[en] Three-dimensional neutron diffusion calculations are routinely performed in support of various NRC-sponsored reactor fuel testing programs conducted in the Power Burst Facility test reactor at the Idaho National Engineering Laboratory. The calculations are done with the PDQ-7-II program. ENDF/B Version IV data provide the basic cross section information used to generate few-group neutron diffusion theory constants used in the calculations. Reactor operating data have been employed to validate the three dimensional PBF diffusion theory model. Results obtained to date show that criticality is quite accurately predicted at various steady-state power levels. In addition, for one reactor configuration considered measured axial power distributions at three different radial locations compare well with the predicted distributions