Process for reprocessing a spent nuclear fuel and of preparing a mixed uranium-plutonium oxide

Abstract

A process for reprocessing a spent nuclear fuel and for preparing a mixed uranium-plutonium oxide. The process: a) separates the uranium and plutonium from fission products, americium, and curium that are present in an aqueous nitric solution resulting from dissolution of the fuel in nitric acid, the separating including at least one operation of coextracting the uranium and plutonium from the solution by a solvent phase; b) partitions the coextracted uranium and plutonium to a first aqueous phase containing plutonium and uranium, and a second aqueous phase containing uranium but no plutonium; c) purifies the plutonium and uranium that are present in the first aqueous phase; and d) coconverts the plutonium and uranium to a mixed uranium/plutonium oxide.

1 - 29 . (canceled) 
   
   
       30 : A process for reprocessing a spent nuclear fuel and of preparing a mixed uranium-plutonium oxide, comprising:
 a) separating the uranium and plutonium from fission products, americium, and curium that are present in an aqueous nitric solution that results from dissolving the spent nuclear fuel in nitric acid, the separating comprising at least one operation of coextracting uranium, in oxidation state (VI), and plutonium, in oxidation state (IV), from the aqueous solution by bringing the solution into contact with a water-immiscible solvent phase containing at least one extractant in an organic diluent;   b) partitioning the uranium and plutonium coextracted in the separating a) into two aqueous phases, of a first aqueous phase containing plutonium and uranium, and a second aqueous phase containing uranium but not containing plutonium;   c) purifying the plutonium and uranium present in the first aqueous phase obtained after the partitioning b) from the fission products also liable to be found in this phase; and   d) coconverting the plutonium and uranium that are present in the aqueous phase obtained after the purifying c) into a mixed uranium-plutonium oxide.   
   
   
       31 : A process according to  claim 30 , in which the separating a) also includes at least one scrubbing operating in which the solvent phase obtained after the uranium-plutonium coextraction operation is scrubbed by bringing this phase into contact with an aqueous nitric phase. 
   
   
       32 : A process according to  claim 30 , wherein:
 the partitioning b) comprises:   b 1 ) back-extracting the plutonium, in oxidation state (III), and a fraction of the uranium, in oxidation state (VI), from the solvent phase obtained after the separating a), by bringing this phase into contact with an aqueous nitric phase containing a reducing agent capable of reducing plutonium(IV) to plutonium(III) without reducing the uranium; and   b 2 ) back-extracting the uranium that has not been back-extracted from the solvent phase during operation b 1 ), by bringing this phase into contact with an aqueous nitric phase; wherein   the purifying c) comprises:   c 1 ) coextracting the plutonium, in oxidation state (IV), and the uranium, in oxidation state (VI), from the aqueous phase obtained after operation b 1 ), by bringing this phase into contact with a water-immiscible solvent phase containing at least one extractant in an organic diluent;   c 2 ) a scrubbing operation in which the solvent phase obtained after operation c 1 ) is scrubbed by bringing this phase into contact with an aqueous nitric phase; and   c 3 ) back-extracting the plutonium, in oxidation state (III), and a fraction of the uranium, in oxidation state (VI), from the solvent phase obtained after operation c 2 ), by bringing this phase into contact with an aqueous nitric phase containing a reducing agent capable of reducing plutonium(IV) to plutonium(III) without reducing the uranium(VI).   
   
   
       33 : A process according to  claim 32 , which further includes, between the partitioning b) and the purifying c), an operation of oxidizing the plutonium(III) present in the aqueous phase obtained after operation b 1 ) to plutonium(IV). 
   
   
       34 : A process according to  claim 32 , in which, neptunium being present in the aqueous phase obtained after operation b 1 ), this neptunium is removed either during the partitioning b) or during the purifying c). 
   
   
       35 : A process according to  claim 34 , in which, to remove the neptunium, the partitioning b) further includes an operation b 3 ) of re-extracting the neptunium, in oxidation state (IV), from the aqueous phase obtained after operation b 1 ), by bringing this phase into contact with a water-immiscible solvent phase containing at least one extractant in an organic diluent. 
   
   
       36 : A process according to  claim 35 , in which operation b 3 ) further includes addition of uranium to the aqueous nitric phase subjected to this operation b 3 ). 
   
   
       37 : A process according to  claim 38 , in which operation c 3 ) further includes addition of uranium to the aqueous nitric phase subjected to this operation c 3 ). 
   
   
       38 : A process according to  claim 36 , in which the added uranium is uranium(VI) or uranium(IV). 
   
   
       39 : A process according to  claim 37 , in which the added uranium is uranium(VI) or uranium(IV). 
   
   
       40 : A process according to  claim 38 , in which, to remove the neptunium, the aqueous nitric phase used during operation c 2 ) includes a reducing agent capable of reducing neptunium(VI) to neptunium(V) without reducing the plutonium(IV) or the uranium(VI). 
   
   
       41 : A process according to  claim 32 , in which, neptunium being present in the first aqueous phase obtained after operation b 1 ), this neptunium is left to follow the plutonium present in this phase up to the coconverting d). 
   
   
       42 : A process according to  claim 34 , in which the coconverting d) comprises:
 stabilization of the plutonium, in oxidation state (III), of the uranium, in oxidation state (IV), and, where appropriate, of the neptunium, in oxidation state (IV), by a singly-charged cation consisting only of atoms chosen from oxygen, carbon, nitrogen and hydrogen atoms;   coprecipitation of the thus stabilized plutonium, uranium and, where appropriate, neptunium by oxalic acid or by one of its salts or of its derivatives; and then   calcination of the coprecipitate thus obtained.   
   
   
       43 : A process according to  claim 41 , in which the coconverting d) comprises:
 stabilization of the plutonium, in oxidation state (III), of the uranium, in oxidation state (IV), and, where appropriate, of the neptunium, in oxidation state (IV), by a singly-charged cation consisting only of atoms chosen from oxygen, carbon, nitrogen and hydrogen atoms;   coprecipitation of the thus stabilized plutonium, uranium and, where appropriate, neptunium by oxalic acid or by one of its salts or of its derivatives; and then   calcination of the coprecipitate thus obtained.   
   
   
       44 : A process according to  claim 34 , which further includes, between the purifying c) and the coconverting d), storing the aqueous phase obtained after operation c 3 ). 
   
   
       45 : A process according to  claim 41 , which further includes, between the purifying c) and the coconverting d), storing the aqueous phase obtained after operation c 3 ). 
   
   
       46 : A process according to  claim 43 , which further includes, between the purifying c) and the coconverting d), storing the aqueous phase obtained after operation c 3 ). 
   
   
       47 : A process according to  claim 46 , which further includes:
 between the purifying c) and the storing, an operation of oxidizing the plutonium(III) present in the aqueous phase obtained after operation c 3 ) to plutonium(IV), followed by an operation of concentrating this aqueous phase; and   between the storing and the coconverting d), an operation of reducing the plutonium(IV), the uranium(VI) and, where appropriate, the neptunium(VI), which are present in the concentrated aqueous phase that has been stored, to plutonium(III), to uranium(IV) and to neptunium(IV).   
   
   
       48 : A process according to  claim 46 , which further includes:
 between the purifying c) and the storing, an operation of oxidizing the plutonium(III) present in the aqueous phase obtained after operation c 3 ) to plutonium(IV), followed by an operation of concentrating this aqueous phase; and   between the storing and the coconverting d), an operation of reducing the plutonium(IV), and, where appropriate, the neptunium(VI), which are present in the concentrated aqueous phase that has been stored, to plutonium(III), followed by an operation of extracting the uranium(VI), by bringing said aqueous phase into contact with a water-immiscible solvent phase containing at least one extractant in an organic diluent.   
   
   
       49 : A process according to  claim 42 , in which the mixed uranium-plutonium oxide obtained after the coconverting d) contains no neptunium. 
   
   
       50 : A process according to  claim 49 , in which the mixed uranium-plutonium oxide has a U/Pu mass ratio of around 50/50. 
   
   
       51 : A process according to  claim 43 , in which the mixed uranium-plutonium oxide obtained after the coconverting d) contains neptunium. 
   
   
       52 : A process according to  claim 51 , in which the mixed uranium-plutonium oxide has a U/Pu/Np mass ratio of around 49/49/2. 
   
   
       53 : A process according to  claim 30 , in which the extractant is a trialkyl phosphate. 
   
   
       54 : A process according to  claim 32 , in which the extractant is a trialkyl phosphate. 
   
   
       55 : A process according to  claim 35 , in which the extractant is a trialkyl phosphate. 
   
   
       56 : A process according to  claim 44 , in which the extractant is a trialkyl phosphate. 
   
   
       57 : A process according to  claim 30 , in which the organic diluent is a dodecane. 
   
   
       58 : A process according to  claim 32 , in which the organic diluent is a dodecane. 
   
   
       59 : A process according to  claim 35 , in which the organic diluent is a dodecane. 
   
   
       60 : A process according to  claim 44 , in which the organic diluent is a dodecane. 
   
   
       61 : A process according to  claim 30 , in which the solvent phase contains tri-n-butyl phosphate in a dodecane, in a volume ratio of around 30/70. 
   
   
       62 : A process according to  claim 32 , in which the solvent phase contains tri-n-butyl phosphate in a dodecane, in a volume ratio of around 30/70. 
   
   
       63 : A process according to  claim 35 , in which the solvent phase contains tri-n-butyl phosphate in a dodecane, in a volume ratio of around 30/70. 
   
   
       64 : A process according to  claim 36 , in which the solvent phase contains tri-n-butyl phosphate in a dodecane, in a volume ratio of around 30/70. 
   
   
       65 : A process according to  claim 32 , in which the reducing agent capable of reducing plutonium(IV) to plutonium(III) without reducing the uranium is uranous nitrate or hydroxyammonium nitrate. 
   
   
       66 : A process according to  claim 65 , in which the reducing agent is used in conjunction with a nitrous acid scavenger, or hydrazine. 
   
   
       67 : A process according to  claim 40 , in which the reducing agent capable of reducing neptunium(VI) to neptunium(V) without reducing either the plutonium(IV) or the uranium(VI) is a compound of the butyraldehyde family or hydrazine. 
   
   
       68 : A process according to  claim 61 , in which the separating a) comprises:
 a first scrubbing operation carried out on the solvent phase obtained after coextracting the uranium and plutonium, by bringing the solvent phase into contact with an aqueous nitric phase containing around 1 to 3 mol/L of HNO 3 ;   a second scrubbing operation carried out on the solvent phase, by bringing the solvent phase into contact with an aqueous nitric phase containing around 3 to 5 mol/L of HNO 3 ; and   a complementary operation of coextracting uranium and plutonium from the aqueous phase obtained after the second scrubbing operation, by bringing this phase into contact with a solvent phase containing about 30% (v/v) tri-n-butyl phosphate in a dodecane.   
   
   
       69 : A process according to  claim 62 , in which the separating a) comprises:
 a first scrubbing operation carried out on the solvent phase obtained after coextracting the uranium and plutonium, by bringing the solvent phase into contact with an aqueous nitric phase containing around 1 to 3 mol/L of HNO 3 ;   a second scrubbing operation carried out on the solvent phase, by bringing the solvent phase into contact with an aqueous nitric phase containing around 3 to 5 mol/L of HNO 3 ; and   a complementary operation of coextracting uranium and plutonium from the aqueous phase obtained after the second scrubbing operation, by bringing this phase into contact with a solvent phase containing about 30% (v/v) tri-n-butyl phosphate in a dodecane.   
   
   
       70 : A process according to  claim 63 , in which the separating a) comprises:
 a first scrubbing operation carried out on the solvent phase obtained after coextracting the uranium and plutonium, by bringing the solvent phase into contact with an aqueous nitric phase containing around 1 to 3 mol/L of HNO 3 ;   a second scrubbing operation carried out on the solvent phase, by bringing the solvent phase into contact with an aqueous nitric phase containing around 3 to 5 mol/L of HNO 3 ; and   a complementary operation of coextracting uranium and plutonium from the aqueous phase obtained after the second scrubbing operation, by bringing this phase into contact with a solvent phase containing about 30% (v/v) tri-n-butyl phosphate in a dodecane.   
   
   
       71 : A process according to  claim 64 , in which the separating a) comprises:
 a first scrubbing operation carried out on the solvent phase obtained after coextracting the uranium and plutonium, by bringing the solvent phase into contact with an aqueous nitric phase containing around 1 to 3 mol/L of HNO 3 ;   a second scrubbing operation carried out on the solvent phase, by bringing the solvent phase into contact with an aqueous nitric phase containing around 3 to 5 mol/L of HNO 3 ; and   a complementary operation of coextracting uranium and plutonium from the aqueous phase obtained after the second scrubbing operation, by bringing this phase into contact with a solvent phase containing about 30% (v/v) tri-n-butyl phosphate in a dodecane.   
   
   
       72 : A process according to  claim 62 , in which:
 the aqueous nitric phases used during operations b 1 ) and c 3 ) contain around 0.05 to 2 mol/L of HNO 3 ;   the aqueous nitric phase used during operation b 2 ) contains around 0 to 0.05 mol/L of HNO 3 ; whereas   the aqueous nitric phase used during operation c 2 ) contains around 1 to 3 mol/L of HNO 3 .   
   
   
       73 : A process according to  claim 40 , which further includes operations of purifying the uranium present in the second aqueous phase obtained after the partitioning b). 
   
   
       74 : A process according to  claim 40 , in which the spent nuclear fuel is a uranium oxide fuel or a mixed uranium-plutonium oxide fuel.