JPH11242095A - Disposal method of nuclear fuel reprocessing waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the production weight of a high level waste solid body, by removing sodium contained in solvent washing waste liquid, and reducing sodium up to a degree determined in response to a phosphorus amount. SOLUTION: In the case where high level waste is made a mineral solid body being the same structural body of zirconium phosphate and sodium, the method is based on a phenomenon largely dependent on a sodium amount whose solidification body amount is produced in a reprocessing process. In other words, sodium is removed from solvent washing waste being the supply source of phosphorus and sodium for high level waste, and it is made the limit value of the amount of sodium determined in relation to the phosphorus amount. For instance, solvent washing waste liquid is supplied from a flow inlet 7, and direct voltage is applied between an anode 3 and a cathode 4. Sodium ions contained in anode chamber liquid 5 permeate sodium selection permeable diaphragm 2, are transferred to cathode chamber liquid 6, and anode liquid in which 60% of sodium is removed is continuously flowed out from a liquid outlet 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of nuclear fuel reprocessing waste mainly composed of solvent washing waste liquid and solvent-extracted aqueous residue generated in the step of reprocessing spent nuclear fuel by the Purex solvent extraction method. Nuclear fuel reprocessing waste characterized by minimizing the amount of waste when the waste is more thermally stable than the vitrified material and is in the form of a crystalline isostructural substance of a small amount of sodium zirconium sodium phosphate. Regarding the processing method.

[0002]

2. Description of the Related Art Nuclear fuel materials used in a nuclear reactor are dissolved by nitric acid, and uranium and plutonium are extracted from a nitric acid solution using tributyl phosphoric acid as a solvent by the Purex solvent extraction method to dilute uranium and plutonium. It is back-extracted with aqueous nitric acid and reused as fuel, and the fission product elements in the residual aqueous solution are discarded.

[0003] In the above-mentioned Purex solvent extraction method, the solvent once used is washed with an aqueous solution of sodium carbonate and sodium hydroxide, and the phosphoric acid degradation product formed in the solvent under the influence of radiation contained in the nuclear fuel solution. And then used repeatedly. Phosphoric acid degradation products increase the concentration of radioactive fission products in the nuclear fuel material in the solvent phase. This solvent washing waste contains a small amount of nuclear fuel material and fission products together with sodium and phosphoric acid components. The solvent wash effluent may be combined with or separately from the solvent-extracted aqueous retentate containing most of the fission products into a concentrated effluent. Finally, the solvent wash effluent is combined with the solvent-extracted aqueous residue to be treated as nuclear fuel reprocessing high-level waste.

[0004] In order to convert the concentrated high-level waste liquid into high-level waste in a form that can be buried underground and safely disposed of,
It is important that the fission product elements are not easily diffused into the environment, and a method of producing a glass containing the fission product elements as a solid to form a solidified body has been widely developed. ing. Above all, a method using borosilicate glass as a component is the most common, and the weight of the vitrified material per ton of uranium fuel loaded into a nuclear reactor and having a burnup of about 45,000 MWD / MTU is most commonly used. Is 450kg.

Since the vitrified material is in a thermodynamically unstable state and crystallizes at a certain temperature and loses its properties, it is necessary to control the center temperature so as not to exceed the recrystallization temperature. In particular, careful management was required during the period when the heat of decay of fission product nuclides was significant.

[0006] Therefore, a rock composed of a plurality of minerals which selectively contain a specific element from among a large number of elements constituting a fission product and which have been geologically confirmed to be more stable than vitreous. Is disclosed in U.S. Pat. No. 54,957 in which most of the elements constituting the fission product are immobilized. This synthetic rock is called thin rock,
A typical host rock composition is zirconolite CaZrT
It is composed of three types of titanate minerals: i ₂ O ₇ , hollandite BaAl ₂ Ti ₆ O ₁₆ , and perovskite CaTiO ₃ . In order to incorporate the elemental composition of the high-level waste liquid into the mineral crystals, each of the constituent elements is accurately mixed and mixed with the high-level waste liquid or its calcined powder, and a rock having the desired mineral composition is synthesized by a ceramic method. The weight of synthetic rock will be 450 kg per ton of uranium fuel loaded into the reactor and having a burnup of about 45,000 MWD / MTU.

On the other hand, in order to eliminate the problem relating to coexistence between a plurality of mineral species constituting a synthetic rock, sodium zirconium phosphate (NaZr ₂ P ₃ O ₁₂ ), which is a single mineral species, is used as a fission product element. A single phase [NZP] ceramic radioactive waste
form, R. Roy, LJ Yang, ER Vance, Scie
ntific Basis for Nuclear Waste Management, Elsevie
r SciencePublishing Co., Inc., Vol.6, p.15-21
(1983) (Reference Document 1) and AnAlternative Conditi
oning Method for the Wastes from LWR Fuel
Reprocessing, Y. Hirose, et al., Proceedings for
the Global '97, Yokohama, October 5-10, 19
97 (Ref. 2). Characteristic of zirconium sodium phosphate is space group

[0008]

[Outside 2]

In the three-dimensional crystal structure having the symmetry represented by the symbol, the charge mismatch caused by the substitution of the element can be matched by incorporating the compensating element into the crystal space, so that the crystal structure is maintained. It is characterized by high flexibility in which constituent elements replace other elements. Due to the very low solubility of sodium zirconium phosphate and the remarkably low coefficient of thermal expansion, its crystalline isostructural material has a lower solubility than cement cement and is more thermally stable than vitrified, high-level waste disposal form. Has been evaluated as. The weight of the solidified material having the same crystal structure as sodium zirconium phosphate is loaded into a nuclear reactor and the burnup is 45,000 MWD / M
It has been shown that one ton of uranium fuel which has reached the TU level may be about one third of the solidified borosilicate glass, but the quantitative effect of the amount of sodium on the solidified solid amount has been studied. Did not.

[0010]

In the conventional method of solidifying nuclear fuel reprocessed high-level waste as borosilicate glass, sodium is a component of the glass host and the sodium contained in the high-level waste is not included. Since it is necessary to add a large amount of sodium as the amount is small, a certain amount of sodium does not affect the amount of the vitrified material,
There was no strong interest in the amount of sodium in high-level waste.

An object of the present invention is to provide a method for treating nuclear fuel reprocessing waste, which can reduce the weight of high-level solidified waste generated.

[0012]

SUMMARY OF THE INVENTION The present invention provides a nuclear fuel reprocessing high-level waste consisting essentially of fission products that only depends on burnup, with a solidified mineral material that is the same structure of sodium zirconium phosphate. In this case, it was performed based on a phenomenon in which the amount of solidified material greatly depends on the amount of sodium generated in the reprocessing step.

[0013] Reference 1 discloses a review of sodium zirconium phosphate or its crystalline structure.

Sodium zirconium phosphate (hereinafter referred to as N
ZP) has a molecular formula of NaZr ₂ P ₃ O ₁₂ (molecular weight: 490.34 g), and the crystal structural formula is generally [M ′ ₁ ] [M ″ ₂ ] [A ₂ ] [B ₃ ] O represented as _12. crystals, ZrO ₆ 8 tetrahedra, bonded by sharing the six PO ₄ 4 tetrahedra and oxygen atoms, each of PO ₄ 4 tetrahedron is four Zr
O ₆ 8 attached share facepiece and oxygen atoms, the basic unit _{(Zr 2 P 3 O 12)} - constitute a ribbon structure is three-dimensional structures ribbon structure is coupled with PO ₄ 4 tetrahedra Is composed. There are vacancies M 'in the ribbon structure where sodium ions coordinate. Another hole M ″ between adjacent ribbon structures
However, it is not satisfied in NZP.

If the B position has a small ionic radius like P ^5+, it is replaced by an ion having a different valence state. If the A position has a slightly larger ionic radius like Zr ⁴⁺ , it is replaced by an ion having a different valence state. Even if it is substituted and the M 'position is replaced by an alkali metal ion having a large ionic radius or an equivalent alkaline earth metal ion like Na ⁺ , the substitution by an ion having a different valence state compensates the valence. As described above, the alkali metal ion is coordinated within two molecules at the M ″ position, and the crystal structure of NZP is preserved. (Same crystal structure that preserves the crystal structure of NZP even when some of the constituent elements are replaced.) The body substance is abbreviated as [NZP].) The type of typical cation that can replace each position in the crystal structure depends on the size of the ion, and the M ′ and M ″ positions are the largest cations. But B position the smallest cation, A position cations intermediate size replaces almost selectively respectively.

M 'position: Na ⁺ , Rb ⁺ , Cs ⁺ , Ag ⁺ ,
Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ , Zn ²⁺ , Cd ²⁺ , P
b ²⁺ M ″ position: Na ⁺ , Rb ⁺ , Cs ⁺ A position: Ti ⁴⁺ , Cr ³⁺ , Fe ³⁺ , Co ²⁺ , Ni ²⁺ , Y
³⁺ , Zr2 ⁺ , Tc4 ⁺ , Ru4 ⁺ , Rh3 ⁺ , Pd3 ⁺ , I
n ³⁺ , La ³⁺ , Ce ⁴⁺ , Pr ³⁺ , Nd ³⁺ , Pm ³⁺ , Sm
³⁺ , Eu ³⁺ , Gd ³⁺ , U ⁴⁺ , Np ⁴⁺ , Pu ⁴⁺ , Am ³⁺ ,
Cm ³⁺ B position: Al ³⁺ , Si ⁴⁺ , P ⁵⁺ , As ⁵⁺ , Se ⁶⁺ , Mo
⁶⁺ , Sn ⁴⁺ , Sb ⁵⁺ , Te ⁴⁺ and the like.

At the M 'position, the ion in a multivalent state is replaced with an equivalent amount of Na. At the M ″ position, a monovalent alkali metal in the equivalent statement coordinates to compensate for the charge of the ion substituted at the A or B position.

The limit of the amount of high-level waste constituent elements that can be contained in the [NZP] molecule is that, at the M 'position, within 1 gram equivalent of alkali metal and alkaline earth metal cations,
At position A, the cation having a medium ionic radius is within 2 gram atoms, and at position B, within 3 gram atoms of a cation having a small ionic radius. Furthermore, the valence of the ion at the positions A and B is 21 gram equivalent and 23
If it is between gram equivalents, the alkali metal ions within 2 gram atoms at the M ″ position as high-level waste components,
Alternatively, it can be compensated by being taken in as an additional component. Reference 2 discloses that the pentavalent phosphorus ion at the B position is replaced with a tetravalent silicon ion to maximize the coordination of the alkali metal at the M ″ position. The technical means of the invention of claim 1 is that, when the amount of sodium in the high-level waste is large, the maximum equivalent coordination number (3) of the element at the M ′ position and the M ″ position per molecule of [NZP] is high. [NZP] The amount of solidified material becomes the limit, and when the amount of sodium in high-level waste decreases, one of [NZP]
The maximum coordination number (2) of the element at the position A per molecule is [N
ZP], which is a limit of the amount of solidified material. Furthermore, if the amount of phosphorus in the high-level waste is large, the maximum coordination number (3) of the element at the position B becomes a limit of the amount of solidified [NZP]. By controlling the amount of sodium in the solvent washing waste liquid constituting the level waste in relation to the amount of phosphorus.

The technical means of the second aspect of the present invention is based on the fact that the main elemental composition of high-level waste is determined depending on the burnup of nuclear fuel, and the effect of the first aspect of the invention is maximized. The upper limit of the amount of sodium in the high-level waste required for nuclear power is related to the amount of phosphorus.
00 MWD / MTU is standardized and given.

According to a third aspect of the present invention, there is provided a method for removing sodium contained in a solvent washing waste liquid, which generally comprises a trade name
Known as NASICON, whose basic composition is Na ₃ Zr ₂ Si ₂ PO
_By electrodialysis using a sodium ion-selective conductive ceramic of ₁₂ (or Zr replaced with a different atom) as a diaphragm. NASICON of sodium in aqueous solution (or
For removal by sodium ion-selective conductive ceramics (Zr is replaced by a different atom), see Ceramic Cleaner
s, Environmental Uses of Sodium Supre-IonicConducti
ng Ceramics, Davor Sutija, et al, The Electrochemical
Society Interface, Winter 1996, Vol.
4, pp. 26-30. The technical means according to claim 4, wherein the solvent washing waste liquid containing butyl phosphate after removing the sodium is converted from high-level waste to a solidified substance which is a mineral substance having the same structure of sodium zirconium phosphate. As a part of the oxide source, and also as a medium for removing excess oxygen when synthesizing the [NZP] solid by adding phosphorus and silicon oxides to the high-level waste oxide.

The technical means of the fifth aspect of the present invention is the third aspect of the present invention.
The sodium recovered by the technical means of (1) is not easily contaminated by other substances contained in the solvent washing waste liquid, and is used for preparing the solvent washing waste liquid.

The function of the basic technical means of the present invention is to synthesize the components of nuclear fuel reprocessing waste [NZ
P] is related to the composition of the solidified waste. Table 1
Is the composition of the amount of the constituent elements of nuclear fuel reprocessing high-level waste per ton of spent uranium to be reprocessed.

[0023]

[Table 1]

The effect of the invention of claim 1 is that, since the amount of the element that substitutes the A position of the solidified [NZP] among the high-level waste components is large, the A position is completely replaced by the high-level waste component. However, configuring the structure at the position A only with the high-level waste component is a means for reducing the amount of the solidified [NZP] to the limit. If the amount of sodium in the high-level waste is large, the maximum equivalent coordination number (3) of the element at the M ′ position and M ″ position per molecule of [NZP] is [NZ
[P] becomes the limit of the amount of solidified body, and if the maximum coordination number (2) of the element at the position A per [NZP] molecule is not satisfied, and the phosphorus content in the high-level waste is larger than a certain level. When the maximum coordination number (3) of the element at the B position is [N
ZP] limits the amount of solids and also reduces the sodium tolerance, especially since the coordination number of sodium at the M ″ position cannot be fully compensated. Phosphorus and sodium sources for high level waste Is removed from the solvent wash effluent to give a limit on the amount of sodium determined in relation to the amount of phosphorus.

According to the second aspect of the present invention, the composition and amount of fission products contained in the solvent extraction residue depend on the burnup, while the phosphorus and sodium amounts of the solvent washing waste liquid are determined in the reprocessing step. , The burnup of nuclear fuel to be reprocessed is 45,000.
It is set for high-level waste per ton of spent fuel uranium standardized to MWD / MTU. [NZP]
In order to achieve the conditions for completely replacing the position A of the solidified body with the high-level waste constituent elements, the phosphorus content of the high-level waste is 100 g-mol or less, 150 g-mol or less, and 200 g-mol or less, respectively. , The amount of sodium must be 200 g-mol or less, 150 g-mol or less, and 100 g-mol or less. If the burnup is 27,000 MWD / MTU,
Since the major constituent of high-level waste per ton of spent uranium becomes 60%, the limit of phosphorus and sodium in high-level waste is 45,000 MWD.
/ MTU to 60%. That is, [NZP]
In order to achieve the condition for completely replacing the A position of the solidified body with the high-level waste composition element, the phosphorus content of the high-level waste per ton of spent fuel uranium is 60 g-mol or less, 90 g or less.
-mol or less, 120g-mol or less, sodium amount is 120g-mol or less, 90g-mol or less, 60g, respectively
It must be less than -mol. Since the amount of phosphorus is derived from the amount of solvent degradation products in the solvent washing waste liquid, the cooling period is short even if the burnup of the nuclear fuel to be treated is the same, so the higher the radioactivity intensity, the more the deterioration of the solvent contained in the solvent washing waste liquid The amount is increased, and thus the amount of phosphorus from the solvent wash effluent is increased relative to the amount of fission products. On the other hand, since the amount of sodium is derived from the amount of solvent washing liquid used, it depends on the amount of nuclear fuel material itself to be treated rather than the amount of fission products. Increases relative to the amount of product. The effect of the invention of claim 2 depends on the relative balance between the components of fission products and phosphorus and sodium.

According to the third aspect of the present invention, the sodium contained in the reprocessed high-level waste is substantially all derived from the solvent washing waste liquid, and the solvent washing waste liquid includes sodium carbonate, sodium hydroxide, and sodium nitrate. , Butyl phosphate-based solvent degradation products, nuclear fuel materials, and radioactive materials consisting of fission products. Generally, cations can be separated from an aqueous solution containing the cations by electrodialysis using a cation exchange membrane. However, a chemically durable fluoropolymer cation exchange membrane represented by the trade name Nafion cannot separate only sodium ions from an aqueous solution containing other cations.
Even if impurities are allowed in the separation of sodium, there is a problem that the ion-exchange membrane is easily deteriorated when cations that generate precipitates are contained as impurities in the high-concentration alkali solution separated and recovered. The polymer-based ion exchange membrane has a disadvantage that it is easily deteriorated by irradiation with radiation.

[0029] NASICON (or including Zr-substituted heteroatom) sodium ion-selective conductive ceramics are also permeable to lithium, sodium and potassium ions under direct current potential, while hydronium ions. It has the property of not transmitting all cations and anions except (H ₂ O ⁺ ) and silver ions. This property means that only sodium ions can be selectively separated from all ions contained in the solvent washing waste liquid. Irradiation has substantially no effect on sodium ion permeability. Inorganic ion exchangers such as zirconium phosphate are not affected by irradiation, but do not have sodium ion selectivity like NASICON and permeate alkali metal and alkaline earth metal radioactive ions such as cesium and strontium. Therefore, the application of NASICON has made it possible for the first time to remove sodium from radioactive solvent wash effluents.

The function of the invention of claim 4 is that the solvent washing waste liquid after the removal of sodium contains butyl phosphates as a part of the source of phosphorus for synthesizing the solidified [NZP]. Although available, it is believed that there is at least a butyl group equivalent to the gram molecular concentration of phosphorus,
The butyl group of the gram molecule is based on the reduction of 12.5 gram molecule of oxygen to 4 gram molecule of carbon dioxide and 4.5 gram molecule of water. The butyl group of butyl phosphate is used as a reducing agent in order to effectively remove excess oxygen at the time of solidification conversion and facilitate the synthesis of [NZP] solidification.

The effect of the invention of claim 5 is that sodium hydroxide recovered by electrodialysis using NASICON as a diaphragm does not contain impurities that hinder reuse as a solvent cleaning material. The concentration of the recovered sodium hydroxide can be controlled in a wide range depending on the purpose because the water does not pass through the water. If the recovered sodium hydroxide is reused as a part of a reagent for preparing a new solvent washing solution, secondary waste is not generated and necessary reagents can be saved.

[0030]

[Embodiment 1] A method for treating nuclear fuel reprocessing waste, which is a preferred embodiment of the present invention, will be described below with reference to FIG. Figure 1 shows a burnup of 45,000 MWD
/ MTU high-level waste of 1 ton of nuclear fuel has phosphorus content of 50
g-mol, 100 g-mol, 150 g-mol, 200 g-mol
, Lines 1, 3, 5, and 7 indicate the oxide weight of the high level waste composition, respectively, and lines 2, 4, 6, and 8 optimize the composition to minimize the solidified material weight [NZP]
The weight of the solidified product (kg / MTU) is shown, and the amount of sodium in the high-level waste (g-m
ol).

(Specific Example 1-1) As shown in Table 1, 50 g of phosphorus contained in high-level waste generated by processing 1 ton of nuclear fuel having a burnup of 45,000 MWD / MTU.
-mol, and the amount of sodium was 500 g-mol. 187.1 g-mol of zirconium oxide (ZrO ₂ ) and 387.4 g-mol of silicon oxide (S
iO ₂ ) and 127.3 g-mol of phosphoric acid (PO _2.5 ) were added and the composition was determined by known methods to [M _2.766 ] [Zr _0.892 A _1.108 ] [P _0.607 Si _1.847
B _0.546] a O ₁₂ (molecular weight = 619 g), was manufactured [NZP] solidified body. Solidification weight is 1
The weight was 29.82 kg. Here, in the composition formula, M is M ′
A and B denote high-level waste composition elements coordinating at the M ″ position, A denotes a high-level waste composition element that substitutes for zirconium at the A position, and B denotes a high-level waste composition element that substitutes for phosphorus at the B position. The constituent elements are shown collectively.
P and Si represent elements such as zirconium, phosphorus and silicon added for synthesizing [NZP].

In the specific example 1-1, the M 'and M "positions reached the sodium equivalent of 3.00 and were saturated,
At position A, only 1.1 of the two molecules of zirconium are substituted.

(Specific Example 1-2) As shown in Table 1, 50 g of phosphorus contained in high-level waste generated by processing 1 ton of nuclear fuel having a burnup of 45,000 MWD / MTU.
-mol, and the amount of sodium was 500 g-mol. The sodium in the solvent washing waste liquid is removed, and the amount of sodium contained in the high-level waste is reduced from 400 g-mol to 300 g-mol.
And zirconium oxide (ZrO ₂ ), silicon oxide (SiO ₂ ) and phosphor oxide (PO _2.5 ) were added, and the composition and weight were reduced to 400 g of Na by a known method as in Example 1-1. mol: [M _2.722 ] [Zr _0.683 A _1.317 ] [P
_0.530 Si _1.821 B _0.649 ] O ₁₂ (molecular weight = 636 g) 11
2.15 kg Na300g-mol: [M _2.657 ] [Zr _0.376 A _1.624 ] [P _0.419 Si
_1.781 B _0.800 ] O ₁₂ (molecular weight = 660 g) A solidified [NZP] having a weight of 94.46 kg was produced. As compared with the specific example 1-1, the weight of the solidified [NZP] decreases as the amount of sodium decreases, but in any case, the substitution at the position A is insufficient, and the amount of sodium further decreases. If so, the weight of the solidified [NZP] may be reduced.

(Specific Examples 1-3) As shown in Table 1, 50 g of phosphorus contained in high-level waste generated by processing 1 ton of nuclear fuel having a burnup of 45,000 MWD / MTU.
-mol, and the amount of sodium was 500 g-mol. The amount of sodium contained in the high-level waste is reduced to 200 g-mol by removing sodium from the solvent washing waste liquid, and the amount of sodium is reduced to 2.4 g.
g-mol of phosphor oxide (PO _2.5 ) and 254.9 g-mol of silicon oxide (SiO ₂ ) were added and the composition was changed to [M _2.412 by a known method in the same manner as in Example 1-1 _. ] [A _2.00 ] [P _0.452 Si _1.563 B _0.985 ] O
_A solidified [NZP] having a molecular weight of ₁₂ (molecular weight = 687 g) was produced. Solidification weight is 7
The weight was 9.81 kg, and the solid density was 5 g / cm ³ .

In Example 1-3, the A position was completely replaced by the high level waste component and no zirconium had to be added. Although the coordination numbers at the positions M 'and M "are smaller than those in Examples 1-1 and 1-2, the phosphorus in the position B is almost completely replaced by the high-level waste component and the added silicon. From this point, it is considered that the amount of sodium is at the limit of the amount of solidified [NZP], which is reduced by 50.01 kg as compared with the specific example 1-1. mol is almost proportional to the amount of sodium removed, and the corresponding sodium oxide (Na ₂
O) The proportional constant relating to the quantity is 5.38.

(Specific Examples 1-4) As shown in Table 1, 50 g of phosphorus contained in high-level waste generated by processing 1 ton of nuclear fuel having a burnup of 45,000 MWD / MTU.
-mol, and the amount of sodium was 500 g-mol. The sodium in the solvent washing waste liquid is further removed, and the amount of sodium contained in the high-level waste is reduced to 20 g-mol.
82.5 g-mol of phosphor oxide (PO _2.5 ) and 1.7 g-mol of silicon oxide (SiO ₂ ) were added, and the composition was changed to [M _0.862 ] by a known method as in Example 1-1. [A _2.00 ] [P _2.001 Si _0.014 B _0.985 ] O
_A solidified [NZP] having a molecular weight of ₁₂ (molecular weight = 656 g) was produced. Solidification weight is 7
The weight was 6.17 kg.

In Examples 1-4, the A position was completely replaced by the high level waste component and no zirconium had to be added. The coordination numbers at the M 'and M "positions are even smaller than in Example 1-2, and in the B position the replacement of high-level waste components equal to that of Example 1-2 because the amount of silicon required for replacement is very small. Nevertheless, if the amount of sodium at the M 'and M "positions is less than 20 g-mol, the low charge at the A position cannot be compensated, and therefore the weight of the solidified [NZP] The lower limit is 76.17 kg. The amount of the solidified [NZP] is reduced by 3.64 kg as compared with the specific example 1-3, and the amount of reduction is proportional to the amount of sodium removed when the amount of sodium is between 200 g-mol and 20 g-mol. The proportional constant relating to the amount of sodium oxide is 0.65.

Example 1 has the following effects.

(1) The amount of sodium contained in high-level waste having a phosphorus content of 50 g-mol generated by the treatment of 1 ton of nuclear fuel is reduced from 500 g-mol to 200 g-mol, and sodium oxide (Na ₂ O) is reduced. ), The weight of the solidified [NZP] is reduced by 50 kg, and
kg. The high level waste (oxide) weight accounted for 90% of the weight of the solidified [NZP], and nearly ultimate weight loss was achieved.

(2) The density of the reduced [NZP] solidified material is 5 g / cm ³ , and the volume of 80 kg [NZP] solidified high-level waste generated by processing 1 ton of nuclear fuel is 16 liters. And only about one tenth of the volume of the solidified borosilicate glass.

(3) The amount of sodium contained in high-level waste generated by processing 1 ton of nuclear fuel is set to 200 g-mol.
From 20 g-mol to sodium oxide (Na ₂
O), the weight of the solidified [NZP] was reduced only by 3.02 kg, and the sodium content was reduced by 200 g-mol.
It has been found that the effect of reduction is small as follows.

(4) It was found that the weight of solidified [NZP] did not become less than 76.79 kg even if the amount of sodium of high-level waste generated by processing 1 ton of nuclear fuel was made less than 20 g-mol.

[Embodiment 2] A method of treating nuclear fuel reprocessing waste as another preferred embodiment of the present invention will be described below with reference to FIG. Figure 1 shows a burnup of 45,000 MWD / M
TU nuclear fuel 1 ton of high-level waste has phosphorus content of 50 g-m
ol, 100 g-mol, 150 g-mol, and 200 g-mol, lines 1, 3, 5, and 7 indicate the oxide weight of the high-level waste composition, respectively, and lines 2, 4, 6, and 8 indicate solidification. The weight (kg / MTU) of the solidified [NZP] compact whose composition was optimized to minimize the body weight is shown, and the effect of the amount of sodium (g-mol) in high-level waste on each is shown. Is shown.

(Specific Example 2-1) Burnup is 45,000 M
50 g-mol of phosphorus per ton of WD / MTU nuclear fuel
, 100g-mol, 150g-mol, 200g-mol Solvent washing waste liquid, 500g-mol to 50g sodium
-[mol], and appropriate amounts of phosphorus and silicon oxides were added so as to minimize the weight of the solidified body, thereby producing a solidified [NZP] body.

When the amount of phosphorus is 50 g-mol, the amount of sodium
[NZP] solidified product and the amount of the solidified product depend on the amount of Na50g-mol: [M_1.120] [A_2.00] [P_1.743Si
_0.272B_0.985] O₁₂(Molecular weight = 661 g) 76.79 kg Na 100 g-mol: [M_1.551] [A_2.00] [P_1.313S
i_0.702B_0.985] O₁₂(Molecular weight = 670 g) 77.80 k
g Na 150 g-mol: [M_1.981] [A_2.00] [P_0.883S
i_1.133B_0.985] O₁₂(Molecular weight = 678 g) 78.89 k
g Na200g-mol: [M_2.412] [A_2.00] [P_0.452S
i_1.563B_0.985] O₁₂(Molecular weight = 687 g) 79.81 k
g Na300g-mol: [M_2.657] [Zr_0.376A_1.624] [P
_0.419S_i1.781B_0.800] O₁₂(Molecular weight = 660 g) 94.4
6 kg Na 400 g-mol: [M_2.722] [Zr_0.683A_1.317] [P
_0.530Si_1.821B_0.649] O₁₂(Molecular weight = 636 g) 112.
15 kg Na 500 g-mol: [M_2.766] [Zr_0.892A_1.108] [P
_0.607Si_1.847B_0.546] O₁₂(Molecular weight = 619 g) 129.
82kg When the amount of phosphorus is 100g-mol, depending on the amount of sodium
[NZP] The solidified product and the amount of the solidified product were Na 50 g-mol: [M_1.120] [A_2.00] [P_1.312Si
_0.273B_1.415] O₁₂(Molecular weight = 661 g) 76.79 kg Na 100 g-mol: [M_1.551] [A_2.00] [P_0.882S
i_0.703B_1.415] O₁₂(Molecular weight = 670 g) 77.80 k
g Na 150 g-mol: [M_1.981] [A_2.00] [P_0.451S
i_1.134B_1.415] O₁₂(Molecular weight = 678 g) 78.89 k
g Na200g-mol: [M_2.412] [A_2.00] [P_0.021S
i_1.564B_1.415] O₁₂(Molecular weight = 687 g) 79.81 k
g Na300g-mol: [M_2.657] [Zr_0.376A_1.624] [P
_0.069Si_1.782B_1.149] O₁₂(Molecular weight = 660 g) 94.
46 kg Na 400 g-mol: [M_2.722] [Zr_0.683A_1.317] [P
_0.244Si_1.824B_0.932] O₁₂(Molecular weight = 636 g) 11
2.15 kg Na 500 g-mol: [M_2.766] [Zr_0.683A_1.108] [P
_0.367Si_1.849B_0.784] O₁₂ (Molecular weight = 619 g) 12
9.82 kg The case where the amount of phosphorus shown in Example 1 is 50 g-mol and this example
In the case where the amount of phosphorus in is 100 g-mol, [NZP]
The amounts of phosphorus and silicon added for synthesis differ, but [N
ZP] has a molecular weight and a solidified amount of sodium regardless of the phosphorus amount.
It turned out to be dependent only on the amount. Also, any of
In some cases, the sodium content exceeds 200 g-mol
Would not give a complete substitution at position A.

(Specific Example 2-2) Burnup of 45,000 M
150 g-m of phosphorus per ton of WD / MTU nuclear fuel
ol and 200 g-mol of the solvent washing waste liquid were adjusted to 500 g-mol to 50 g-mol sodium, respectively.
A solidified [NZP] body was prepared by adding phosphorus and silicon oxides.

When the amount of phosphorus was 150 g-mol, the solidified [NZP] and the amount of the solidified solid were as follows depending on the amount of sodium.

Na 50 g-mol: [M_1.120] [A_2.00]
[P_0.883Si_0.271B_1.846] O₁₂(Molecular weight = 661
g) 76.79 kg Na 100 g-mol: [M_1.551] [A_2.00] [P_0.453S
i_0.701B_1.846] O₁₂(Molecular weight = 670 g) 77.80 k
g Na 150 g-mol: [M_1.981] [A_2.00] [P_0.022S
i_1.132B_1.846] O₁₂(Molecular weight = 678 g) 78.89 k
g Na200g-mol: [M_2.188] [Zr_0.185A_1.815] [Si
_1.325B_1.675] O₁₂(Molecular weight = 667 g) 85.38 kg Na 300 g-mol: [M_2.487] [Zr_0.480A_1.520] [Si
_1.597B_1.403] O₁₂(Molecular weight = 648 g) 99.07 kg Na 400 g-mol: [M_2.697] [Zr_0.695A_1.305] [Si
_1.796B_1.204] O₁₂(Molecular weight = 634 g) 112.92 kg Na 500 g-mol: [M_2.766] [Zr_0.892A_1.022] [P
_0.129Si_1.849B_1.022] O₁₂ (Molecular weight = 619 g) 129.
82kg When the phosphorus content is 200g-mol, depending on the sodium content
[NZP] The solid and the amount of the solid were as follows.

Na 50 g-mol: [M _1.120 ] [A _2.00 ]
[P _0.469 Si _0.255 B _2.276 ] O ₁₂ (molecular weight = 661
g) 76.80 kg Na 100 g-mol: [M _1.551 ] [A _2.00 ] [P _0.021 S
i _0.703 B _2.276 ] O ₁₂ (molecular weight = 670 g) 77.80 k
_{g Na150g-mol: [M 1.783} ] [Zr 0.20 A 1.80] [P
_{0.034 Si 0.917 B 2.049] O 12} ( molecular weight = 658 g) 84.
87 kg Na 200 g-mol: [M _1.990 ] [Zr _0.35 A _1.65 ] [P
_0.008 Si _0.114 B _1.878 ] O ₁₂ (molecular weight = 649 g) 91.
40 kg Na300 g-mol: [M _2.291 ] [Zr _0.60 A _1.40 ]
[Si _1.398 B _1.593 ] O ₁₂ (molecular weight = 634 g) 10
5.23 kg Na400 g-mol: [M _2.521 ] [Zr _0.78 A _1.22 ]
[Si _1.611 B _1.389 ] O ₁₂ (molecular weight = 624 g) 11
8.75 kg Na 500 g-mol: [M _2.697 ] [Zr _0.92 A _1.08 ]
[Si _1.771 B _1.229 ] O ₁₂ (molecular weight = 615 g) 13
2.37 kg The amount of phosphorus and silicon added for synthesizing [NZP] is different between 150 g-mol and 200 g-mol of phosphorus, but the former contains 200 g-mol of sodium and the latter contains 150 g-mol of sodium. Until now, it was found that the molecular weight and solidified amount of [NZP] depended only on the amount of sodium, regardless of the amount of phosphorus, as in the case of a lower amount of phosphorus. 15 phosphorus
When the amount of sodium exceeds 0 g-mol and the amount of phosphorus is 200 g-mol, when the amount of sodium exceeds 150 g-mol and 100 g-mol, respectively, complete substitution at the A position cannot be given. A
It has been found that as long as the complete substitution at the position is given, the molecular weight and the amount of the solidified [NZP] are determined only by the amount of sodium regardless of the amount of phosphorus.

The following effects were obtained by the specific example 2.

(1) When the amount of phosphorus in high-level waste per ton of nuclear fuel is 100 g-mol, the amount of sodium required to reduce the weight of the solidified [NZP] as in the case of 50 g-mol Was found to be 200 g-mol.

(2) When the amount of phosphorus in the high-level waste per ton of nuclear fuel is 150 g-mol, the limit value of the amount of sodium required to reduce the weight of the solidified [NZP] is 1
It was found to be 50 g-mol.

(3) When the amount of phosphorus in high-level waste per ton of nuclear fuel is 200 g-mol, the limit of the amount of sodium necessary to reduce the weight of the solidified [NZP] is 1
It was found to be 00 g-mol.

(4) It was found that the weight of the solidified [NZP] in which the position A was completely substituted by the high-level waste component was dependent only on the amount of sodium, regardless of the amount of phosphorus.

[Embodiment 3] A method for treating nuclear fuel reprocessing waste as another preferred embodiment of the present invention will be described below with reference to FIG. FIG. 2 is an apparatus for electrodialytically removing sodium from a solvent washing waste liquid. 1 is a container and 2 is a NASICO having a composition of sodium permselectivity of Na ₃ Zr ₂ Si ₂ PO _12.
A diaphragm formed by processing a high-density sintered body of N into a cylindrical shape with a bottom, 3 is a cylindrical shape formed by plating platinum on a titanium mesh, and an anode is disposed on the outer periphery of the diaphragm. 4 is a cylindrical shape formed by plating platinum on a titanium mesh. , A cathode chamber liquid containing solvent washing waste liquid, 6 a cathode chamber liquid containing sodium hydroxide, 7 an inlet for a solvent washing waste liquid containing sodium, and 8 a sodium concentration decrease. Reference numeral 9 denotes an inlet for water, and reference numeral 10 denotes an outlet for an aqueous solution of sodium hydroxide.

(Specific Example 3) Burnup of 45,000 MWD
/ MTU Nuclear fuel reprocessing per ton of radioactive solvent washing waste liquid generated in the reprocessing is sodium carbonate
(Na ₂ CO ₃ 100 g-mol) 10.6 kg, sodium bicarbonate (NaHCO ₃ 120 g-mol) 10.1 kg, sodium nitrate (NaNO ₃ 100 g-mol) 8.5 kg, butyl phosphate sodium salt (R-PO ₄ 50g-mol) 1
It was an aqueous solution containing 0.5 kg and the like, and its volume was 1000 liters. The total sodium content was 500 g-mol.

The solvent washing waste liquid having the above-mentioned composition is supplied from the inlet 7 to the container 1 at a rate of 0.5 liter per minute, a DC voltage is applied between the anode 3 and the cathode 4, and
A DC current of 480 amps was passed through the diaphragm 2 having a height of 0 cm and a height of 63.7 cm (effective surface area: 2000 cm ² ). Carbon dioxide gas was generated from the anode, and hydrogen gas was generated from the cathode. The sodium ion contained in the anode compartment liquid 5 is 0.15
The liquid permeated through the diaphragm 2 at a rate of g-mol per minute and transferred to the cathode compartment liquid 6. When one molecule of sodium ion permeates the diaphragm 2, about one molecule of hydronium ion (H ₂ O ⁺ ) secondarily passes through the diaphragm 2 and the current efficiency of sodium transfer is 50%.
Became. The anolyte from which 60% of the sodium had been removed flowed continuously from the anolyte outlet 8. Water was added to the cathode compartment liquid at a rate of 25 cc / min from the water inlet 9, and a sodium hydroxide aqueous solution having a concentration of 6 g-mol / l flowed out of the sodium hydroxide outlet 10 at a rate of 25 cc / min. The 0.15 g-mol / min hydronium ion per minute transferred from the anolyte to the catholyte was consumed to produce sodium hydroxide from sodium ions and hydrogen gas.
In the solvent washing waste liquid after the removal of sodium, sodium carbonate and sodium bicarbonate were lost, but sodium phosphate butyl ester and sodium nitrate did not change, and the liquid property was weakly acidic. The radioactivity contained in the recovered sodium hydroxide aqueous solution was 0.1% of the radioactivity contained in the solvent washing waste liquid through the fine voids remaining in the ceramic cylinder constituting the diaphragm. Pure enough to be prepared.

Example 3 has the following effects.

(1) A specific method for removing sodium was provided in conformity with the conditions such as the chemical composition of the solvent washing waste liquid and radioactivity.

(2) The recovered sodium hydroxide aqueous solution was sufficiently pure to be used for preparing a solvent washing solution.

[Embodiment 4] A method for treating nuclear fuel reprocessing waste as another preferred embodiment of the present invention will be described below.

(Specific Example 4-1) 50 g-mol of phosphorus and 500
After removing 300 g-mol sodium from the solvent washing waste liquid containing g-mol sodium by electrodialysis, the solvent washing waste liquid is concentrated, and further heated to thermally decompose the butyl phosphate to remove the butyl group component. The phosphoric acid was converted to a sodium salt and mixed with a concentrate of an aqueous solvent-extracted residue produced by reprocessing 1 ton of nuclear fuel at a burnup of 45,000 MWD / MTU, and further containing 52.5 g-mol of phosphorus oxide (PO
_2.5 ) and 181.6 g-mol of silicon oxide (SiO ₂ ) were added to form a dry powder.
To synthesize a solidified [NZP]. The mixture before sintering contains 13.0 g-mol oxygen per molecule and requires 12 hours of high temperature heat treatment to finally reach the stoichiometric 12.0 g-mol oxygen composition Met.

(Specific Example 4-2) 50 g-mol of phosphorus and 50
After 300 g-mol sodium was removed from the solvent washing waste liquid containing 0 g-mol sodium by electrodialysis, the solvent washing waste liquid was concentrated and burned while leaving butyl phosphate corresponding to 50 g-mol as a butyl group. Degree 45,0
A MWD / MTU is mixed with a retentate of the solvent-extracted aqueous retentate produced in the reprocessing of 1 ton of nuclear fuel, and a further 52.
5 g-mol of phosphorus oxide (PO _2.5 ) and 181.6 g-mol of silicon oxide (SiO ₂ ) were added to form a dry powder, and after compacting, sintered at 1200 ° C. in the air [ [NZP] was synthesized. The mixture before sintering is 1 per molecule
Six hours of high temperature heat treatment was sufficient to contain 3.0 g-mol of oxygen and finally reach a stoichiometric oxygen composition of 12 g-mol.

Example 4 has the following effects.

(1) The butyl group in the solvent washing waste liquid after the removal of sodium is removed, and then mixed with the solvent-extracted aqueous residue to form a high-level waste, which is compared with the case of solidifying [NZP]. Thus, it was possible to synthesize a solidified [NZP] having a stoichiometric oxygen composition with a shorter heating time.

Embodiment 5 A method for treating nuclear fuel reprocessing waste according to another preferred embodiment of the present invention will be described below.

(Specific Example 5) The volume of the solvent washing waste liquid generated in the reprocessing of 1 ton of nuclear fuel is 1000 liters,
It contained 0 g-mol of sodium. In order to reduce the amount of [NZP] solidified high-level waste, 300 g-mol of sodium was separated from the solvent washing waste liquid by electrodialysis using a NASICON ceramic cylinder as a diaphragm, and a concentration of 6 M containing 12 kg as sodium hydroxide was obtained. Of sodium hydroxide aqueous solution was recovered. If sodium hydroxide is neutralized with nitric acid to form sodium nitrate, the amount will be increased to 25.5 kg, and if the cement is to be solidified and discarded, it will be at least 50 kg. However, the recovered sodium hydroxide was used as a part of the 500 g-mol sodium reagent required to prepare a solvent washing solution for processing 1 ton of nuclear fuel. No outbreak occurred, saving 60% of the new reagent.

Example 5 has the following effects.

(1) Since the recovered sodium was used to prepare a solvent washing solution for treating nuclear fuel, 60% of the reagent for preparing a new solvent washing solution was saved without being used as a secondary waste. did it.

[0070]

The effect of the first aspect of the present invention is that 9.3 of sodium oxide (Na ₂ O) corresponding to the amount of sodium in the solvent washing waste liquid constituting the high-level nuclear fuel reprocessing waste.
kg, reducing high-level waste [NZP]
The weight of the solidified body was reduced by 50 kg.

The effect of the second aspect of the present invention relates to the amount of phosphorus in the high-level waste and limits the amount of sodium necessary and sufficient to bring about the effect of reducing the weight of [NZP] solidified material. Was done. Exceeding the limit of the necessary and sufficient amount of sodium, if the amount of sodium oxide (Na ₂ O) is further reduced by 5.58 kg, the weight of the solidified [NZP] of high-level waste is further reduced by 3.83 kg. It was not too much.

The effect of the third aspect of the present invention is to provide a method for removing sodium which is adapted to the composition of the solvent washing waste liquid and the radioactivity conditions.

The effect of the invention of claim 4 is that phosphorus contained in the solvent washing waste liquid after the removal of sodium is reduced to [NZP].
In addition to being a part of the phosphorus source for solidification synthesis, it also facilitated [NZP] solidification synthesis as a medium to remove excess butyl phosphate by reducing excess oxygen.

The effect of the fifth aspect of the present invention is that the aqueous sodium hydroxide solution recovered from the solvent washing waste liquid is used for the preparation of a new solvent washing liquid, so that secondary waste associated with the treatment is not generated and a new reagent is used. Can be saved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a first embodiment;

FIG. 2 is an apparatus configuration diagram for explaining a third embodiment.

Claims (5)

[Claims] 1. A phosphorus group and a silicon oxide are added to a nuclear fuel reprocessing high-level waste composed of a solvent washing waste liquid containing phosphorus and sodium and a solvent-extracted aqueous residue containing fission products to form a space group. 1) Sodium zirconium phosphate (NaZr ₂ P ₃ O ₁₂ ) having a symmetrical three-dimensional crystal structure represented by the symbol
In the treatment method of solidifying mineral substances having the same structure, the sodium contained in the solvent washing waste liquid is removed in advance, and the amount of sodium contained in the nuclear fuel reprocessing high-level waste is determined according to the amount of phosphorus. A method for treating nuclear fuel reprocessing waste, characterized in that the waste is reduced to a minimum. 2. Burnup of 45,000 MWD / MTU
The amount of phosphorus in the high-level waste per ton of spent fuel uranium standardized to 100 g-mol or less and 150 g-m
ol or less and 200 g-mol or less, the sodium content is 200 g-mol or less, 150 g-mol or less, and 10 g or less, respectively.
2. The method for treating nuclear fuel reprocessing waste according to claim 1, wherein the amount is 0 g-mol or less. 3. The method according to claim 1, wherein the removal of the sodium contained in the solvent-washing radioactive waste liquid is performed by using a sodium ion-selective conductive material synthesized by partially replacing the phosphorus of zirconium sodium phosphate with silicon as a diaphragm. 2. The method for treating nuclear fuel reprocessing waste according to claim 1, wherein only sodium ions are selectively removed by electrodialysis from the constituent materials. 4. A solvent waste liquid containing water-soluble butyl phosphate after the removal of sodium is used for synthesizing a stable mineral solid having the same structure as zirconium sodium phosphate (NaZr ₂ P ₃ O ₁₂ ). 2. The method for treating nuclear fuel reprocessing waste according to claim 1, wherein: 5. The method for treating nuclear fuel reprocessing waste according to claim 3, wherein sodium separated from said solvent washing waste liquid is reused for preparing a solvent washing liquid.