state of the nuclear fuel cladding tube, and the release rate for each model is expressed by the following equation.

If radioactive noble gas is released from Trump uranium without damage to the nuclear fuel cladding, then 8- Recoil model Ai = K. If radioactive noble gas is released from Y1λi damage hole, then diffusion model A1-Ko.
YIλ, equilibrium model A1-center Yl where Ai is the emission rate of nuclide i (m Ci /sec)
, Yi is the fission yield of nuclide i, A1 is the decay constant (1/5ec) of nuclide 1, and KFL, K, ,K,
each has a constant C.

In order to calculate the composition ratio of each release model, apply the analysis and calculation results for the release rate of each radioactive noble gas nuclide to the following formula % formula %, and minimize the value of S expressed by the following formula. After finding the values of KO and KE using constants, S= and (β0(
1(Ai /Yi) -AO(1(Kl(5 to λ1+)
Ai"+Ka)) 2 Using these values, each composition ratio of the entire radioactive rare gas nuclide is calculated from the following formula.

Good for R-Σ Yiλ1/Σ(KIYiλi+KD・Y1
λi and +KEYi) The results calculated by performing the above calculations are sent from the central processing unit 18 to the printer 19 and printed out, and are also sent to the display device 20 and displayed on the RXD, E
The changes over time and the total value of the release rate of radioactive noble gas nuclides are plotted on the graph.

Further, an alarm 21 is provided which is activated in response to a signal output from the central process unit 18, and an alarm is issued from this when R decreases and D and [ increase.

3 and 4 are graphs r showing the total value of the release rate of radioactive rare gas nuclides and changes over time of R, D, and E monitored by the system of the present invention and displayed on the display device 20.

As is clear from these graphs, when damage to the nuclear fuel cladding occurs, not only does the total value of the emission rate increase rapidly, but also R decreases sharply and the value of R increases accordingly. Therefore, there is no need to wait until the alarm 21 is activated, and by continuously preparing and monitoring these graphs, it is possible to detect damage immediately after it occurs.

In addition, in the system of the present invention, C is the gamma ray detection unit 1
By providing a delay tube 22 and a β-ray detector 23 as shown in FIG. 5C between the air bubble separator 16 and the bubble separator 16, radioactive noble gas nuclides that emit β-rays can be measured and detected.

That is, after the off-dregs water leaves the measuring section 5, it passes through the delay tube 22.
After being delayed and attenuated for more than 5 hours, it is introduced into the measurement section 24 of the beta ray detection section 23, where it is introduced into the measurement section 24 of the beta ray detection section 23, where it is introduced into the measurement section 24 of the beta ray detection section 23, where it is introduced into the measurement section 24 of the beta ray detection section 23.
The β rays are measured and detected by the line detector 11 25 .

The detection results are sent to the central process unit 1 via the h1 measuring section 26.
8, where the β-ray nuclide is identified and quantified.

In other words, the main nuclides that emit β-rays in the measuring section 24 due to attenuation in the delay tube 22 are Xe-133, Kr-85, and Kr.
-85m, Kr-88, Xe-,135, but
The β-ray]-energy (about 660 KOV) of Kr-85 is significantly higher than that of the other four nuclides, and the measurement results mainly identify and quantify Kr-85.

The quantitative measurement of Kr-85 has not been done in the past.This measurement makes it possible to evaluate the fuel content of damaged nuclear fuel, and the location of the damage can also be used to some extent.

[Effects of the Invention] As is clear from the above description, according to the off-gas monitoring system of the present invention, the release rate of radioactive rare gas nuclides in the off-gas and the composition ratio of each release model of recoil, diffusion, and equilibrium can be continuously monitored. Since the nuclear fuel cladding tube is monitored automatically and automatically, any damage to the nuclear fuel cladding tube can be detected immediately, and accidents can be prevented from occurring.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a gamma ray detection section in an embodiment of the present invention, FIG. 2 is a block diagram of an off-gas monitoring system in an embodiment of the present invention, and FIGS. 3 and 4 are an embodiment of the present invention. The sum of the emission rates of radioactive rare gas nuclides obtained from the example h
1 value and changes over time of R, D, and E (graph; Figure 5 is a vertical cross-sectional view of the β-ray detection section. 1...... Gamma ray detection section 6.22・
...Delay tube 7...Qe detector 8...
・・・・・・Off gas transfer pump 9・・・・・・・・・
... Off-gas main pipe 10 ... Bypass pipe 11.12 ... Valve 13 ... Off-gas mixer 14 ...
・・・・・・・・・Water pump 16・・・・・・・・・
...Bubble separator 17... Wave height analyzer 18... Central process unit 19... Printer 20...
......Display device 23...
...Beta-ray detector 25...Beta-ray detector 26...Representative Patent Attorney of the Removal Measurement Department Satoshi Suyama −

Claims (1)

[Claims] (1) An off-gas mixer that mixes A fugas and water, and a detection unit that divides the radioactive gas nuclides contained in the off-gas discharged from the off-gas mixer into a short-life group and a long-life group, and measures and detects each of them. and a wave height analyzer that analyzes the data detected by the detection unit to identify and quantify the radioactive gas nuclide; and a wave height analyzer that analyzes the data detected by the detection unit to identify and quantify the radioactive gas nuclide; and based on the data analyzed by the wave height analyzer, recoil, diffusion, and An off-gas monitoring system for detecting damage to nuclear fuel cladding, comprising a process calculator that calculates the composition ratio of each equilibrium release model.