Analysis of the anticipated transient without scram (ATWS) initiated by emergency power mode through the full scope simulator

The integrity of the reactor coolant system is severely challenged as a result of an Emergency Power Mode – ATWS event. The purpose of this paper is to simulate the Anticipated Transient without Scram (ATWS) using the full scope simulator of Angra 2 Nuclear Power Plant with the Emergency Power Case as a precursor event. The results are discussed and will be used to examine the integrity of the reactor coolant system. In addition, the results were compared with the data presented in Final Safety Analysis Report (FSAR – Angra 2) in order to guarantee the validation of the methodology and from there analyze other precursor events of ATWS which presented only plausibility studies in FSAR – Angra 2. In this way, the aim is to provide and develop the knowledge and skill necessaries for control room operating personnel to ensure safe and reliable plant operation and stimulate information in the nuclear area through the academic training of new engineers. In the presented paper the most severe scenario is analyzed in which the Reactor Coolant System reaches its highest level of coolant pressure. This scenario is initiated by the turbine trip jointly with the loss of electric power systems (Emergency Power Mode). In addition, the failure of the reactor shutdown system occurs, i.e., control rods fail to drop into the reactor core. The reactor power is safely reduced through the inherent reactivity feedback of the moderator and fuel, together with an automatic boron injection. Several operational variables were analyzed and their profiles over time are shown in order to provide data and benchmarking references. At the end of the event, it was noted that Reactor shutdown is assured, as is the maintenance of subcriticality. Residual heat removal is ensured.

Characteristics of the Waviness End-Face Mechanical Seal in Reactor Coolant Pump Considering the Viscosity-Temperature Effect

Mechanical seals prevents flow leakages in reactor coolant pumps thus playing an important role in their operational safety. However, their operational performance depends on different parameters, the seal geometrical design and the sealing medium characteristics among others. This study investigates the main performances of the waviness end-face mechanical seal, considering the effect of fluid flow and thermal characteristics. The involved coupled thermal-hydraulic process is simulated using the OpenFOAM, based on the coupled Navier-Stokes and energy balance equations. Study results showed that the viscosity-temperature effect may increase the flow leakage, and decrease both the opening force and the liquid film stiffness. The later may be decreased to negative values under specific conditions. It’s therefore generally found that visco-thermal characteristics of the sealing medium may negatively affect mechanical seal’s operational stability. On the other hand, from the perspective of liquid film temperature rise, the visco-thermal effect may lead to the regulation of the temperature rise in the liquid film, which improves the mechanical seal’s operational safety in some aspects. Through a comprehensive analysis, the optimal structural parameters of the waviness mechanical seal investigated in this study are found to be hi = 2.5μm, β = 900μrad (Rd-Ri)/(Ro-Ri) = 0.2, α = 0.8, and k = 9.

Decontamination of a Contaminated RCP Shaft Using the SP-HyBRID Process

It is very important to minimize the waste generation for decontamination of the reactor coolant system in a nuclear facility. As an alternative to commercial decontamination technologies, an inorganic acid chemical decontamination (SP-HyBRID) process can be effectively applied to the decontamination because it can significantly reduce the waste generation. In this study, the decontamination of a contaminated reactor coolant pump shaft from a nuclear facility was conducted using the SP-HyBRID process. First, equipment for a mock-up test of the decontamination was prepared. Detailed experimental conditions for the decontamination were determined through the mock-up test. Under the detailed conditions, the contaminated shaft was successfully decontaminated. The dose rate on the shaft surface was greatly reduced from 1400 to 0.9 μSv/h, and the decontamination factor showed a very high value (>1500).