JP2003004888A - Spent fuel inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise detection sensitivity of gamma ray emitted by radioactive gas such as Kr-85 and improve quantification accuracy by suppressing the incidence into a detector, of background gamma ray such as scattered gamma ray to be a disturbance of measurement. SOLUTION: A spent fuel storage vessel 1 storing spent fuel, an inspection shield body 2 covering the spent fuel storage vessel and a gamma ray detector are provided. The gamma ray radiated out of the radioactive gas to a measurement space set near the fuel in the spent fuel storage vessel is measured with the gamma ray detector through a collimator built in the shield body. In a position in the measurement space 8 excluding the region that the collimator 10 views, a gamma ray shield member 14 is provided. Nearby the wall of the spent fuel storage vessel in the region the collimator 10 views, magnetic field devices 16 and 17 for a positron reflection are placed so that the magnetic field is arranged vertical to the collimator direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spent fuel inspection apparatus for detecting damage of fuel irradiated in a nuclear reactor and stored in a spent fuel storage container (canister) by external gamma ray measurement.

[0002]

2. Description of the Related Art When storing spent fuel in a spent fuel storage container for a long period of time, it is necessary to check the integrity of the fuel inside the container periodically or at any time. However, after opening the spent fuel storage container, taking out the fuel inside and inspecting it, move the container to the water pool and open it,
After the inspection, a large work load occurs, such as having to perform sealing operation and decontamination work again.

Therefore, a technique for measuring the gamma ray from the outside to check the state of the internal fuel without opening the container has been studied. That is, it is a method of nondestructively inspecting the presence or absence of damage by measuring gamma rays emitted by a radioactive gas such as Kr-85 which is emitted when the spent fuel is damaged.

Conventionally, as such an inspection method, a collimator designed not to expect the spent fuel itself, which is a strong gamma ray source, is used, and a gamma ray detector is arranged so as to see only the space of the container. It is considered.

[0005]

However, in the above-described inspection device under study, the gamma rays emitted from the spent fuel are prevented from entering the gamma ray detector such as secondary gamma rays scattered by the wall of the container. Design is not considered. For this reason, there are many background gamma rays that interfere with the measurement of signal gamma rays, and there is a problem that it is difficult to quantify the gamma rays emitted by a radioactive gas such as Kr-85 having a low concentration.

When the object to be measured is Kr-85, the measured gamma ray energy is 514 keV,
At this energy, it occurs when the positrons generated in the field where gamma rays of more than 1022 keV exist disappear.
Gamma rays of 11 keV are close in energy and interfere, but there has been a problem that measures have not been taken.

Further, even if the fuel is damaged, the concentration of radioactive gas such as Kr-85 diffused in the entire space inside the storage container is low, and the space (gas) inside the container that is expected by the collimator is low.
There is a problem that it is difficult to count sufficient gamma rays because the volume of radioactive gas is small.

The present invention has been made in consideration of such a conventional situation, and suppresses the incidence of background gamma rays such as scattered gamma rays which interferes with the measurement on the detector and suppresses the incidence of Kr-85. An object of the present invention is to provide a spent fuel inspection device capable of increasing the detection sensitivity of gamma rays emitted by radioactive gas and thereby improving the quantitative accuracy.

[0009]

In order to achieve the above object, in the invention according to claim 1, a spent fuel storage container for storing spent fuel, and an inspection shield for covering the spent fuel storage container are provided. And a gamma ray detector provided on the side of the shielding body for inspection, which shields gamma rays emitted from radioactive gas generated at the time of fuel damage into a measurement space set near the fuel in the spent fuel storage container. In the spent fuel inspection device for detecting the damage of the spent fuel stored in the spent fuel storage container by measuring with the gamma ray detector through the collimator incorporated in, the collimator in the measurement space is expected. A gamma ray shielding member is provided at a position other than the range, and a positron reflection member is provided near the wall surface of the spent fuel storage container in the range expected by the collimator. Established a field device, it provides a spent fuel inspection apparatus is characterized in that the arrangement in which the magnetic field is perpendicular to the collimator direction.

According to the second aspect of the present invention, a cylindrical or prismatic spent fuel storage container for storing a plurality of spent fuels in a vertical state, an inspection shield for covering the spent fuel storage container, A gamma ray detector provided on the inspection shield side, and a measurement space is set below the lower support structure for fuel support in the spent fuel storage container or above the upper support structure material, and the measurement space is set. The gamma ray emitted from the radioactive gas generated at the time of fuel damage is measured by the gamma ray detector through a collimator incorporated in the shield to prevent damage of the spent fuel stored in the spent fuel storage container. In the spent fuel inspection device for detecting, the inside of the spent fuel storage container has three surfaces, that is, an upper surface and both side surfaces thereof, or a lower surface and three side surfaces thereof. The gamma ray shielding members, the gamma ray shielding members, the bottom plate or ceiling plate of the spent fuel storage container, and the side wall surface of the spent fuel storage container form a closed space, and are arranged on the both side surfaces. Provided is a spent fuel inspection device, characterized in that a plurality of gas flow holes are provided in the gamma ray shielding member.

According to a third aspect of the present invention, in the spent fuel inspection apparatus according to the first or second aspect, a heater for heating a part of a lower side surface or a bottom surface of the spent fuel storage container, and the spent fuel storage. Provided is a spent fuel inspection device, comprising at least one of a cooler for cooling a part of an upper side surface or a ceiling surface of a container.

In the invention according to claim 4, a spent fuel storage container for storing spent fuel, an inspection shield covering the spent fuel storage container, and a gamma ray detector provided on the inspection shield side. And a gamma ray emitted from a radioactive gas generated at the time of fuel damage in a measurement space set near the fuel in the spent fuel storage container is measured by the gamma ray detector through a collimator incorporated in the shield. Thereby, in the spent fuel inspection device for detecting the damage of the spent fuel stored in the spent fuel storage container, in the range in which the collimator in the measurement space is expected, a container body made of a gamma ray shielding material is provided, While accommodating the gas adsorbent in the container body, a gas flow hole is provided in the peripheral wall of the container body, and gamma rays generated from spent fuel are provided in the gas flow hole. The contact provides a spent fuel inspection apparatus is characterized in that is opened so as not to reach the gas adsorbent.

According to a fifth aspect of the present invention, in the spent fuel inspection apparatus according to the fourth aspect, the container body made of the gamma ray shielding material is provided in an upper space in the spent fuel storage container, or the spent fuel is used. Provided is a spent fuel inspection device, which is provided in a lower space in a storage container.

According to a sixth aspect of the present invention, in the spent fuel inspection device according to the fourth or fifth aspect, the heat is provided by providing the inspection shield with the peripheral wall of the container housing the gas adsorbent. Provided is a spent fuel inspection device characterized by being connected to a cooling device via a heat transfer member made of a metal having high conductivity.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a spent fuel inspection apparatus according to the present invention will be described below with reference to the drawings.

First Embodiment (FIGS. 1 to 7) FIG. 1 is a vertical cross-sectional view of a central portion showing the entire structure of a spent fuel inspection apparatus according to the first embodiment of the present invention, and FIG. FIG. FIG. 3 is a plan view of FIG. 4 is an enlarged cross-sectional view showing the main part of FIG. 1, and FIG. 5 is a schematic cross-sectional view taken along the line BB of FIG. 6 and 7 are operation explanatory views.

As shown in FIGS. 1 to 3, in the present embodiment, a vertical cylindrical spent fuel storage container 1 and a cylindrical shape in which an upper portion surrounding the spent fuel storage container 1 is opened. And the shield 2 for inspection. In the spent fuel storage container 1, a plurality of spent fuel assemblies 3 burned in a nuclear reactor are held by a lower support structure member 4 and an upper support structure member 5. Since the lower support structural member 4 supports the weight of the spent fuel assembly 3, the bottom plate 1 of the spent fuel storage container 1
It is joined to a through a plurality of columnar bottom plate connecting members 6. The upper end of the spent fuel storage container 1 is closed by the upper cover plate 7.

The lower portion of the spent fuel storage container 1, that is, the space between the bottom plate 1a and the lower support structure member 4 is a measuring space 8 for measuring gamma rays. Then, a gamma ray detector 9 is provided below the outer surface of the inspection shield 2 via a detector surrounding shield member 9a. The gamma ray detector 9 forms a collimator space 11 of a collimator 10 formed in the inspection shield 2. The measurement space 8 is arranged so as to be seen through. The collimator 10 includes a collimator main member 12 and a collimator inner surface member 13 that penetrate the peripheral wall portion of the inspection shield 2, and has a collimator space 11 at the center. As shown in FIG. 2, the bottom plate connecting member 6 described above has a collimator 10 in the measurement space 8.
With the arrangement excluding the range in which the gamma ray detector 9 is expected through
It is provided at intervals.

A plurality of gamma ray shielding members 14 are provided in the measuring space 8 of the spent fuel storage container 1 at a position other than the area where the gamma ray detector 9 can be seen through the collimator 10. . These gamma ray shielding members 14 are arranged in the upper portion of the measurement space 8, that is, on the side of the spent fuel assembly 3 with a horizontal interval, whereby
The gamma rays emitted from the spent fuel assembly 3 are prevented from directly entering the wall surface of the storage container 1 expected by the gamma ray detector 9. The shield 2 for inspection is provided with a facing surface shield member 15 at a portion facing the collimator space 11 with respect to the measurement space 8.

Further, in this embodiment, as shown in detail in FIGS. 4 and 5, the magnetic field device for positron reflection is located near the wall surface of the spent fuel storage container 1 in the range where the collimator 10 is expected. A pair of permanent magnets 16 and 17 are provided. That is, one permanent magnet 16 is arranged on the collimator 10 side to be a front permanent magnet, and a pair of permanent magnets 16 face each other in the direction orthogonal to the detection axis of the gamma ray detector 9. The other permanent magnet 17 is a rear surface permanent magnet, is arranged on the side opposite to the collimator 10, and a pair of permanent magnets similarly faces each other. Then, in these permanent magnets 16 and 17, as shown in FIG. 6, the N pole and the S pole are opposed to each other, whereby a magnetic field orthogonal to the detection axis of the gamma ray detector 9 is generated, and the positron is caused by this magnetic field. It is designed to prevent the incidence of light. That is, in the present embodiment, as a magnetic field device for positron reflection so as to prevent positrons from being incident on a portion of the wall plate of the spent fuel storage container 1 which is in the range where the gamma ray detector 9 can be seen through the collimator space 10. The means of attaching a permanent magnet is applied.

At the time of inspection, as shown in FIG. 7, gamma rays emitted from radioactive gas generated at the time of fuel damage are placed in the measurement space 8 set near the spent fuel assembly 3 in the spent fuel storage container 1. By using the gamma ray detector 9 through the collimator 10 incorporated in the inspection shield 2, the damage of the spent fuel assembly 3 housed in the spent fuel storage container 1 is detected. In addition, in FIG. 7, the inspection line in the gamma ray detector 9 is indicated by a straight line, and the reference numeral 18 indicates the inspection line at the upper visual field limit.

In such an inspection, in this embodiment, as shown in FIG. 2, the gamma ray shielding member 14 is provided so that the gamma rays emitted from the spent fuel are not directly incident on the side wall surface of the container which is expected by the collimator. As shown in FIG. 3, a directional marker 19 is provided on the upper surface of the spent fuel storage container 1 so that the position where the gamma ray shielding member 14 is attached matches the direction of the collimator. A directional marker 20 is provided on the upper surface of 2.

As a result, the spent fuel assembly 3 is placed in a portion of the wall plate of the spent fuel storage container 1 which is in the range where the gamma ray detector 9 can be seen through the opening of the collimator 10.
Since the gamma rays from the above are not directly incident, it has an effect of reducing scattered gamma rays incident on the gamma ray detector 9, and since the gamma ray shielding member 14 is attached only to a part of the inner surface of the spent fuel storage container 1, a line shielding member is added. It is possible to reduce an increase in the weight of the container.

Further, in the present embodiment, when the inspection shield 2 is made of concrete as a main material, the pair of collimator main members 12 which are located in front of and behind the collimator 10 and define an opening cross section. Collimator space 1 between
The inner surface of the concrete in No. 1 is provided with a collimator inner surface member 13 made of a metal material so that gamma rays emitted from the concrete do not enter the gamma ray detector 9.

Therefore, it is possible to suppress the gamma rays emitted by the natural radioactivity contained in the concrete from entering the gamma ray detector 9, so that it is possible to reduce the incident background gamma rays which hinders the measurement.

On the inner surface of the inspection shield 2 facing the collimator 10, an opposing surface shield member 15 made of a metal material is provided so that gamma rays emitted from concrete do not enter the detector. Because
It is possible to suppress gamma rays emitted by natural radioactivity contained in concrete from entering the gamma ray detector, and to reduce incident background gamma rays that interfere with measurement.

Further, in this embodiment, the gamma ray shielding member 14 is installed above the upper visual field limit 18 of the collimator prospective range, and shields the gamma rays emitted from the spent fuel assembly 3 located above the gamma ray shielding member 14 to shield the gamma ray. The member 14 is arranged so as not to overlap the expected range of the collimator. The bottom plate connecting member 6 is also arranged so as not to overlap the collimator prospective range.

Therefore, since the gamma ray detector 9 does not expect the gamma ray shielding member other than the side wall surface of the spent fuel storage container 1 and other structural materials, the gamma rays generated from the spent fuel assembly 1 are directly Alternatively, secondary gamma rays scattered and emitted by the gamma ray shielding member or the like are suppressed from entering the gamma ray detector 9, and the incident background gamma rays that interfere with the measurement can be reduced.

As described above, the combination of the spent fuel storage container 1 and the inspection shield 2 makes it possible to reduce scattered gamma rays which interfere with the measurement as a device for measuring gamma rays of radioactive gas. However, with the above configuration alone, it is not possible to prevent positrons secondarily generated from disturbing gamma rays from entering the side wall surface of the spent fuel storage container 1 expected by the collimator 10.

In this case, in this embodiment, as described above, two pairs of permanent magnets 16 and 1 are provided around the inside of the side wall surface of the spent fuel storage container 1 which is expected by the collimator 10.
7, namely, the front permanent magnet 16 and the rear permanent magnet 17
Is installed so that the magnetic field near the space wall surface of the collimator 10 formed by the permanent magnets 16 and 17 is perpendicular to the axial direction of the collimator, so that positrons generated around the measured space are It is possible to prevent the gamma ray detector 9 from being incident on a portion in a range that can be seen through the opening of the collimator space 11. That is, when focusing on Kr-85 as a radioactive gas that serves as an indicator of fuel damage, the energy is close to the 514 keV gamma ray emitted by Kr-85, which interferes with the quantitative determination of Kr-85.
Since the positron annihilation gamma ray of keV can be suppressed from entering the gamma ray detector, it is possible to reduce the incident background gamma ray which interferes with the measurement.

According to the first embodiment described above, it is possible to effectively suppress the incidence of background gamma rays, such as scattered gamma rays, which interferes with the measurement, on the detector.
The detection sensitivity of gamma rays emitted by radioactive gas such as 85 can be increased, and thereby the quantitative accuracy can be improved.

Second Embodiment (FIGS. 8 to 10) FIG. 8 is a vertical cross-sectional view of a central portion of the spent fuel inspection apparatus according to the second embodiment of the present invention, and FIG. It is a C1-C1 line sectional view. FIG. 10 shows C2-C2 of FIG.
It is a line sectional view.

The present embodiment is different from the above-described first embodiment in that the gamma ray shielding member 21 surrounds almost the entire range of the measurement space 8 formed in the spent fuel storage container 1 which is expected by the collimator 10. There is something I did.

That is, as shown in FIGS. 8 to 10, in this embodiment, the lower support structure member 4 of the spent fuel storage container 1 is used.
Of the measurement space 8 formed below the collimator 10
The upper shielding member 21a whose upper surface in the range of
The same area is covered by both side surfaces of the upper shield member 21a by substantially vertical side shield members 21b hanging from both side edges of the upper shield member 21a. This allows
The gamma ray shielding member 21, the bottom plate 1a of the spent fuel storage container 1, and the front and rear side walls 1b form a substantially completely closed space.

The upper shield member 21a of the gamma ray shield member 21 is formed in a fan shape that gradually widens from the end on the collimator 10 side toward the side wall end of the spent fuel storage container 1 on the opposite side. The side shield members 21b are spaced apart along the fan-shaped side edges of the upper shield member 21a. Further, a plurality of small-diameter gas circulation holes 22 are provided at intervals in the side shield member 21b.

In the illustrated example, the gamma ray shielding member 2
1 has a configuration in which the entire length of the diameter of the storage container 1 is included in a plane, but the present invention is not limited to this, and the length may be shorter than the entire length of the diameter of the storage container 1, and the end portion thereof may be closed with a shielding member. Good. The other configurations are almost the same as those in the first embodiment, and thus the description thereof will be omitted.

According to this embodiment having such a configuration, 1b facing the gamma ray detector 9 side of the spent fuel storage container 1 is provided.
Of the above, since the part in the range where the gamma ray detector 9 can be seen through the opening of the collimator 10 is covered with the gamma ray shielding member 21 almost over the front surface, gamma rays from the spent fuel assembly 3 are directly in the same range. Not only the incident gamma rays but also the secondary gamma rays scattered by the wall plate and the bottom plate 1a of the spent fuel storage container 1 and other structural materials can be hardly incident. Therefore, there is an effect that the scattered gamma rays incident on the gamma ray detector 9 are greatly reduced.

Further, since the gamma ray shielding member 21 has a fan-shaped configuration in a plan view, the gamma ray shielding member 21 and the range in which the collimator 10 can be seen in the measurement space 8 can be arranged so as not to overlap each other. The gamma rays scattered by the shielding member 21 are prevented from directly entering the gamma ray detector 9 side.

Further, the measurement space 8 is formed as a closed space by the gamma ray shielding member 21, the bottom plate 1a of the spent fuel storage container 1 and the side walls 1b of the front and rear containers, but the side shielding members 21b on both sides are formed. Since a plurality of gas circulation holes 22 are provided, krypton gas or the like released when the spent fuel assembly 3 is damaged can be mixed. Since the direction of the gas flow holes 22 is horizontal or nearly horizontal, the gamma ray from the spent fuel assembly 3 located above does not directly enter the measurement space 8. Further, the direction of the gas flow hole 22 is inclined at a right angle or near a right angle with respect to the collimator 10 side, so that secondary gamma rays scattered at the side wall 1b of the spent fuel storage container 1 are also
It does not enter the side wall 1b in the range where the gamma ray detector 9 can be expected.

Although not shown, in the case where the measurement space is located above the spent fuel storage container, the configuration is upside down with respect to the case where the measurement space 8 is located below the spent fuel storage container 1 described above. do it. With this, the upper lid plate serving as the container ceiling can be used as the one surface for forming the closed space, and the same operation can be performed.

According to the present embodiment, not only the gamma ray from the spent fuel does not directly enter the portion of the wall plate of the spent fuel storage container which is in the range where the gamma ray detector can be expected through the collimator opening, The secondary gamma rays scattered by the wall plate and bottom plate of the spent fuel storage container and other structural materials will almost never enter the wall plate in the range where the detector can be expected, so the scattered gamma rays incident on the gamma ray detector will be It can be significantly reduced. The measured space forms a closed space by the peripheral wall made of gamma ray shielding material, the container bottom plate, and the side wall surfaces of the front and rear containers, and a plurality of gas circulation holes are provided in the gamma ray shielding members on both side surfaces. Therefore, krypton gas or the like released when the fuel is damaged can be mixed.

Third Embodiment (FIGS. 11 and 12) FIG. 11 is a central longitudinal sectional view showing the entire spent fuel storage container of the spent fuel inspection apparatus according to the third embodiment of the present invention. FIG. It is the DD sectional view taken on the line of FIG.

In this embodiment, a heater 23 that heats a part of the lower side surface or the bottom surface of the spent fuel storage container 1, and a cooler that cools a part of the upper side surface or the ceiling surface of the spent fuel storage container 1. 24 is provided. Note that FIG.
12 and FIG. 12 show a configuration based on the second embodiment, but a configuration based on the first embodiment may be used. Further, in the present embodiment, the heater 23 and the cooler 24
Both are provided, but the configuration may be provided with only one of them.

As described above, the heater 23 or the cooler 24 is operated by installing a device for cooling and heating from the outside of the spent fuel storage container 1 so that convection of gas occurs in the spent fuel storage container 1. It is possible to cause gas convection in the spent fuel storage container 1 to uniformly mix the radioactive gas inside the spent fuel storage container 1.

Specifically, as shown in FIGS. 11 and 12, a heater 23 is provided below the inner surface of the shield 2 for inspection, which is close to the spent fuel storage container 1, and the spent fuel storage container 1 is provided with the heater 23. Cooling 24 is provided on the upper part of the inner surface which is close to. In the present embodiment, a configuration in which a plurality of heaters 23 and a plurality of coolers 24 are provided, a configuration in which only a single heater 23 or only a single cooler 24 is provided, and a single heater each diagonally are provided. The heater 23 and the cooler 24 may be provided.

According to this embodiment, even in the sealed spent fuel storage container 1, the gas in the container can be agitated by thermal convection before the inspection, so the krypton gas released when the fuel is damaged. Etc. can be uniformly mixed in the container, and the leak amount or concentration of radioactive gas can be accurately quantified.

Fourth Embodiment (FIGS. 13 to 15) FIG. 13 is a vertical cross-sectional view of the central portion of the spent fuel inspection apparatus according to the fourth embodiment of the present invention, and FIG. It is the EE sectional view. FIG. 15 is an F-F of FIG.
It is a line sectional view.

In this embodiment, a container body 25 made of a gamma ray shielding material is provided in a range in which the collimator 10 in the measurement space 8 of the spent fuel storage container 1 is expected, and the gas adsorbent is provided in the internal space 26 of the container body 25. , Accommodating, for example, activated carbon 27, and providing gas circulation holes 28 in the peripheral wall of the container body 25,
The gas flow hole 28 is opened in a direction in which gamma rays from the spent fuel assembly 3 do not directly reach the activated carbon 27.

Specifically, as shown in FIGS. 13 to 15,
When there is a measurement space 8 in the lower part or the upper part of the spent fuel storage container 1, the collimator 1 is set inside the spent fuel storage container 1.
In a range where 0 can be expected, a laterally cylindrical container body 25 made of a gamma ray shielding material having five surfaces of upper and lower surfaces, both side surfaces and a front surface (the inner surface of the spent fuel storage container 1) is provided.
The position of the front surface of the container body 25 is set within a range of, for example, 10 to 20 cm from the inner surface of the side plate contacting the collimator 10 of the spent fuel storage container 1.

Activated carbon 27 as a gas adsorbent is housed in the internal space 26 of the container 25, and gas flow holes 28 are formed in a part of the container 25 made of a gamma ray shielding material, for example, the lower surface and both side surfaces of the peripheral wall. The gas in the spent fuel storage container 1 is circulated so that the radioactive gas in the gas is adsorbed and concentrated.

The plurality of gas flow holes 28 provided on the lower surface and the side surface of the container body 25 are refracted in the peripheral wall of the container body 25, and gamma rays from the spent fuel assembly 1 are scattered on the container wall and the like. The scattered gamma rays generated as a result do not reach the activated carbon 27.

The activated carbon 27 is accommodated in a small container (not shown) and is easily accommodated in the container body 25 of this embodiment. At least a part of this small container has a wire mesh shape, and the gas in the spent fuel storage container 1 is activated carbon 2
It can now be distributed through 7.

According to the fourth embodiment as described above, the gas in the storage container passes through the gas flow holes 28 and the activated carbon adsorbent 27
Since the radioactive gas such as krypton gas is adsorbed and concentrated there, the gamma ray to be measured can be detected with high efficiency. Further, since the disturbing gamma rays are shielded by the gamma ray shielding member 25, it is possible to perform measurement with a high signal-to-noise ratio (S / N ratio), and it is possible to obtain an effect that the sensitivity of detecting fuel damage can be increased. That is, since krypton gas, which is diluted in the gas in the spent fuel storage container, is concentrated on the activated carbon adsorbent, the amount of krypton gas, etc. expected by the gamma ray detector increases, and the target gamma ray detection signal count rate is increased. Can be increased. Further, since the gas adsorbent is surrounded by the gamma ray shielding material, the background gamma rays from the interfering fuel can be reduced.

Fifth Embodiment (FIGS. 16 and 17) FIG. 16 is a vertical cross-sectional view of the central portion of the spent fuel inspection apparatus according to the fifth embodiment of the present invention. It is a GG line sectional view.

In this embodiment, the same structure as that of the fourth embodiment is applied to the upper space in the spent fuel storage container 1.

That is, as shown in FIGS. 16 and 17, in this embodiment, the upper lid plate 7 of the spent fuel storage container 1 is used.
Gamma rays can be measured from above through the portion, and in a part of the upper end side of the spent fuel storage container 1, for example, in one corner, a vertically long tubular shape made of a gamma ray shielding material, which is composed of four side surfaces and a lower surface. Container body 25 with five sides closed
The inner space 26a of a is filled with activated carbon 27 as a gas adsorbent as in the fourth embodiment.

The upper lid plate 7 of the spent fuel storage container 1
In order to perform gamma ray measurement in a state where the spent fuel storage container 1 is kept airtight, the gamma ray lead-out hole 29 formed of a through hole as a collimator at the upper coaxial position of the container body 25A.
And a lower end of the gamma ray lead-out hole 29 is closed by a closing plate 30.

Gamma ray derivation hole 2 of spent fuel storage container 1
At the time of inspection, an upper collimator 31 is installed above 9 to match the central axis with the gamma ray lead-out hole 29, and the gamma ray detector 9 is installed above it together with the detector surrounding shielding member 9a.

A small container (not shown) containing activated carbon 27 is installed in the vicinity of the upper cover plate 7 of the spent fuel storage container 1 and surrounds the side surface and the lower surface of the small container containing the activated carbon 27. 25a made of a gamma ray shielding material
Is installed, and a plurality of gas circulation holes 28a are provided on the lower surface and upper side surface of the container body 25a. The plurality of gas flow holes 28a are refracted in the peripheral wall of the container body 25a, and direct rays of gamma rays generated from the spent fuel assembly 3 and scattered gamma rays scattered by the vessel wall of the spent fuel storage vessel 1 and the like. However, it does not reach the activated carbon 27.

This embodiment is similar to the fourth embodiment in that the activated carbon 27 as a gas adsorbent and the container body 25a made of a gamma ray shielding material surrounding the activated carbon 27 are installed in the spent fuel storage container 1. Although the configuration is adopted, the configuration in which the upper collimator 31 and the gamma ray detector 9 are arranged above the spent fuel storage container 1 and applied to the measurement is different.

Also according to the present embodiment having such a configuration,
Since the gas in the spent fuel storage container 1 passes through the activated carbon 27 through the gas flow hole 28a and the radioactive gas such as krypton gas is adsorbed and concentrated, the gamma ray to be measured can be detected with high efficiency. Further, since the interfering gamma rays are shielded by the container body 25a made of the gamma ray shielding material, a high signal-to-noise ratio (S / N ratio) can be measured, and the effect of increasing the fuel damage detection sensitivity can be obtained. .

The upper lid plate 7 of the spent fuel storage container 1
May also have a function as a shielding member at the stage of hermetic welding after the fuel is inserted into the spent fuel storage container 1. Also in this case, since the container body 25a made of a gamma ray shielding material is installed below the gamma ray lead-out hole 29, leakage of gamma rays from the spent fuel assembly 3 is suppressed. Further, if necessary, the gamma ray derivation hole 29
It is also possible to insert a shielding plug into the to enhance the shielding effect. The function of the gamma ray lead-out hole 29 can be made effective by pulling out the shielding plug only during the radioactivity measurement inspection.

Sixth Embodiment (FIGS. 18 and 19) FIG. 18 is a vertical cross-sectional view of a central portion showing the essential structure of a spent fuel inspection apparatus according to a sixth embodiment of the present invention. It is a HH sectional view.

As in the fifth embodiment, the present embodiment is such that the container body 25a containing the gas adsorbent is arranged in the upper space of the spent fuel storage container 1, but the container body 25a
The fins 32 are provided on the test fuel shielding container 2, and the container 25a is cooled by the cooling means provided on the inspection shield 2 via the fins 32, thereby cooling the activated carbon 27 as a gas adsorbent, and the spent fuel storage container 1 The heat convection of the gas inside is promoted, and the gas adsorption of the activated carbon is enhanced by cooling.

That is, as shown in FIGS. 18 and 19, a part of the upper end side of the spent fuel storage container 1, for example, one corner, is a vertically long cylindrical shape made of a gamma ray shielding material, and is formed from the four side surfaces and the lower surface. The inner space 26a of the container body 25a whose five surfaces are closed is filled with activated carbon 27 as a gas adsorbent as in the fifth embodiment.

The upper cover plate 7 of the spent fuel storage container 1
In order to perform the gamma ray measurement while keeping the airtightness of the spent fuel storage container 1, the gamma ray lead-out hole 29, which is a through hole as a collimator, is provided at the upper coaxial position of the container body 25a.
And a lower end of the gamma ray lead-out hole 29 is closed by a closing plate 30.

Gamma ray derivation hole 2 of spent fuel storage container 1
At the time of inspection, although not shown, an upper collimator is installed above 9 in the same manner as in the fifth embodiment, with the central axis aligned with the gamma ray lead-out hole 29, and a gamma ray detector is installed above it.

A small container (not shown) containing activated carbon 27 is installed in the vicinity of the upper cover plate 7 of the spent fuel storage container 1 and surrounds the side surface and the lower surface of the small container containing the activated carbon 27. 25a made of a gamma ray shielding material
Is installed, and a plurality of gas circulation holes 28a and 28b are provided on the lower surface and the upper portion of the side surface of the container body 25a. These plural gas flow holes 28a and 28b are bent in the peripheral wall of the container body 25a, and direct rays of gamma rays generated from the spent fuel assembly 3 and the spent fuel storage container 1
The scattered gamma rays scattered by the container wall of No. 1 do not reach the activated carbon 27.

In such a structure, the fin 32 is provided in the container 25a for accommodating the activated carbon 27 as the gas adsorbent.
Are attached, and these container body 25a and fin 3
2 is made of copper, aluminum, or another material having a high thermal conductivity. And the fin 32 is
It is in contact with the inner surface 1b of the spent fuel storage container 1.

On the other hand, the inspection shield 2 has a heat transfer member 33 and a cooling medium container 34 thermally connected to the heat transfer member 33 at a position facing the fin 32 when the spent fuel storage container 1 is stored at the time of inspection. And are provided. The cooling medium container 34 is connected via a flexible cooling medium pipe 35 to a cooling medium supply device 36 provided above the inspection shield 2.

Further, the cooling medium container 34 includes the push rod 3
7 is connected to a pressing mechanism 38 provided on the outer side of the inspection shield 2, and the cooling medium container 34 presses the heat transfer member 33 by the operation of the pressing mechanism 38. Can be pressed against the fin 32 side of the container body 25a. Of the outer surface of the cooling medium container 34,
The surfaces other than the surface in contact with the heat transfer member 33 are covered with a heat insulating material, and the cooling medium pipe 35 is also covered with a heat insulating material.

At the time of inspection, after the spent fuel storage container 1 is stored in the inspection shield 2, the pressing medium 38 causes the cooling medium container 34 and the heat transfer member 33 to come into contact with the spent fuel storage container 1.
It is pressed against the side wall 1b of to realize thermal contact.

Next, a cooling medium such as liquid nitrogen is injected into the cooling medium container 34 from the cooling medium supply device 36. As a result, the fins 32 are cooled through the side wall 1b of the spent fuel storage container 1, and the activated carbon 27 is further cooled. After the cooling state of the activated carbon 27 is maintained for a while, the activated carbon 27
The gamma rays emitted by the part are measured.

According to this embodiment having such a configuration, the activated carbon 27 is cooled, so that the adsorption of radioactive gas such as krypton to the activated carbon 27 is promoted, and the activated carbon 27 is cooled, so that the used carbon is not used. The thermal convection of the gas in the fuel storage container 1 is promoted. That is, the gas cooled in the activated carbon 27 flows out through the lower gas flow hole 28a, and the gas in the spent fuel storage container 1 flows in through the upper gas flow hole 28b. A large amount of gas passes through the activated carbon 27 in time, and the effect that the adsorption of radioactive gas to the activated carbon 27 is promoted is obtained. That is, the activated carbon adsorbent is cooled,
Due to the convection of the gas, the concentration and the rate of concentration of the krypton gas or the like on the activated carbon adsorbent are increased.
The amount of krypton gas or the like expected by the gamma ray detector is further increased, and the target gamma ray detection signal count rate can be further increased.

As a result, the radioactive gas such as krypton gas is efficiently adsorbed and concentrated in a short time, so that the gamma ray to be measured can be detected with high efficiency and the measurement with a high signal-to-noise ratio (S / N ratio). It is possible to obtain the effect that the detection sensitivity of fuel damage can be increased.

Although the present embodiment has been described based on the fifth embodiment, it can be applied to the case where the container body 25 is provided below the spent fuel storage container 1 in the fourth embodiment.

Regarding the adsorption characteristics of krypton gas on activated carbon, reference can be made to a document (JAERI-m) issued by Japan Atomic Energy Research Institute.
emo 9425 Eiji Sakai et al. "Development test of cover gas online gamma ray monitor (III)" March 1981). According to this document, krypton gas is adsorbed by activated carbon even at room temperature, but it is known that the adsorption coefficient is increased by lowering the temperature of activated carbon.

The present embodiment is based on such a fact.
In order to promote the adsorption of radioactive gas to the activated carbon 27, a means for installing a component for cooling the adsorbent from the outside of the spent fuel storage container 1 is used.

[0079]

As described in the above embodiments, according to the present invention, it is possible to suppress the incidence of background gamma rays, such as scattered gamma rays, which interferes with the measurement, on the detector and reduce the Kr.
It is possible to increase the detection sensitivity of gamma rays emitted by radioactive gas such as -85, thereby improving the quantification accuracy.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a central portion showing the entire structure of a spent fuel inspection device according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a plan view of FIG.

FIG. 4 is a cross-sectional view showing an enlarged main part of FIG.

5 is a schematic cross-sectional view taken along the line BB of FIG.

FIG. 6 is an explanatory view of the operation of the first embodiment.

FIG. 7 is an operation explanatory view of the first embodiment.

FIG. 8 is a vertical cross-sectional view of a central portion showing a main part configuration of a spent fuel inspection device according to a second embodiment of the present invention.

9 is a sectional view taken along line C1-C1 of FIG.

10 is a sectional view taken along line C2-C2 of FIG.

FIG. 11 is a vertical cross-sectional view of a central portion showing the entire spent fuel storage container of the spent fuel inspection device according to the third embodiment of the present invention.

12 is a cross-sectional view taken along the line DD of FIG.

FIG. 13 is a vertical cross-sectional view of a central portion showing a main part configuration of a spent fuel inspection device according to a fourth embodiment of the present invention.

14 is a cross-sectional view taken along the line EE of FIG.

15 is a cross-sectional view taken along line FF of FIG.

FIG. 16 is a vertical cross-sectional view of a central portion showing the main configuration of a spent fuel inspection device according to a fifth embodiment of the present invention.

17 is a cross-sectional view taken along the line GG of FIG.

FIG. 18 is a central longitudinal cross-sectional view showing the main configuration of a spent fuel inspection device according to a sixth embodiment of the present invention.

19 is a cross-sectional view taken along the line HH of FIG.

[Explanation of symbols]

1 Spent fuel storage container 2 Shield for inspection 3 spent fuel assemblies 4 Lower support structure 5 Upper support structure 6 Bottom plate connection structural material 7 Upper cover plate 8 measurement space 9 Gamma ray detector 9a Detector surrounding shielding member 10 Collimator 11 Collimator space 12 Collimator main member 13 Collimator inner surface member 14 Gamma ray shield 15 Opposing surface shielding member 16 Front permanent magnet 17 Rear permanent magnet 18 Upper visual field limit 19 direction marker 20 direction marker 21 Gamma ray shielding member 22 Gas flow holes 23 heater 24 Cooler 25 Container (gamma ray shielding material) 26 Internal space of container 27 Activated carbon (gas adsorbent) 28 Gas flow holes 29 Gamma ray derivation hole 30 closure plate 31 Upper Collimator 32 fins 33 Heat transfer member 34 Cooling medium container 35 Cooling medium pipe 36 Cooling medium supply device 37 Push rod 38 Pushing mechanism

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G21F 5/12 G21F 5/00 E (72) Inventor Tetsuo Goto 8 Shinsugita-cho, Isogo-ku, Yokohama, Kanagawa, Ltd. Share Ceremony Company Toshiba Yokohama Works (72) Inventor Tetsuo Matsumura 2-11-1, Iwatokita, Komae-shi, Tokyo F-Term in Komae Research Center, Central Research Institute of Electric Power Industry (reference) 2G075 AA18 CA50 DA03 DA07 DA16 EA05 FA04 FA12 FA18 FA20 FC02 GA36 2G088 EE12 EE23 FF04 JJ01

Claims (6)

[Claims] 1. A spent fuel storage container for storing spent fuel, and an inspection shield for covering the spent fuel storage container,
A gamma ray detector provided on the side of this inspection shield is provided, and a gamma ray emitted from radioactive gas generated at the time of fuel breakage in the measurement space set near the fuel in the spent fuel storage container is emitted to the shield. In the spent fuel inspection device for detecting the damage of the spent fuel stored in the spent fuel storage container by measuring with the gamma ray detector through the built-in collimator, the range that the collimator in the measurement space can expect. A gamma ray shielding member is provided at a position other than that, and a magnetic field device for positron reflection is installed in the vicinity of the wall surface of the spent fuel storage container in the range expected by the collimator, and the magnetic field is arranged to be perpendicular to the collimator direction. A spent fuel inspection device characterized in that 2. A columnar or prismatic spent fuel storage container for storing a plurality of spent fuels in a vertical state, an inspection shield for covering the spent fuel storage container, and an inspection shield provided on the inspection shield side. And a gamma ray detector provided in the spent fuel storage container, and a measurement space is set below the lower support structure for supporting fuel in the spent fuel storage container or above the upper support structure, and the measurement space is generated when the fuel is damaged. Spent fuel inspection for detecting damage of spent fuel stored in the spent fuel storage container by measuring gamma rays emitted from radioactive gas with the gamma ray detector through a collimator incorporated in the shield. In the device, gamma ray shielding members are arranged on the upper surface and three side surfaces of the space, or the lower surface and both side surfaces, of the space seen by the collimator inside the spent fuel storage container. On the other hand, these gamma ray shielding members, a bottom plate or a ceiling plate of the spent fuel storage container, and a side wall surface of the spent fuel storage container form a closed space, and the gamma ray shielding members arranged on the both side surfaces. A spent fuel inspection apparatus having a plurality of gas flow holes. 3. The spent fuel inspection apparatus according to claim 1, wherein a heater for heating a part of a lower side surface or a bottom surface of the spent fuel storage container, and an upper side surface or a ceiling of the spent fuel storage container. A spent fuel inspection device comprising at least one of coolers for cooling a part of a surface. 4. A spent fuel storage container for storing spent fuel, and an inspection shield for covering the spent fuel storage container,
A gamma ray detector provided on the side of this inspection shield is provided, and a gamma ray emitted from radioactive gas generated at the time of fuel breakage in the measurement space set near the fuel in the spent fuel storage container is emitted to the shield. In the spent fuel inspection device for detecting the damage of the spent fuel stored in the spent fuel storage container by measuring with the gamma ray detector through the built-in collimator, the range that the collimator in the measurement space can expect. In addition, a container body made of a gamma ray shielding material is provided, and a gas adsorbent is housed in the container body, and a gas flow hole is provided in the peripheral wall of the container body. The spent fuel inspection device is characterized in that it is opened so as not to reach the gas adsorbent. 5. The spent fuel inspection device according to claim 4, wherein the container body made of a gamma ray shielding material is provided in an upper space inside the spent fuel storage container, or a lower space inside the spent fuel storage container. The spent fuel inspection device, which is provided in the. 6. The spent fuel inspection apparatus according to claim 4 or 5, wherein the peripheral wall of the container in which the gas adsorbent is stored is made of a metal having a high thermal conductivity provided on the inspection shield. A spent fuel inspection device, characterized in that it is connected to a cooling device via a configured heat transfer member.