MONTE-CARLO TRANSPORT CALCULATIONS AND ANALYSIS FOR REACTOR PRESSURE-VESSEL NEUTRON FLUENCE

The application of Monte Carlo methods for reactor pressure vessel (RP V) neutron fluence calculations is examined. As many commercial nuclea r light water reactors approach the end of their design lifetime, it i s of great consequence that reactor operators and regulators be able t o characterize the structural integrity of the RPV accurately for fina ncial reasons, as well as safety reasons, due to the possibility of pl ant life extensions. The Monte Carlo method, which offers explicit thr ee-dimensional geometric representation and continuous energy and angu lar simulation, is well suited for this task. A model of the Three Mil e Island unit 1 reactor is presented for determination of RPV fluence; Monte Carlo (MCNP) and deterministic (DORT) results are compared for this application; and numerous issues related to performing these calc ulations are examined. Synthesized three-dimensional deterministic mod els are observed to produce results that are comparable to those of Mo nte Carlo methods, provided the two methods utilize the same cross-sec tion libraries. Continuous energy Monte Carlo methods are shown to pre dict more (15 to 20%) high-energy neutrons in the RPV than determinist ic methods.