JP2004226385A - Canister abnormality detection system - Google Patents

Abstract

A canister abnormality detection system capable of accurately detecting the presence or absence of heat removal gas, that is, the soundness of a canister.
A container contains a spent nuclear fuel, a basket for preventing the spent nuclear fuel from coming into contact with the spent nuclear fuel, and a heat removal gas. A temperature sensor 62 is installed on the lid 48a and / or the bottom plate 40 of the container 14 or the pedestal 22 on which the container is installed. Based on the temperature of the lid 48a or the bottom plate 40 or the pedestal 22 measured by the temperature sensor 62, a monitoring device monitors a temperature change of the lid 48a or the bottom plate 40 or the pedestal 22, or a change of a temperature difference between the lid 48a and the bottom plate 40 or the pedestal 22. 64a.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a canister abnormality detection system, and more particularly, to a canister abnormality detection system that detects leakage of heat removal gas sealed in a canister.
[0002]
[Prior art]
At present, it is practically used in the United States to store spent nuclear fuel of a nuclear reactor in a steel cylindrical container called a canister in a sealed state, and practical use in Japan is being studied.
[0003]
In this storage system, He (helium) is sealed as a heat-removing gas inside the canister to prevent the temperature of spent fuel during storage from rising, while the canister is double-lided and welded to each other. It has a structure to prevent the release of radioactive substances contained in it.
[0004]
Although the probability of occurrence of an abnormality in the canister due to the filling of such a double lid or an inert gas such as helium is extremely low, if He gas leaks from the inside of the canister, the heat removal performance is reduced and the canister is deteriorated. The internal temperature can increase significantly.
[0005]
By the way, since the calorific value does not change even if such an abnormality (temperature rise) inside the canister occurs, the temperature gradient increases inside the canister, but the surface temperature of the canister and the exhaust of the concrete cask containing the canister are increased. Since the change in air temperature at the mouth is considered to be very small, it is difficult to detect an abnormality of the canister by measuring the temperature at these points.
[0006]
Therefore, as shown in FIG. 8, a thermocouple 62 is provided at the center of the outer surface of the secondary lid 52 of the canister 14, and the detector 64 electrically connected to the thermocouple 62 provides an outer surface of the secondary lid 52. It is known to monitor the presence or absence of leakage of the heat removal gas, that is, the soundness of the canister 14 by detecting a change in the temperature of the canister 14 (see, for example, Patent Document 1).
[0007]
[Patent Document 1]
JP-A-2002-202400 (page 7, FIG. 6)
[0008]
[Problems to be solved by the invention]
However, as shown in FIG. 9, this canister 14 has a primary lid 48 and a shielding body 44 inside a secondary lid 52, and a helium sealed between the primary lid 48 and the secondary lid 52. Because of the space 55, the temperature change on the outer surface of the secondary lid 52 is presumed to be extremely small.
[0009]
Therefore, it is presumed that it becomes difficult to accurately determine whether or not helium leaks, that is, the soundness of the canister 14 with high accuracy. 6 and 7, reference numeral 10 denotes a concrete cask, 12 denotes a concrete container, 15 denotes a container body, and 20 denotes a lid.
[0010]
The present invention has been made in order to solve such a conventional problem, and an object of the present invention is to accurately detect the presence or absence of a heat removal gas leak, that is, the integrity of a canister. It is an object of the present invention to provide a canister abnormality detection system that can perform the above.
[0011]
[Means for Solving the Problems]
A canister abnormality detection system according to the present invention that achieves the above object contains a spent nuclear fuel, a basket for preventing contact between the spent nuclear fuel and a heat removal gas, and a lid and / or bottom plate of the container. Alternatively, a temperature sensor is installed on the pedestal on which the container is installed, and a temperature change of the lid or the bottom plate or the pedestal based on the temperature of the lid or the bottom plate or the pedestal measured by the temperature sensor, or a temperature difference between the lid and the bottom plate or the pedestal. The change is monitored by a monitoring device.
[0012]
In the canister abnormality detection system according to the present invention, the temperature sensor is installed on the outer surface or inside of the primary lid among the primary and secondary lids closing the opening of the container, and the primary lid is closed by welding. The secondary lid covering the welded portion of the primary lid is closed by welding.
[0013]
The canister abnormality detection system of the present invention uses a thermocouple as a temperature sensor. Helium is used as a heat removal gas.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of a canister abnormality detection system according to the present invention.
[0015]
In FIG. 1, reference numeral 10 denotes a concrete cask in which a metal canister 14 is accommodated on a pedestal 22 therein.
[0016]
The concrete cask 10 is formed of a bottomed cylindrical concrete container 12 mainly made of concrete, and a cask lid 11 closing an upper opening thereof. In the concrete container 12, the surface of the concrete 13 is covered with a liner 16 made of a steel plate.
[0017]
The size of the concrete cask 10 is, for example, about 6 m in height, about 4 m in diameter, and about 0.9 m in wall thickness. The size of the canister 14 is, for example, about 4.5 m in height and about 1 in diameter. 0.7 m.
[0018]
The cask lid 11 has a concrete lid 18 on the inner surface of a disk-shaped steel plate end plate 17, and has an annular shielding block 19 on the outer surface of the end plate 17. The cask lid 11 is bolted to the upper end of the concrete container 12 by a plurality of bolts (not shown).
[0019]
The canister 14 is mounted on a pedestal 22 at the bottom 21 of the concrete container 12. At that time, the canister 14 is arranged coaxially with the concrete container 12, and forms a cooling air passage 23 between the outer peripheral surface of the canister 14 and the inner peripheral surface of the concrete container 12.
[0020]
Further, the concrete container 12 has a plurality of, for example, four intake ports 24 at the bottom 21 at equal intervals in the circumferential direction, and a plurality of, for example, four exhaust ports 25 at the upper section at equal intervals in the circumferential direction. are doing. The intake port 24 and the exhaust port 25 communicate with the cooling air passage 23, respectively, and the air flowing into the concrete container 12 from the intake port 24 removes the canister 14 while passing through the cooling air passage 23. Heat is applied, and after that, it flows out of the exhaust port 25 into the storage.
[0021]
On the other hand, the canister 14 is formed of, for example, stainless steel, and a large number of spent fuel assemblies (not shown) are supported by a honeycomb-shaped basket 26 in a cylindrical container body 15 having a bottom. It is enclosed in the state that it was. The basket 26 is also formed of aluminum, stainless steel, or the like.
[0022]
As shown in FIG. 2, the basket 26 has a honeycomb structure in which a first horizontal partition plate 27 and a second vertical partition plate 28 are assembled in a grid pattern. In addition, an angle member 31 is arranged in each of the partitions 30 partitioned by the first and second partition plates 27 and 28 to form a spent fuel assembly storage portion 32 and a gap portion 33. The gap portion 33 has two functions of preventing the spent fuel assemblies from coming too close to each other and promoting the helium circulation.
[0023]
Then, the heat generated in the spent fuel assembly is radiated to the outside of the canister 14 through the helium filled in the basket 26 and the canister 14.
[0024]
As shown in FIG. 3, the first and second partition plates 27 and 28 and the angle member 31 each have a semicircular upper cutout 34 at each upper end, and a trapezoidal lower cutout 35 at each lower end. Helium circulation is further promoted.
[0025]
As shown in FIG. 4, the helium a heated by the spent fuel assembly (not shown) and ascended in the spent fuel assembly housing portion 32 contacts the primary lid 48a and is cooled. After that, it flows into the gap 33 through the upper cutout 34. Thereafter, the helium a flows down in the gap 33 and returns from the lower notch 35 to the inside of the spent fuel assembly accommodating portion 32, and continues removing heat of the spent fuel assembly.
[0026]
Returning to FIG. 1, the upper opening of the canister 14 is closed by a disc-shaped primary lid 48a and a ring-shaped secondary lid 52a. More specifically, as shown in FIG. 5, the disc-shaped primary lid 48a is welded to the upper end of the container body 15 over the entire circumference. In addition, the welded portion welding the primary lid 48a, that is, the primary lid welded portion 36 is sealed by the ring-shaped secondary lid 52a. That is, the primary cover welding portion 36 is covered with the ring-shaped secondary lid 52a, and the inner peripheral portion of the ring-shaped secondary lid 52a is welded to the primary cover 48a over the entire circumference to form the secondary lid welding portion. 37a and the outer peripheral portion of the secondary lid 52a is welded to the upper end of the container body 15 over the entire periphery to form a secondary lid welded portion 37b.
[0027]
Further, in the present invention, a thermocouple 62, which is one of the temperature sensors, is attached to the primary lid 48a to measure the temperature of the primary lid 48a. In this embodiment, the thermocouple 62 is buried in the vertical hole 38 provided on the outer surface of the primary lid 48a. The thermocouple 62 may be provided at the center of the outer surface of the primary lid 48a with an auxiliary tool (not shown), if desired. May be used. The thermocouple 62 is electrically connected to the monitor panel 64a via the cable 39, and measures a change in the temperature of the primary lid 48a by the monitor panel 64a.
[0028]
For example, if the primary and secondary lid welds 36 and 37 have a welding defect, helium a filled in the canister 14 leaks therefrom, and the pressure in the canister 14 decreases. Then, since the temperature of the primary lid 48a decreases, the monitoring panel 64a stores the change in the temperature of the primary lid 48a, that is, the measured temperature T ₂ (° C.) of the primary lid 48a, in advance in the monitoring panel 64a. By measuring the temperature difference ΔT (° C.) from the initial temperature T ₁ (° C.), the leakage of helium a, that is, the soundness of the canister 14 can be known.
[0029]
If the alarm lamp (not shown) is turned on when the temperature difference ΔT (° C.) exceeds a predetermined value, the malfunction of the canister 14 can be known at a glance.
[0030]
According to the present invention, the thermocouple 62 is installed on the bottom plate 40 of the canister 14 instead of being installed on the primary lid 48a of the canister 14, or the thermocouple 62 is attached to the primary lid 48a and the bottom plate 40 of the canister 14, respectively. Installation is also possible. Then, based on the temperature of the primary lid 48a or the bottom plate 40 measured by the temperature sensor 62, a change in the temperature of the primary lid 48a or the bottom plate 40 or a change in the temperature difference between the primary lid 48a and the bottom plate 40 is monitored by the monitoring panel 64a. Monitor. In particular, when the change in the temperature difference between the primary lid 48a and the bottom plate 40 is monitored by the monitoring panel 64a, there is an advantage that the detection performance is improved because it is hardly affected by changes in the outside air temperature or the like.
[0031]
Further, instead of providing the thermocouple 62 on the bottom plate 40 of the canister, as shown in FIG. 7, by providing the thermocouple 62 on the pedestal 22 in contact with the canister bottom plate 40 and measuring the temperature of the surface or the inside of the pedestal 22, Equivalent detection performance is obtained.
[0032]
Note that the same reference numerals are given to the same devices as those of the first embodiment (see FIG. 1), and detailed description is omitted.
[0033]
Here, the temperature difference between the lid and the bottom plate or the pedestal of the canister will be supplementarily described. The temperature of the lid and the bottom plate or the pedestal changes as shown in FIG. 6 due to the pressure of He inside the canister, and as the pressure of He decreases, The temperature of the lid decreases, but the temperature of the bottom plate and the pedestal increases. That is, when the pressure of He is high, the temperature difference (A-a) between the lid and the bottom plate or the pedestal is large, but when the pressure of He decreases, the temperature difference (C-c) between the lid and the bottom plate or the pedestal becomes large. Become smaller.
[0034]
Therefore, if the temperature difference between the lid and the bottom plate or the pedestal is monitored, the change in the He pressure can be determined. In this method, the detection performance is considered to be higher because the method is hardly affected by a change in the outside air temperature.
[0035]
【The invention's effect】
As described above, the present invention accommodates a spent nuclear fuel, a basket for preventing contact between the spent nuclear fuel and the heat removal gas, and installs a lid and / or a bottom plate of the container or the container. A temperature sensor is installed on the pedestal to be measured, and a change in the temperature of the lid or bottom plate or the pedestal, or a change in the temperature difference between the lid and the bottom plate or the pedestal based on the temperature of the lid or the bottom plate or the pedestal measured by the temperature sensor is monitored by the monitoring device. Since the monitoring is performed, the presence or absence of leakage of the heat removal gas, that is, the soundness of the canister can be grasped with higher accuracy than before.
[0036]
In particular, according to the present invention, since the temperature sensor is installed on the outer surface or inside of the primary lid among the primary and secondary lids closing the opening of the container, the temperature of the lid is higher than before. It has become possible to measure with accuracy.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing one embodiment of a canister abnormality detection system according to the present invention.
FIG. 2 is a cross section of a canister.
FIG. 3 is a longitudinal section of the canister.
FIG. 4 is an explanatory diagram showing a flow of a heat removal gas.
FIG. 5 is an enlarged view of a portion X in FIG. 1;
FIG. 6 is a graph showing a change in a temperature distribution along a height direction of the canister with a decrease in pressure in the canister.
FIG. 7 is a schematic configuration diagram showing another embodiment of the canister abnormality detection system according to the present invention.
FIG. 8 is a cross-sectional view of a conventional radioactive substance storage system.
FIG. 9 is a partially cutaway side view of a conventional canister.
[Explanation of symbols]
a Gas for heat removal 14 Container 22 Pedestal 26 on which container is installed Basket 40 Bottom plate 48a Cover 62 Temperature sensor 64a Monitoring device

Claims (4)

In the container, a spent nuclear fuel, a basket for preventing contact of the spent nuclear fuel and a heat removal gas are accommodated, and a temperature sensor is installed on a lid and / or a bottom plate of the container or a pedestal on which the container is installed, Based on the temperature of the lid, the bottom plate, or the pedestal measured by the temperature sensor, a temperature change of the lid, the bottom plate, or the pedestal, or a change in a temperature difference between the lid and the bottom plate or the pedestal is monitored by a monitoring device. Canister abnormality detection system. A temperature sensor is installed on the outer surface or inside of the primary lid among the primary and secondary lids closing the opening of the container, and the primary lid is closed by welding, and a welded portion of the primary lid is provided. The canister abnormality detection system according to claim 1, wherein the secondary cover that covers the canister is closed by welding. 3. The canister abnormality detection system according to claim 1, wherein a thermocouple is used as the temperature sensor. The canister abnormality detection system according to claim 1, wherein helium is used as the heat removal gas.

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