7884079775

reactor cavity (Fig. 4, top frame), resulting m the axial distnbution of maximum fuel temperaturę peaking towards the inlet (left, or top of the core). Depending on the high-temperature capabilities of the vessel Steel, some variations in vessel insulation strategies may be needed.

1400

800

200

0 4--

0    20    40    60    80    100    120    140

Time (h)

FIG. 3. GT-MHR P-LOFC reference case - mcaimum fuel and vessel temperatures

The parameter most likely to affect the “success” of P-LOFC outcomes, assuming that the RCCS is functioning properly, is the emissivity controlling the radiation heat transfer between the vessel and RCCS (assumed to be 0.8 over the fuli rangę of normal-to-accident temperatures).

For an assumed (unlikely) 25% decrease in both vessel and RCCS surface effective emissivities, the peak vessel temperaturę is 37°C higher. The difference in peak fuel temperatures is smali (7°C), which is typical of the decoupling between the peak fuel and vessel temperatures in LOFC events.

3.2 D-LOFC: The D-LOFC reference case assumes a rapid depressurization along with a flow coastdown and scram at time = zero, with the passive RCCS operational. It also assumes that the depressurized coolant is helium (no air ingress). This event is also known as a “conduction-heatup” accident, sińce the core effective conductivity is the dominant mechanism for the transfer of afterheat from the fuel to the vessel. In the reference case, the maximum fuel temperaturę peaks at 1494°C 53 hr into the transient, and the maximum vessel temperaturę (555°C ) occurs at time = 81 hr (Fig. 5). Notę that in this case, the peak fuel (and vessel) temperatures occur near the core beltline, or center (Fig. 4, bottom frame), rather than near the top as in the P-LOFC, sińce the convection effects for atmospheric pressure helium are nil.

6

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