The PATHS code is a drift-flux thermal hydraulics code. It was developed to solve the thermal hydraulic solution for a boiling water reactor. Beginning in 2008, the NRC was interested in modeling the first three cycles of Peach Bottom Unit-2. At that time, the only option for boiling water feedback was the TRACE code. However, a single statepoint required approximately 30 days of wall time. Therefore, a fast and simple TH solver for PARCS depletion was needed. Over the next few years, PATHS was developed and improved. It was applied to Peach Bottom, Edwin Hatch, FIRGG, BFBT, and various other research projects. Additional features were added to model modern BWR fuels including Atrium-10, GE, GNF, and SVEA type fuels. It is currently used by the NRC for various licensing calculations.

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v1.06 (Aug 2018) 

Major improvements to file handling, input testing, and output edits. This version was released into PARCS v3.3.2.

v1.05 (Aug 2017) Updated

Minor improvements to output edits. This version was released into PARCS v3.3.1.

v1.05 (Aug 2017)

Improved robustness of the field equation solution. Further closure relationships were added as well. Hexagonal geometry support was also finalized. Both FRIGG and BFBT experiments were modeled with PATHS and showed excellent agreement with the experimental data. This version was released into PARCS v3.3.0.

v1.00 (July 2014)

Preliminary support for IAPWS steam tables and advanced BWR fuel geometry. The advanced fuel includes part length rods, empty rods, and also large water holes. Channel orificing can also be modeled independent of the channel geometry. This version is within a developmental fork.

v0.90 (January 2013)

The first stable version of PATHS, which can be found in PARCS v32m10. This version was used to model both Peach Bottom and Hatch startup depletion. In both cases, excellent agreement was observed for both core k-eff as well as the detector response.