JPS63252296A - Fuel element helium leak detection test method - 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 Industrial Application] The present invention relates to a gas replacement chamber, and in particular, in equipment handling nuclear materials, a glove box with a negative pressure atmosphere (inert gas or air) and a gas exchange chamber with an atmospheric side. This relates to a gas replacement chamber that is connected to an open box and is used to accurately detect the amount of helium gas leaking online for each fuel element.

[Conventional technology]

Conventional helium leak tests include one method that is performed after assembling multiple fuel elements into an assembly, and one method that is performed after assembling multiple fuel elements into an assembly, as shown in the ``Light Water Reactor Behavior J There is a method in which more than 20 fuel elements are lined up on one pallet.

Even with the method using pallets, there is no need to pass between the glove box and the open box in the conventional manufacturing process from pellet filling to upper end plug welding, and a gas exchange chamber is unnecessary. It is. However, recently, in order to efficiently produce highly toxic nuclear fuel pellets, the pellet filling and upper end plug welding steps are handled in a glove box with a negative pressure atmosphere, and then in the later steps, they are handled in an air atmosphere through a gas exchange chamber. It's a process.

FIG. 3 is a diagram showing part of a conventional system configuration in which a helium leak test is performed by arranging fuel elements on a pallet. This system section is equipped with an inert gas negative pressure (e.g.
It consists of a glove box A maintained at -30 mmAq±5 ms Aq), a gas replacement chamber B which is the object of the present invention, an open box C at atmospheric pressure, and a helium leak test facility. Glove box A is a place where cladding tube pellets, springs, etc. supplied from the previous process are inserted, filled with helium, and then the upper end plug is welded. The open box C is a place where the appearance of the welded parts and the like of the fuel element thus formed is inspected. After the inspection in open box C is completed, the fuel elements are sent to a helium leak test facility, stored on pallets up to a predetermined number, and subjected to a helium leak test. Gas replacement chamber B
is installed to send the fuel element with the upper end plug sealed to the open box C side so as not to disturb the negative pressure on the glove box A side and to prevent nuclear material from scattering into the atmosphere.

Next, an overview of the operations in these system parts will be explained. Weld the upper end plug of the fuel element in a helium atmosphere in glove box A. When sending this fuel element from glove box A to open box C, open box C
Make sure that the air on the side does not mix with the helium gas on the glove box A side.

In addition, in order to prevent nuclear material from the glove box A side from scattering to the open box C side, first open the gas exchange chamber B.
With the shutters on both sides closed, open the gas exchange chamber B.
The interior is once evacuated to 10-" Torr. Next, helium gas is introduced into gas replacement chamber B, and the same negative pressure as in glove box A (-30 Aq ± 5 m Aq
), then the welded fuel element is pulled out from glove box A to gas replacement chamber B, and the shutter on the glove box A side is closed. Thereafter, the shutter on the open box C side is opened to send out the fuel element.

In open box C, the appearance of the welded parts of the fuel element is inspected, and the fuel element is sent to a pallet for helium leak testing equipment.

The helium leak test equipment performs a helium leak test on each pallet when a predetermined number of fuel elements are delivered, and then sends them to the next process.

[Problem that the invention seeks to solve]

Now, with the method of performing a helium leak test after assembling multiple fuel elements into an assembly, if a leak is detected, it is unclear which of the many assembled fuel elements is causing the leak, and I also had to repeat the test.

On the other hand, even in the conventional example of storing fuel elements on a pallet as shown in Fig. 3 and carrying out a helium leak test, the situation has not been improved much.

In this method, usually several to ten fuel elements are stored on a pallet and tested, so even if a leak occurs, pass/fail judgment can only be made for each pallet, and it is difficult to identify the fuel element with the leak. In this case, 100% inspection is required for each piece off-line, resulting in twice the effort.

Even more problematic is the gas released from the pallets. 4, in which a is the amount of gas released from the helium leak test chamber itself when there are no pallets and fuel elements (background), b is
For example, 3 X without pallets and fuel elements
The amount of gas released when helium gas is released from a standard leak source of 10-' Torr-Q see, C is the amount of gas released when a pallet and a fuel element not filled with helium gas are inserted (pack ground) , c2 is
The amount of released gas when a pallet and a fuel element filled with helium gas are inserted, d is the amount of released gas (background) when only a fuel element not filled with helium gas is inserted, and e is, for example, IXl 0-' Torr-
This is the pass/fail judgment standard level for Q/see.

In this case, the detection sensitivity f of the helium leak test is (3X
10-'Torr-Q /see ) / (b-
It is given by a). In addition, the actual fuel element determination is (
c2-c) This is done by measuring whether or not Xf is less than a predetermined reference value e.

The pallets used in the helium leak test facility have undergone various testing processes since the last test. Therefore, it was necessary to measure the amount of gas released from the pallet itself each time. Moreover, the amount of gas emitted from the pallet itself was not constant due to machine oil, moisture, etc. adhering to the pallet, and the amount of gas emitted from the pallet was too large, causing a problem that reduced the accuracy of helium leak tests for fuel elements. .

In other words, when a pallet and a fuel element that does not contain helium gas are inserted, the amount of released gas C far exceeds the pass/fail criterion e and is unstable, so it is included in the calculation conditions as a constant background C. Ok,
It takes skill to judge from the actual pre-chamber result c2 whether (c2-c)
Since we are measuring a leakage of about 6 Torr-Q/sec, the chamber is evacuated to about 10 Torr, and
Measure the leakage amount of 0-8/10''5=10''312/see. If the pallet is dirty and the vacuum level of the chamber within the specified time is, for example, 10'''3 Torr, the
/10'''3=10-I5Q/sec, which makes measurement increasingly difficult.

In the end, the amount of gas released from the pallet itself had to be measured online immediately before the helium leak test, which was time-consuming and did not improve the accuracy of measuring helium leaks from fuel elements.

The purpose of the present invention is to provide a gas replacement chamber that can quickly measure helium leaks for each fuel element on-line and also has the function of a helium leak detection device that fundamentally eliminates the influence of pellets that emit a large amount of gas. It is to provide.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention provides a gas exchange chamber for transferring objects to be transferred from the first chamber to the second chamber having an atmospheric atmosphere so that the atmospheres of the first chamber having a negative pressure atmosphere and the second chamber having an atmospheric atmosphere do not mix. There is a rough evacuation system that evacuates the chamber to a predetermined low vacuum before receiving the object, a gas supply system that supplies the same type of gas as the first chamber to the chamber while changing the flow rate, and a gas supply system that evacuates the object from the first chamber. There is a main evacuation system that evacuates to the vacuum conditions for a helium leak test after receiving it, a helium leak test system that performs a helium leak test under vacuum conditions, and a helium leak test system that measures the helium detection sensitivity in the chamber under vacuum conditions before operation. The present invention provides a gas replacement chamber equipped with a helium leak detection device consisting of a standard leak exhaust system.

[Effect]

An overview of the configuration of the present invention will be explained with reference to FIG. As is clear from a comparison between FIG. 2 and FIG. 3 showing the conventional example, the present invention is characterized in that the gas replacement chamber B performs the function of a helium leak test facility.

If pallets, which are the biggest source of disturbance noise in helium leak tests, are not brought into the helium leak test facility, they can be freed from this influence. In this case, in order to eliminate the risk of internal exposure, it is best to place the helium leak test in front of the open box C in the air atmosphere, where the gas exchange chamber B is located, and as already mentioned, with gloves When transferring the fuel element from box A to open box C, it is designed to be evacuated once.

Therefore, by improving the vacuum capacity and adding a helium leak test function, we have created a gas exchange chamber that fundamentally eliminates the negative effects of pallet gas emissions and saves space and cost overall. will be obtained.

〔Example〕

FIG. 1 is a system diagram showing one embodiment of a gas replacement chamber according to the present invention. In the figure, 1 is the first chamber (glove box) maintained at negative pressure of inert gas (helium).
, 2 is the fuel element produced there and carried out into the air atmosphere, 3 is the main body of the gas exchange chamber that connects the first chamber and the second chamber (+- pump box) in the air atmosphere, 4 is the vacuum roughing system, and 5 is the vacuum roughing system. Standard leak exhaust system, 6 is a water exhaust system, 7 is a helium leak test system, 8 is a helium supply amount control system, 9 is a vacuum gauge (Pirani vacuum gauge), 10 is an on-off valve (air operated valve),
11 is a differential pressure vacuum gauge, 12 is a shutter, 13 is a solenoid valve, 1
4 is an ionization vacuum gauge, 15 is a standard radiation source, 16 is a solenoid valve, 17
is a vacuum switch.

Using the gas replacement chamber configured in this way.

We will explain the process of transferring fuel elements one by one from the first chamber to the second chamber while conducting a helium leak test.

First, the shutters 12A and 12B on both sides are closed, the switch 17 is turned on, and the chamber 3 is evacuated to a predetermined vacuum (for example, Ix10-''Torr) by the vacuum roughing system 4.

At this point, if you open the shutter 12A as it is, the fuel element 2
When the helium gas is carried out, contaminated helium gas flows from the first chamber 1 to the gas replacement chamber 3, and the first chamber negative pressure monitoring device (not shown) is activated, and the helium control system on the first chamber side is activated, and the specified negative pressure is activated. The fuel element cannot be removed until pressure is restored, leading to time loss.

To prevent this, after evacuating the gas replacement chamber 3,
Helium is supplied from the helium supply port via the helium flow control system 8, and the same negative pressure as the first chamber 1 (for example, -30 nm) is applied.
Aq).

In this case, a predetermined vacuum (I x 10''zTorr
) to the vacuum of the first chamber -30nnAq (approximately 758 To
rr) to a value slightly lower than 10 Torr/s (hereinafter referred to as point A) through a large flow restriction in the first pipe line.
Flow with a pressure gradient of ec or higher, from point A pressure to -30 naA
7Tor through the small flow rate restriction in the second pipe line.
Flow at a pressure gradient of less than r/see.

Here, in order to protect the differential pressure gauge 11 using a digital manometer, a certain vacuum (-2000 rrm A q
), the signal that activates the on-off valve 10 that opens after reaching
Obtained from Pirani vacuum gauge 9. In addition, the switching signal between the first pipe line and the second pipe line of the helium supply amount control system 8 is controlled by the differential pressure gauge 1.
It is issued from 1.

The reason for changing the flow rate midway in this manner is to achieve the target pressure in a short time and with high precision without causing temperature changes within the glove box.

When the negative pressures in the first chamber 1 and the gas replacement chamber 3 become the same, the shutter 12A is opened and one fuel element is inserted into the gas replacement chamber 3.

Next, the shutter 12A on the side of the first chamber 1 is closed, and the set pressure of the vacuum switch 17 (I
Roughly pull down to 0'''' Torr).

Further, while monitoring with an ionization vacuum gauge, the vacuum is evacuated to 1×10″″ Torr using the water pumping system 6.

Therefore, the degree to which the pressure in the gas displacement chamber increases from I x 10-' Torr due to background effects is recorded.

In this case, in order to keep the background low and increase sensitivity, it is necessary to perform measurements under as high a vacuum as possible. Currently, in the laboratory, it is possible to evacuate the chamber to about 1X10''''' Torr, but it is technically difficult to repeatedly operate from atmospheric pressure to ultra-vacuum on a production line. Since productivity also does not increase, it is practical to measure at a degree of vacuum of about I X IO-' Torr. In this gas replacement chamber, the pallet, which was a major destabilizing factor for the background, is not brought into the helium leak test area, so the background is stable and has a value d that is considerably lower than C in FIG. 4.

After inserting one fuel element 2 into the gas replacement chamber 3 and drawing it to a predetermined degree of vacuum, let p be the pressure rise in the gas replacement chamber 3 after several minutes have elapsed, calculate (p-d)Xf, Compare with e in Fig. 4 to determine pass/fail.

In addition, the standard leak exhaust system evacuates the gas replacement chamber 3 to lXl0''''' Torr before operation, closes all valves, and removes the background a that enters the chamber.
3 x 10-' from the standard radiation source.
This is to emit a gas of Torr-n/see, measure the background b, and determine the device sensitivity f.

〔Effect of the invention〕

According to the present invention, the gas exchange chamber connecting the glove box in the first room and the open box in the second room also serves as a helium leak test function, and the pallet, which was a source of background instability, is eliminated from this stage. Since it is possible to measure each fuel element individually, helium leak tests on fuel elements can be performed online in a short time and with high accuracy, and there is no need to create a gas replacement chamber specifically for helium leak tests, resulting in overall savings. A space-saving and low-cost gas exchange chamber is obtained.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing an embodiment of the gas replacement chamber according to the present invention, Fig. 2 is a diagram showing an outline of the configuration of the gas replacement chamber of the present invention, and Fig. 3 shows the gas replacement chamber and helium leak test equipment. FIG. 4 is a diagram showing an outline of a conventional system configuration provided separately. FIG. 4 is a diagram showing the relationship between gas levels in helium leak test measurements. 1... First chamber (glove box), 2... Fuel element. 3... Gas replacement chamber, 4... Vacuum roughing system, 5...
・Standard leak exhaust system, 6... Honkawa exhaust system, 7...
Helium leak test system, 8... Helium supply amount control system, 9... Pirani vacuum gauge, 10... Open/close valve, 11.
... Differential pressure vacuum gauge, 12 ... Shutter, 13 ... Solenoid valve, 14 ... Electromagnetic vacuum gauge, 15 ... Standard radiation source, 16
...Solenoid valve, 17...Vacuum switch.

Claims (1)

[Scope of Claims] 1. In a gas purge chamber where objects to be transported are transferred so that the atmospheres of a first chamber with a negative pressure atmosphere and a second chamber with an atmospheric atmosphere are not mixed, the object to be transported is transferred from the first chamber. a rough evacuation system that evacuates the chamber to a predetermined low vacuum before receiving the gas; a gas supply system that supplies the same type of gas as the first chamber to the chamber while changing the flow rate; A main exhaust system that evacuates to the vacuum conditions for a helium leak test after receiving a conveyed object; A helium leak test system that performs a helium leak test under the vacuum conditions; and A helium leak test system that evacuates the helium in the chamber under the vacuum conditions before operation. A gas replacement chamber characterized by being equipped with a helium leak detection device consisting of a standard leak exhaust system for measuring detection sensitivity.