POWER TRANSIENT ANALYSES OF EXPERIMENTAL IN-REFLECTOR DEVICES DURING SAFETY SHUTDOWN IN JULES HOROWITZ REACTOR (JHR)

The Jules Horowitz Reactor (JHR) is designed to be a 100 MW material testing reactor (MTR) and it is expected to become the reference facility in the framework of European nuclear research activity. As the core neutron spectrum is quite fast, several experimental devices concerning fuel studies have been conceived to be placed in the reflector in order to exploit a proper thermal neutron flux irradiation. Since the core power is relatively high, the neutronic coupling between the reactor core and the reflector devices has to be taken into account for different rod insertions. In fact the thermal power produced within the fuel samples is considerable. Heat removal during shutdown is a main topic in nuclear safety and it is worth to analyse thermal power transients in fuel samples as well. Here a thermal hydraulic model for JHR core is proposed aiming at a simple and representative description as far as reactivity feedbacks are concerned. Then it is coupled with a neutronic pointwise kinetics analysis by means of the DULCINEE code to compute core power transient calculations. Moreover, some reflector-core coupling evaluations are performed through Monte Carlo method using the TRIPOLI 4.7 code. The JHR equilibrium cycle is considered with respect to four fuel compositions namely Beginning of Cycle (BOC), Xenon Saturation Point (XSP), Middle of Cycle (MOC) and End of Cycle (EOC). Then thermal power transients in the experimental reflector devices are evaluated during safety shutdowns and they are verified for all these cycle steps

THERMAL HYDRAULIC AND NEUTRONIC CORE MODEL FOR POWER TRANSIENT ANALYSES OF REFLECTOR EXPERIMENTAL DEVICES DURING SHUTDOWNS IN JULES HOROWITZ REACTOR (JHR)

The Jules Horowitz Reactor (JHR) is expected to become the most important material testing reactor in the framework of European nuclear research and development. It is designed to exploit a fast in-core spectrum as well as a thermal neutron flux within the experimental locations in the reflector. The latter are mainly used to investigate fuel behaviour under nominal, abnormal and post-failure operating conditions. Since the core power is relatively high (100 MW), the power released within the reflector fuel devices is not negligible. Heat removal is a main topic in nuclear safety and power transient analyses concerning these experimental devices are requested in order to control fuel samples heating. Here a model of JHR core is implemented by means of the pointwise kinetics code DULCINEE. It takes into account both the neutronic features of the system and the thermal hydraulic properties as far as reactivity feedbacks are concerned. The core power transients are evaluated with respect to normal shutdown and safety shutdown. Then neutronic coupling between reflector and core is computed by means of the Monte Carlo calculation code TRIPOLI 4.7. Thus power evolution in experimental devices is obtained accounting for four burnup levels during the equilibrium cycle \u2013 namely Beginning of Cycle (BOC), Xenon Saturation Point (XSP), Middle of Cycle (MOC) and End of Cycle (EOC). Fission energy is released through different nuclear interactions. Depending on the considered radiation, the yield of energy deposition is different and the time behaviours are specific to particle production mechanisms. Finally neutrons and gammas are considered in terms of energy deposition and contribution to total in-reflector fuel sample power transients during the considered shutdown procedures

Power transient analysis of fuel-loaded reflector experimental devices in Jules Horowitz Material Testing Reactor

The Jules Horowitz Reactor (JHR) is designed to be the 100 MW Material Testing Reactor (MTR) which achieves the most important experimental capacity in Europe. It has been conceived to perform several irradiation tests at a time - taking advantage of many positions both in the core and in the reflector. The locations inside the reflector zone may utilize an intense thermal neutron flux to test the properties of fuel materials and to produce radioisotopes for medical purposes. High sample irradiation rates are achieved in the reflector area and a relevant power can be generated here, due to fissile materials inside these fuel test samples: about 60 kW for ADELINE test devices, some 120 kW for MADISON and up to about 650 kW for MOLFI. Then, power transient analyses are requested for these devices, mainly in connection with the reactor shutdowns. Energy deposition in the fuel samples - which are placed in the reflector - has been evaluated considering both normal operation and different reactor shutdown procedures. The analysis has been carried out by dividing the reactor system into two portions: the core as a neutron source and the reflector as a subcritical system. First, core power transients have been simulated by means of DULCINEE point kinetics code. Then, the neutron flux inside the reflector has been evaluated through the Monte Carlo transport code TRIPOLI 4.8, starting from the previously computed source. Both nominal operation and different configurations of control rod insertions have been taken into account. This evaluation provided a description of core-device coupling in terms of flux shape in the reflector. Main focus is on power deposition in samples which is of course affected by flux shape. Thus, point kinetics approach has been applied to the core as a source irradiating the samples that are considered coupled through the parameters evaluated by Monte Carlo. Power transients have been calculated both for energy deposition due to neutron-induced fission reactions and for gamma radiation as well. Results matched technical needs for the cooling loops optimization and the safety scenarios