Neutronic Analysis of Horizontal-Compact High Temperature Gas-cooled Reactor

Abstract

To address the significant cost challenges associated with advanced reactors, a 150MWt horizontal compact high temperature gas-cooled reactor (HC-HTGR) has been proposed. The HC-HTGR has potential to reduce the capital cost of a traditional vertical oriented HTGR by 20% through reduction in reactor building volume. This benefit comes with a trade-off in control system design that requires the usage of control drums due to sagging thin rods in a horizontal layout. Commonly utilized in microreactors, a thorough investigation of control drums must be conducted in reactors with power >100MWt. Parametric studies using OpenMC were carried out to ensure its feasibility. With a uniform enriched core, 12 rotating control drums with an outer radius of 23.4407cm, 0.5cm thickness of 90% enriched B₄C, and 0.3cm incoloy cross supports, achieved the highest shutdown margin (SDM) of 3.23%. A sensitivity study on fuel enrichment yielded a SDM of 6.29%, that satisfied the HTGRs design requirement. 2D radial and axial power peaking factor (PPF) with the new enrichment pattern was found at 1.847 and 1.344, respectively. Homogenization using ring reactivity equivalent physical transformation (RRPT) method was developed to reduce the complexity of the core and showed a good performance with a 4pcm difference in steady-state calculation. Depletion analysis was modeled to ensure the reliability of the new fuel enrichment pattern. The first cycle core sustained criticality for 2.37 years with an average enrichment of 15.5% which meets the design target goal of 2 years cycle length. Overall, the neutronics assessment of HC-HTGR core met the initial safety and design requirements.