Hi Everyone, We'll start our CPS talks this all-hands Monday meeting with a presentation by John Tramm, details below. Please do send your talk title and abstracts to Samantha. We'll set up a calendar to make sure all focus areas are well-represented with appropriate talks. Best Salman ********************* Title: The Random Ray Method of Neutral Particle Transport: A New "HPC-Friendly" Method for Nuclear Reactor Simulation Abstract: A central goal in computational nuclear engineering is the high-fidelity simulation of a full nuclear reactor core by way of a general simulation method. General full core simulations can potentially reduce design and construction costs, increase reactor performance and safety, reduce the amount of nuclear waste generated, and allow for much more complex and novel designs. To date, however, the time to solution and memory requirements for a general full core high-fidelity 3D simulation have rendered such calculations impractical, even using leadership class supercomputers. Reactor designers have instead relied on calibrated methods that are accurate only within a narrow design space, greatly limiting the exploration of innovative concepts. In an effort to develop reactor simulation applications that are at once fast, accurate, and general purpose -- we have developed a fundamentally new computational algorithm. This new algorithm, known as The Random Ray Method (TRRM), can be viewed as a stochastic formulation of the traditionally deterministic Method of Characteristics (MOC) approach of numerically solving PDEs. TRRM's three largest advantages compared to traditional MOC are that it can handle arbitrary 3D geometries, it offers extreme improvements in memory efficiency, and (most importantly) it allows for significant reductions in algorithmic complexity by allowing for unbiased sparse iterations. In addition, TRRM naturally exposes a massive amount of task-based parallelism and can efficiently utilize SIMD vector units on modern HPC architectures. In this talk, I will briefly introduce the new TRRM algorithm and a massively parallel implementation of it known as the Advanced Random Ray Code (ARRC). I will then present a selection of performance results for reactor simulation benchmark problems run with ARRC on the Theta supercomputer, and will compare ARRC's performance against state-of-the-art traditional deterministic neutron transport applications.