Mark DeHart, PhD, is a Senior Reactor Physicist at Idaho National Laboratory (INL). He currently leads a multiphysics analysis team performing simulations of SIRIUS fuel samples for nuclear thermal propulsion (NTP) materials characterization and directly supporting NASA staff for full-core NTP transient simulations. He is also the conceptual design lead for development of pre-conceptual designs for potential replacement the INL Advanced Test Reactor (ATR) after 2040. Over the past several years DeHart has led and directed a team of reactor physicists and computational methods staff performing applied multiphysics methods for numerous advanced reactor designs (including pebble bed, high-temperature gas, molten salt designs), support of industrial microreactor design efforts, and ad modeling/simulation efforts for INL’s Advanced Test Reactor and Transient Test Reactor (TREAT). Dr. DeHart joined INL in 2010 from ORNL; during 17 years at ORNL, Dr. DeHart worked in both methods and analysis related to criticality safety, burnup credit, data validation, and reactor physics. He is the primary author of the NEWT lattice physics code and the TRITON lattice physics and depletion sequence within the SCALE code system and led development of modern lattice physics methods at ORNL. Dr. DeHart has extensive experience in reactor physics, criticality safety, depletion and spent fuel characterization, cross-section processing, and computer code verification and validation. He holds BS, MS, and Ph.D. degrees in nuclear engineering from Texas A&M University. He is a Fellow of the American Nuclear Society (ANS) and a member and past Chair of the local section of ANS. Dr. DeHart has served as session organizer and chair for numerous technical sessions at national conferences and was the Technical Program Chair for PHYSOR 2016, held in Sun Valley, ID May 2016 and co-chair for PHYSOR 2018, Cancun, Mexico and M&C 2019, Portland, OR. He is a past Chair of the ANS Reactor Physics Division (2013-2014) and of the ANS 19.5 Standard Working Group. He has more than 150 publications in journals, conference proceedings, and national laboratory reports related to computational methods and applications in reactor physics, radiation transport, criticality safety, and depletion methods for spent nuclear fuel.