Boron transient effects on the behavior of IRIS reactor using dynamic modeling

• Published in: Progress in nuclear energy (New series) Vol. 69; pp. 44 - 52
• Main Authors: Alencar de Sá Magalhães, Mardson, Brayner de Oliveira Lira, Carlos Alberto, Bezerra da Silva, Mário Augusto, de Lima Bezerra, Jair, de Andrade Lima, Fernando Roberto
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2013
• Subjects: Boron; Boron transients; Dynamic simulation; Dynamics; Homogenizing; IRIS reactor; Mathematical models; Nuclear engineering; Nuclear power generation; Nuclear reactor components; Nuclear reactors; IRIS reactor; Boron transients; Dynamic simulation
• ISSN: 0149-1970
• DOI: 10.1016/j.pnucene.2013.05.006

Small Modular Reactors (SMR) are considered as having several advantages over typical nuclear reactors under various specific conditions. They are thought to be installed in countries with small or medium power grid, in which a large power plant is not necessary or in isolated communities far from distribution centers. A plenty of developing countries are in this situation, so that a significant demand on this type of reactor is expected in a near future. The IRIS reactor is the top-front of SMRs, making its complete development very attractive, since it can fulfill the essential requirements for a future nuclear power plant: better economics, safety-by-design, low proliferation risk and environmental sustainability. IRIS reactor is an integral type PWR in which all primary components are arranged inside the pressure vessel. This configuration involves important changes when compared with a conventional PWR. These changes require several studies to comply with the safe operational limits for the reactor. In light water reactors, a solution of boric acid is used in the coolant of the primary loop to absorb neutrons, aiming to adjust the reactivity of the reactor. A significant decrease in the boron concentration in the core might lead to a considerable power excursion. Several studies on PWR have established correlations between power excursions and deficiencies in homogenization of boric acid diluted in the coolant. The IRIS reactor, due to its integral configuration, does not possess a spray system for boron homogenization which may cause power transients. In this paper, a study has been conducted to develop a dynamic model (named MODIRIS) for transient analysis, implemented in the MATLAB'S software SIMULINK, allowing the analysis of IRIS behavior by considering the neutron point kinetics model for power generation. The methodology is based on generating a set of differential equations of neutronic and thermal-hydraulic balances which describes the dynamics of the primary circuit, as well as a set of differential equations describing the dynamics of secondary circuit. The equations and initialization parameters at full power were inserted into the SIMULINK and the code was validated by comparing with RELAP simulations for a transient of feedwater reduction in the steam generators. Furthermore, the current paper looks for studying and developing a dynamic model for calculating the variations in the boric acid concentration. Then, a simplified model for boron dispersion was implemented into the code MODIRIS to simulate power transients which occur due to variations in the boron concentration in the primary loop of the IRIS reactor. The results for boron concentration, inserted reactivity and steam production showed a good precision and represented the expected behavior very well in the range of operational transients. •The configuration of advanced reactors demands researches for operational maneuvers.•Due to the lack of spray system, power transients in IRIS may differ from PWRs.•A dynamic model combining point kinetics and thermal-hydraulics is developed.•Operational transients due to variations of boron concentrations are simulated.