HTGR Technology Family Assessment for a Range of Fuel Cycle Missions

Abstract

ACKNOWLEDGEMENTSWe acknowledge help from key people in the NGNP Deep Burn study -Dave Petti, Mike Pope, Brian Boer, Francesco Venneri, and Abderrafi Ougouag. They have been helpful in clarifying information and issues. Dave is the lead of Very High Temperature Reactor (VHTR) technology development for the Next Generation Nuclear Program (NGNP); he reviewed an earlier draft of this report. a Mike and Brian had to do some extra work to create isotopic information suitable for fuel cycle analyses for once through and "deep burn" HTGR cases (both pebble bed and prismatic).Chemical separation experts Roger Henry and Dave Meikrantz were involved in this effort this fiscal year until their retirements in July. Prior to his retirement, Kent Williams was very helpful in suggesting information valuable for eventual economic/cost analyses. We hope all three are happy in retirement.Proliferation resistance and physical protection experts Robert Bean, Richard Metcalf, Fernando Gouveia, and their intern Amanda Rynes helped clarify HTGR proliferation issues.Prof. Mary-Lou Dunzik-Gougar was very helpful in providing information and answering questions regarding graphite and C-14 impurities.The lead author thanks Brent Dixon for his review of the draft report and apologizes for not giving him more time.a VHTR is a subset of HTGR. The NGNP is a specific VHTR/HGTR reactor project. HTGR Study iv August 23, 2010This page intentionally left blank. Several issues are outside the scope of this report, including the following: thorium fuel cycles, gascooled fast reactors, the reliability of TRISO-coated particles (billions in a reactor), and how soon any new reactor or fuel type could be licensed and then deployed and therefore impact fuel cycle performance measures. HTGR Study HTGRs in the context of LWRsAs the HTGR and LWR are both thermal neutron spectrum reactors, the report frequently compares the two as suggested by authors of the Option Study.[Wigeland2009] There are four major LWR-HTGR differences with fuel cycle implications -solid moderator, higher operating temperatures, higher fuel burnup associated with the TRISO fuel coating, and the "pebble bed" design approach (as opposed to the "prismatic" design approach, which is more directly comparable to LWRs).The solid moderator has several effects. First, it means that there is no accident sequence involving voiding of the core's moderator. Thus, there is no void coefficient problem in HTGRs. The void coefficient issue in LWRs constrains TRU loading in recycled fuel (modified open cycle, full recycle).[Youinou2009] The lack of the void coefficient problem in HTGRs suggests MOC or full recycle HTGR could consume transuranics faster than a LWR. Second, carbon is a less effective moderator than hydrogen (or deuterium), leading to neutron energy spectral changes that slightly decrease uranium utilization relative to an LWR. This reactor physics disadvantage is compensated by the higher operating temperatures hence higher thermal efficiency. Third, the solid moderator in an HTGR (grap...