Brian N. Aviles’s research while affiliated with Bechtel Marine Propulsion Corporation and other places

The continuous energy Monte Carlo neutron transport code, MC21, was coupled to the CTF subchannel thermal-hydraulics code using a combination of CASL tools and in-house Python scripts. An MC21/CTF solution for VERA Core Physics Benchmark Progression Problem 6 demonstrated good agreement with MC21/COBRA-IE and VERA solutions. The MC21/CTF solution for VERA Core Physics Benchmark Progression Problem 7, Watts Bar Unit 1 at beginning of cycle (BOC) hot full power (HFP) equilibrium xenon conditions, is the first published coupled Monte Carlo neutronics/subchannel T-H solution for this problem. MC21/CTF predicted a critical boron concentration of 854.5 ppm, yielding a critical eigenvalue of 0.99994 ± 6.8E-6 (95% CI). Excellent agreement with a VERA solution of Problem 7 was also demonstrated for integral and local power and temperature parameters.

The Virtual Environment for Reactor Applications (VERA) core physics benchmark problem #6, 3D Hot Full Power (HFP) assembly, from the Consortium for Advanced Simulation of Light Water Reactors (CASL) was simulated using the MC21 continuous energy Monte Carlo code coupled with the COBRA-IE subchannel thermal-hydraulics code using the R5EXEC coupling framework. The converged MC21/COBRA-IE solution was compared to results from CASL's VERA-CS code system, MPACT coupled to COBRA-TF (CTF). MPACT is a three-dimensional (3D) whole core transport code, executed in a 2D/1D approach employing planar method of characteristics (MOC) solutions with SP3 in the axial direction, and CTF is a subchannel thermal-hydraulics code designed for Light Water Reactor analysis. Eigenvalues agreed within 63 pcm, axially-integrated normalized radial fission distributions agreed within ±0.2% (root mean square (RMS) difference of 0.1%), local volume-averaged fuel pin temperatures agreed within +8.8/-4.3 C (RMS difference of 3.9 C), and local subchannel coolant temperatures agreed within +0.8/-1.5 C (RMS difference of 0.5 C). A sensitivity study to guide tube heat transfer indicated that a statistically-significant increase in reactivity and shift in radial pin power distribution occurred within the assembly when guide tube heating was enabled.