Experimental investigation effective of glass-peened Calandria tube surfaces on. critical heat flux during an accident in PHWR

Indian Pressure Heavy Water Reactors generally consists of 300-400 horizontal fuel channels depending on the rating of the plant. It consists of a hot Pressure Tube (PT) and a concentric Calandria tube (CT) with a 9 mm annulus containing CO₂ gas as annulus gas monitoring system. Inside each pressure tube there are 10-12, 0.5 m long fuel bundles, each consisting of 19 or 37 fuel pins with fuel elements containing natural UO₂ pellets and Zircraloy-4 clading. During a postulated loss of coolant accident (LOCA), the coolant supply is lost and designed Emergency Core cooling system (ECCS) will actuate and removes decay heat from fuel. Aim of the present research is to find means of enhancing the heat transfer efficiency between the CT and moderator, such that in the case of any accident, film boiling period is reduced and channel integrity is ensured. One of the ways to enhance heat transfer from CT to moderator is by increasing the critical heat flux (CHF) on the outer surface of the calandria tube. Increasing the CHF for a given subcooling on the outer surface of the calandria tube can be achieved by surface modifications. The ability of the surface modification to increase the CHF on the outside surface of the calandria tube is demonstrated in a series of small scale experiments on a 15.2 mm OD and 0.4 mm thick zircaloy tube. Analysis of the test results indicated that increasing the tube's CHF using a glass-peening or grounded or grit blasted process is a promising option for reducing moderator subcooling requirements