Full length channel pressure tube sagging study under postulated LOCA with un-availability of ECCS in an Indian PHWR

An experimental investigation consisting of two experiments was conducted to assess the thermal behavior of the Indian-made full length Pressure Tube (PT) of an Indian PHWR. Loss of Coolant Accident (LOCA) with Emergency Core Cooling System (ECCS) failure postulated scenario was simulated by resistance heating the pressure tube to generate heat equal to the decay heat of nuclear fuel under such scenario after shutdown. On heating, the pressure tube deformed by sagging and eventually contacted the Calandria Tube (CT). After first contact, the temperature rise was arrested near the contact region but locations far away from the first contact continued to get heated up. The second contact, however, arrested the PT temperature rise completely, hence safeguarding the PT integrity and establishing moderator as an effective heat sink. The initiation of sagging occurred at around 460 °C. The PT-CT contact took place at a contact temperature of 665-669 °C at the bottom of the PT.