HYDROGEN PRODUCTION WITH FULLY INTEGRATED FUEL CYCLE GAS AND VAPOUR CORE REACTORS

摘要

This paper presents results of a conceptual design study involving gas and vapour core reactors (G/VCR) with a combined scheme to generate hydrogen and power. The hydrogen production schemes include high temperature electrolysis as well as two dominant thermochemical hydrogen production processes. Thermochemical hydrogen production processes considered in this study included the calcium-bromine process and the sulphur-iodine processes. G/VCR systems are externally reflected and moderated nuclear energy systems fuelled by stable uranium compounds in gaseous or vapour phase that are usually operated at temperatures above 1 500K. A gas core reactor with a condensable fuel such as uranium tetrafluoride (UF_4) or a mixture of UF_4 and other metallic fluorides (BeF_2, LiF, KF, etc.) is commonly known as a vapour core reactor (VCR). The single most relevant and unique feature of gas/vapour core reactors is that the functions of fuel and coolant are combined into one. The reactor outlet temperature is not constrained by solid fuel-cladding temperature limits. The maximum fuel/working fluid temperature in G/VCR is only constrained by the reactor vessel material limits, which is far less restrictive than the fuel clad. Therefore, G/VCRs can potentially provide the highest reactor and cycle temperature among all existing or proposed fission reactor designs. Gas and vapour fuel reactors feature very low fuel inventory and fully integrated fuel cycle that provide for exceptional sustainability and safety characteristics. With respect to fuel utilisation, there is no fuel burn-up limit for gas core reactors due to continuous recycling of the fuel. Owing to the flexibility in nuclear design characteristics of cavity reactors, a wide range of conversion ratio from completely burner to breeder is achievable. The continuous recycling of fuel in G/VCR systems allow for complete burning of actinides without removing and reprocessing of the fuel. The only waste products at the backend of the gas core reactors' fuel cycle are fission fragments that are continuously separated from the fuel. As a result the G/VCR systems do not require spent fuel storage or reprocessing. Due to very low fuel inventory and continuous burning and transmutation of actinides, gas core reactors minimise the environmental impact and stewardship burden. G/VCR systems also feature outstanding proliferation resistance characteristics and minimum vulnerability to external threats. Even for comparable spectral characteristic, gas core reactors produce fissile plutonium two orders of magnitude less than light water reactors (LWRs). In addition, the continuous recycling and burning of actinides further reduces the quality of the fissile plutonium inventory. Results of the study indicate that due to high temperature operation of G/VCR systems an overall combined electricity and hydrogen production efficiencies of well over 50% are feasible. The high production efficiency is demonstrated for combined electric power generation and hydrogen production using all three schemes for wide range of output ratio.