Noise methods play increasingly important role in core monitoring and diagnostics. Contemporary calculation methods allow for the determination of the reactor transfer function, based on which, with proper assumptions, the noise source (e.g. vibrating absorber, core barrel or other anomalies) can be located from the fluctuations of the neutron detector signals. The goal is the early recognition and quantification of anomalies in order to forecast commencing severe failures and help the prevention or the mitigation of consequences. The nuclear engineering group of Chalmers University of Technology has been cooperating with the Ringhals nuclear power plant for more than two decades in power plant noise diagnostics, and the CORTEX H2020 project coordinated by Chalmers concerns the development of such calculation tools and their validation.
Experimental validation of such methods are generally performed in zero power critical assemblies by creating a periodic reactivity perturbation in the core. The Training Reactor of BME has the advantage over zero power facilities that it can operate at a power level where neutron detectors operate in current mode and the reactivity feedbacks have also effect. Therefore a similar experiment is planned at the Training Reactor, which can significantly contribute to the development of noise diagnostic methods. The measurements require an equipment to oscillate a small absorber in the reactor core with a chosen frequency in accordance with the operation and safety regulations. Response for the periodic perturbation has be monitored besides the ex-core detectors of the reactor control system, also by detectors in several positions in the core or the reflector in pulse or current mode, depending on the power. The experiment needs careful planning to ensure that the effects of interest are measurable and the results are suitable for validation purposes. Optimal measurement set-up has to be chosen based on detailed simulations for which the CORE SIM code developed at Chalmers can be a suitable tool.
The two principal objectives of the PhD project are the validation at the BME Training Reactor of the computational and simulation tools to be used in the concrete applications, as well as the application of the methods developed to the concrete investigation and solution of problems occurring in power reactors. Hence, in the course of the work, the following tasks are to be handled and solved:
implementation of the CORE SIM code and its adaptation for simulation of the BME Training Reactor (geometry, input files, etc.);
design of the validation experiments that suit the BME Training Reactor with the help of detailed simulations;
participation in the execution of the experiments and in the evaluation of the measurements (in case the measurements are realised during the PhD project);
elaboration of the theory of, and implementation of a quantitative method for the diagnostics of the so-called „tilted mode” vibrations, observed in the Ringhals PWRs, and their elimination from the beam mode (pendular) vibrations, as well as for the relative quantification of the vibration amplitudes, which makes it possible to perform trend analysis partly within one cycle, and partly over several cycles;
use of the code CORE SIM for the decoupling of the effect of the vibrations of the core barrel as a whole from that of the individual and uncorrelated vibrations of the fuel assemblies in the ex-core detector signals, and by this way understanding and interpretation of the cyclic trends observed in the individual fuel cycles;
to investigate whether by the joint noise analysis of ex-core and in-core neutron it is possible to draw conclusions on the vibrations of in-core components, such as the thimble tube vibrations, as well as to diagnose other, turbulent flow induced vibrations and impacting, such as the so-called baffle jetting;
to investigate the practical applicability of the methods in VVER reactors by taking into account the specific placing of the ex-core and in-core detectors and their operational principles.
The PhD project will be realized in a double degree program with Chalmers University of Technology (Gothenburg, Sweden, supervisor: Paolo Vinai, associate prof.), where the student will spend approximately half of the time at each institution. English proficiency is required to work in an international environment.
Good computer programming skills.
Basic knowledge of reactor physics.