Computations of fuel management in MARIA reactor with highly poisoned beryllium matrix

The high-flux research reactor MARIA has been operated in Poland since 1975. Its core consists of loop type fuel channels placed in a beryllium block matrix. Irradiation of beryllium by neutrons results in a build-up of 6Li, and 3He isotopes with large thermal neutron absorption cross-sections. In addition, tritium is formed and decays into 3He which complicates the transmutation chains. Thus, the fuel management of the reactor depends on the beryllium poisoning. The isotopic transmutations in beryllium have to be computed in parallel to the fuel depletion. In this paper a comparison of the measured and computed results is given during: reactor operation in the period up to January 2004, modernization break in the reactor operation from January 2004 to February 2005 and reactor operation from February 2005. The measured and computed effects comprise: reactivity effects due to the fuel burn-up and beryllium poisoning by 6Li, and 3He.