Thermodynamic analysis of a solid nuclear fuel element surrounded by flow of coolant through a concentric annular channel

Highlights: •We perform an entropy generation analysis of a simple model of nuclear fuel element in an annular coolant channel. •The temperature profiles used in entropy analysis are in agreement with RELAP code. •Optimum Reynolds numbers are found for different sets of design parameters and their effects are analysed. •Inclusion of pumping power to heat transfer rate ratio in the objective function gives lowers the optimum Reynolds number. •Temperatures obtained from the present analysis do not surpass the safety limits if the suitable design parameters are chosen. -- Abstract: A continuous quest for efficient utilization of energy resources has motivated the researchers to search for optimal design and operating conditions during various energy conversion techniques. These conditions for such systems are often proposed by minimizing the destroyed exergy potential in course of the process. In the present paper a second law analysis is done for a nuclear fuel element inside a concentric annular coolant passage. The entropy generation analysis has been carried out through a conjugate approach, with steady state temperature profiles within the fuel element and a thermodynamic approach within fluid. The effect of solid core heat generation and the temperature gradients inside solid core, fuel-clad gap and cladding are considered as well along with the irreversibilities arising out of fluid flow under turbulent condition. The effect of Reynolds number, duty parameter, diameter ratio, Biot number, dimensionless heat flux and thermal conductivity ratios on overall entropy generation characteristics have been investigated and interpreted physically. The validation of the present calculations was confirmed by best-estimate thermal-hydraulic code RELAP. The new thermodynamic design methodology presented in this paper adheres to the safety limits in temperature. The present analysis can be extended for complex fuel pellet arrangements in subchannel structures by an "equivalent annulus model".