GCFR

The GCFR programme had taken place in the US from early in the country’s history on nuclear power. It was considered in parallel to the US LMFBR programme, being perceived to offer a number of advantages. The conceptual GCFR was in principle simpler to operate compared with the sodium-cooled LMFBR and, if required, has the potential for higher breeding gain. Considerable experience had also accrued from the operation of the HTR Peach Bottom and Fort St Vrain reactors.

Regarding the fuel and core design, the GCFR was based on the Liquid Metal Fast Reactor (LMFR) design, incorporating niobium stabilised stainless steel pins and wrappers. The coolant was helium and the pin design was based on pressure equalised vented pins. This has the advantage for pin design and performance at the expense of a removal of a fission product release barrier. Reactivity was controlled by two independent and diverse shutdown systems.

The primary heat removal system was an upward flow system through the core, driven by active circulators. The design also included an independent and redundant decay heat removal system. The reactor vessel was engineered from pre-stressed concrete. On the helium side, it was insulated and there was water cooling on the outside.

The containment building incorporated a molten fuel containment system, below the bottom of the vessel.

The GCFR programme was halted by the USDOE in 1981, because Liquid Metal Fast Breeder Reactor (LMFBR) technology had progressed sufficiently to become a credible option. The GCFR had no proliferation advantages over the LMFBR design. There were also some economic, safety and technical factors that affected the decision to go forward. The multi-cavity pre-stressed concrete posed problems for manufacture and inspection and also problems for extrapolation. From a safety perspective, vented pins implied that the first barrier for fission product release was lost. Finally, there were concerns over spent fuel assembly cooling. Nevertheless, the initial work over the first few decades was viewed as providing a positive story in terms of technical design development and the safety and licensing activities that were carried out.

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