Simulation of nuclear fuel rod behavior in experimental facilities

The document deals with the application of a numerical model, called POTEL, to determine the electrical power to be supplied to filled rods, available in the PIPER-ONE experimental simulator, in order to simulate the performance of the nuclear fuel. Filled rods are difficult to construct but have a thermal capacity close to the one which characterizes the reference nuclear fuel rods. However, density and other material properties (e.g. conductivity) of electrical rods are still different from the prototype nuclear fuel; the difference may become important in selected transient conditions. In those conditions electrical power must be controlled in order to reproduce the temperature transient expected on the surface of the nuclear fuel rods. A complex software was developed to determine the electrical power transient based on the inverse solution for transient conduction heat transfer, i.e. the Fourier equation. Reference conditions (surface temperature and heat flux) were calculated by the RELAP code for nuclear fuel in the expected experimental conditions and were transformed into electrical power to be supplied to PIPER-ONE heaters during the actual experimental conditions (obviously if the code prediction was wrong – to be demonstrated a posteriori – the calculated transient for electrical power resulted inconsistent with the occurring thermal-hydraulic conditions). The application of the software to the commissioning experiments performed in PIPER-ONE is discussed in this report. PIPER-ONE was a Boiling Water Reactor (BWR) simulator installed at the Scalbatraio Laboratory managed by Dipartimento di Costruzioni Meccaniche e Nucleari (DCMN, now DICI) of University of Pisa