JP2012002599A - Sludge cleaning apparatus for used fuel and sludge cleaning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sludge cleaning apparatus for used fuel capable of removing and rinsing sludge which adheres to the inside of a centrifugal clarifier, etc. and cannot be cleaned off with water, and a sludge cleaning method.SOLUTION: A sludge cleaning apparatus for separating insoluble solid content from used fuel liquid using a centrifugal clarifier 1A comprises: aqueous nitrate solution supply means 6,7,8 for supplying an aqueous nitrate solution to the centrifugal clarifier 1A; water supply means 9,10,11 for supplying water to the centrifugal clarifier 1A; and alkali aqueous solution supply means 2,3,4 for supplying an alkali aqueous solution to the centrifugal clarifier 1A.

Description

  This technology removes and cleans sludge stuck to the surface of equipment for reprocessing and the surface of filters when reprocessing spent fuel used in nuclear reactors. The present invention relates to a cleaning method.

  Spent fuel used in nuclear reactors, such as spent fuel used in light water reactors, is subject to reprocessing in fuel reprocessing plants. In this spent fuel reprocessing plant, a spent fuel dissolution process, a uranium and plutonium separation process, a uranium or plutonium purification process, a denitration process, and the like are performed in combination (see Patent Document 1, etc.).

  In the spent fuel dissolving step, a process of heating and melting the spent fuel with nitric acid is performed. However, it is known that sludge (solid content) consisting of fission products (FP element) that is difficult to dissolve in nitric acid is present in the shear pieces (chips) of the cladding tube (hull) of spent fuel. Conventionally, in spent fuel reprocessing plants, centrifugal clarifiers and filters are installed to remove this sludge.

  In the centrifugal clarifier, sludge is removed by centrifuging sludge and depositing the separated sludge on the wall surface in the centrifugal clarifier. Then, after centrifugal separation is performed for a certain period of time to deposit sludge, the accumulated sludge is removed from the centrifugal clarifier.

  As for the sludge removal method in the prior art, a method has been proposed in which the bowl of the centrifugal clarifier is slowly rotated while spraying with high-pressure water, and the sludge is scraped off by a protrusion provided on the inner surface side of the centrifugal clarifier. (Refer to patent document 2 etc.).

  Also, in a fuel reprocessing plant for light water reactors, if sludge accumulates on the bowl wall in the centrifugal clarifier, the sludge deposited on the centrifugal clarifier wall is rinsed with an aqueous nitric acid solution, and then the water from the water tank enters the centrifugal clarifier. It is also known that spray cleaning is performed with high-pressure water using a supplied pump, and the cleaning liquid is collected in a cleaning liquid tank (see Patent Document 3).

  Furthermore, as a method for inspecting that the sludge accumulated on the wall of the centrifugal clarifier has been cleaned, a method of observing the inside of the centrifugal clarifier with a fiberscope has been proposed (see Patent Document 4).

  There are plans to reprocess spent fuel used in the fast breeder reactor (FBR). The fuel used in the fast breeder reactor contains a large amount of sludge, especially ions such as Zr and Mo, in the solution compared to the spent fuel in the light water reactor. The ions such as Zr and Mo are fission products. And about 15 to 20% of the total weight of the transuranium element (see Patent Document 5), and it is also known that these elements chemically react to form a colloidal precipitate called zirconium molybdate. .

JP 2006-290777 A JP-A-11-156244 JP-A-2-210297 JP-A-9-220493 JP 2002-333497 A

  In the fuel reprocessing process for the spent fuel of the light water reactor, after the spent fuel is melted in the dissolution tank, unnecessary sludge is removed by a centrifugal clarifier or a filter. The sludge accumulated on the inner surface of the centrifugal clarifier and the filter is washed with high-pressure water.

  The main components of sludge generated in a light water reactor are sheared pieces (chips) when the spent fuel cladding tube (hull) is sheared, fission product (FP) elements that are difficult to dissolve in nitric acid, and the like.

  In the future spent fuel, the amount of sludge will increase, and there will be a large amount of ions such as Zr and Mo in the solution, and these will chemically react to form a colloidal precipitate called zirconium molybdate. When generated, these precipitates stick to the wall surface or filter surface in the centrifugal clarifier, and if the conventional cleaning method is applied as it is, sludge accumulated on the wall surface or the like may not be removed.

  In addition, when the accumulated sludge cannot be removed, the balance of the centrifugal clarifier may be lost, the centrifugal clarifier bowl may not rotate, and the sludge may be clogged in the filter and may not be filtered.

  In view of the above circumstances, in this proposal, even if sludge accumulates on the wall of the centrifugal clarifier, the surface of the filter, etc. and sticks, the sludge can be washed away and the balance of the centrifugal clarifier is improved. A sludge washing device that can hold and rotate the bowl of the centrifugal clarifier smoothly, and in the case of a configuration equipped with a filter, can prevent clogging of the filter and sufficiently perform the filtering action. The purpose is to provide.

  In the reprocessing step of reprocessing spent fuel used in a nuclear reactor, when the spent fuel is dissolved by the fuel solution, sludge that is an insoluble solid content is removed from the fuel solution. A sludge cleaning device for separating, a nitric acid aqueous solution supplying means for supplying a nitric acid aqueous solution to the spent fuel solution, a water supplying means for supplying water to the used fuel solution, and the spent fuel dissolving There is provided a spent fuel sludge cleaning apparatus comprising an alkaline aqueous solution supply means for supplying an alkaline aqueous solution to a liquid.

  Further, in this proposal, in the reprocessing step of reprocessing spent fuel used in a nuclear reactor, when the spent fuel is dissolved by the fuel solution, a centrifugal clarifier is used to remove the spent fuel from the fuel solution. Provided a method for cleaning sludge of spent fuel, wherein sludge that is insoluble solid content is separated, sludge adhering to the wall of the centrifugal clarifier is washed with an alkaline aqueous solution, and then washed with water To do.

  According to the above configuration, it becomes possible to wash the sludge such as zirconium molybdate adhering to the wall of the centrifugal clarifier or the surface of the filter by dissolving it in an alkaline aqueous solution. Can be washed.

The block diagram which shows the sludge washing | cleaning apparatus by 1st Embodiment. The flowchart which shows the washing | cleaning process by 1st Embodiment. The diagram which shows the solubility of the zirconium molybdate applied in 1st Embodiment. The system block diagram which shows the sludge washing | cleaning apparatus by 2nd Embodiment. The flowchart which shows the washing | cleaning process by 2nd Embodiment.

  Hereinafter, an embodiment of a sludge cleaning apparatus will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is an overall configuration diagram showing a sludge cleaning apparatus according to a first embodiment.

  As shown in FIG. 1, the sludge cleaning apparatus 1 includes a centrifugal clarifier 1A as a container that stores and rotates spent fuel that is a processing target. The centrifugal clarifier 1A is configured, for example, as an inverted conical bowl 1a, and spent fuel to be processed is accommodated in the centrifugal clarifier 1A.

  Below the bowl 1a, an alkaline aqueous solution tank 2 for containing an alkaline aqueous solution is installed. The alkaline aqueous solution tank 2 is provided with an alkaline aqueous solution supply pipe 3 and a pump 4 so that the alkaline aqueous solution can be supplied (injected) into the bowl 1a.

  A nitric acid aqueous solution tank 6 is installed below the bowl 1 a adjacent to the alkaline aqueous solution tank 2. The nitric acid aqueous solution tank 6 is provided with a nitric acid aqueous solution supply pipe 7 and a pump 8. Thus, the aqueous nitric acid solution can be supplied (injected) into the bowl 1a.

  Further, a water tank 9 is installed adjacent to the nitric acid aqueous solution tank 6. A water supply pipe 10 and a pump 11 are provided in the water tank 9, and the water tank 9 is connected to the inside of the bowl 1 a via the water supply pipe 10. The water can be supplied (injected) to the tank.

  Further, below the bowl 1a, waste cleaning liquid tanks 5, 13a, 13b for storing the waste cleaning liquid used in the bowl 1a are provided.

  As described above, the centrifugal clarifier 1A is provided with the alkaline water supply pipe 3 and the alkaline aqueous solution supply pump 4 for supplying the alkaline aqueous solution from the alkaline aqueous solution tank 2 containing the alkaline aqueous solution as the processing solvent to the bowl 1a. The alkaline aqueous solution can be supplied into the bowl 1a from the supply port 3a of the alkaline aqueous solution supply pipe 3.

  Further, a nitric acid aqueous solution tank 6 and a pump 8 for supplying nitric acid aqueous solution connected to the tank 6 are provided adjacent to the pump 4 on the lower lid side of the bowl 1 a, and the nitric acid aqueous solution supply connected to the pump 8 is provided. A nitric acid aqueous solution is supplied (injected) into the bowl 1 a from the nitric acid aqueous solution supply port 7 a of the pipe 7.

  Below the bowl 1a, a water tank 9 for supplying cleaning water into the bowl 1a is provided, and a pump 11 is provided in a water supply pipe 10 connected to the water tank 9. Further, waste cleaning liquid tanks 13a and 13b for supplying the waste cleaning liquid are provided, and the waste cleaning liquid is supplied into the waste cleaning liquid tanks 13a and 13b via the pipes 12 and 14, respectively.

  Next, the action will be described with respect to the “shear / dissolution step 27”, “separation step 28” and the like. The centrifugal clarifier 1A performs solid-phase separation from the lysate, and insoluble components contained in the lysate hinder safe operation of the extraction process, and thus need to be removed in advance.

  As the centrifugal clarifier 1A, the development of a remote maintenance type centrifugal clarifier with less waste generation was advanced. In a performance evaluation test using a prototype, it was confirmed that the required performance was satisfied using simulated particles such as alumina.

  Further, in the present embodiment, a liquid feed pump (not shown) is provided, and the dissolved liquid can be transferred. That is, the liquid feed pump that transfers the dissolved component before removing the insoluble component in the clarification step needs to be less likely to be clogged with the insoluble component. Moreover, the thing which reduces the nitric acid density | concentration cannot be used for the transfer of the aqueous solution containing a lot of plutonium.

  In the present embodiment, a reverse flow diverter type full index pump was developed, and a liquid transfer test including simulated particles was performed. We also developed a centrifugal extractor as an extractor to replace the pulse column. The centrifugal clarifier 1A according to the present embodiment is small in size, has a small hold-up amount, and has a short contact time with a lysate, so that radiation degradation of the solvent can be reduced.

  Next, the operation of the centrifugal clarifier 1b will be described in detail with reference to FIG. FIG. 2 is a flowchart showing a washing process of the centrifugal clarifier.

  In the present embodiment, a centrifugal clarifier equipped with a sludge cleaning device using an aqueous alkali solution and an aqueous nitric acid solution is applied.

  As described above, the spent fuel is sheared and dissolved in the shearing / dissolution step (apparatus) 27, and the solution is separated from the sludge in the centrifugal clarifier 1 </ b> A and transferred to the separation step (apparatus) 28. The centrifugal clarifier 1A includes an alkaline aqueous solution tank 2 and an alkaline aqueous solution supply port 3a for supplying the alkaline aqueous solution.

  Moreover, the pump 4 which supplies alkaline aqueous solution to the centrifugal clarifier 1A, the waste washing | cleaning liquid tank 5 which stores the alkaline aqueous solution after washing | cleaning, and the nitric acid aqueous solution tank 6 are further provided.

In the present embodiment, zirconium molybdate (Zr (OH) ₂ Mo ₂ O ₇ (H ₂ O) ₂ ) can be assumed as the main component of the sludge. This zirconium molybdate sticks to the wall of the centrifugal clarifier 1A, and there is a possibility that it cannot be cleaned by a conventional cleaning method.

Therefore, for zirconium molybdate, molybdenum is selectively dissolved under alkaline conditions, for example, based on the following reaction formula [Chemical Formula 1].
[Chemical 1]
Zr (OH) ₂ Mo ₂ O ₇ (H ₂ O) ₂ + 4OH ⁻ → 2MoO ₄ ²⁻ + ZrO ₂ · 2 (H ₂ O) + 3H ₂ O

  Here, a cleaning method when the spent fuel of the FBR is reprocessed will be described.

  As shown in FIG. 2, first, when sludge is accumulated on the wall surface in the bowl 1a of the centrifugal clarifier 1A, the nitric acid aqueous solution is supplied from the nitric acid aqueous solution tank 6 to the nitric acid aqueous solution supply pipe 7 using the pump 8, The wall surface of the centrifugal clarifier 1A is washed through the aqueous solution supply port 7a (S101).

  When the cleaning process is completed, the cleaning liquid is collected in the cleaning liquid tank 13, and then water is supplied from the water tank 9 to the centrifugal clarifier 1 </ b> A and from the water supply pipe 10 through the water supply port 10 a using the pump 11. Supplying at high pressure, the centrifugal clarifier 1A is operated to process the wall surface (S102).

  Then, it is confirmed whether or not a predetermined sludge process has been performed (S103). When it is confirmed that the sludge process has been completed (YES), a recovery process of the cleaning liquid from the waste cleaning liquid tanks 13a and 13b is performed (S104). ).

  When the centrifugal clarifier 1A is subsequently restarted, if sludge remains in the bowl 1a, vibration may occur when the centrifugal clarifier 1A is restarted (S103, NO). In that case, the centrifugal clarifier 1A is stopped, and the pump 4 is used to supply an alkaline aqueous solution from the alkaline aqueous solution tank 2 to the centrifugal clarifier 1A to the centrifugal clarifier 1A, and the wall of the bowl 1a of the centrifugal clarifier 1A is removed. Wash (S105).

Next, using the pump 11, water is supplied from the water tank 9 to the water supply port 10a of the centrifugal clarifier 1A at a high pressure, and the wall surface of the centrifugal clarifier 1A is washed (S106).
Each waste cleaning liquid after cleaning is collected in a waste cleaning liquid tank 5. Note that direct observation or the like may be performed with a fiberscope to confirm whether the sludge has been cleaned (S107).
Thereafter, the centrifugal clarifier 1A is operated (S108).

  FIG. 3 shows the calculation of the amount (g) of zirconium molybdate in which the aqueous sodium hydroxide solution is dissolved per liter (L), assuming that the reaction according to the above formula (1) (1) proceeds 100%. It is the graph computed by these. The vertical axis of the graph shown in FIG. 3 indicates the amount of zirconium molybdate dissolved, and the horizontal axis indicates PH.

  As shown in FIG. 3, zirconium molybdate hardly dissolves in an aqueous solution having a pH of 12 or lower. When zirconium molybdate is actually dissolved in sodium hydroxide at pH 13, the dissolution amount is 3.8 g / L, and when zirconium molybdate is dissolved in sodium hydroxide at pH 14, the dissolution amount is 56 g / L. L and a value close to this graph are obtained.

  Based on this graph, it is desirable to apply an alkaline aqueous solution having a pH of 12 or more to the cleaning liquid. The higher the pH of the cleaning liquid, the smaller the amount of the alkaline aqueous solution of the solvent. From the viewpoint of reducing the waste liquid, it is desirable that the concentration of the alkaline aqueous solution is as high as possible so that the pH becomes high.

  When washing with an alkaline aqueous solution, in order to reduce the waste liquid, it is not necessary to completely dissolve the adhering sludge with the alkaline aqueous solution. Sufficiently wet the sludge with the alkaline aqueous solution, and then use the high-pressure water in the subsequent process. It may be peeled off during the cleaning process. After washing, the recovered alkaline waste liquid is vitrified as high-level waste.

  By the way, when spent fuel is reprocessed in the future, zirconium molybdate may adhere as sludge adhering in the bowl 1a of the centrifugal clarifier 1A.

  Conventionally, this adhered zirconium molybdate could not be washed with an aqueous nitric acid solution or high-pressure water. On the other hand, when the sludge cleaning apparatus 1A according to the present embodiment is installed, the cleaning treatment can be performed by dissolving the adhering zirconium molybdate in an alkaline aqueous solution.

  As described above, according to the present embodiment, the sludge cleaning apparatus 1A is installed, and it becomes possible to perform the cleaning process by dissolving the adhering zirconium molybdate in the alkaline aqueous solution, and the sludge that cannot be cleaned due to sticking is cleaned. can do. Thus, in the past, there was a possibility that zirconium molybdate adhered as sludge to the surface of the filter, and this adhered zirconium molybdate could not be washed with a nitric acid aqueous solution or water, but according to this embodiment, it can be washed by sticking. The sludge that was not present can be washed.

[Second Embodiment]
FIG. 4 is a system configuration diagram showing the sludge cleaning apparatus 1 (1B) according to the second embodiment, and FIG. 5 is a flowchart showing the cleaning process.

  In the sludge cleaning apparatus 1B of this embodiment, a case will be described in which a sludge cleaning apparatus for removing sludge adhering to the filter 29 provided in the bowl 1b is applied.

  As shown in FIG. 4, the spent fuel is sheared and dissolved in a shearing / dissolution step (apparatus) 27, and the solution is supplied into the bowl 1 b (arrow a 1) and separated from sludge by the filter 29. It is transferred to the separation step (apparatus) 28.

  An alkaline aqueous solution tank 15 for cleaning the filter 29 is provided, and a pump 18 is provided in a pipe 31 for supplying the alkaline aqueous solution from the alkaline aqueous solution tank 15. An alkaline aqueous solution supply port 16 that opens upward is formed at the tip of the pipe 31 so that the alkaline aqueous solution can be sprayed from below into the filter 29 in the bowl 1b.

  Further, a nitric acid aqueous solution tank 19 for supplying a nitric acid aqueous solution to the filter 29 is provided, and a nitric acid aqueous solution supply port 20 opened upward at the tip of a pipe 32 for supplying the nitric acid aqueous solution from the nitric acid aqueous solution tank 19 into the bowl 1b. Is formed. The nitric acid aqueous solution can be sprayed from below toward the filter 29 in the bowl 1b.

  The piping 32 for supplying the aqueous nitric acid solution is provided with a branch piping 32a for supplying an alkaline aqueous solution at a position above the filter 29 in the bowl 1b so that the aqueous nitric acid solution can be sprayed onto the filter 29.

  Further, a pump 21 for supplying an aqueous nitric acid solution is provided in the bowl 1 b, and a water supply port 23 for supplying water toward the filter 29 is formed in the water tank 22. Further, a water supply pump 24 for supplying water to the centrifugal clarifier is provided.

  Furthermore, waste cleaning liquid tanks 25 and 26 for storing the waste cleaning liquid after cleaning, and pipes 34a and 34b for supplying the waste cleaning water after cleaning are installed.

  FIG. 5 is a flowchart for explaining the cleaning process.

As shown in FIG. 5, in this embodiment, when sludge is accumulated on the surface of the filter 29 during cleaning, a nitric acid aqueous solution is supplied from the nitric acid aqueous solution tank 19 to the nitric acid aqueous solution supply port 20 using the pump 21. The sludge accumulated in 29 is rinsed (S201).
The aqueous nitric acid solution is basically caused to flow from the upper side to the lower side of the filter through the water supply pipe 10. Note that an aqueous nitric acid solution may flow from below to above. The rinse liquid is collected in the waste cleaning liquid tank 25 (S202).

Next, using the pump 24, water is supplied from the water tank 22 to the filter 29 through the water supply port 23, and the filter 29 is cleaned (S203).
The waste cleaning liquid after cleaning is collected in the waste cleaning liquid tank 26 (S204).
After the necessary waste cleaning liquid is collected, water is supplied from the water supply port 23 of the water tank 22 to the filter 29 (S205), and the filter is washed (S206). In this case, water flows from downstream to upstream.
Thereafter, the differential pressure or the inlet pressure or the flow rate of the filter 29 is measured (S207).

Further, it is determined whether sludge remains in the filter (S208). In this case, if sludge remains, the pressure on the inlet side increases and the flow rate decreases due to the differential pressure of the filter 29.
In that case, the pump 18 is used to supply the alkaline aqueous solution from the alkaline aqueous solution tank 15 to the alkaline aqueous solution supply port 16 to the filter 29, and the filter 29 is washed (S209).

  In the present embodiment, the alkaline aqueous solution is basically supplied from the lower side to the upper side of the filter 29 in reverse to the nitric acid aqueous solution, but conversely, it may be configured to flow from the upper side to the lower side.

Next, water is supplied from the water tank 22 to the water supply port 23 using the pump 24, and water is supplied from the water supply port 23 to the filter 29 (S210), thereby cleaning the filter 29 (S211).
After the cleaning is completed, each cleaning solution is collected in the waste cleaning solution tank 25.
Note that it may be confirmed (S212) whether the sludge has been cleaned by directly observing with a fiberscope.
After confirming that the sludge has been cleaned, operation is performed (S213).

  As shown in the graph of FIG. 3, it is desirable to apply an alkaline aqueous solution having a pH of 12 or more to the cleaning liquid. This is because the higher the pH of the cleaning liquid, the smaller the amount of the alkaline aqueous solution that is the solvent. Therefore, from the viewpoint of reducing the waste liquid, it is desirable to apply a cleaning solution of an alkaline aqueous solution as concentrated as possible so as to increase the pH.

  Also, when washing with an alkaline aqueous solution, the waste liquid is reduced, so it is not necessary to completely dissolve the attached sludge with the alkaline aqueous solution. When the sludge is sufficiently wetted with the alkaline aqueous solution and washed with water in the subsequent steps. Alternatively, it may be peeled off. After washing, the recovered alkaline waste liquid is vitrified as high-level waste.

  In the future, when the spent fuel of FBR is reprocessed, zirconium molybdate may adhere to the filter surface as sludge. The adhering zirconium molybdate may not be cleaned with a nitric acid aqueous solution or water, but by applying the sludge cleaning device of this embodiment, the zirconium molybdate adhering to the surface of the filter is dissolved in an alkaline aqueous solution. It becomes possible to wash.

  Therefore, according to the present embodiment, sludge can be removed even when colloidal precipitates such as zirconium molybdate stick to the wall surface or filter surface in the centrifugal clarifier.

  And by removing the accumulated sludge, the balance of the centrifugal clarifier can be maintained, so that the bowl of the centrifugal clarifier does not rotate and the sludge is not clogged in the filter, so that the filtering action can be performed smoothly. Become.

  As a result, sludge stuck to the wall of the centrifugal clarifier, the surface of the filter, etc. can be removed by cleaning, and the centrifugal clarifier bowl can be smoothly rotated while maintaining a good balance of the centrifugal clarifier. In the case of a configuration provided with a filter, clogging can be prevented and the filtration function can be sufficiently performed.

DESCRIPTION OF SYMBOLS 1 Sludge washing apparatus 1A Centrifugal clarifier 1B Sludge washing apparatus 1a Bowl 1b Bowl 2 Alkaline aqueous solution tank 3 Alkaline aqueous solution supply pipe 3a Alkaline aqueous solution supply port 4 Pump 5 Waste washing liquid tank 6 Nitric acid aqueous solution tank 7 Nitric acid aqueous solution supply pipe 7a Nitric acid aqueous solution supply port 8 Pump 9 Water tank 10 Water supply pipe 10a Water supply port 11 Pump 12 Pipes 13a, 13b Waste cleaning liquid tank 14 Pipe 15 Alkaline aqueous solution tank 16 Alkaline aqueous solution supply port 18 Pump 19 Nitric acid aqueous solution tank 20 Nitric acid aqueous solution supply port 21 Pump 22 Water tank 23 Water supply port 24 Pump 25 Waste cleaning liquid tank 26 Waste cleaning liquid tank 27 Shearing / dissolution process (equipment)
28 Separation process (equipment)
29 Filter 31 Pipe 31a Branch pipe 32 Pipe 32a Branch pipe 33 Pipe 34a, 34b Pipe for supplying waste cleaning water

Claims (8)

In a reprocessing step of reprocessing spent fuel used in a nuclear reactor, when the spent fuel is dissolved by a fuel solution, sludge that is an insoluble solid content is separated from the fuel solution. A sludge cleaning apparatus, a nitric acid aqueous solution supply means for supplying a nitric acid aqueous solution to the spent fuel solution, a water supply means for supplying water to the used fuel solution, and an alkaline aqueous solution for the used fuel solution A spent fuel sludge cleaning device comprising an alkaline aqueous solution supply means for supplying 2. The spent fuel sludge cleaning apparatus according to claim 1, wherein the alkaline aqueous solution supply means includes: an alkaline aqueous solution tank containing an alkaline aqueous solution; a pump for supplying alkaline water from the alkaline aqueous solution tank to the spent fuel; A spent fuel sludge cleaning apparatus comprising a waste cleaning liquid tank for storing a later waste cleaning liquid. 3. The spent fuel sludge cleaning apparatus according to claim 1, wherein the pH of the alkaline aqueous solution to be supplied is set to 12 or more. 4. A spent fuel sludge cleaning apparatus according to claim 1, wherein a device for separating insoluble solids from the spent fuel solution is a centrifugal clarifier. . The spent fuel sludge cleaning apparatus according to any one of claims 1 to 3, wherein the spent fuel sludge cleaning apparatus uses an apparatus for separating an insoluble solid content from the spent fuel solution as a filter. In a reprocessing step of reprocessing spent fuel used in a nuclear reactor, when the spent fuel is dissolved by the fuel solution, a centrifugal clarifier is used to remove insoluble solids from the fuel solution. A spent fuel sludge washing method comprising separating a sludge, washing the sludge adhering to the wall of the centrifugal clarifier with an alkaline aqueous solution, and then washing with water. A sludge cleaning method using the spent fuel sludge cleaning apparatus according to claim 5, wherein the sludge adhering to the surface of the filter is cleaned with an alkaline aqueous solution instead of a nitric acid aqueous solution, and then washed with water. A method for cleaning spent fuel sludge. A sludge cleaning method using the spent fuel sludge cleaning apparatus according to any one of claims 1 to 5, wherein an alkaline waste liquid is recovered after cleaning, and the recovered alkaline waste liquid is vitrified as a high-level waste. How to clean spent fuel sludge.

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