Options for management of containment integrity during severe accident in Indian PHWR

Severe accident progressions have the potential to raise the containment pressure beyond the design pressure of the structure. Although the load withstanding capability of the containment structure has been assessed to be substantially higher than the design pressure of the structure (typically 2 times of design pressure), it is possible that a few components of Containment System may degrade leading to excessive release of radioactive fission gases at ground level. Additionally, possible cracks in the concrete of the containment at high pressure may aggravate the release at ground level. Over and above, maintaining high containment pressure high for a longer period increases the ground level release due to leakage from the containment, which effect on dose might be high. For maintaining the Integrity of the Containment, containment pressure can be reduced by either energy management system such as removing the heat from the calandria vault (CVWC) water by using CV water heat exchanger intermittently or reliving the containment atmosphere either through Primary Containment Controlled Discharge (PCCD) or Containment Filtered Venting System (CFVS). Further, it is necessary that these provisions must be initiated below design pressure. This paper presents the analysis for the containment depressurization by using CVWC system restored, manual opening of (PCCD) line and operation of CFVS during the progressions of the accident