PHWR DISASSEMBLED CHANNEL - AN INVESTIGATIVE STUDY

Abstract

For the growth and development of an economy energy plays a very vital role. We can divide the energy sources into main categories: renewable and non-renewable sources of energy. As the production of energy from renewable sources are yet not completely developed and are still in developing phase; Non- renewable sources of energy is the main source to run au economy effectively with respect to the energy needs. Nuclear energy is one of such a source of energy in which heat is produced by the controlled nuclear fission reaction. As the working of nuclear reactor is always associated with the high temperature heat transfer from core to the steam boiler through a coolant channel, it becomes necessary to account for the convection heat transfer along with the radiation effect for its proper analysis. In India 220 MW (e) and 540MW (e) pressurized heavy waler reactor (PHWR) are in use. In addition to this 700MW (e) nuclear reactor has been designed and is in construction phase. Nuclear power plants are always designed to work for long service runs. The probability of the accidents in nuclear reactor is very low but in case of long running plants accidents are supposed to occur. The nuclear emission caused by these accidents produces severe affects to environment and hence can never be ignored. These are very low frequency (<10-6 per year) accidents. But as severe consideration of these accidents is an essential component in the nuclear safety analysis. From the reactor safety point of view it important to study the nature and magnitude of the deformation. One of the case of design based accident is Loss of Coolant Accident (LOCA). During LOCA, the decay heat is generated which is removed by using emergency core cooling system (ECCS). Even with complete failure of ECCS, the surrounding moderator i.e. heavy water (D20) would act as heat sink. Accumulation of the heat would take place if the heat removed is not proper and temperature of fuel pin bundles start rising significantly. At high temperature a metal-water reaction takes place in between zirconium cladding and coolant fuel would be exposed due to the perforations in the cladding and which could lead to catastrophic failure of fuel channel integrity. In India the Department of Atomic Energy (DAE) is the nodal energy agency, which is actively involved in nuclear power generation and its safety issues. The leading technical 10 universities in India are also collaboratively supporting to design and development of nuclear projects and the issues related to the safety from nuclear power projects run accidents. A Page I iv numerical simulation has been carried out on one of design based accident in the department of Mechanical and Industrial Engineering. lIT Roorkeeto understand the behavior of IPHWR channel during LOCA i.e. Loss OF Coolant Accident. The CFI) simulation was carried out under steady state condition to investigate the heat transfer and fluid flow characteristics for two different cases: r When there is heat tip condition due to LOCA for horizontal 19 pin IPl-IWR channel. When there is heat up condition due to LOCA for inclined 19 pin IPHWR channel. The second case where the channel has been inclined is supposed to be happened by virtue of failure under high heat up condition which is an after effect of LOCA. In our case we have taken the breakdown at inlet section of the PHWR channel due to which the whole channel has been inclined and the angle of inclination depends upon the channel length and the gap between the two consecutive horizontal channels. As according to these dimensions we have chosen very close values for channel inclination and that are 5°, 10° and 150. - In this present thesis, the detailed investigation has been carried out on the commercially available software ANSYS Fluent 16.2. The simulation results obtained showed that - • When the angle of inclination increases for fixed value of decay heat the temperature, velocity and H2 mole fraction decreases continuously. • When the decay heat increases for fixed value on inclination, the temperature, velocity and H2 mole fraction increases continuously.