Some nuc . reactors

1. Some nuc. reactors

2. Nuclear reaction by Fission • Nuclear fission: All commercial power reactors are based on nuclear fission. • generally use uranium and its product plutonium as nuclear fuel, though a thorium fuel cycle is also possible. • Fission reactors can be divided roughly into two classes, depending on the energy of the neutrons that sustain the fission chain reaction: • Thermal reactors • Fast neutron reactors

3. smoke

7. TYPES of reactors

8. Boiling water R • Boiling Water Reactors (BWR) • Heat water in the core and allow it to boil into steam. • The steam goes directly to the turbine outside the reactor.

9. Rods & Replacement • A modern BWR fuel assembly comprises 74 to 100 fuel rods, • and there are up to approximately 800 assemblies in a reactor core, • holding up to approximately 140 tons of U. Replacement: • The reactor fuel rods are occasionally replaced by removing them from the top of the containment vessel. • Because they are hot both radioactively and thermally, this is done via cranes and under water.

14. Pressurized Water Reactor (PWR) • In a PWR, water is kept under pressure to keep it from boiling, even at 300 C. • The pressurized water is pumped through a closed system of pipes called the primary circuit. • Heat from the primary circuit warms up water in the secondary circuit. • The water in the secondary circuit comes to a boil and its steam turns the turbine. • The water in the primary circuit returns to the reactor core after giving up some of its heat.

20. Pressurized Heavy Water Reactor • A Candu reactor is an example of a PHWR. • Fuel assemblies are placed horizontally in a tank called a calandria. • Heavy water coolant is pumped through tubes containing the fuel assemblies to pick up the heat generated from the nuclear reaction. • The coolant then moves to the steam generators to produce steam from ordinary water and back to the reactor.  Heavy water is virtually identical, except each of the hydrogen atoms have an extra neutron. This hydrogen isotope is called deuterium - D2O

24. Fast Breeder Reactor • FBR has a core of plutonium surrounded by rods of U-238. • The U-238 nuclei absorb neutrons from the core and are transformed into plutonium (P-239). • For every four atoms of plutonium that are used up in the core of the breeder, five new plutonium atoms are made from the U-238. • Therefore, FBRs "breed" plutonium. • Fast breeder reactors work at such a high temperature that they need a special coolant such as liquid sodium. • In addition, they are not equipped with a moderator to slow down neutrons, and for this reason are called "fast" breeders.

26. High temperature gas cooled reactors • HTGR offer an alternative to conventional light-water cooled and moderated reactors. • They use graphite as the moderator and helium as the coolant. • One design concept, called a pebble bed reactor, uses a fuel made of tennis-ball sized spheres known as "pebbles". • Each pebble contains thousands of tiny "kernels" consisting of enriched uranium and graphite compressed together and coated externally with temperature resistant ceramic. • The pebbles are stacked in the reactor and cooled by helium.

28. Nuclear Power Reactors: Typical Characteristics Type Fuel Form Coolant Moderator BWR Enriched Uranium Dioxide Water Water PWR Enriched Uranium Dioxide Water Water PHWR Natural Uranium Dioxide Heavy Water Heavy Water GCR Natural Uranium CO2 Graphite AGR Enriched Uranium Dioxide CO2 Graphite LWGR Enriched Uranium Dioxide Water Graphite FBR Plutonium Oxide & Uranium Dioxide Liquid Sodium None • Boiling Water Reactors (BWR) • Pressurized Water Reactor (PWR) • Pressurized Heavy Water Reactor (PHWR) • Gas-Cooled Reactors (GCR) • Advanced Gas-Cooled Reactors (AGR) • Light Water Graphite Reactor (LWGR) • Fast Breeder Reactor (FBR)

29. Fusion reactor