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.

Quantum yield optimization of carbon dots using response surface methodology and its application as control of Fe3+ ion levels in drinking water

Early detection of heavy metals in drinking water is a fundamental step that must be taken to prevent adverse effects on health. This research aims to develop a heavy metal ion detector by utilizing the fluorescence properties of carbon dots. Cdots were synthesized using the microwave irradiation method based on the central composite design: urea mass 0.31-3.68 gr; reactor power 200-1000 W; synthesis time is 13-46 min, and the response is quantum yield. Material characterization includes PL, TEM, UV-VIS, XRD, and FTIR. The selectivity and sensitivity of Cdots as detectors were tested for Ag+, Bi3+, Ni2+, Al3+, Co2+, Pb2+, Fe3+, Zn2+, Zr4+, and Hg2+ ions at concentrations of 0-10 µM. The results showed that Cdots were successfully synthesized by fluorescent light green at 544 nm. An adequate response model is quadratic with the formulation QY= +58.36+10.41X1+14.06X2+13.59X3–5.57X2X3–4.89X12-8.60X22– 5.40X32. The best Cdots were obtained in the formulation of R9 (3 g, 800 W, 40 min), which resulted in a QY of 74.39%. The characteristics of Cdots are spherical, diameter 6.6 nm, the bandgap of 2.53 eV, and having an amorphous structure. The surface of Cdots contains various functional groups such as O-H, C-H, C=O, C N, and C=C. In the heavy metal detection test, Cdots showed specific sensitivity to Fe- 3+ ions. The addition of Fe3+ concentration and the extinction of Cdots fluorescence intensity formed a linear correlation F0/F=0.08894[Fe3+]+0.99391 (R2=0.99276). The detection ability of Cdots for Fe3+ ions reaches a concentration of 0.016 ppm, much lower than the regulatory threshold limit of SNI, WHO, and IBWA. The detection of Fe3+ ions in drinking water uses a fluorescence technique consistent with the SSA and ICP-OES. Based on these results, the fluorescence technique using Cdots can be an instrument for quality control of the final drinking water product.

Axial Shuffling on Pebble Bed Reactor using PRAKTIK 3D-HTR

With moving fuel, the pebble bed reactor (PBR) provides flexibility in the fuel management process due to the capability of online fuel refueling. This capability allows the reactor to operate at any given time without the need to shut down for refueling. The complexity of the depletion and burnup analysis requires the problem to be solved with sophisticated and robust computer codes that can handle the fuel shuffling. Since the fuel refueling is conducted from top to bottom, the shuffling and fuel movement in the axial direction should be modeled with acceptable accuracy. The purpose of the simulation is to obtain the equilibrium or even a critical condition of the reactor. The model used is based on the simplified pebble bed reactor with 200 MWt of thermal reactor power, 3 meters of core diameter, and 10 meters of core height. To model the axial shuffling on the reactor, a neutronic computer code called PRAKTIK 3D-HTR is used. The code utilizes the diffusion method in a three-dimensional cylindrical geometry to model the neutronic phenomena in the reactor. Moreover, PRAKTIK 3D-HTR is equipped with the burnup calculation and depletion analysis to be able to handle fuel movement. Finally, the axial shuffling mechanism is implemented using the once-through-then-out (OTTO) method. Implementing this method to the reactor, an equilibrium condition can be obtained. In this condition, the reactor condition in terms of criticality and flux shape is relatively constant. The critical condition can also be searched using PRAKTIK 3D-HTR to obtain the condition when the multiplication factor is equal to unity. The criticality search is conducted by changing the fuel movement speed. If the multiplication factor is less than 1, then the shuffling speed needs to be increased. Otherwise, if it is more than 1, the shuffling speed will be decreased.