Control rod shadowing effect in PWR core utilizing Urania-Gadolinia fuel

Safety analysis of nuclear power plants requires the assessment of all the systems important to safety. Control rods are one of the important safety systems for nuclear reactors. The control rod worth is affected by location of control rod banks, enrichment of uranium fuel in the assembly where the bank is inserted and the enrichment of gadolinium in the assembly. Also, the Interactions between control rods, phenomena known as shadowing effect, influence the worth of control rods. In this paper shadowing effect and the factors affecting the control rod worth are investigated for four types of control rod banks of an EPR Reactor. Parameters investigated are control rod worth, degree of interaction between rods and amplification factor. Moreover, the effect of interactions between control rod banks on the fluctuation of flux distribution in the core is studied. The calculations are evaluated at BOC and EOC using MCNP6 code. The results showed that the location of control rod bank in the core has the highest effect on the worth of a certain bank, second is the number of control rod bank groups in the core, followed by the fuel enrichment. The gadolinium burnable absorber has a slight effect on the control rod worth. The results obtained represent an important contribution that would support safety analysis of the EPR reactor design. •Shadowing effect and the factors affecting the control rod worth are investigated.•The degree of interaction between control rods is evaluated using MCNP6 code.•The location of control bank is the most effective factor that affects the worth.•Number of control rod bank groups is the second factor that affects the worth.•The next factors are the fuel enrichment and the presence of gadolinium.