Submission Title
Demonstration of Corium Retention in Calandria of PHWRs in Severe Accident
Presentation Type
Invited
Start Date
16-12-2018 11:00 AM
Abstract
In Pressurized Heavy Water Reactors (PHWRs), multiple failures of engineered safety features may cause failure of core cooling eventually leading to core collapse. The failed channels relocate to the bottom of the calandria vessel and form a terminal debris bed which generates decay heat. With time, the moderator evaporates and terminal debris bed ultimately melts down and forms a molten pool of corium. If corium breaches the calandria vessel and enters the calandria vault, large amount of hydrogen and other fission gases may be generated due to molten core concrete interaction (MCCI), which may pressurise the containment leading to containment failure. In addition, the passive catalytic recombiner devices (PCRDs) may be incapable to manage such large amount of hydrogen. Hence, in- vessel retention of corium is the only option to avert progression of accident.
The heat removal capability of calandria vessel to contain the corium during severe accidents needs to be demonstrated experimentally in order to attain the goal of in-vessel retention. In this work, several experiments have been conducted for demonstration of retention of molten corium in simulated canadria vessel with vault water cooling with different corium simulants from 10 kg to 500 kg, and from temperatures ranging from 1200 deg. C to more than 2500 deg. C with decay heat simulation. These experiments showed that the maximum vessel temperatures was well below the safety limits with external cooling. Even the melt was retained without leaking through the drain pipes. The imposed heat flux and thermal strains in the stepped welded calandria vessel was lower than the measured CHF limits and creep values.
Recommended Citation
Nayak, A. K. (2018). "Demonstration of Corium Retention in Calandria of PHWRs in Severe Accident," Symposium on Advanced Sensors and Modeling Techniques for Nuclear Reactor Safety.
Demonstration of Corium Retention in Calandria of PHWRs in Severe Accident
In Pressurized Heavy Water Reactors (PHWRs), multiple failures of engineered safety features may cause failure of core cooling eventually leading to core collapse. The failed channels relocate to the bottom of the calandria vessel and form a terminal debris bed which generates decay heat. With time, the moderator evaporates and terminal debris bed ultimately melts down and forms a molten pool of corium. If corium breaches the calandria vessel and enters the calandria vault, large amount of hydrogen and other fission gases may be generated due to molten core concrete interaction (MCCI), which may pressurise the containment leading to containment failure. In addition, the passive catalytic recombiner devices (PCRDs) may be incapable to manage such large amount of hydrogen. Hence, in- vessel retention of corium is the only option to avert progression of accident.
The heat removal capability of calandria vessel to contain the corium during severe accidents needs to be demonstrated experimentally in order to attain the goal of in-vessel retention. In this work, several experiments have been conducted for demonstration of retention of molten corium in simulated canadria vessel with vault water cooling with different corium simulants from 10 kg to 500 kg, and from temperatures ranging from 1200 deg. C to more than 2500 deg. C with decay heat simulation. These experiments showed that the maximum vessel temperatures was well below the safety limits with external cooling. Even the melt was retained without leaking through the drain pipes. The imposed heat flux and thermal strains in the stepped welded calandria vessel was lower than the measured CHF limits and creep values.
