Transient behavior studies of TRIGA core for variations in reactor kinetics

Abstract

This paper illustrates the transient characteristics of TRIGA core at different kinetics conditions that arise from variations of externally inserted reactivity together with variations in other kinetic parameters such as prompt neutron life time, lp and effective delayed neutron fraction, βeff provided the reactor scram system is disabled. From the concern of severity of fast reactivity accident which could lead to most dangerous consequences, the inserted reactivity considered herein was fast reactivity which was a step type within the range 1$–2$ with insertion time 0.5s. The initial power was 100W and full power, 3MW whereby the values of lp and βeff had been kept fixed at their recommended values 30μs and 0.007, respectively. The observed parameters were reactor peak power and maximum clad temperature of the hottest channel. The analysis infers that clad temperature remains within its design limit value even for the maximum inserted reactivity, 2$ at full power operation of reactor. Also, the peak power took relatively higher values for transients at low power level. For each inserted reactivity, values of lp and βeff were varied individually within certain ranges. In this case, although both power and clad temperature are more sensitive to the variation in effective delayed neutron fraction than to the variation in prompt neutron life time, however, clad temperature remained within its design limit even for the maximum value of inserted reactivity with minimum βeff value considered. Prompt negative temperature coefficient of reactivity that stems from U-ZrH fuel moderator materials of TRIGA core seems to play a vital role during such variation in reactor kinetics to keep the reactor completely safe. Coupled point kinetics, neutronics and thermal hydraulics code EUREKA-2/RR was used in the study.