Once spent fuel pool cooling is lost, the water temperature will increase at a rate dependent on the pool volume and heat load. The critical step will be once departure from nucleate boiling occurs, which will be followed by a significant increase in fuel temperatures. This is because the steam blanket that forms next to the assemblies significantly reduces the cooling capabilities of the water. Fuel temperatures below 1300 F do not result in any damage to the cladding, fuel or control rods. Cladding damage begins above 1300 F when the zircaloy cladding may balloon as a result of increased internal pressure of helium gas and fission-product gases. Oxidation of the cladding will also begin. At temperatures greater than 1600 F, the oxidation rate of the cladding becomes significant. The oxidation reduces the strength and ductility of the fuel rods. Additionally, the reaction is exothermic which can be a significant contributor to the heat load. It also generates a significant amount of hydrogen, which was the cause of the explosions at Fukushima. Once the pool boils down to a level that the fuel assemblies are uncovered, the fuel temperatures will again increase. Above 2000 F, the fuel lattice structure begins to breakdown and fission products will be released if the cladding has failed. At 2600 F the cladding oxidation process becomes self-sustaining. Even if the external heat source were removed at this point, the oxidation reaction would generate enough heat by itself to maintain temperatures high enough for the reaction to continue at a high rate. Beyond 4900 F, fuel melt begins to occur. At 5100 F the fuel is fully melted and will begin to flow and puddle out. This is significant because the loss of fuel geometry makes it significantly harder to cool the fuel if spent fuel pool cooling is restored.
Mitsubishi has designed the US-APWR. Hitachi has partnered with GE on the ABWR and ESBWR designs. The Westinghouse AP 1000 design is currently in construction in China.
I have multiple years experience as a reactor engineer at a commercial nuclear power plant as well as experience with secondary side systems. This field requires quality work at a high level of technical rigor on time. This can be expected for your project.