Patent Number: 
Section: claims

1. An axial power distribution prediction device, comprising:an axial offset calculation unit that calculates an axial offset of a current power distribution (AOP), an axial offset of the power distribution which would give a current xenon distribution under equilibrium condition (xenon-corresponding axial offset: AOX), and an axial offset of the power distribution which would give a current iodine distribution under equilibrium condition (iodine-corresponding axial offset: AOI), using the following expressions (1) to (3) or (1)′ to (3)′, respectively:AOP=(PT−PB)  Expression (1)AOX=(PTX−PBX)  Expression (2)AOI=(PTI−PBI)  Expression (3)AOP=(PT−PB)/(PT+PB)  Expression (1)′AOX=(PTX−PBX)/(PTX+PBX)  Expression (2)′AOI=(PTI−PBI)/(PTI+PBI)  Expression (3)′, wherePTX: relative power in an upper half of a core that would we a current xenon concentration under equilibrium condition,PBX: relative power in a lower half of the core that would give the current xenon concentration under equilibrium condition,PTI: relative power in the upper half of the core that would give a current iodine concentration under equilibrium condition, andPBI: relative power in the lower half of the core that would give the current iodine concentration under equilibrium condition,based on a relative power (PT) in the upper half of the nuclear reactor core and a relative power (PB) in the lower half of the nuclear reactor core;a parameter calculating unit that calculates a xenon parameter represented by using a difference between AOP and AOX during an operation of the reactor and an iodine parameter represented by using a difference between AOI and AOX during the operation of the reactor;a trajectory display unit that acquires the xenon parameter and the iodine parameter calculated by the parameter calculating unit, and generates an ellipse-shaped plot trajectory by setting the xenon parameter as x-coordinate and the iodine parameter as y-coordinate in a Cartesian coordinate system on a display unit; andan axial offset determining unit that predicts whether a core axial offset of the power distribution after a current time is increased or decreased, by drawing a major axis in the ellipse-shaped plot trajectory and generating a plot point using a xenon parameter and an iodine parameter at the current time, wherein the core axial offset of the power distribution after the current time is determined to be decreased when the plot point is located above the major axis and the core axial offset of the power distribution after the current time is determined to be increased when the plot point is located below the major axis. 2. The axial power distribution prediction device according to claim 1, further comprising:a margin calculating unit that calculates a margin from a difference between the core axial offset of the current power distribution and an allowable value of the core axial offset;an allowable range determining unit that determines whether the margin is smaller than a preset threshold value and whether the core axial offset of the power distribution after the current time is predicted to make a change in a direction with which the margin is decreased; andan alarming unit that alerts a need to operate a control rod if the margin is smaller than the preset threshold value and the core axial offset of the power distribution after the current time is predicted to make a change in the direction with which the margin is decreased. 3. The axial power distribution prediction device according to claim 1, further comprising:a margin calculating unit that calculates a margin from a difference between the core axial offset of the current power distribution and an allowable value of the core axial offset;an allowable range determining unit that determines whether the margin is smaller than a preset threshold value and whether the core axial offset of the power distribution after the current time is predicted to make a change in a direction with which the margin is decreased; andan control rod moving unit that moves a control rod in such a manner that the xenon parameter and the iodine parameter moves toward the major axis of the ellipse if the margin is smaller than the preset threshold value and the core axial offset of the power distribution after the current time is predicted to make a change in the direction with which the margin is decreased.