The US Department of Energy’s high temperature reactor research and development program – Progress as of 2019

•The High Temperature Gas-Cooled Reactor is a relatively mature technology; deployable within a decade.•US Department of Energy sponsorship of HTGR technology research and development is resulting in the retirement of significant risks confronting deployment.•Extensive testing confirms that modern TRISO and graphite grades meet designer requirements.•Alloy 617 has been approved by the ASME for nuclear construction up to 425 °C.•Design and high fidelity fuel core analysis tools are being developed and benchmarked.•Significant gains have been made in the advanced reactor regulatory framework.