Lecture 14,15 types of reactor

POWER PLANT ENGINEERING

1. Types of Reactor Prof. Swapnil Gadgune

2. TYPES OF REACTORS Nuclear Reactors are of two types- Heterogeneous - It has a large number of fuel rods with the coolant circulating around them and carrying away the heat released by nuclear fission . Homogeneous - the fuel and moderator are mixed , e.g. a fissionable salt of uranium like uranium sulphate (or nitrate) dissolved in the moderator like H2O or D2O. The solution is critical in the core. Due to difficulties in component maintenance, induced radioactivity, erosion and corrosion, homogeneous reactors are not common .

3. Reactor C lassification Present day nuclear reactors are of the heterogeneous class. These reactors are again classified according to the type of fuel used, the neutron flux spectrum, the coolant, and the moderator, if used. Neutron flux spectrum Moderator Coolant Fuel material Thermal Light water Light water Enriched uranium Heavy water Heavy water Natural uranium Graphite Gas (CO2) Natural or enriched uranium Fast Nil Liquid metal (Na, K) Plutonium, Thorium

4. Reactor Classification Light water-cooled and moderated reactors (LWR) using slightly enriched uranium fuel are the type most commonly used for power production. Fast reactors which use high energy neutrons for fission and require no moderator utilize a liquid metal as a coolant with either plutonium or a plutonium–uranium mixture for fuel. These reactors are further divided into : Pressurized water reactor ( PWR) Boiling water reactor ( BWR) High temperature gas-cooled reactors (HTGCR ) are used in countries like the UK, France and Germany. Liquid metal fast breeder reactors (LMFBR) are likely to be the source of electrical power for the future. A breeder reactor produces more fissionable isotope then what it consumes.

5. PRESSURIZED WATER REACTOR (PWR) A PWR power plant is composed of two loops in series, the coolant loop, called the primary loop, and the water–steam or working fluid loop. The coolant picks up heat in the reactor and transfers it to the working fluid in the steam generator. The steam is then used in a Rankine type cycle to produce electricity .

6. BOILING WATER REACTOR (BWR) A BWR differs from the PWR in that the steam flowing to the turbine is produced directly in the reactor core. Steam is separated and dried by mechanical devices located in the upper part of the pressure vessel assembly. The dried steam is sent directly to the high pressure turbine thus eliminating the need for steam generators. The coolant thus serves the triple function of coolant, moderator and working fluid .

7. GAS-COOLED REACTORS The first gas-cooled reactors with CO2 gas (at a pressure of 16 bar) as coolant and graphite as moderator were developed in Britain during 1956–69. The fuel was a natural uranium, clad with an alloy of magnesium called Magnox . A dvanced G as-cooled R eactor (AGR) system- uses UO2 as the fuel clad in stainless steel tubes with CO2 gas as coolant and graphite as moderator . helium-cooled, graphite-moderated systems ( HTGR- high-temperature gas-cooled reactor )- designed to use U-233 as the fissile material and thorium as fertile material

8. LIQUID METAL FAST BREEDER REACTOR Fast breeder reactors are designed to create or breed new fissile material, while producing useful electric power. Most produce fissile plutonium from fertile uranium 238. The high concentration of fissile fuel and the absence of moderator makes the core of a fast reactor smaller than a thermal reactor of the same power . Sodium is the most common coolant for fast reactors . Because of induced radioactivity of liquid sodium, an inter mediate loop using Na or NaK as coolant is used between the primary radioactive coolant and the steam cycle.

9. HEAVY WATER REACTORS The very low neutron capture cross section of heavy water makes it an excellent moderator and coolant. CANDU-PHW (Canadian Deuterium Uranium Pressurized Heavy Water ) The moderator is contained in a cylindrical steel vessel, called the calandria , with a large number of zircaloy tubes through it parallel to its axis, which is horizontal. The heavy water coolant pressure in the reactor is 88.3 bar, and the inlet and outlet temperatures are 250 °C and 290 °C, respectively. In heat exchangers, steam is generated at 41 bar, 251 °C .

10. INDIA’S NUCLEAR POWER PROGRAMME http:// www.barc.gov.in/about/anushakti.html https://www.world-nuclear.org/information-library/country-profiles/countries-g-n/india.aspx Photo Credit: civilsdaily.com/ indias -nuclear-energy-program /

11. References P K Nag, "POWER PLANT ENGINEERING", Fourth Edition (Book), McGraw Hill Education (India) Private Limited, NEW DELHI

12. Thank You