The Evaluation Of Rcs Depressurization To Prevent Core Melting In Pressure Tube Reactors (candu-type)

摘要

Pressure tube reactors, especially of the CANDU-type, have a low-pressure vessel calandria - under an internal pressure near atmospheric. The calandria vessel is immersed into the water contained inside a concrete structure - the calandria vault. In the case of accidents with the loss of normal core heat sinks, the moderator inside the calandria (heavy water) could become the ultimate heat sink. Accident analysis using a newly developed model (ASQR) strengthens the importance of the inside cooling of the fuel channels in order to prevent severe accidents. Even if implementing those methods related to moderator for eliminating the impairment of the outside cooling of fuel channels, these are not sufficient. The new model has been compared against the well-known in-reactor LOCA experiment - PBF - NRU.rnThus, the paper makes a review of author's article [Mehedinteanu, S., 2001. An application of the new way to prevent core melting in pressure tube reactors (CANDU-type). Annals of Nuclear Energy 28, 79-88] and describes a new method to prevent the core melting in the pressure tube reactors. The method concerns the use of a safety depressurization of the pressurizer (PDS) by means of a new safety valve block located on the line to the degasser-condenser (DC) and subsequent "re-pumping" of the water as collected in the DC, by the pressure difference intrinsically created, back to RCS through new lines connected with the emergency core cooling system (ECCS) lines. The result of the calculation shows a full prevention of the core melting in the pressure tube reactor (CANDU-type) and this conclusion could also be extended to LWR.