CASMO5

Unparalleled Accuracy: First-Principle Physics

CASMO5 represents the culmination of Studsvik’s 25 years of experience in transport-based lattice physics. Using the well-established Method of Characteristics for its 2D transport solution, the increase in calculational energy groups helps CASMO5 deliver unparalleled fidelity with production-level run times.

Several high-level physics enhancements have been added to CASMO5, making it the most accurate lattice physics code available.

Quadratic Gd Depletion

The strong spatial self-shielding of Gd-155 and Gd-157 require small depletion steps (and longer calculation time) for Gd-bearing fuel assemblies. CASMO-5 now includes a quadratic depletion model to overcome this difficulty, allowing for larger depletion step sizes without compromising accuracy.

Resonance Upscattering

Asymptotic elastic scattering models traditionally used in the epithermal energy range in NJOY and Monte Carlo codes lead to ~10% under prediction of Doppler coefficients of light water reactor lattices. CASMO-5 now corrects for this phenomenon using a more exact scattering kernel.

Energy Release Model

Lattice physics codes have typically used fixed energy release per fission values, which miss important features that impact reactor depletion results. CASMO5 now explicitly computes the isotopic energy yields as lattice compositions evolve, maintaining the physical dependence on fuel exposure, Gd, and boron concentrations, MOX composition, and void fractions.

Cutting-Edge Data: ENDF/B-VII Cross-Section Library

CASMO-5 has been updated with the latest available neutron and gamma data, fine-tuned to provide the most accurate solutions ever achieved with a lattice physics code. Using the most recent ENDF/B-VII nuclear data available, Studsvik has developed a high-resolution, 586-group neutron library for use with CASMO5.

This extensive update from the previous CASMO library improves accuracy and enhances resonance treatments. CASMO5 now includes an updated 18-group gamma library for gamma-sensitive in-core detector modeling and gamma energy deposition calculations. Cross-section data is available for over 400 nuclides and materials including more than 200 explicitly defined fission products, 45 heavy nuclides, and an expanded array of detailed depletion chains.

Special attention has been paid to low- and intermediate-energy resonances of uranium and plutonium isotopes with a proprietary explicit resonance mapping below 10eV that includes over 400 energy groups. Resonance self-shielding has been added or improved for most material definitions and a first-of-its-kind heavy nuclide resonance upscattering model has been implemented to produce the highest-fidelity solutions.

Next-Generation Analysis: Support for SIMULATE-5

CASMO5 has been developed to support SIMULATE-5, Studsvik’s advanced nodal simulator analysis code. CASMO5 automatically generates all required neutron and gamma cross-section data banks, discontinuity factors, and control rod depletion data for SIMULATE5, comprising the most advanced light water reactor physics analysis system in the world.

The improvements in CASMO5, coupled with the enhanced models in SIMULATE5, have shown marked impact on several core simulator parameters including gadolinium worth, reactivity coefficients, and stronger void feedback, significantly reducing calculated-to-measured error.

Fully capable of modeling challenging heterogeneous fuel designs, such as high mixed-oxide (MOX) concentrations and high burnable poison concentrations, CASMO5 and SIMULATE5 meet the demands of current and future reactor analysis. CASMO5 is also capable of performing full-scope lattice physics calculations and can help support efforts in the following areas:

• Fuel management
• Core follow
• Plant operations
• Reload physics

Extensively Benchmarked: Proven to be the best, CASMO5 has been rigorously tested against measured critical experiments, post-irradiation benchmarks, and continuous-energy Monte Carlo calculations, including:

• B&W Series 1810 and 1484, DIMPLE, and KRITZ-4 criticals
• MCNP (BOL and MCODE depletions) for pin-cells and whole assemblies
• JAERI nuclide benchmarks

These tests have demonstrated excellent agreement with no significant bias versus the number of Gd pins, number of AIC rods, boron concentration, geometry, or presence of reflector/baffle. The overall accuracy of CASMO5 and its associated ENDF/B-VII neutron data library have been repeatedly validated, ensuring reliably accurate results regardless of core type, fuel type, or operating strategy.