Abstract
This work presents the thermal-hydraulic simulation of the Brazilian Multipurpose Reactor (RMB) using the RELAP5/Mod3 code. The RMB will provide Brazil with a fundamental infrastructure for the national development on activities of the nuclear sector in the areas of social, strategic, industrial applications and scientific and technological development. A RELAP5/Mod3 code model was developed for thermal-hydraulic simulation of the RMB to analyze the phenomenology of the Siphon Breakers device (four flap valves in the cold leg and one open tube for the atmosphere in the hot leg) during a Loss of Coolant Accident (LOCA) at different points in the primary circuit. The Siphon Breaker device is an important passive safety system for research reactors in order to guarantee the water level in the core under accidental conditions. Different simulations were carried out at different location in the Core Cooling System (CCS) of the RMB, for example: LOCA before the CCS pumps with and without pump trip and LOCA after the CCS pumps and the heat exchanger. In all RELAP5/Mod3 code simulations, the Siphon Breaker device's performance after a LOCA was effective to allow enough air to enter the outlet pipe of the CCS in order to break the siphon effect and preventing the pool level from reaching the riser (chimney) and the RMB core discovering. In all cases, the reactor pool level stabilized at about 5.5 m after the end of the LOCA simulation and the fuel elements were kept underwater and cooled.
Highlights
The Brazilian Nuclear Energy Commission (Comissão Nacional de Energia Nuclear—CNEN) is leading the project of the Brazilian Multipurpose Reactor (RMB) aimed to be projected, constructed, and operated to attend the present Brazilian needs for a multipurpose neutron source, which will be able to supply the radioisotope demand, carrying out material tests, scientific development, commercial, and medical applications with the use of neutron beams.Currently, the RMB project is in detail engineering design phase, which is being done by the engineering companies INVAP (Argentina), AMAZUL (Brazil) and IPEN (Brazil).In the present work, a nodalization for the Core Cooling System (CCS), service and reactor pools and the most important components of the RMB are performed using the RELAP5/Mod3 code
In the RMB project there are four flap valves located at the inlet pipes, the RELAP5/Mod3 nodalization of the RMB presented on the Figure 3, shows two flap valves
The locations of the cases simulate was: 1 - Loss of Coolant Accident (LOCA) at CCS pump suction line; 2 - LOCA at CCS pump discharge line. Analyses of both cases are very similar, because in the beginning of LOCA the coolant goes out by rupture and the water level of the reactor pool drops until the upper flap valves and the siphon break tube injected air on the coolant outlet pipe, which will act as siphon breakers and will prevent the water level from dropping below level the reactor chimney
Summary
The Brazilian Nuclear Energy Commission (Comissão Nacional de Energia Nuclear—CNEN) is leading the project of the Brazilian Multipurpose Reactor (RMB) aimed to be projected, constructed, and operated to attend the present Brazilian needs for a multipurpose neutron source, which will be able to supply the radioisotope demand, carrying out material tests, scientific development, commercial, and medical applications with the use of neutron beams. A nodalization for the Core Cooling System (CCS), service and reactor pools and the most important components of the RMB are performed using the RELAP5/Mod code. The assessment and validation of thermal-hydraulic system code have been performed in order to investigate the applicability of RELAP5/Mod3.2 to evaluate safety margins of a MTR research reactor [11]. A siphon breaker mechanism can be adopted as a passive safety device to protect the reactor core avoiding the lack of water in the fuel elements. These devices consist in a tube connected at the highest point in the outlet pipe of the primary cooling system and flap valves. The very good agreement between numerical and experimental results was obtained, allowing the RELAP5/Mod code to represent the main phenomena resulting from the performance of the siphon break
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