JP7011845B2 - How to collect fuel debris - Google Patents

Description

The present invention relates to a method for recovering fuel debris for recovering fuel debris remaining in a reactor containment vessel (PCV).

For the debris recovery work at Units 1 to 3 of the Fukushima Daiichi Nuclear Power Station, which caused the hydrogen explosion accident, specific extraction methods are being studied for each method such as the upper access method and the lower lateral access method. Regarding the removal procedure, (1) high radiation shielding method (prevention of work exposure), (2) prevention of various α scattering, (3) from any debris in the reactor pressure vessel (RPV) or in the reactor pressure vessel. There are various issues such as whether to collect them, and these are being studied repeatedly.

Among them, a method of temporarily covering the inside of the reactor containment vessel (PCV) with a strong material with barite or the like and collecting debris while shielding radiation is generally known.
For example, there is a method of collecting debris by forming a barite sedimentation layer using sedimentation type muddy water in which barite and bentonite are mixed.

However, in the sedimented muddy water containing bentonite, under relatively high temperature conditions of 80 ° C., the heat of bentonite promotes hydration and swells, resulting in an increase in viscosity and hydrolysis of the dispersant, resulting in a decrease in dispersion force. As a result, there was a problem that gelation occurred and the sedimentation of barite did not occur at all.

Further, Patent Document 1 discloses, for example, a technique for recovering debris using sedimented muddy water in which fuel debris is mixed with barium sulfate (barite) and an organic polymer.

However, when an organic polymer is used, the performance deteriorates under high radiation, so there is a risk that the deterioration will change depending on the strength of the dose. There was a drawback that it took a long time to handle.

Japanese Patent No. 6542780

In view of the above-mentioned conventional drawbacks, the present invention provides settling muddy water that can shield radiation even in a high temperature environment and can take out fuel debris without causing the problem of scattering of α-nuclide. It is an object of the present invention to provide a method for recovering the fuel debris used .

The method for recovering fuel debris according to claim 1 is a settling type muddy water manufacturing step for producing a settling type muddy water containing a settling barium sulfate and an effervescent barium sulfate, and the settling type manufactured in the settling type muddy water manufacturing step. The muddy water is filled in a reactor containment vessel having fuel debris inside, the sedimentation barium sulfate of the sedimentation type muddy water is settled in the reactor containment vessel, and the fuel debris in the reactor containment vessel is settled. It is composed of a barium sulfate sedimentation step covered with a barium sulfate sedimentation layer and a fuel debris recovery step for recovering the fuel debris covered with the barium sulfate sedimentation layer. It is composed of a precipitating barium sulfate addition step of adding and stirring, and an effervescent barium sulfate addition step of further adding and stirring barium sulphate to the water obtained in the barium sulphate addition step. It is characterized by.

In the settling barium sulfate addition step of the method for recovering fuel debris according to claim 2 , 2% to 80% by weight of the settling barium sulfate is added to water, and in the inferior barium sulfate addition step. It is characterized in that the barium sulfate is added so that the barium sulfate and the sedimentary barium sulfate are combined and the weight ratio is 400% with respect to water.

In the sedimentation type muddy water production step of the method for recovering fuel debris according to claim 3 , after the sedimentation barium sulfate addition step, a dispersant is added to the water to which the sedimentation barium sulfate is added and the mixture is stirred. It is characterized in that the step is further carried out, and then the above-mentioned barium sulfate addition step is carried out.

The dispersant addition step of the method for recovering fuel debris according to claim 4 is characterized in that a dispersant of 0.1% to 0.5% by weight is added to water.

The method for recovering fuel debris according to claim 5 is a method for producing sedimented muddy water containing barium sulfate, which is a settling type muddy water, and the settling type muddy water produced in the settling type muddy water manufacturing step. Barium sulfate in the settling muddy water is settled in the reactor storage container, and the fuel debris in the reactor storage container is covered with the barium sulfate settling layer. It is composed of a settling step and a fuel debris recovery step of recovering the fuel debris covered with the barium sulfate settling layer. It is characterized by comprising a barium sulfate addition step and a dispersant addition step of adding a dispersant to the water to which the precipitated barium sulfate is added and stirring after the precipitating barium sulfate addition step.

In the settling barium sulfate addition step of the method for recovering fuel debris according to claim 6 , 80% to 400% by weight of the settling barium sulfate is added to water, and in the dispersant adding step, water is added. It is characterized in that a dispersant having a weight ratio of 0.2% to 1.5% is added.

As is clear from the above description, the following effects can be obtained in the present invention.
(1) In each of the inventions according to claim 1 and claim 2 , since barium sulfate having fine particles is used as a thickener, deterioration of muddy water is prevented even under high radiation. Can be done.
(2) Further, since the sedimentation barium sulfate has a large specific surface area, it is easy to get used to, the mixing efficiency is improved, and it can be manufactured with good handling.
(3) Since it does not contain bentonite, muddy water does not gel even in a high temperature environment, and a barite subsidence layer can be formed.
(4) Each of the inventions according to claims 3 and 4 also has the same effects as those of (1) to (3) above, and is settled muddy water by adding, for example, sodium pyrophosphate as a dispersant. The fluidity of the above can be adjusted as appropriate.
(5) Each of the inventions according to claims 5 and 6 can obtain muddy water having a simple composition, having appropriate fluidity, and not deteriorating even under high radiation and high temperature.

1 to 9 are explanatory views showing a first embodiment of the present invention.
10 to 13 are explanatory views showing a second embodiment of the present invention.
The process drawing of the manufacturing method of the sedimentation type muddy water of 1st Embodiment. The table which shows the flow characteristic of the sedimentation type muddy water produced by the method for producing the sedimentation type muddy water of this invention. The table which shows the composition of the sedimentation type muddy water produced by the method for producing the sedimentation type muddy water of this invention, and the muddy water of a comparative example. The table which shows the experimental result of the time passage and the sedimentation height of barium sulfate at a high temperature (80 ° C.) of the sedimentation type muddy water of the composition of FIG. 3 and the muddy water of a comparative example. The table which shows the time passage and the experimental result of the erythrocyte sedimentation rate of barium sulfate at a high temperature (80 ° C.) of the sedimentation type muddy water and the muddy water of the comparative example of the composition of FIG. The table which shows the density of the barium sulfate sedimentation layer at a high temperature (80 ℃) of the sedimentation type muddy water of the composition of FIG. 3 and the muddy water (part) of a comparative example. A table showing the experimental results of the cone penetration test. (A) Composition of sedimentation type muddy water used in the cone penetration test. (B) Experimental results of cone penetration test. The process chart of the fuel debris recovery method of 1st Embodiment. Schematic diagram of the fuel debris recovery process. The process drawing of the manufacturing method of the sedimentation type muddy water of 2nd Embodiment. The table which shows the relationship between the shear rate and the viscosity of the sedimentation type muddy water produced by the method of producing the sedimentation type muddy water of this invention. The table which shows the flow characteristic of the sedimentation type muddy water produced by the method for producing the sedimentation type muddy water of this invention. The process chart of the fuel debris recovery method of 2nd Embodiment.

Hereinafter, the present invention will be described in detail in accordance with the embodiments shown in the drawings for carrying out the present invention.
In the first embodiment for carrying out the present invention shown in FIGS. 1 to 9, 1 is settling used in the fuel debris recovery method 4 for recovering the fuel debris 3 remaining in the reactor containment vessel (PCV) 2. This is a method for producing a sedimentation type muddy water for producing the type muddy water 5.

The method 1 for producing settling barium is added to the settling barium sulfate addition step 6 in which the settling barium sulfate is added to the water and stirred, and the water to which the settling barium sulfate obtained in the settling barium sulfate addition step 6 is added. Further, it is composed of a barium sulfate addition step 7 in which barium sulfate is added and stirred.

In the precipitating barium sulfate addition step 6, a predetermined amount of water (mainly tap water) is put into a container, the precipitating barium sulfate is added while stirring the water with a mixer or the like, and the mixture is further stirred for about 10 minutes. The added precipitate barium sulfate is a scientifically produced barium sulfate having very fine particles and a diameter of 50% (median diameter D50) of 0.01 to 0.1 μm.
The precipitating barium sulfate is added in a weight ratio of about 2% to 300% with respect to water and stirred, and considering the sedimentation property, the weight ratio is 2% to 80% with respect to water, and more preferably 5% to 5%. It is desirable to add about 20%.

In the present embodiment, before performing the barium sulfate addition step 7, that is, after the precipitation barium sulfate addition step 6, dispersion in which sodium pyrophosphate is added as a dispersant to water to which precipitated barium sulfate is added and stirred. The agent addition step 8 is further performed, and then the above-mentioned barium sulfate addition step 7 is performed.

The flow value (fluidity) of the sedimentation type muddy water 5 can be appropriately adjusted by adding, for example, sodium pyrophosphate as a dispersant to the water to which the precipitating barium sulfate is added.

In the dispersant addition step 8, a predetermined amount of sodium pyrophosphate is added to the water to which the precipitate barium sulfate is added in the precipitate barium sulfate addition step 6, and the mixture is stirred for about 10 minutes using a mixer or the like until the lumps disappear.

It is desirable to add sodium pyrophosphate as this dispersant in an amount of about 0.1 to 0.5% by weight with respect to water. With such an addition amount, good sedimentation characteristics can be obtained as shown in FIGS. 4 to 6.

The barium sulfate addition step 7 is a step of adding barium sulfate (so-called barite) to water containing barium sulfate (in this embodiment, water further added with a dispersant). The barium sulfate added in this step has the same composition as the sedimentary barium sulfate, but its particle size is significantly different, and the particle size of the barium sulfate is several μm to several tens of μm, usually 10 It is ~ 20 μm, which is much larger than that of barium sulfate that precipitates.

In the step 7 of adding barium sulfate, sedimentation type muddy water 5 is produced by adding barium sulfate to water containing barium sulfate and stirring with a mixer or the like for about 10 minutes. It is desirable to add barium sulfate and barium precipitate sulfate so as to have a specific gravity of 2.00 (g / cc) or more, and more preferably, add them so as to have a specific gravity of 2.5 (g / cc) or more. It is desirable to do. By adding barium sulfate and barium sedimentation sulfate together so as to be preferably about 400% with respect to water, the sedimentation type muddy water 5 having such a specific gravity can be obtained. For example, when 50 g of precipitating barium sulfate is added to 100 g of water in the precipitating barium sulfate addition step 6, 350 g of effervescent barium sulfate is added in the effervescent barium sulfate addition step 7.

The settling type muddy water 5 produced by mixing this settling barium sulfate and barium sulfate is muddy water with the idea that the settling barium sulfate is used as a thickener and the shortage of the weighting agent is supplemented with barium sulfate. As shown in FIG. 2, a high specific density muddy water having good flow characteristics can be obtained in a short time even at a target specific gravity of the subsidence type muddy water 5: 2.56 (barium 400%).

If the amount of precipitating barium sulfate blended is less than 100%, the flow value can be maintained at 200 mm or more without using a dispersant. Therefore, in such a blending, the dispersant addition step 8 can be omitted. As a characteristic of the flow of the sedimentation type muddy water 5 without using a dispersant, the phenomenon that the flow continues to spread with time does not occur because the gel strength is high.

The results of comparative experiments between the sedimented muddy water 5 produced by the method 1 for producing the sedimented muddy water and the muddy water containing bentonite and the muddy water containing an organic polymer will be described with reference to FIGS. 3 to 6.
First, FIG. 3 shows the composition of the sedimentation type muddy water 5 and the comparative example.

As the settling type muddy water 5, among those showing the flow characteristics in FIG. 2, No. 1 to No. Examples 1 to 4 were obtained by mixing 1.05 g of sodium pyrophosphate with each of 4, and 30 g of precipitated barium sulfate and 1170 g of barium sulfate were mixed with 300 g of water, and 0.9 g of sodium pyrophosphate was further mixed. In Example 5, 60 g of precipitated barium sulfate and 1140 g of barium sulfate were mixed with 300 g of water, and 0.9 g of sodium pyrophosphate was further mixed in Example 6.

On the other hand, those to which bentonite was added as comparative muddy water were designated as Comparative Example 1 and Comparative Examples 3 to 9, and those to which an organic polymer was added were designated as Comparative Example 2, respectively.

First, FIG. 4 shows the experimental results of the passage of time and the sedimentation depth of barium sulfate under high temperature (80 ° C.), and FIG. 5 shows the experimental results of the passage of time and the settling ratio of barium sulfate to volume.

As is clear from these figures, the muddy water containing bentonite can obtain a certain sedimentation height if the content of bentonite is low, but the sedimentation height is less than half as compared with the sedimentation type muddy water of the present invention. It can be seen that the erythrocyte sedimentation rate is about 1/4 at the maximum. As described above, the muddy water containing bentonite has poor sedimentation property under high temperature, while the sedimentation type muddy water 5 of the present invention can maintain good sedimentation property even at high temperature.

In muddy water using an organic polymer, a barite sedimentation layer is formed even at high temperatures, but performance deterioration progresses under high radiation conditions, so there is a risk that deterioration will change depending on the intensity of the dose.

On the other hand, since the sedimentation type muddy water 5 produced by the sedimentation type muddy water production method 1 of the present application does not use an organic polymer, there is no risk of performance deterioration even in a high radiology department, and FIGS. 4 to 6 show. As shown, good sedimentation property can be obtained.

Further, as shown in FIG. 7, the barium sulfate sedimentation layer 9 formed by the sedimentation type muddy water 5 of the present application forms a very dense sedimentation layer having a cone index (qc) of 1400 (kN / m2) or more. Therefore, it is possible to put a small heavy machine or the like into the reactor containment vessel 2 for work.
As for the sedimentation type muddy water 5 used in this cone penetration test, the sedimentation type muddy water 5 having the composition shown in FIG. 7A was settled in a 10 × 10 cm mold for 3 days, and the cone penetration test was carried out.

As shown in FIG. 8, the fuel debris recovery method 4 uses the settling muddy water 5 manufactured in the settling muddy water manufacturing step 10 for manufacturing the settling muddy water 5 using the settling muddy water manufacturing method 1 as fuel. The reactor containment vessel 2 having the debris 3 inside is filled, the barium sulfate of the sedimentation type muddy water 5 is settled in the reactor containment vessel 2, and the fuel debris 3 in the reactor containment vessel 2 is settled. It is composed of a barium sulfate sedimentation step 11 covered with a barium sulfate sedimentation layer 9 and a fuel debris recovery step 12 for recovering the fuel debris 3 covered with the barium sulfate sedimentation layer 9.

The barium sulfate sedimentation step 11 is a step of filling the reactor containment vessel 2 with the sedimentation type muddy water 5 to form the barium sulfate sedimentation layer 9. The barium sulfate sedimentation layer 9 may be formed by using either or both of the sedimentation barium sulfate and the barium sulfate, and does not particularly distinguish between them to form the barium sulfate sedimentation layer 9. However, since the sedimentation barium sulfate has a small particle size, the sedimentation rate is slower than that of barium sulfate, and when the sedimentation time is short, the barium sulfate sedimentate mainly forms the barium sulfate sedimentation layer 9. ..
By setting the filling time to a long time, an appropriate barium sulfate sedimentation layer 9 can be formed.

Specifically, in the barium sulfate sedimentation step 11, after the sedimentation type muddy water 5 is filled, the barium sulfate is settled by leaving it for several hours, preferably about 24 hours to several days, and scattered in the reactor containment vessel 2. The fuel debris 3 is covered with the barium sulfate sedimentation layer 9.

As described above, this barium sulfate subsidence layer 9 forms a very dense subsidence layer having a cone index (qc) of 1000 (kN / m2) or more, so that a small heavy machine or the like can be used as a reactor containment vessel. It is also possible to put it in 2 and work. For example, the barium sulfate sedimentation layer 9 having a reaction force with a cone index of 1200 (kN / m2) or more is used by heavy machinery such as a work base, a buffer layer for dropping a damaged pressure vessel at the top, and a self-propelled caterpillar work device. Apply as a possible work platform.

As shown in FIG. 9, the fuel debris recovery step 12 is a step of excavating the barium sulfate subsidence layer 9 using an excavator 13 such as a boring machine or a guided excavator to recover the fuel debris 3.

In the present embodiment, the fuel debris 3 is recovered by the excavator 13, but the fuel debris recovery step 12 may be performed by using a small heavy machine or the like.

In the fuel debris recovery step 12, the barium sulfate settling layer 9 (shielding layer) is excavated until the fuel debris 3 is reached. The barium sulfate settling layer 9 shows high shear stress at a high shear rate, but is low. Since it exhibits characteristics similar to those of a dilatancy fluid, which has a low shear stress at a shear rate, for example, as shown in FIG. 9, excavation is performed while vibrating a rod 15 or the like provided with an excavator 14 of an excavator 13 in a fuel debris 3 recovery operation. This makes it possible to easily excavate the barium sulfate sedimentation layer 9 and direct the excavator 14 in the direction of the fuel debris 3.

Since the barium sulfate sedimentation layer 9 is in close contact with the excavator 14 and the like when recovering the fuel debris 3 and has no voids, radiation can be shielded during the work, and the hole after the excavator 14 is extracted is self-repaired. Since the flow value is maintained, it is possible to shield the high-dose radiation from the fuel debris 3 by blocking it immediately.

In addition, fine debris and the like scattered when the fuel debris 3 is recovered are not scattered beyond the barium sulfate settling layer 9 because the work is performed with the barium sulfate settling layer 9 covering the fuel debris 3. The debris is taken into the barium sulfate sedimentation layer 9 and can be safely recovered by sucking the barium sulfate sedimentation layer 9.

Since the barium sulfate sedimentation layer 9 has a high specific gravity, it can be easily separated from the fuel debris 3 sites in the cyclone classification step, and the classified barium and the like can be reused, so that waste can be reduced.

[Different forms for carrying out the invention]
Next, different embodiments for carrying out the present invention shown in FIGS. 10 to 13 will be described. In the description of the different embodiments for carrying out the present invention, the same components as those of the first embodiment for carrying out the present invention are designated by the same reference numerals, and duplicate description will be omitted.

In the second embodiment for carrying out the present invention shown in FIGS. 10 to 13, the main difference from the first embodiment for carrying out the present invention is that sedimentation barium sulfate is added to water and stirred. A method for producing sedimented muddy water, which comprises a step of adding a settling barium sulfate and a step of adding a dispersant in which a dispersant is added to the water to which the settling barium sulfate is added and stirred after the step of adding the settling barium sulfate. Such settling type muddy water is set to 1A and the fuel debris recovery method 4A using the settling type muddy water manufacturing step 10A for producing the settling type muddy water 5 by using the settling type muddy water manufacturing method 1A. Even in the production method 1A and the fuel debris recovery method 4A, the same action and effect as in the first embodiment for carrying out the present invention can be obtained.

As shown in FIG. 10, the composition of the muddy water using only the sedimentary barium sulfate is 80% to 400%, more preferably 300, in view of the flow characteristics (mainly the influence of the gel value) and the spread of the flow value. It seems that a compounding composition in which a dispersant is used in combination of 0.2% to 1.5%, more preferably about 0.3% in the range of% to 350% is suitable.

Further, as shown in FIG. 11, the viscosity of the precipitating barium sulfate increases as the amount added increases. In particular, since the YV value and the gel strength value are high, the viscosity is increased like bentonite. Therefore, it is possible to construct a sedimentation type muddy water 5 having a very simple composition without using bentonite in a heavy muddy water that does not require high water impermeability such as a sedimentation type high specific density muddy water.

The sedimentation type muddy water 5 produced by the sedimentation barium sulfate alone has a very small particle size, so that the sedimentation time is long. In addition, if the compounding composition is a high-concentration compounding composition (400%) such as standard barium sulfate, the gel strength value becomes very high, and even if a dispersant is used in combination, the effect is small and the phenomenon of not precipitating occurs. Therefore, when it is desired to form the barium sulfate sedimentation layer 9 within 24 hours, it is not suitable to be used alone, and when it is desired to form the barium sulfate sedimentation layer 9 in a short time, the first embodiment is described above. It is advisable to use a mixture of barium sulfate and barium sulfate.

The present invention is utilized in an industry that uses a fuel debris recovery method for recovering fuel debris remaining in a reactor containment vessel (PCV).

1, 1A: Method for producing sedimented muddy water, 2: Reactor containment vessel,
3: Fuel debris, 4, 4A: Fuel debris recovery method,
5: Precipitated muddy water, 6: Precipitating barium sulfate addition step,
7: Barium sulfate addition step, 8: Dispersant addition step,
9: Barium sulfate sedimentation layer, 10, 10A: Subsidence type muddy water production process,
11: Barium sulfate sedimentation process, 12: Fuel debris recovery process,
13: Excavator, 14: Excavator,
15: Rod.

Claims (6)

A reactor containment vessel having fuel debris inside a settling muddy water manufacturing process for producing settling barium sulfate and barium sulfate containing effervescent barium sulfate and the settling muddy water produced in the settling type muddy water manufacturing step. A barium sulfate settling step of filling the inside to settle the settling barium sulfate in the settling muddy water in the reactor containment vessel and covering the fuel debris in the reactor containment vessel with a barium sulfate settling layer. It is composed of a fuel debris recovery step for recovering the fuel debris covered with the barium sulfate sedimentation layer.
In the sedimentation type muddy water production step, the precipitate barium sulfate addition step of adding the sedimentation barium sulfate to water and stirring, and the water obtained by the sedimentation barium sulfate addition step, further adding the effervescent barium sulfate. A method for recovering fuel debris, which comprises a step of adding barium sulfate and stirring. In the precipitating barium sulfate addition step, the precipitating barium sulfate is added in a weight ratio of 2% to 80% with respect to water, and in the effervescent barium sulfate addition step, the effervescent barium sulfate and the precipitated barium sulfate are added. The method for recovering fuel debris according to claim 1 , wherein the barium sulfate is added so as to have a weight ratio of 400% with respect to water. In the sedimentation type muddy water production step, after the sedimentation barium sulfate addition step, a dispersant addition step of adding a dispersant to the water to which the sedimentation barium sulfate is added and stirring the mixture is further performed, and then the effervescent barium sulfate addition step is performed. The method for recovering fuel debris according to any one of claim 1 or 2 , wherein the addition step is performed. The method for recovering fuel debris according to claim 3 , wherein in the dispersant addition step, the dispersant is added in a weight ratio of 0.1% to 0.5% with respect to water. The reactor containment vessel having fuel debris inside is filled with the sedimentation type muddy water manufacturing process for producing sedimentation type muddy water containing barium sulfate and the sedimentation type muddy water produced in the sedimentation type muddy water production process. , The barium sulfate sedimentation step of precipitating the barium sulfate of the sedimentation type muddy water in the reactor containment vessel and covering the fuel debris in the reactor containment vessel with the barium sulfate sedimentation layer, and being covered with the barium sulfate sedimentation layer. It consists of a fuel debris recovery process that recovers the fuel debris.
In the sedimentation type muddy water production step, the sedimentation barium sulfate addition step of adding the sedimentation barium sulfate to water and stirring the mixture, and the dispersant added to the water to which the sedimentation barium sulfate is added after the sedimentation barium sulfate addition step. A method for recovering fuel debris, which comprises a dispersant addition step of adding and stirring. In the precipitating barium sulfate addition step, 80% to 400% by weight of the precipitating barium sulfate is added to water, and in the dispersant addition step, 0.2% to 1% by weight is added to water. The method for recovering fuel debris according to claim 5 , wherein the dispersant is added in an amount of 5.5%.

Images