HTR code package neutronics developments and benchmarks

•Implementation of new spectrum code in HTGR comprehensive simulation code package HCP.•Implementation and verification of latest Dancoff factor calculation methods for HTGRs.•Excellent agreement with other deterministic and Monte Carlo codes against the HTR-10 experimental data.•Integration of the new spectrum code and the new library generation in HCP with focus on user-friendliness. The HTR Code Package (HCP) is a code system well suited to simulate most of relevant aspects related to the design and the safety assessment of a high temperature gas reactor in a consistent and integrated way. HCP has seen the addition of new functionalities and modules; each of them has been thoroughly verified and validated. With respect to neutronics, it now includes a new spectrum code that features two different 0D solvers as well as two new and fast analytical ways to deal with the HTGR double heterogeneity neutron resonance issue. The new spectrum code, neutron TRansport Integral Spectrum and Homogenization Application (TRISHA), is designed and implemented in order to be able to exploit the benefits of a multi-physics platform, keeping a well-balanced trade-off between accuracy and computational burden, while being user-friendly at the same time. This paper provides an overview on the neutronics of HCP focusing, in particular, on the newly developed spectrum code and the refactoring work done on MGT-Neutronics. Furthermore, it shows the most important results achieved during the long benchmark campaign that followed these latest developments. That is, the HTR-10 first criticality benchmarks B1 and B2 and the MGT-N/MGT-3D comparison.