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The Consortium for Advanced Simulation of Light Water Reactors (CASL) Challenge Problems range from CRUD to pellet-clad interaction, requiring validated, high-resolution multiphysics predictions of nuclear reactor operation and fuel performance throughout the life of a nuclear power plant. The Virtual Environment for Reactor Analysis (VERA) is an ORNL-led collaboration with the University of Michigan, the Massachusetts Institute of Technology (MIT), North Carolina State University (NCSU), Tennessee Valley Authority, Westinghouse, the Electric Power Research Institute, and Idaho, Sandia, and Los Alamos Laboratories, with contributions from many other partners in academia, industry, and the national laboratory system.

The CASL tool sets leverage key components of the SCALE system, most notably the fundamental nuclear data processing and isotopic depletion capabilities, and they have rapidly enhanced the state of the practice for advanced multiphysics simulation of light-water reactors (LWRs). Integrating high-resolution neutronics using (1) the MPACT code, jointly developed with the University of Michigan, with subchannel two-phase   flow with CTF and (2) high-fidelity depletion with ORIGEN provides fully coupled estimates of the state of every pin and coolant channel in a pressurized water reactor’s core without traditional homogenizing of materials. Coupling with CRUD chemistry (Los Alamos National Laboratory’s MAMBA chemistry code) and fuel performance (Idaho National Laboratory’s BISON fuel performance codes) enables advanced solutions to complex industry problems.

Prediction of CRUD-Induced Power Shift (CIPS) and pellet-clad mechanical interaction (PCMI), along with their effects on operational limits, may enable utilities to safely operate at higher power for longer periods of time with lower enrichment costs, resulting in great returns.

The ORNL-developed Shift Monte Carlo code provides solutions for high-fidelity reactor physics and radiation transport and shielding solutions within VERA. The Shift Monte Carlo code and the Denovo deterministic transport code are part of the Exnihilo massively parallel radiation transport framework. In addition to using Shift for benchmark-quality high-fidelity solutions, the Shift and Denovo capabilities are used with the hybrid methods pioneered by ORNL to provide advanced variance reduction capabilities for ex-core applications. The combination of these technologies is being used to develop state-of-the-art capability for high-fidelity simulation pressure vessel and concrete bioshield fluence of entire reactor operational lifetimes.

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Licensing: VERA is available from RSICC upon request for non commercial licensees, or through the VERA Users’ Group for commercial licenses. Contact Andrew Godfrey ( for more information.