Coupled Experimental and Computational Approach for CABRI Power Transients Analysis

Abstract

CABRI is an experimental pulse reactor, funded by the French Nuclear Safety and Radioprotection Institute (IRSN) and operated by CEA at the Cadarache research center. It is designed to study fuel behavior under RIA (Reactivity Initiated Accident) conditions. In order to produce the power transients, reactivity is injected by depressurization of a neutron absorber ( 3 He) situated in the so-called "transient rods" inside the reactor core. The CABRI reactivity injection system allows us to generate structured transients based on specific sequences of depressurization. For such transients, the time difference between the openings of two valves of the reactivity injection system has an important impact on the power pulse shape. A kinetic point code, SPARTE, was developed in order to replace the older DULCINEE code dedicated to the modeling and prediction of CABRI power transients. The SPARTE code includes new models of 3 He depressurization based on CFD calculations, variable Doppler coefficient based on Monte Carlo calculations and variable axial neutron flux profile. The density and Doppler models have a large impact on power transient prediction. For low initial pressure transients, the major uncertainty comes from the reactivity injected by the 3 He depressurization. For high initial pressure transients, the 3 He heating during the power pulse ("TOP effect") is responsible of an additional injection of reactivity that needs to be modeled precisely.

Multiphysics CATHARE2 modeling and experimental validation methodology against CABRI transients

“…The challenging goal of this sequential validation methodology is to validate, as much as possible, each effect separately. As the experimental uncertainties are sufficiently low (1 % for the 3 He pressure and 3 % for the neutronic power [10]), they do not jeopardize this validation methodology.…”

“…Two calculation tools have been specially developed in order to simulate CABRI transients: DULCINEE [9] and SPARTE [10]. DULCINEE was developed in the 1970s [9] to design and characterize the behavior of the CABRI core during several types of transients (RIA, overpower...).…”

“…Thus, for example, an artificial neural network surrogate model for the inserted reactivity was established from 750 TRIPOLI4 simulations taking as inputs: the control rods height, the 3 He density and the fuel temperature. More details on these surrogate models could be found in [10] and [13]. These latter improvements allowed to better predict CABRI transients but its fault lies in the calculation of the injected reactivity which is uncoupled to the core calculation.…”

Some Considerations on the Energy Deposition During a RIA Transient Based On Monte Carlo Simulations

“…The transient characteristics, such as the helium depressurization, the average fuel temperature and core water temperature variations are obtained with the SPARTE code. SPARTE [2] (Simulation Prediction and Analysis for RIA Transients an Excursions) is a recently developed code dedicated to R&D studies on the physical characteristics of the CABRI transients, such as the power peak, transient length and power trace.…”

“…Specific research reactors are capable of reproducing reactivity injection accidents in order to study the behavior of the nuclear fuel pins in accidental situations. In the CABRI research reactor [2], funded by the French Institute for Radioprotection and Nuclear Safety (IRSN) and located in the Cadarache research center of the French Alternative Energies and Atomic Energy Commission (CEA), the fuel pin to be examined (test pin) is placed at the center of the core, in a dedicated test loop, and is then subjected to a power transient obtained by the fast depressurization of the neutron absorber 3 He gas from the transient rods located in the core. The main parameters of the power pulse such as the peak power, the pulse length and the total energy deposition, depend on the operational characteristics of the reactor and are adjustable by experimental design.…”