Method for monitoring a nuclear core comprising a relaxation of a threshold, and associated programme, support and nuclear reactor

A method for monitoring a nuclear reactor comprising a core in which fuel assemblies are loaded, each fuel assembly comprising nuclear fuel rods each including nuclear fuel pellets and a cladding surrounding the nuclear fuel pellets, the method comprising the following steps:

• determining at least one operating time limit for an operation at a reduced power of the nuclear reactor, so as to avoid a rupture of at least one of the claddings, the reduced power being inferior or equal to 92% of a nominal power of the nuclear reactor;
• operating the nuclear reactor at the reduced power for an actual time strictly less than the operating time limit;
• measuring and/or calculating a distribution of a linear power at any point of the core as a function of time and determining from the distribution of the linear power a thermomechanical state between the cladding and the nuclear fuel pellets;
• recalculating the operating time limit in real time as a function of the thermomechanical state between the cladding and the nuclear fuel pellets;
• relaxing a threshold linear power of the nuclear reactor as a function of a difference between the operating time limit and the actual time, the threshold linear power being a threshold of the linear power at any point of the core below which a rupture by Pellet/Cladding Interaction is avoided even in case of a power spike or a transition to operation at nominal power;
• and
• further operating the nuclear reactor at the reduced power according to the threshold linear power from the relaxing step.

A method for monitoring a nuclear reactor comprising a core in which fuel assemblies are loaded, each fuel assembly comprising nuclear fuel rods each including nuclear fuel pellets and a cladding surrounding the nuclear fuel pellets, the method comprising the following steps:

• calculating a threshold linear power;
• and
• calculating a linear power at 100%, the linear power at 100% being an estimate of the linear power at any point of the core and as a function of time if the nuclear reactor is operating at nominal power from a measurement and/or a calculation of a distribution of an actual power at any point of the core as a function of time,
• determining at least one operating time limit for an operation at a reduced power of the nuclear reactor as a function of a difference between the threshold linear power and the linear power at 100%, so as to avoid a rupture of at least one of the claddings, the reduced power being inferior or equal to 92% of a nominal power of the nuclear reactor;
• operating the nuclear reactor at the reduced power for an actual time strictly less than the operating time limit;
• and
• relaxing the threshold linear power of the nuclear reactor as a function of a difference between the operating time limit and the actual time;
• and
• further operating the nuclear reactor at the reduced power according to the threshold linear power from the relaxing step.