Patent Number: 
Section: claims

1. An apparatus comprising:a pressurized water reactor (PWR) including a pressure vessel and a nuclear reactor core comprising fissile material disposed inside the pressure vessel at the bottom of the pressure vessel; anda secondary core containment structure including:a containment basket comprising zirconia insulation containing the bottom of the pressure vessel, the containment basket spaced apart from the bottom of the pressure vessel by a clearance gap, the containment basket having an open top located at an elevation above the top of the nuclear reactor core, anda radiological containment structure containing the PWR and the secondary core containment structure, the radiological containment structure having a sump in which the bottom of the pressure vessel is disposed; andconduits disposed between the containment basket and the bottom of the pressure vessel and having inlets disposed both above the top of the containment basket and in the sump and outlets inside the containment basket, so that water disposed in the sump flows into the conduits via the inlets and discharges into the containment basket via the outlets. 2. The apparatus of claim 1 wherein the clearance gap between the containment basket and the bottom of the pressure vessel is no larger than one meter. 3. The apparatus of claim 1 wherein the containment basket of the secondary core containment structure further includes an inner steel liner and an outer steel support structure with the zirconia insulation disposed between the inner steel liner and the outer steel support structure. 4. The apparatus of claim 3 wherein the outer steel support structure includes bottom supports via which the secondary core containment structure is bottom-supported on a floor of the sump of the radiological containment structure. 5. The apparatus of claim 4 further comprising:zirconia insulation boards disposed on the floor of the sump of the radiological containment structure. 6. The apparatus of claim 1 wherein the secondary core containment structure further includes a cylindrical collar comprising refractory fiber insulation, the cylindrical collar extending upward from the open top of the containment basket and spaced apart from the pressure vessel by a clearance gap. 7. The apparatus of claim 1 wherein the secondary core containment structure is effective to support the weight of a corium mass comprising the nuclear reactor core in the containment basket of the secondary core containment structure. 8. An apparatus comprising:a nuclear reactor including a pressure vessel and a nuclear reactor core comprising fissile material disposed inside the pressure vessel at the bottom of the pressure vessel; anda secondary core containment structure including a containment basket comprising insulation with a maximum stable temperature of at least 2200K cladded by steel;a radiological containment structure having a sump containing the nuclear reactor and the secondary core containment structure; andconduits disposed between the containment basket and the bottom of the pressure vessel and having inlets disposed both above the top of the containment basket and in the sump and outlets inside the containment basket, so that water disposed in the sump flows into the conduits via the inlets and discharges into the containment basket via the outlets,wherein the bottom of the pressure vessel and the nuclear reactor core are disposed inside the containment basket with the containment basket spaced apart from the bottom of the pressure vessel by a clearance gap, and the containment structure has an open top located at an elevation above a top of the nuclear reactor core. 9. The apparatus of claim 8 wherein the containment basket of the secondary core containment structure comprises zirconia insulation cladded by steel. 10. The apparatus of claim 9 wherein the clearance gap between the containment basket and the bottom of the pressure vessel is no larger than one meter. 11. The apparatus of claim 9 wherein the containment basket includes bottom supports via which the secondary core containment structure is bottom-supported on a floor of the sump of the radiological containment structure. 12. The apparatus of claim 9 further comprising:zirconia insulation disposed on the floor of the sump of the radiological containment structure beneath the nuclear reactor and the secondary core containment structure. 13. The apparatus of claim 9 wherein the secondary core containment structure further includes a cylindrical collar comprising refractory fiber insulation, the cylindrical collar extending upward from a lip of the containment basket. 14. The apparatus of claim 9 wherein the secondary core containment structure is effective to support the weight of a corium mass comprising the nuclear reactor core in the containment basket of the secondary core containment structure. 15. The apparatus of claim 9 wherein the secondary core containment structure further comprises pipes arranged to inject water into the clearance gap between the containment basket and the bottom of the pressure vessel.