Research and development in the reactor physics field is necessary in both the design phase and the licensing/commissioning phase. In the design phase, the reactor core designers need tools and nuclear data that are most fitted to the task. In the licensing/commissioning phase, these designers need to show that their tools, nuclear data and work methodology are indeed validated and trustworthy.
Neutronic tool developments
The basic tools for the neutronic core design are deterministic or stochastic neutron transport codes. These provide the designers with the neutron flux in the core. However, extra tools are necessary to evaluate the core performance. One of these tools is a burn-up code, i.e. a code that evaluates the change in composition of the nuclear fuel as function of time. In the past, a PhD project has resulted in the code ALEPH. In a next step, a new PhD project has started to develop a core optimization tool: given a set of fresh and spent (at different burn-up levels) fuel, provide the user with an optimal core configuration for the next cycle. The major challenge in this PhD is the definition of the optimality criterion for a research facility like MYRRHA and to keep the running time of the code within reason.
Neutronic code and nuclear data validation
Since MYRRHA represents several innovative features compared with what is available in standard codes and libraries, namely its sub-criticality and criticality, its heavy liquid metal coolant (and thus fast spectrum), the many in-pile sections with unique characteristics and its complex core management, a dedicated experimental facility for validation experiments is needed. In this respect, the GUINEVERE project, will allow us to evaluate our calculation method, our tools and the libraries used. In close connection is the set-up of a uncertainty and sensitivity analysis. Even the best data has a level of uncertainty associated with it, so it is important for the designers to know the uncertainty and to have an idea of the propagation of this uncertainty on the scale of the core.
On-line reactivity monitoring
In critical reactors, the monitoring of the criticality is easily done by monitoring the flux and power levels. Only when these are constant in time, we know that the reactor is critical. In a sub-critical system, however, we need to determine the level of sub-criticality based on measurements . At this moment, a PhD is in progress to study a possible technique called "current-to-flux mapping". Based on the measurements of the proton current and neutron flux, the sub-criticality level should be deduced. In theory, this is perfectly possible; in practice however, we measure neutron flux only at certain positions and hence we need to configure optimal detector positions. Of course, this methodology has to be validated, for which we can use again the GUINEVERE facility.