Operating method for nuclear power plants

Claim 1

A method of safely operating a boiling water nuclear reactor power plant upon the occurrence of a failure, said reactor being changeable between several non-failure conditions and a plurality of failure conditions and having control rods for controlling the power level thereof, said control rods including a first group having all rods in the outermost peripheral region of said nuclear reactor and a second group having all rods not in the outermost peripheral region, said method comprising the steps of: identifying a failure as a failure which occurs outside said power plant; selecting control rods from said first group that are in a fully withdrawn position and that do not adjoin each other during normal operation; selecting control rods only from those control rods in said second group which are in a fully withdrawn position and which are spaced from each other at a distance greater than the distance between adjoining rods during normal operation of said nuclear reactor; said selected control rods from said first group and said second group being selected on the basis that if scrammed, the axial power distribution and natural circulation flow are maintained in a stable condition so that the power plant may operate at a reduced power level; subjecting said selected control rods from said first group and said second group to a scram, whereby the power level of said nuclear reactor power plant is reduced to a power level lower than the normal operating power level but large enough to supply the needs of the power plant itself so that said nuclear reactor power plant can continue operating.

Claim 2

A method of safely operating a boiling water nuclear reactor power plant upon the occurrence of a failure, said reactor being changeable between several non-failure conditions and a plurality of failure conditions and having control rods for controlling the power level thereof, said control rods including a first group having all rods in the outermost peripheral region of said nuclear reactor and a second group having all rods not in the outermost peripheral region, said method comprising the steps of: identifying a failure as a failure which occurs outside said power plant; selecting control rods from said first group that are in a fully withdrawn position and that do not adjoin each other during normal operation; selecting control rods only from those control rods in said second group which are in a fully withdrawn position and which are spaced from each other at a distance greater than the distance between adjoining rods during normal operation of said nuclear reactor; said selected control rods from said first group and said second group being selected on the basis that if scrammed, the axial power distribution and natural circulation flow are maintained in a stable condition so that the power plant may operate at a reduced power level; subjecting said selected control rods from said first group and said second group to a scram, whereby the power level of said nuclear reactor power plant is reduced to a power level lower than the normal operating power level but large enough to supply the needs of the power plant itself so that said nuclear reactor power plant can continue operating.