Patent Number: 043022871
Section: claims

1. A method for controlling the operation of a nuclear reactor to at least initially increase the reactor power in a range in which pellet-clad-mechanical-interaction occurs comprising the steps of at least initially increasing the reactor power from a power level in which pellet-clad-mechanical-interaction begins to take place up to a predetermined power level for the nuclear reactor and controlling the rate of increase of the linear heat generating rate to a rate no less than 0.15 KW/ft/hr., and no greater than a predetermined critical rate so as to shorten the time necessary to at least initially raise the reactor power to the predetermined power level without causing pellet-clad-mechanical-interation damage of the fuel elements. 2. A method for controlling the operation of a nuclear reactor to increase the reactor power in a range in which pellet-clad-mechanical-interaction occurs comprising the steps of at least initially increasing the reactor power from a power level in which pellet-clad-mechanical-interaction begins to take place up to a predetermined power level for the reactor and controlling the rate of increase of the linear heat generating rate P so as to be no less than 0.15 KW/ft/hr. and no greater than a critical rate determined in accordance with the equation ##EQU7## during at least the initial increase of the reactor power from the power level in which pellet-clad-mechanical-interaction begins to take place up to the predetermined power level for the reactor, wherein: P: linear heat generating rate (KW/ft);  P: rate of increase of the linear heat generating rate (KW/ft/hr);  A: numeral determined by a coefficient .alpha. of thermal expansion of a pellet and smear density;  B: a constant determined by Young's modulus of a pellet and smear density;  C: a constant determined by a rate of creep of a pellet; and  D: a constant determined by a coefficient .alpha. of thermal expansion of a pellet, Young's modulus and smear density. 3. A method according to claim 2, wherein A is (8.0+0.5 P.sub.I), B is 3.3, C is 0.45 and D is (6.6-0.35 P.sub.I). 4. A method according to claim 2, wherein A is 8.0, B is 3.3, C is 0.45, D is 6.6, and P.sub.I is 0. 5. A method according to claim 2, 3 or 4, wherein the rate of increase of the linear heat generating rate P is controlled by the adjustment of the amount of heavy water through a core of the nuclear reactor. 6. A method according to claim 2, 3 or 4, wherein the rate of increase of the linear heat generating rate P is controlled by the adjustment of the amount of coolant through a core of the nuclear reactor. 7. A method according to claim 2, 3 or 4, wherein the rate of increase of the linear heat generating rate P is controlled by the adjustment of the consistency of liquid poison included in a coolant. 8. A method for controlling the operation of a nuclear reactor to increase the reactor power in a range in which pellet-clad-mechanical-interaction occurs comprising the steps of at least initially increasing the reactor power from a power level in which pellet-clad-mechanical-interaction begins to take place up to a predetermined power level for the nuclear reactor and controlling the rate P of increase of the linear heat generating rate during at least the initial means of reactor power to a rate no less than 0.15 KW/ft/hr. and no greater than a critical rate determined in accordance with the equation: ##EQU8## wherein P is a linear heat generating rate of no less than 8 KW/ft and no greater than about 20 KW/ft and the pellet-clad-mechanical-interaction begins at a linear heat generating rate no less than 2 KW/ft and no greater than 10 KW/ft. 9. A method for controlling the operation of a nuclear reactor wherein a fuel consists of a plurality of cylindrical pellets of fuel in oxide form of about 10.4-18.8 mm in diameter contained in a plurality of elongated zirconium alloy cladded tubular fuel elements with a cladding thickness of about 0.4-0.9 mm and an outside diameter of about 11-20 mm, to at least initially increase the reactor power in a range in which pellet-clad-mechanical-interaction occurs comprising the steps of at least initially increasing the reactor power from a power level in which pellet-clad-mechanical-interaction begins to take place up to a predetermined power level for the nuclear reactor and controlling the rate P of increase of the linear heat generating rate during at least the initial power increase to a rate no less than 0.15 KW/ft/hr. and no greater than a critical rate determined in accordance with the equation: ##EQU9## wherein P is a linear heat generating rate of no less than 8 KW/ft and no greater than about 20 KW/ft and the pellet-clad-mechanical-interaction begins at a linear heat generating rate no less than 2 KW/ft and no greater than 10 KW/ft. 10. A method for controlling the operation of a nuclear reactor wherein a fuel consists of a plurality of cylindrical pellets of fuel in oxide form of about 10.4-18.8 mm in diameter contained in a plurality of elongated zirconium alloy cladded tubular fuel elements with a cladding thickness of about 0.4-0.9 mm and an outside diameter of about 11-20 mm, to at least initially increase the reactor power in a range in which pellet-clad-mechanical-interaction begins to take place up to a predetermined power level for the nuclear reactor and controlling the rate P of increase of the linear heat generating rate during at least the initial power increase to a rate no less than 0.15 KW/ft/hr. and no greater than a critical rate determined in accordance with the equation: ##EQU10## wherein P is a linear heat generating rate no less than 10 KW/ft and no greater than about 20 KW/ft and the pellet-clad-mechanical-interaction begins at a linear heat generating rate no less than 4 KW/ft and no greater than 6 KW/ft. 11. A method according to claim 8, 9 or 10, wherein the rate of increase of the linear heat generating rate P is controlled by the adjustment of the consistency of liquid poison included in a coolant.