Nuclear reactor start-up method

Claim 1

A method of starting up a boiling water nuclear reactor in a cold shut-down condition, comprising the steps of: i. forming a map of an output E-vs-subcooled temperature in accordance with the output E of the nuclear reactor core, and with the subcooled temperature ΔT(P) of coolant at a reactor core inlet, which is a function of the pressure P of the coolant and which is determined by the following equation: ΔT(P)=T.sub.B -T.sub.C ( 1) where T B is the boiling point of coolant under a predetermined pressure (saturation temperature), and T C is the actual temperature of the coolant under the predetermined pressure; ii. plotting outlet quality curves x(E, ΔT) on the map which outlet quality curves are determined by the following equation on the map: x=m.sub.V /m.sub.T ( 2) where m V is the mass of vapor passing through the reactor core outlet per unit time, and m T is the total mass of coolant passing said through the reactor core outlet per unit time; iii. determining critical quality curves among a group of outlet quality curves on the map, the critical quality curves being obtained by the following equations: x(E, ΔT)=x.sub.c1 ( 3) X(E, ΔT)=x.sub.c2 ( 4) where x c1 >x c2 , the critical guality curves defining boundaries along which first and second instabilities occur; iv. selecting one of the outlet quality curves, corresponding to a boiling initiation curve which is obtained from the following equation: x(E, ΔT)=0 (5); v. determining a minimum subcooled temperature ΔT'min which is crossing point between the boiling initiation curve of equation (5) and the critical quality curve of equation (4) relating to the second instability; and vi. starting increase of the output E of the nuclear reactor core from zero output at a point having a subcooled temperature of the coolant at the nuclear reactor core inlet which satisfies the following condition: ΔT<ΔT'min, between the critical quality curves of equation (3) and equation (4) on the map.

Claim 2

A method of starting up a boiling water nuclear reactor in a cold shut-down condition, comprising the steps of: i. forming a map of an output E-vs-subcooled temperature in accordance with the output E of the nuclear reactor core, and with the subcooled temperature ΔT(P) of coolant at a reactor core inlet, which is a function of the pressure P of the coolant and which is determined by the following equation: ΔT(P)=T.sub.B -T.sub.C ( 1) where T B is the boiling point of coolant under a predetermined pressure (saturation temperature), and T C is the actual temperature of the coolant under the predetermined pressure; ii. plotting outlet quality curves x(E, ΔT) on the map which outlet quality curves are determined by the following equation on the map: x=m.sub.V /m.sub.T ( 2) where m V is the mass of vapor passing through the reactor core outlet per unit time, and m T is the total mass of coolant passing said through the reactor core outlet per unit time; iii. determining critical quality curves among a group of outlet quality curves on the map, the critical quality curves being obtained by the following equations: x(E, ΔT)=x.sub.c1 ( 3) X(E, ΔT)=x.sub.c2 ( 4) where x c1 >x c2 , the critical guality curves defining boundaries along which first and second instabilities occur; iv. selecting one of the outlet quality curves, corresponding to a boiling initiation curve which is obtained from the following equation: x(E, ΔT)=0 (5); v. determining a minimum subcooled temperature ΔT'min which is crossing point between the boiling initiation curve of equation (5) and the critical quality curve of equation (4) relating to the second instability; and vi. starting increase of the output E of the nuclear reactor core from zero output at a point having a subcooled temperature of the coolant at the nuclear reactor core inlet which satisfies the following condition: ΔT<ΔT'min, between the critical quality curves of equation (3) and equation (4) on the map.