Basic reactor theory lesson 1&2 PHYSICS/SCIENCE LATEST EDITION 2024/25 GUARANTEED GRADE A+

Basic reactor theory lesson 1&2 PHYSICS/SCIENCE LATEST EDITION 2024/25 GUARANTEED GRADE A+ Binding energy The energy equivalent of the mass defect; the amount of energy released when a nucleus is formed from its component parts, also the amount of energy that must be supplied to a nucleus to separate it into its components Bohr model A model of the atom proposed by Nobel Laureate Niels Bohr in 1913 that describes the atom as composed of a dense, positively-charged nucleus with electrons orbiting around it in fixed orbits of discrete radii with associated discrete energy states for the atom Boiling water reactor (BWR) A nuclear reactor in which water is allowed to boil directly inside the reactor, thus creating steam; the steam is dried and used to drive turbines Breeding reaction A nuclear reaction whereby a fertile isotope undergoes a series of radiative captures (n, g) and b- decays to convert to a fissile isotope Burnable poison Sacrificial neutron absorbers placed within the core at the beginning of the irradiation cycle; these absorbers are necessary to compensate for the excess fuel required such that the reactor can remain critical until the end of the irradiation cycle Condenser A component of a power plant that condenses the steam leaving the turbines, changing the steam to liquid water Control rods A rod made up of a substance that controls the neutron population inside a reactor; control rods are used to control the reactor power and also to provide a mechanism for rapid shutdown of the reactor, if necessary Coolant The medium used to remove heat from the reactor core; the coolant keeps the reactor from overheating Coulombic repulsion Electrostatic force that makes particles with like charge repel each other along a straight line between their centers; the repulsive force decreases with the square of the distance between the two charges Critical State of a reactor when the number of neutrons in each generation (also, reactor power) remains constant over time Cross section A measure of the probability that an interaction of a given kind will take place between a nucleus and an incident neutron Daughter A nucleus formed as the result of radioactive decay Delayed neutron Neutron released by a fission product several seconds after the fission event; delayed neutrons play a very important role in the ability to control the rate of fission and hence, the power generation within nuclear reactors Electron A negatively-charged particle with little mass orbiting the nucleus Electron shells Areas corresponding to energy levels of electrons Electron volt The amount of energy gained by an electron when accelerated through a potential difference of one volt Electrostatic attraction Electrostatic force causing opposite charges to attract Element The type of atom determined by the number of protons Fast fission Fission caused by fast neutrons Fertile isotope A non-fissile isotope such as 238U that becomes fissile when it absorbs one or more neutrons through radiative capture and undergoes radioactive decay Fissile isotope An isotope such as 235U whose binding energy of the last neutron added is sufficient to provide the critical energy for fission; such isotopes can undergo fission even with neutrons of negligibly small kinetic energy such as thermal neutrons Fission A neutron interaction in which a nucleus absorbs a neutron, splits into two new nuclei and releases a large amount of energy; the resulting fission fragments emit neutrons and gamma rays and then undergo radioactive decay Fission fragments Nuclei formed as the result of fission Fission products The resulting fission fragments after colliding with neighboring fuel atoms; they slow down and eventually stop moving Fuel assembly An array of fuel rods generally arranged in a square lattice and held in place by metal straps called grid spacers Fuel rod A stack of fuel pellets contained within a metal cladding Ground state The lowest energy state of a nucleus or an electron Heat exchanger A device used to transfer heat from one medium to another; in nuclear plants, steam generators and condensers are examples of heat exchangers, the former transferring heat from the primary coolant to the secondary coolant of a PWR and the latter transferring the heat from steam to water from a cooling tower or pond Isotopes Atoms with the same number of protons (same element) but different numbers of neutrons Light water reactor (LWR) A nuclear reactor that uses H2O, or "light water," as the moderator and coolant Mass defect The difference between the mass of a nucleus and the sum of the masses of its individual components Mass-energy equivalence E=mc2 - the equivalence relationship for mass (m) and energy (E) derived by Albert Einstein from his Special Theory of Relativity (parameter c is the speed of light in a vacuum); the equation says that mass and energy are interchangeable Moderator The medium used to slow down fast neutrons Neutron A sub-atomic particle with no charge and about the same mass as that of a proton Neutron flux A measure of the intensity of neutron radiation in neutrons/cm2-sec. It is the number of neutrons passing through 1 square centimeter of a given target in 1 second Nuclear force The attractive, short range force among nucleons Nucleon A particle inside a nucleus (a proton or a neutron) Nucleus The center of an atom containing 99.9% of its mass and comprised of neutrons and protons held together in a very small volume by nuclear force Periodic table A chart with information about elements (an interactive version can be accessed online at Pressurized water reactor (PWR) A nuclear reactor system that pressurizes the coolant water to a high enough pressure to prevent boiling in the core; the heated water leaves the core and flows through a steam generator where steam is produced and used to drive turbines Pressurizer A component in the primary system of a PWR that is used to maintain the design pressure of the primary coolant (water) Primary coolant The cooling water that flows through the core of a PWR Proton A positively-charged particle that, along with neutrons, comprises a nucleus Radiation Sub-atomic particles and energy emitted by unstable isotopes to become stable Radiative capture Capture of a particle by a nucleus followed by immediate gamma radiation Radioactive decay Unstable atomic nucleus loses energy by emitting ionizing particles and radiation Radioactivity Unstable nuclei naturally releasing energy by means of radioactive decay Radioisotope A radioactive isotope of an element Reactivity The fractional difference in the value of the multiplication factor, k, from unity, or (k-1)/k. It is a convenient measure of the non-critical state of the reactor Reactivity coefficient The amount that the reactivity will change for a given change in the parameter. Example: coolant temperature Reactor core The part of a nuclear reactor where the heat is generated; it includes the fuel, cladding, fuel assemblies, moderator/coolant and control rods Reactor vessel A large steel pressure vessel that contains the reactor core Scattering A category of neutron interaction in which a neutron and nucleus reappear with different energy levels after colliding with each other Secondary coolant The coolant that flows on the outside (steam side) of steam generators in a PWR; the secondary coolant is converted to steam, which is then directed to the turbines Soluble poison Creates a spatially uniform neutron absorption during the operation of the reactor when dissolved in the water coolant Subcritical State of a reactor when the number of neutrons in each generation (also, reactor power) decreases with time Supercritical State of a reactor when the number of neutrons in each generation (also, reactor power) grows with time Thermal Neutrons Neutrons that are in "thermal" equilibrium (at the same temperature) with their surroundings Turbine A device with rotating blades that are connected to a shaft and turned by having a fluid do work on the blades; in a nuclear power plant, steam turbines are rotated by expanding steam Void The volume fraction of steam in a boiling system (in reality, no true "void" exists, as the steam space is occupied by a low density gas) Fission A neutron interaction in which a nucleus absorbs a neutron, splits into two new nuclei and releases a large amount of energy; the resulting fission fragments emit neutrons and gamma rays and then undergo radioactive decay. NSSS Nuclear Steam Supply System Typical diameter of pellet 0.4 in Typical length of pellet 0.5 in Why do pellets have small diameters? So that heat can be removed effectively What is one pellet of uranium equivalent to? 149 gallons of oil or 1.3 tons of coal How many feet of pellets are in a fuel cladding tube? CONTINUED...