MC21/CTF Solutions to OECD/NEA TVA Watts Bar Unit 1 Multiphysics Cycle 1 Benchmark Exercises

Three Cycle 1 exercises of the Organisation for Economic Co-operation and Development (OECD)/Nuclear Energy Agency (NEA) Tennessee Valley Authority (TVA) Watts Bar Nuclear Plant Unit 1 (WBN1) multiphysics benchmark were simulated using the MC21 stochastic neutral particle transport code, coupled with the CTF subchannel thermal-hydraulics code. The exercises included exercise 1 [cycle 1 beginning of cycle (BOC) hot zero power (HZP)], exercise 2 [BOC hot full power (HFP)], and exercise 3 (cycle 1 depletion).The key results include a computed BOC HZP initial critical eigenvalue of 0.99939 for the full-core MC21 model (exercise 1), a computed HFP critical boron concentration of 862.2 ppm for the full-core coupled MC21/CTF model (exercise 2), and a computed equivalent critical boron concentration of −6.3 ppm boron (ppmB) at cycle 1 end of cycle for the 1/4-core coupled MC21/CTF model, with most depletion steps within 10 ppmB of measurements (exercise 3). All outputs requested in the OECD/NEA WBN1 benchmark specification was computed and have been submitted to the OECD/NEA website.