JPH0140942B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a shipping device used to check whether or not a spent nuclear fuel assembly is damaged. The present invention relates to a method of inspecting whether or not there is a gas leak point in each pipe line.

Generally, nuclear fuel assemblies are
Damage occurs due to various causes of damage, such as breakage, welding damage, and hydrogenation damage, but the damage points are often not visible with underwater television, especially pinholes in the cladding of the same assembly. If there is a damaged part in the hidden part of the array, the presence or absence of damage cannot be confirmed without using the above-mentioned shipping device.

By the way, the basic principle of the shipping device is
The spent nuclear fuel assemblies are placed in the spent nuclear fuel handling pool and stored in the main body of the shipping device,
The temperature of the assembly is raised by placing it under adiabatic conditions, thereby increasing the pressure inside the cladding tube and causing fission products to leak out from pinholes in the tube.

Among the leaked products, the gaseous ones are collected by a carrier gas circulated through a predetermined circulation pipe system, and the water-soluble fission products are eluted into the water in the pool, and each gas analyzer , which attempts to confirm the presence or absence of nuclear fission products using a water analyzer.

The present invention aims to inspect the various on-off valves and pipelines for gas leakage in a shipping device newly constructed based on the above principle.In this type of shipping device, a large number of on-off valves and If pipes are used and there is a gas leak in these pipes, it will be impossible to correctly detect the fission products, especially if the on-off valves are automatically controlled according to a predetermined sequence to perform measurements. However, there has been no suitable leakage testing method for this type of shipping equipment.

The present invention focuses on the above-mentioned points and aims to provide a leakage testing method that can be carried out simply and quickly and is highly reliable.The present invention will be explained in detail below with reference to the drawings.

First, to explain in detail the shipping device to which the present invention is to be implemented, a spent nuclear fuel handling pool 1 is provided with a shipping device main body 3 in pool water 2 containing boric acid. The shipping cap 5 provided on the shipping can 4 of the main body 3 can be opened to store the spent nuclear fuel assembly A in the shipping can 4. The inside of the pin can 4 is opened so that the pool water 2 can freely enter from the bottom thereof.

Furthermore, on the outer side of the shipping can 4,
An air jacket 6 is provided around the bottom through which the pool water 2 can freely enter, and gas is force-fed from the top of the jacket 6 through an air jacket conduit 7. In the illustrated example, a carrier gas supply conduit 8, which will be described later, is used.
Nitrogen gas, which is a carrier gas, is fed under pressure through the air jacket line 7 provided with a main valve 9.

Therefore, by adjusting the supply amount of the nitrogen gas, the water level in the air jacket 6 can be lowered and a gas insulation layer 6' of a required length can be formed. The spent nuclear fuel assembly A is prevented from radiating heat by the gas insulation layer 6', and as a result, the pressure within the cladding tube of the assembly A can be increased.

Now, when the pressure inside the cladding tube increases as described above, if there is damage such as a pinhole in the cladding tube, the fission products inside will leak out from such a damaged point. As mentioned above, there are gaseous types and water-soluble types, and the latter is eluted into the pool water 2 that has entered the shipping can 4.
Water is taken at appropriate times through the water sample pipe 13 in which a quantitative water intake section 12 with pipes 1' and 11" is disposed, and the water thus sampled is carried into a separately provided water analyzer. By focusing on changes in the concentration of iodine 131 (I ¹³¹ ) and cesium 137 (Cs ¹³⁷ ) in the boric acid solution, leakage of water-soluble fission products will be determined.

Further, in this shipping device, in order to detect leakage of the gaseous fission products, carrier gas is supplied from the carrier gas supply pipe 8 to the carrier gas circulation pipe system 14, and the carrier gas circulating through the pipe system 14 is used to detect leakage of the gaseous fission products. , to collect gaseous fission products leaked into the water entering the shipping can 4.

That is, a carrier gas source 15, two sets of gas pressure regulating valves 16, 16', and carrier gas main valves 17, 1.
The carrier gas from the carrier gas supply line 8 comprising the carrier gas circulation line 14
Once the gas is filled and filled, the gas circulation pump 19 provided in the gas measuring pipe 18, which is the first pipe of the pipe system 14, is driven, and the gas flow rate regulator 20 of the pipe 18 is operated. The carrier gas at a predetermined flow rate is sent into the shipping can 4 via the gas supply/discharge pipe 21 of the pipe system 14, and the carrier gas that has collected gaseous fission products is transferred to the shipping can. The gas is circulated from the upper layer of the gas pipe 4 through the gas introduction pipe 22 connected to the shipping cap 5 to the original gas measuring pipe 18.

The pump 1 is connected to the gas measuring pipe line 18.
9. In addition to the gas flow rate regulator 20, a pressure gauge 23,
A gas analysis detector 26 with a scintillation probe 25 that sends a signal to the gas analyzer 24 and a flow meter 27 are provided, and 28 in the figure is the gas flow regulator 20, and its flow regulating valve 29. This is an automatic control unit that controls the

Further, the gas supply/discharge pipe 21 has gas circulation valves 30 and 30' on the front side and the rear side, and the gas introduction pipe 22 has a carrier gas introduction valve 31, a drain separator 32, and a gas outlet valve 33 in this order. It is set up.

Furthermore, in the same device, a gas introduction pipe 22 between the drain separator 32 and the carrier gas introduction valve 31 and a gas supply/discharge pipe 21 between the gas circulation valves 30 and 30' are connected to a discharge valve 34. A discharge pipe 37 having a discharge valve 36 is branched from between the drain separator 32 and the gas outlet valve 33, and the drain separator 32 is connected to the drain separator 32 by a pipe 35. A drainage pipe 39 equipped with a separated water drainage valve 38 is connected to the separator 3 for discharging water.
A water level detector 40 is attached to detect when the separated water of No. 2 is stored and reaches an abnormally high water level.
The gas outlet valve 32 is automatically closed by an electric signal generated when the water level is detected, and the separated water flows into the gas measurement pipe 18 together with the circulating carrier gas, where it is used for gas analysis. Scintillation probe 25 attached to detector 26
This prevents troubles such as those caused by the adhesion of fission products.

Furthermore, in the illustrated example of the device, the shipping cap 5 is opened and closed by an air cylinder 41, and numeral 42 in the figure is a switching valve, and the cylinder 41 is configured to open and close the shipping cap 5 using an air cylinder 41. The piping is designed to be expanded and contracted by the

Furthermore, in the example shown in the figure, while the spent nuclear fuel assembly A is being measured by the shipping device main body 3, the shipping device main body 3a is installed so that another same assembly can be set, and the same main body is 3
The piping is arranged so that it can be switched to operation a.

When operating the device, the gas circulation valves 30, 30' and the carrier gas outlet valve 3, which have already been described, are required.
1, gas outlet valve 33, discharge valve 34, discharge valve 36,
It is preferable to configure the separation water drain valve 38 and other on-off valves to be automatically controlled to open and close according to a predetermined sequence, and it is also preferable to take into account automatic control of the on-off valves when an abnormality occurs.

Since this shipping device is constructed as described above, in order to use it, the carrier gas supplied from the carrier gas main valve 17 of the carrier gas supply pipe 8 is transferred to the discharge valve 36 of the discharge pipe 37.
By closing the discharge valve 34 of the discharge pipe 35, the carrier gas can be sealed in the carrier gas circulation pipe system 14, and then the gas circulation pump 19 is driven, and the gas flow rate set by the gas flow regulator 20 is A predetermined flow rate of carrier gas is circulated through the carrier gas circulation pipe system 14 for a predetermined period of time.

The carrier gas thus introduced from the bottom of the shipping can 4 rises together with the leaked gaseous fission products, and after water is removed by the drain separator 32, the gas in the gas measurement pipe 18 It is introduced into the analytical detector 26.

In this way, the carrier gas collects the above-mentioned products each time it is circulated, and its concentration gradually increases, so that the gas analyzer 24 attached to the gas analysis detector 26 The presence or absence of nuclear fission products will be tested, but considering the half-life and yield, the gamma ray energy is 81KeV.
Focusing on xenon 133 (Xe ¹³³ ), the radioactivity count of xenon 133 and the presence or absence of its peak within the predetermined time are measured.

During the measurement as described above, when the drain separator 32 reaches an abnormally high water level, the gas outlet valve 33 is closed by the output electric signal of the water level detector 40 as described above, so that the pool water, which is the separated water, becomes gaseous. It is possible to prevent the water from flowing into the measurement pipe line 18, and if this condition occurs, the separated water drain valve 38 is opened to discharge the separated water, and the measurement is restarted.

When the measurement for a certain period of time is completed, the gas outlet valve 33 is closed and the release valve 36 is opened, and the carrier gas in the shipping can 4 and the gas introduction pipe 22 passes through the drain separator 32 and is released into the release pipe 37.
is discharged from.

On the other hand, if the discharge valve 34 is opened and the gas circulation valve 30 on the upstream side of the gas supply/discharge pipe 21 is closed, the residual carrier gas in the pipe 21 will flow into the gas introduction pipe 22 from the discharge barrier 35. The carrier gas is discharged from the discharge pipe 37 via the drain separator 32 and the discharge valve 36, and the pool water accompanying the carrier gas is separated by the drain separator 32, leaving only the carrier gas. is discharged from the discharge pipe 37,
At this time, the separated water in the drain separator 32 is discharged by opening the separation and drain valve 38.

Regarding the residual carrier gas in the gas measurement pipe 18, the downstream side gas circulation valve 30' is closed.
Carrier gas main valve 17 of carrier gas supply pipe 8
New carrier gas is caused to flow into the gas measurement pipe 18 from the previous stage gas circulation valve 30 - discharge pipe 35 - gas introduction pipe 2 from the same pipe 18 with the new carrier gas.
The carrier gas containing nuclear fission products is not introduced into the gas measuring pipe 18, and the carrier gas containing the fission products is not introduced into the gas measuring pipe 18, and even when the residual carrier gas is discharged, 18 and is eliminated.

The present invention examines whether there is any leakage in the various on-off valves before starting measurement by the shipping device, especially when the on-off valves are automatically controlled according to a predetermined sequence as described above. It is important to check whether the on-off valves close completely and whether there are any leakage points in the pipelines in which these on-off valves are installed.

The present invention is intended to satisfy these demands. First, when various on-off valves are sequentially controlled, the control system is released and a separately provided control signal transmitter is used to control the carrier gas main valve 1.
7, gas circulation valve 30 on the front stage side of the gas supply and discharge pipe 21;
The carrier gas introduction valve 31 and gas outlet valve 33 of the gas introduction pipe 22, the discharge valve 34 of the discharge pipe 35, the discharge valve 36 of the discharge pipe 37, and the separated water discharge valve 38 of the drain pipe 39 are all closed.

Next, the carrier gas source valve 17 is opened, and high-pressure carrier gas of, for example, 2 atm. flows from the carrier gas supply line 8 into the gas measurement line 18, and the source valve 17 is then closed to seal in the gas. The pressure of the sealed gas at the beginning is measured by the pressure gauge 23.

After being left in this condition for a certain period of time, read the pressure gauge 23 and compare it with the initial pressure value. If a drop in pressure is found, the gas outlet valve 33 and the previous gas It can be confirmed that the carrier gas is leaking from one of the on-off valves of the circulation valve 30 or the gas measurement pipe 18.

If it is confirmed that there is no leakage as described above, then the gas outlet valve 33 is opened, whereby the high pressure carrier gas sealed in the gas measurement pipe is transferred to the carrier gas introduction valve of the gas introduction pipe 22. 31, the water is allowed to flow into the discharge valve 36 of the discharge pipe 37, the discharge valve 34 of the discharge pipe 35, and the separated water drain valve 38 of the drain pipe 39, so that the pressure of the enclosed high-pressure carrier gas of 2 atmospheres drops. Therefore, the pressure drop value is measured by the pressure gauge 23.

If the pressure drop value is a predetermined value of, for example, 1.2 atmospheres, it is known that there is no leakage in any of the on-off valves and pipelines, and if the pressure drop value is smaller than the predetermined pressure drop value, then It is confirmed that there is a leak in any of the on-off valves or pipelines mentioned above.

If it is confirmed through such inspection that there is a leakage point, check the on-off valves and pipes,
This can be repaired, and by using an automatic opening/closing valve, not only the operation of the device but also the inspection can be carried out easily and quickly.

The present invention relates to the pipeline system of the above-mentioned shipping device, in which high-pressure carrier gas is sealed from the carrier gas supply pipeline 8 into the gas measurement pipeline 18 while the front gas circulation valve 30 and the gas outlet valve 33 are closed. , the pressure gauge 2 at the time when the gas measurement pipe 18 is initially sealed.
3 and the reading of the same pressure gauge 23 after a predetermined period of time, the front gas circulation valve 30,
Gas leakage in the gas outlet valve 33 and the gas measurement pipe 18 is detected, and then the gas outlet valve 33 is closed while the carrier gas outlet valve 31, discharge valve 34, discharge valve 36, and separated water discharge valve 38 are closed. Each opening/closing valve and each pipe leading to the opening/closing valve are determined depending on whether the reading of the pressure gauge 23 after opening is smaller than the predetermined pressure drop value compared to the reading of the pressure gauge 23 before opening. By detecting gas leaks in pipelines, gas leaks between multiple valves and pipelines can be easily and quickly confirmed by supplying high-pressure carrier gas at the beginning and opening and closing a small number of designated valves. In this case, if an automatic opening/closing valve is used, the pipe system of the shipping equipment can be inspected generally efficiently and with high reliability without having to deploy a large number of workers.

[Brief explanation of drawings]

The figure is an explanatory diagram of a piping system showing a shipping device that is a target of the inspection method according to the present invention. 1...Spent fuel handling pool, 2...Pool water, 3...Shipping device main body, 4...Shipping can, 5...Shipping cap, 8...Carrier gas supply pipe, 14...Carrier gas circulation pipe Line system, 17...Carrier gas main valve, 18...Gas measurement pipe line, 19...Gas circulation pump, 20...
...Gas flow rate regulator, 21...Gas supply and discharge pipe, 22
...Gas introduction pipe, 23...Pressure gauge, 26...Gas analysis detector, 27...Flowmeter, 30...Previous gas circulation valve, 30'...Later gas circulation valve, 3
1...Carrier gas introduction valve, 32...Drain separator, 33...Gas outlet valve, 34...Discharge valve,
35...Discharge pipe line, 36...Discharge valve, 37...Discharge pipe line, 38...Separated water drain valve, 39...Drain pipe line, A...Spent nuclear fuel assembly.

Claims (1)

[Claims] 1 Carrier gas is freely introduced from the carrier gas main valve of the carrier gas supply pipe, and the gas measurement pipe is equipped with a pressure gauge, a gas analysis detector, a gas flow rate regulator, and a flow meter, and the gas circulation on the front stage side. valve,
A shipping can that can easily be submerged into water, where the spent nuclear fuel assembly of the main body of the shipping device is installed in the water of the spent nuclear fuel handling pool, and the gas supply/discharge pipe line with a gas circulation valve on the latter stage is interposed. A gas inlet pipe is connected to a shipping cap that can be opened and closed in the same shipping can, and has a carrier gas inlet valve, a drain separator, and a gas outlet valve. The discharge pipe has a carrier gas circulation pipe system in which the carrier gas is circulated by a pump, and the discharge pipe branches from between the drain separator and the carrier gas introduction valve in the gas introduction pipe and has a discharge valve interposed therein. A discharge valve is connected between the front-stage gas circulation valve and the rear-stage gas circulation valve of the gas supply/discharge pipe, and a discharge valve is interposed between the drain separator of the gas introduction pipe and the gas outlet valve. In the pipe system of a shipping equipment where the pipe line is branched and the drain separator is provided with a drain pipe line with a separated water drain valve interposed, it is necessary to close the preceding gas circulation valve and the gas outlet valve as described above. Under the conditions, high-pressure carrier gas is sealed from the carrier gas supply pipe into the gas measurement pipe, and the reading of the pressure gauge at the time of filling the gas measurement pipe,
By comparing the reading of the same pressure gauge after a predetermined period of time, gas leakage in the front gas circulation valve, gas outlet valve, and gas measurement pipe is detected, and then the carrier gas inlet valve, discharge valve, release valve, and separation valve are detected. With the water drain valve closed, the gas outlet valve is opened, and the pressure gauge reading after opening is determined to be smaller than the predetermined pressure drop value compared to the pressure gauge reading before the opening. A method for inspecting leakage of on-off valves and pipelines of a shipping device for nuclear fuel assemblies, characterized in that gas leakage is detected in each of the above-mentioned on-off valves and each of the pipelines leading to the on-off valves.