Measurements were performed at the VENUS critical facility for the validation of neutron codes in the case of a reactor core loaded with weapon-grade plutonium. Since the e€ective delayed neutron fraction βeff€ and the mean neutron lifetime l are two impo

Measurements were performed at the VENUS critical facility for the validation of neutron codes in the case of a reactor core loaded with weapon-grade plutonium. Since the effective delayed neutron fraction βeff and the mean neutron lifetime l are two important parameters in the characterisation of the dynamic behaviour of a reactor, an absolute measurement of these parameters is necessary to assure the correct validation of neutron transport codes. To meet this requirement, the RAPJA-technique was used. The RAPJA technique combines a Prompt Jump with a Rossi-Alpha measurement at the stationary subcritical level associated with the antireactivity level obtained after the Prompt Jump. The obtained results are well in accordance with calculated values for MOX-cores at VENUS. The measurements also show that uncertainties of 3 and 1.5% on respectively βeff and l are achievable on a core loaded with weapon-grade plutonium.