Among a series of important safety parameters necessary for a complete analysis of a nuclear reactor core, the nuclear safety operating margin of a nuclear reactor is of great importance. The methodology generally used is to combine thermalhydraulic calculations with neutronic calculations. In this work, new Power Peaking Factors (PPFs) are calculated for the NUR nuclear research reactor core X-1 configuration by two ways; a deterministic way using WIMSD-CITVAP neutronic calculation in a fine calculation model, and a second way by a probabilistic method using MCNP5 model. The obtained results give the PPFs for each nuclear reactor core channel and the hot channel is then determined. Once this channel known, an asymptotic thermalhydraulic model is applied. This model gives the coolant and the cladding temperature evolutions in the hot channel for the calculated PPFs in the two presented models. All these results are compared with those obtained using the old PPF commonly used in such calculations. Results show that PPFs obtained by deterministic method are the most conservative. Thus, this last result is retained for a nuclear safety evaluation. An equation set-up is made for calculating the critical heat flux ratio. This ratio is verified to be greater than the limit of nuclear safety operating margin for NUR nuclear reactor.