Patent Number: 
Section: claims

1. A method of measuring Doppler reactivity coefficient, comprising:measuring time-series data of neutron flux in which reactor power is increased by a prescribed amount by applying reactivity to a reactor core which is in sub-critical or achieves super critical, and obtaining time-series data of in-reactor average moderator temperature in which reactor power is increased by the prescribed amount by applying reactivity to the reactor core which is in sub-critical or achieves super critical, whereinin said measuring step, neutron flux during this period is measured as time-series data, andin said step of obtaining time-series data of in-reactor average moderator temperature, average moderator temperature in the reactor is obtained as time-series data;obtaining time-series data of reactivity in which the time-series data of reactivity is obtained from the measured time-series data of neutron flux, said time-series data of reactivity being calculated by applying an inverse kinetic method based on a one-point reactor kinetic equation;obtaining time-series data of reactor power by calculating the time-series data of reactor power based onsaid obtained time-series data of in-reactor average moderator temperature andthe time-series data of neutron flux,such that the obtained time-series data of reactor power matches said two time-series data which are the time-series data of in-reactor average moderator temperature and the time-series data of neutron flux,obtaining time-series data of fuel temperature in which the time-series data of fuel temperature subjected to a prescribed averaging is obtained from the time-series data of reactor power obtained above and a reactor kinetic model;obtaining time-series data of reactivity feedback contribution component in which the time-series data of reactivity feedback contribution component is calculated fromthe time-series data of reactivity obtained above in said step of obtaining time-series data of reactivity, andthe reactivity of constant reactor period; andobtaining Doppler reactivity coefficient, in which the Doppler reactivity coefficient is obtained fromthe obtained time-series data of in-reactor average moderator temperature,the obtained time-series data of fuel temperature subjected to said prescribed averaging,an isothermal temperature reactivity coefficient, andthe obtained time-series data of reactivity feedback contribution component. 2. The method of measuring Doppler reactivity coefficient according to claim 1, whereinmeasurement of the time-series data of neutron flux at said step of measuring neutron flux measures neutron flux as well as γ-ray; andsaid step of obtaining time-series data of reactivity has a removal procedure of removing influence of the γ-ray from the measured time-series data of neutron flux, and, from the time-series data with the influence of γ-ray removed, time-series data of reactivity is obtained from said inverse kinetic method with respect to the one-point reactor kinetic equation. 3. The method of measuring Doppler reactivity coefficient according to claim 2, wherein, in said removal procedure, an error function is evaluated by the least squares method in the following way:the error function is defined froma time-change numerically evaluated value calculated by a nuclear reactor kinetic equation based on a reactivity of constant reactor period and a γ-ray mixture rate as parameters related to reactor power response in a low power range in which reactivity feedback contribution is negligible, anda time-change part corresponding to the reactor power response of actually measured time-series data of neutron flux,the error function being calculated as a difference between these two in logarithmic value; anda combination of the reactivity of constant reactor period and the γ-ray mixture rate that minimizes the error function value is aimed. 4. The method of measuring Doppler reactivity coefficient according to any one of claims 1-3, whereinat said step of obtaining time-series data of in-reactor average moderator temperature, the average moderator temperature is obtained in the form of time-series data, when the reactor power is increased by a prescribed amount by applying reactivity to a reactor core which is in sub-critical or achieves super critical. 5. The method of measuring Doppler reactivity coefficient according to claim 4, whereinat said step of obtaining time-series data of reactor power,a time constant τsg,12 related to heat transfer from a primary side to a secondary side of a steam generator associated with the reactor, and an initial reactor power P0 are selected as parameters, anda combination of said time constant τsg,12 and the initial reactor power P0 is obtained that minimizes the value of the error function E(τsg,12, PO) represented by:      E    ⁡          (                        τ                      sg            ,            12            ,                          ⁢                  P          0                    )        =                    (                  1.0          -                                    t              p              s                                      t              p              m                                      )            2        +                  (                  1.0          -                                    ΔT                              c                ,                av                            s                                      ΔT                              c                ,                av                            m                                      )            2      wherein tsp represents analytical time of average moderator temperature to maximum, tmp represents measured time of average moderator temperature to maximum temperature, ΔTsc,av represents analytical value of maximum change width of average moderator temperature, and ΔTmc,av represents measured value of maximum change width of average moderator temperature. 6. The method of measuring Doppler reactivity coefficient according to claim 1, whereinat said step of obtaining time-series data of fuel temperature, volume-averaged fuel temperature is numerically evaluated from a fuel rod heat conduction equation related to average fuel rod temperature, and time-series data of reactor power is modified based on a correction coefficient obtained in consideration of distributions of neutron flux and adjoint neutron flux (neutron importance) in a moderator flow path direction in zero-power state,such that time-series data of fuel temperature subjected to prescribed averaging, based on the first-order perturbation theory, is obtained. 7. The method of measuring Doppler reactivity coefficient according to claim 1, whereinsaid prescribed averaging is importance power averaging in said step of obtaining time-series data of fuel temperature,wherein said time-series data of fuel temperature is used for obtaining the Doppler reactivity coefficient αf, such that:in said step of obtaining Doppler reactivity coefficient, the Doppler reactivity coefficient αf is obtained from the following equation:Δρfd(t)=αf(βTf,av(t)−ΔTc,av(t))+αitcΔTc,av(t)wherein in said equation Δρfd(t) represents a reactivity feedback contribution component related to Doppler reactivity feedback, αf represents a Doppler reactivity coefficient, ΔTf,av(t) represents a change amount of average fuel rod temperature, ΔTc,av(t) represents change amount of average moderator temperature, and αitc represents an isothermal temperature reactivity coefficient. 8. The method of measuring Doppler reactivity coefficient according to claim 7, whereinin said step of obtaining Doppler reactivity coefficient based on the equation of claim 7, the actual Doppler reactivity coefficient αf is estimated as the coefficient that minimizes the value of an error function Erdf which is defined as:      E    rdf    =            1      N        ⁢                  ∑                  i          =          1                N            ⁢                        {                      1.0            -                                                            α                  f                                ⁡                                  (                                                                                    c                        ip                                            ⁢                      Δ                      ⁢                                                                                          ⁢                                                                        T                                                      f                            ,                            av                                                                          ⁡                                                  (                                                      t                            i                                                    )                                                                                      -                                                                  ΔT                                                  c                          ,                          av                                                                    ⁡                                              (                                                  t                          i                                                )                                                                              )                                                                              Δρ                  fc                                ⁡                                  (                                      t                    i                                    )                                                              }                2            wherein N represents the number of data, ti represents time corresponding to data i, Δρfc(t) represents a reactivity contribution component, and cip represents a correction coefficient defined as:      c    ip    =            Δ      ⁢                          ⁢              T                  f          ,          av                ip                    Δ      ⁢                          ⁢              T                  f          ,          av                    wherein ΔTipf,av(t) represents a change amount of importance power-averaged value of fuel temperature, andwherein ΔTf,av(t) represents a change amount of average fuel rod temperature, and ΔTc,av(t) represents a change amount of average moderator temperature as recited in claim 7.