Chapter 16 1

All matter is made up of atoms. Parts of an atom: 1. Nucleus – the center of an atom. Proton – Positively charged. ( + ) Neutron – have no charge ; considered neutral. 2. Electrons – found outside the nucleus. Negatively charged ( - ) 2 Section 16.1 – Atoms and Radioactivity

Atoms Atomic number – the number of protons in an atom. # of protons always equals # of electrons Mass number – also known as atomic mass. The number of protons plus the number of neutrons. 3 Section 16.1 – Atoms and Radioactivity

Isotopes Atoms of the same element that have different numbers of neutrons. For example: All atoms of oxygen have 8 protons, most atoms of oxygen have 8 neutrons and a mass number of 16. However, some oxygen atoms may have 9 or 10 neutrons. 4 Section 16.1 – Atoms and Radioactivity

Radioactivity Radioactive atoms – are unstable isotopes that decay while emitting particles and energy from their nuclei. After a series of decay changes, a radioactive element becomes stable and stops decaying. ONLY some isotopes are radioactive. 5 Section 16.1 – Atoms and Radioactivity

Radioactivity 2 kinds of particles are given off by the nuclei of radioactive atoms 1. Alpha particles Made up of 2 protons and 2 neutrons 2. Beta particles A high speed electron Beta decay converts a neutron into a proton 6 Section 16.1 – Atoms and Radioactivity

Radioactivity Radioactive elements can also give off energy in the form of gamma rays. Gamma rays are a form of electromagnetic radiation. Alpha and Beta particles, and Gamma rays given off in the decaying of unstable nuclei are called radiation. Half- life is the amount of time it takes for half of the atoms in a sample of a radioactive element to decay. Radioactive decay is the process in which an atom loses an alpha particle and changes to a different element. Half-lives for various radioactive elements range from a few seconds to billions of years. 7 Section 16.1 – Atoms and Radioactivity

Energy is required to hold an atom’s nucleus together. One way to release the energy is to split the nucleus of the atom. Nuclear fission – a reaction in which the nucleus of a large atom is split into smaller nuclei. When an atom is broken apart through nuclear fission, it emits large amounts of energy. This energy can be used to generate electricity. 8 Section 16.2 – Reactions and Reactors

Nuclear Fission An atom splits when its nucleus is struck by a neutron is called fissionable. Energy is released and new nuclei are formed; called daughter nuclei. 9 Section 16.2 – Reactions and Reactors

Section 16.2 – Reactions and Reactors

1. A neutron is fired into the nucleus of an atom. 2. The neutron strikes the nucleus, which splits, forming 2 daughter nuclei. 3. The reaction also releases energy and several more neutrons. 4. These other neutrons can strike other nuclei causing those nuclei to split and release more energy and more neutrons. 5. This continuous action of neutrons splitting atomic nuclei is called a chain reaction. Steps in nuclear fission:

Nuclear fusion – a reaction in which energy is released as the result of 2 nuclei join to form one. The problem is that there are too many technical difficulties to solve before the use of it becomes practical. The suns energy comes from nuclear fusion. 12 Nuclear Fusion

Nuclear Reactors Heat is produced through the fission of nuclear material instead of burning fossil fuels. Nuclear fuel is usually about 97% U-238 and 3% U U-238 is not fissionable. Video 13 Section 16.2 – Reactions and Reactors

In a typical American reactor the fission of U-235 takes place inside a nuclear reactor vessel. The reactor is housed inside a thick concrete containment building. The fuel for the reactor consists of long rods filled with pellets that contain fissionable U-235. The fuel rods are positioned vertically in the center of the reactor so that water can circulate between them. Water acts as a coolant, which absorbs the heat and keeps the core from melting, and it also slows the movement of the neutrons released during the chain reaction. 14 Parts of a Reactor

The speed of the chain reaction is regulated by control rods, which absorb neutrons. Control rods are typically made of cadmium which help absorb neutrons. Raising or lowering the control rods also regulates the amount of heat/energy output produced. The temperature of the coolant water can reach temps. above 275°C This hot water moves inside pipes to a heat exchanger, where it heats water for steam. The steam is then used to turn turbines connected to electric generators. 15 Parts of a Reactor

16 Boiling Water Reactor

Over 99% of the naturally occurring Uranium is the non- fissionable isotope, U-238 However, U-238 can absorb a neutron giving rise to a fissionable atom of plutonium-239 (Pu-239) A breeder reactor uses this process to produce new fuel while it generates usable energy. Fuel is not a problem in breeder reactors because plutonium is generated. Breeder reactors are not used in the U.S. because of the concerns about nuclear terrorism The plutonium produced by breeder reactors can be used to make atomic bombs as well as energy Breeder reactors produce more fuel than they consume. 17 Section 16.2 – Reactions and Reactors

Large doses of radiation can cause severe, immediate effects, including skin burns and anemia, even death. Radiation also causes changes in DNA, leading to long-term effects such as cancer and genetic mutations. High-level wastes – emit large amounts of radiation. Such as fuel rods, control rods, vessel Low-level wastes – not as radioactive. Radioactive waste produced by hospitals and labs. Greater hazard because they are so abundant 18 Section 16.3 – Radioactive Waste

Safety Meltdown – the process by which a nuclear chain reaction goes out of control and melts the reactor core. A full meltdown would release huge amounts of radiation into the environment. March 1979 – three mile island (Harrisburg) a partial meltdown of the core. April 1986 – Chernobyl (Ukraine) a full meltdown Nuclear Meltdown 19 Section 16.3 – Radioactive Waste