| Abstract: | An investigation of the sodium spray burning phase of LMFBR hypothetical low probability core disruptive accidents (HCDAs) has been undertaken in order to test the response of various containment designs. The HCDAs are produced by arbitrarily inserting unrealistically large amounts of reactivity in a short period of time. The spray fires result from a HCDA which causes head failure due to high-velocity impact by the sodium pool followed by rotating plug jump, loss of rotating plug seals, control rod ejection, failure of instrument tubes, or breach of in-vessel transfer machine ports. Head failure can in principle lead to the injection of significant amounts of sodium into the reactor containment building by residual pressure of the HCDA gas bubble, which forces the upper plenum sodium through the interstitial spaces (e.g., rotating plug gaps, control rod housings, etc.) in the breached head structure.Calculations were made of the hydraulic behavior of the sodium under various injection scenarios for both pool and loop reactor systems. In the case of plug jump, although massive amounts of sodium can be injected into the containment building, the injection will be primarily in a radial direction, and the major consequences could be a low-intensity pool fire rather than a high-intensity sodium spray fire. However, if the bearing housing on the rotating plug fails, a 20 atm initial HCDA residual bubble pressure has the potential for injecting a sodium stream through the rotating plug gaps which could potentially impact the containment building ceiling. Sodium discharges through broken control rod housings could also impact the ceiling and become widely dispersed.The SOMIX-1 sodium spray fire code was used to calculate the energy releases corresponding to a variety of head failure scenarios corresponding to the cases where a high velocity jet impinges on the ceiling of the containment building. The calculated maximum pressure rise was about 2.1 atm. The analysis showed that containment building pressures do not always increase with increasing sodium injection rates since the oxygen concentration can be reduced to a level where the spray begins to cool rather than heat the gas. |
