A reactivity accident is a situation in which such a control device that absorbs neutrons malfunctions or is accidentally removed for some reason, causing a sharp increase in the nuclear reaction, leading to an output surge and sometimes a runaway reaction. Some SMRs, however, are not confined to the existing light water reactor (LWR) concept of ‘no fuel supply during operation’, but have the concept that fuel supply during operation is possible. Since such reactors are not overloaded with fuel, there is no possibility of a reactivity accident even if there is a failure in the control devices.

Page 4. Describing exactly what i said.

n Japan, where even at 30% power with zero coolant flow, the reactor shuts DON automatically without the insertion of control rods, and heat can be removed without mechanical means by radiation and natural convection to the water-cooled cooling panels outside the reactor. Figure 2.2 shows the results of the zero-coolant test.

The US metal-fuelled fast reactor, the Experimental Breeder Reactor-II (EBR-II, 19 megawatts electrical (MWe)), shows similar results to the above when the coolant flow is set to zero […] Aurora (4 MWth) by Oklo, which applied for a Combined Construction and Operating License (COL) in 2020, has the same characteristics as the EBR-II.

Page 6, which refers to the graphic on page 7. So this only applies if the reactor was at around 30% or less of the design power output.

Meanwhile, the largest equipment in an NPP is the containment vessel. Containment vessels are generally much larger than reactor vessels. With a diameter of more than 10 m and a height of more than 30 m, they cannot be transported by ordinary means, such as by trucks on public roads. Although a containment vessel is important equipment for preventing the release of radioactive materials in the event of an accident, it is possible to have a design concept without a containment vessel if the NPP has other equipment that has equivalent functions or safety characteristics. The presence or absence of a containment vessel is another guideline for determining whether modularisation can be achieved.

Page 10.

Yeah great idea. This is Titanic all over again. We don’t need a last resort because we have been so smart, that all preliminary features are deemed infaillable. A story as old as humans building complex technology.