Patent Number: 
Section: claims

1. A method for measuring a La content dissolved in a (U,La)O2 nuclear fuel pellet, wherein the method comprises a step of;measuring the weight (W1) of (U1−xLax)3O8 powder obtained by oxidizing a (U1−xLax)O2+z pellet in an oxidizing gas atmosphere at a temperature of 300–950° C. (step 1),measuring the total weight (W2) of (U1−yLay)O9/4 phase and U3O8 phase obtained by heat treating the (U1−xLax)3O8 powder in an oxygen-containing gas or an inert gas atmosphere at a temperature of 950–1800° C. (step 2), andmeasuring the La content using the following equation 1(step 3)                                                        W              1                        -                          W              2                                            W            1                          =                              M            ⁢                                                  ⁢                          W                              O                2                                      ×                          (                                                5                  ⁢                  x                                                  24                  ⁢                  y                                            )                                            M            ⁢                                                  ⁢                          W                                                (                                                            U                                              1                        -                        x                                                              ⁢                                          La                      x                                                        )                                ⁢                                  O                                      8                    /                    3                                                                                                          (                  Equation          ⁢                                          ⁢          1                )            whereinMW02 is the O2 molecular weight,MW(U1−xLax)08/3 is the (U1−xLax)O8/3 molecular weight,x is the La content dissolved in (U,La)O2, andy is the La cation content dissolved in the (U,La)O9/4 phase. 2. The method according to claim 1, wherein La is selected from a group consisting of Gd(Gadolinium), Er(Erbium), Eu(Europium) amd Sm(Samarium). 3. A method for measuring the La content dissolved in a (U,La)O2 nuclear fuel pellet, wherein the method comprises steps of;measuring the weight(W0) of a (U1−xLax)O2+z nuclear fuel pellet(step 1),measuring the total weight (W2) of(U1−yLay)O9/4 phase and U3O8 phase obtained by heat treating (U1−xLax)3O8 powder in an oxygen-containing gas pr am omert gas atmosphere at a tmeperature of 950–1800° C. (step 2), andmeasuring the La content using the following equation 2(step 3)                                                        W              0                        -                          W              2                                            W            0                          =                              M            ⁢                                                  ⁢                          W                              O                2                                      ×                          (                                                                    5                    ⁢                    x                                                        24                    ⁢                    y                                                  +                                  z                  2                                -                                  1                  3                                            )                                            M            ⁢                                                  ⁢                          W                                                (                                                            U                                              1                        -                        x                                                              ⁢                                          La                      x                                                        )                                ⁢                                  O                                      2                    +                    z                                                                                                          (                  Equation          ⁢                                          ⁢          2                )            wherein,MW02 is the O2 molecular weight,MWU1−x)o2+z is the (U1−x)Ohd 2+z molecular weight,x is the La content dissolved in(U,La)O2,y is the La cation content dissolved in the (U,La)O9/4 phase, andz is the value when the O/(U+La) rate of the initial sample is higher than 2. 4. The method according to claim 3, wherein La is selected from a group consisting of Gd(Gadolinium), Er(Erbium), Eu(Europium) amd Sm(Samarium).