JPH0553237B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is a fast breeder reactor that is configured so that, when the fuel of a fast breeder reactor is damaged, a fuel assembly having a damaged fuel pin can be identified during reactor operation. This invention relates to a damaged fuel position detection device.

[Technical background of the invention and its problems] If the fuel constituting the core is damaged during reactor operation, the safety and operation rate of the reactor will be significantly reduced, so it is necessary to immediately detect the damaged fuel. There is.

In fast breeder reactors, cover gas method and DN (Delayed
Neutron) method is also used. Among these methods, the cover gas method removes activated Kr and Xe (inert gas) from the fission products (FP) accumulated in the fuel pin, which are released into the coolant when the fuel pin is damaged. The DN method detects delayed neutrons emitted from activated Br, I, etc. among fission products.

However, if damaged fuel is left in the reactor, fission products may diffuse into the coolant, contaminating not only the coolant but also reactor system equipment. Therefore, it is necessary to replace the fuel assembly with damaged fuel with a new one. Therefore, there is a need for a damaged fuel location detection device that can identify the location of damaged fuel for each fuel assembly.

Conventionally, tag gas systems, selector valve systems, shipping systems, and the like have been considered as damaged fuel position detection devices for detecting the position of damaged fuel in fast breeder reactors. Among these, the tag gas method uses a tag gas (Kr, Xe) whose gas composition is known to the fuel pin in advance.
This method involves sealing up the fuel, and then analyzing the tag gas that migrates into the cover gas in the event of fuel failure to identify the location of the failure. The selector valve method samples the coolant passing through the fuel assembly, measures the radioactivity in the coolant, and detects the presence or absence of damage. By switching the valve, the sampling line is switched and the location of damage is detected. do. The shipping method is a method for detecting the location of damage by efficiently detecting fission products released from the damaged assembly after the reactor is shut down.

Among these methods, the tag gas method has limitations on the types of tag gas, making it difficult to reliably detect the location of damage in large reactor cores. Additionally, the shipping method is restricted in that it can only be used when the reactor is shut down. While the selector valve method has the advantage of being usable regardless of the size of the reactor core and even while the reactor is operating, it requires a larger device compared to the tag gas method and shipping method, which poses the risk of having an impact on the reactor structure.

FIG. 5 is a schematic diagram showing an example of a general selector valve type device. This device is equipped with a selector valve 3 above the core 1 that is operated by a rotary drive device 2 . Coolant sampled from the upper part of the fuel assembly 4 in the reactor core 1 is introduced into the selector valve 3 through a sampling pipe 5. The selector valve 3 can be rotated in the circumferential direction via a shaft by the rotary drive device 2. By rotating, the selector valve 3 selects a specific sampling tube 5 and transfers the coolant in the selected sampling tube 5 to the sampling chain. A line leading to the bar 6 is formed.

The coolant in the sampling pipe 5 selected by the selector valve 3 is pressurized by the electromagnetic pump 7, the flow rate is monitored by the electromagnetic flow meter 8, and then guided to the sampling chamber 6. A neutron detector 9 is installed near the sampling chamber 6, and detects fuel damage by detecting delayed neutrons emitted from delayed neutron leading nuclei in the coolant inside the sampling chamber 6. However, by knowing from which sampling line the damage was detected, the location of the damage can be determined. Note that the reference numeral 10 in the figure indicates a shielding plug that covers a reactor vessel (not shown).

It is also possible to add a system that separates the gas in the coolant and detects the presence or absence of damage by measuring gamma rays so that even fission product gas dissolved in the coolant can be detected.

In order to collectively identify the location of damage using the above method, sampling must be performed for each fuel assembly and guided to the selector valve 3. For this reason, when the core 1 of the nuclear reactor becomes larger, the number of samplings increases, leading to an increase in the size of the selector valve 3, which poses a problem that impacts the reactor structure.

[Purpose of the invention]

The present invention was made to solve the above problems, and it reduces the number of sampling pipes connected to the selector valve by sampling coolant from a plurality of fuel assemblies in one operation. Another object of the present invention is to provide a damaged fuel position detection device that prevents the selector valve from increasing in size and has less impact on the reactor structure.

[Summary of the invention]

The present invention switches a selector valve to which a plurality of sampling tubes are connected to sample the coolant passing through the fuel assembly at an arbitrary position in the reactor core, detects the radioactivity of the sampled coolant, and detects damaged fuel. In the damaged fuel position detection device for detecting the position, each of the sampling tubes is provided with a sampling post having a plurality of sampling holes, and each sampling hole of the sampling post corresponds to a plurality of adjacent fuel assemblies. On the other hand, the sampling posts adjacent to each other are set to be able to sample coolant from a common fuel assembly located between the two sampling posts, and the sampling posts and the sampling pipes are connected by switching the selector valve. This is a damaged fuel position detection device configured to logically process combinations and identify damaged fuel assemblies by sampling the coolant from the fuel assemblies using one selected sampling post or two adjacent sampling posts. .

According to the present invention, the radioactivity in the coolant is measured by sampling the coolant passing through a plurality of fuel assemblies all at once using the device having the above configuration, and the location of the damaged fuel assembly can be identified by sampling the damage detected. This can be done by logically determining the combination of posts and sampling tubes, and the location of the damaged fuel assembly can be detected.

[Embodiments of the invention]

Hereinafter, one embodiment of the damaged fuel position detection device according to the present invention will be described with reference to FIGS. 1 to 4.

In FIG. 1, the same parts as those in FIG. 5 are given the same reference numerals, and the explanation of the overlapping parts will be omitted.

The basic difference between the present invention and the conventional example is that a plurality of sampling pipes 5 are connected to a selector valve 3.
The sampling post 11 is connected to each.

These sampling posts 11 are arranged above each fuel assembly 4 as shown partially in the plane of the core in FIG. These sampling posts 11 are branched from a central channel hole 14 and provided with, for example, seven sampling holes 11a to 11g, as shown in a longitudinal section in FIG. Also,
These sampling posts 11 are supported by supports 12
It is detachably supported by. The sampling holes 11a to 11g extend radially from the central hole 11a and have holes 11b to 11g divided into hexagons, and each hole 11a to 11g has a hexagonal groove, etc. of the fuel assembly 4a to 4g. top surface,
That is, they are formed at positions corresponding to the coolant outflow holes of the handling head. FIG. 4 shows an example in which sampling holes 13b to 13g are provided in the control rod guide tube 13 in the reactor core 1.
In this example, since the control rod 15 is inserted between the adjacent fuel assemblies 4, the adjacent fuel assemblies 4a,
The coolant from 4d is sampled from sampling holes 13e and 13b located off-center.

Note that the reference numeral 15 in FIG. 1 is a shielding body that surrounds the rotary drive device 5, the sampling chamber 6, the electromagnetic flowmeter 8, the neutron detector 9, and the shaft 16. Further, reference numeral 17 is a moderator that surrounds the neutron detector 9.

As is clear from FIGS. 1 to 3, in the apparatus configured as described above, a sampling post 11 is installed above the fuel assembly 2, and the sampling post 11 has a sampling hole 11a.
Seven pieces of ~11g were formed. These sampling holes 11a to 11g are sampling posts 1
One fuel assembly 2a located directly below the fuel assembly 2a, and six fuel assemblies 2 adjacent to this fuel assembly 2a.
Sample the coolant from b~2g. Also, as is clear from FIG. 4, since a sampling post cannot be installed above the control rod guide tube 18, six sampling holes 13b are provided in the guide tube tube 13.
~13g is provided, and the structure is such that sampling can be performed from six fuel assemblies 2 adjacent to the control rod 15. The coolant sampled by the sampling post 11 or the guide tube tube 13 is collected into one tube by the sampling tube 5 and guided to the selector valve 3, respectively.

Next, an example of detecting damaged fuel using the damaged fuel position detection device will be described.

1 and 2, it is assumed that the selector valve 3 shown in FIG. 1 is sequentially switched to sample a damaged fuel assembly. As shown in Figure 2, damage was detected when the part corresponding to the sampling pipe from sampling post 11A was surveyed, and the selector valve 3 was further switched and the part corresponding to the sampling pipe from sampling post 11B was surveyed. If a signal of damage is detected at the same time, sampling post 11A,
Fuel assembly 4c commonly sampled by 11B
It can be determined that the fuel pin was damaged. Similarly, if a damage signal is detected only when surveying the portion corresponding to the sampling pipe from the sampling post 11B, it can be identified that the fuel pin of the fuel assembly 4b is damaged. The same applies to sampling from the control rod guide tube 13.

That is, if damage occurs to the fuel assembly 4a shown in FIG.
e and the sampling hole 13e of the guide tube tube 13
will be sampled from. Therefore, when the selector valve 3 is rotated on the selector valve 3 side and the sampling tube of the sampling post 11A is selected, the neutron detector 9 detects delayed neutrons and damage can be confirmed. Also, if the sampling hole of the guide tube tube 13 is selected, damage is detected, so the selector valve 4 is set to 1.
When rotated, the fuel assembly 4a from the portion corresponding to the sampling post 11A and the guide pipe tube 13
can be identified.

On the other hand, if the other fuel assembly 4b is damaged, FP cannot be detected from the sampling hole 11a of the other sampling post 11B, and the damage is found only from the sampling post that matches the sampling post 11B, so the fuel assembly 4b It can be identified as damage. In other words, it is possible to identify damaged fuel assemblies based on logical judgment.

As explained above, the damaged fuel position detector of the present invention is capable of identifying the position of a single damaged fuel assembly, and has the same detection ability as a method that samples each fuel assembly individually. ing.

〔Effect of the invention〕

As explained above, the damaged fuel position detection device according to the present invention samples the coolant passing through the fuel assembly at an arbitrary position in the reactor core by switching the selector valve to which a plurality of sampling pipes are connected. In the apparatus for detecting the position of damaged fuel by detecting the radioactivity of sampled coolant, each of the sampling tubes is provided with a sampling post having a plurality of sampling holes, and each sampling hole of the sampling post has a plurality of adjacent sampling holes. The sampling posts adjacent to each other are configured to be able to sample coolant from a common fuel assembly located between the sampling posts, and the selector valve By switching, the combination of sampling post and sampling pipe is processed logically, and a damaged fuel assembly can be identified by sampling the coolant from the fuel assembly using one selected sampling post or two adjacent sampling posts. By switching the selector valve, the sampling post can sample the coolant passing through multiple fuel assemblies. By reducing the number of tubes, even if the number of fuel assemblies in the reactor core increases, it is possible to avoid increasing the size of the selector valve, and furthermore, it is possible to reduce the impact on the reactor structure.

Furthermore, the present invention is capable of identifying a single fuel assembly including a damaged fuel pin during nuclear reactor operation, and has an excellent effect in terms of performance.

[Brief explanation of the drawing]

FIG. 1 is a device layout diagram showing a partial cross section of an embodiment of the damaged fuel position detection device according to the present invention, FIG. 2 is a plan view showing a state in which the sampling post in FIG. The figure is a partial cross-sectional view of Figure 2, Figure 4 is a partial cross-sectional view showing the state in which the sampling post is placed on the CRD guide tube in Figure 1, and Figure 5 is a schematic diagram of a conventional damaged fuel position detection device. FIG. DESCRIPTION OF SYMBOLS 1... Core, 2... Rotation drive device, 3... Selector valve, 4... Fuel assembly, 5... Sampling pipe, 6
...Sampling chamber, 7...Electromagnetic pump, 8...
Electromagnetic flowmeter, 9... Neutron pulling detector, 10...
Shielding plug, 11...Sampling post, 11a
~11g...Sampling hole, 12...Supporter, 1
3... Guide pipe tube, 14... Center channel hole, 15
...shielding body, 16... shaft, 17... moderator.

Claims (1)

[Claims] 1 Switch the selector valve to which multiple sampling tubes are connected to sample the coolant passing through the fuel assembly at any position in the reactor core, detect the radioactivity of the sampled coolant, and locate the damaged fuel. In the detection apparatus, each of the sampling tubes is provided with a sampling post having a plurality of sampling holes, and each sampling hole of the sampling post is formed to correspond to a plurality of adjacent fuel assemblies, while being formed to correspond to a plurality of adjacent fuel assemblies. The sampling posts adjacent to the two sampling posts are set to be able to sample the coolant from the common fuel assembly located between the two sampling posts, and the combination of the sampling post and the sampling pipe is processed logically by switching the selector valve. A damaged fuel position detecting device, characterized in that the damaged fuel assembly can be identified by sampling the coolant from the fuel assembly using one selected sampling post or two adjacent sampling posts.