Download Nuclear Engineering Exam 2: Understanding Nuclear Reactions and Neutron Interactions and more Exams Nuclear Engineering in PDF only on Docsity!
Nuclear Engineering Exam 2 What is the difference between spontaneous disintegrations of nuclei and the neutron-nucleus collision events? -Spontaneous disintegrations of nuclei depend only on the properties of an individual nucleus -Neutron-nucleus collision events depend on the properties of the colliding particles and the relative velocity with which they strike one another. units: barns macroscopic or microscopic cross-section or m.f.p? microscopic cross section characterizes the probability of an interaction with only single nucleus macroscopic or microscopic cross-section or m.f.p? microscopic cross section units: 1/cm macroscopic or microscopic cross-section or m.f.p? macroscopic cross section the probability of a n interaction in a chunk of material macroscopic or microscopic cross-section or m.f.p? macroscopic cross-section units: [cm] macroscopic or microscopic cross-section or m.f.p? mean free pass the average distance a neutron goes without interaction macroscopic or microscopic cross-section or m.f.p? mean free path
In general, interaction rate does not depend on a. microscopic neutron cross section b. size of nucleus c. kinetic energy of neutrons d. isotopic composition of medium in which neutrons are traveling e. population densities of nuclei and of neutrons b neutron interaction rate increases as the population density of atoms decreases true or false? false microscopic neutron cross-sections increase at resonance energies true or false? true neutron absorption cross-section of thermal neutrons increases linearly with neutron speed true or false? false neutron cross section always increases with radius of the interacting nucleus true or false? false Total microscopic cross section is sigma_t = 32b. Scattering microscopic cross section is sigma_s = 5b. What is the absorption neutron rate (in %)?
What nuclides most probably will undergo alpha decay?
0.511 MeV What fraction of a certain number of radioactive atoms will have decayed after 3 half-lives? a. 1/ b. 5/ c. 7/ d. 1/ c The decay constants of 2 different isotopes are 0.01 [1/h] for Isotope I and 0.01 [1/d] for Isotope II. Which one will decay faster? a. Isotope I b. both will decay at the same time c. Isotope II a The electron that is emitted in b- (minus) decay is one of the orbital electrons around the nucleus of the parent atom. true of false false All alpha particles emitted in the radioactive decay of a particular radioisotope have the same energy true or false true all beta particles emitted in the radioactive decay of a particular radioisotope have the same energy true of false false
daughter isotopes of alpha and beta decays often de-excite by emitting gamma rays true or false true half-lives for alpha decay are typically short, of the order of a few minutes true or false true Electron-positron annihilation results in the generation of two gamma rays of 0.511 MeV each true or false true alpha particles being heavy, positively charged ions of energy around 4-6 MeV a. do all the listed b. lose their energy mostly by ionization c. do none of the listed d. travel in straight lines e. typically will penetrate only of the order of a few micrometers in solid media a match radiation with a type of ionizing -charged particles -neutral particles directly or indirectly ioninzing? -charged: directly -neutral: indirectly check what is true for transmutation a. can occur through nuclear reactions (in which an outside particle reacts with a nucleus b. can occur only through photoelectric absorption
false the higher the value of the linear attenuation coefficient, the smaller the average depth of penetration of gamma rays true or false? true how do ionization chambers detect radiation? a. radiation entering the chamber causes ionization in a gas. the ions emit light like in a neon tube, and the light intensity is measured b. b-particles attach themselves to atoms inside the ion chamber producing negative iones, and these ions are collected by an electrode held at a positive potential c. radiation ionizes atoms of a gas. the ions and electrons are collected using electrodes held at a high potential, and the resulting current is measured c Check all the cases when we need to take into account the nuclei motion. a. one can no longer treat the nuclei as stationary b. when considering processes in which the cross sections exhibit sharp resonances c. if the neutron speeds are comparable to the nuclear speeds d. when considering processes are far from the regions in which cross sections exhibit sharp resonances e. if the neutron speeds are much smaller than the nuclear speeds a, b, c Check all that is true for the Doppler effect a. as the temperature T increases, the increase broadens b. as the temperature T increases the absorbing material will decrease the rate at which neutrons are absorbed c. as the temperature T increases the resonance peak magnitude increases d. as the temperature T increases, the absorbing material will increase at the rate at which neutrons are absorbed
e. as the temperature T increases the resonance peak magnitude decreases a, d, e explain the effect of neutron up-scattering a. neutron scatters to 90 degrees b. neutron scatter 180 degrees c. neutron scatters to 0 degrees d. neutron gains energy in a scattering collision e. neutron loses energy with scattering d Name neutron classification by energy (several answers possible, check all that are related to the question) a. delayed b. fast c. slow (thermal) d. intermediate e. prompt b, c, d Check all that apply to prompt neutrons a. constitute over 99% of fission neutrons b. emitted at the time of fission c. constitute only less that 1% of all fission neutrons a, b What is spent fuel? a. fuel assemblies that are loaded to the reactor at the reactor start up b. fuel assemblies at beginning of fuel cycle c. fuel assemblies that are discharged from the reactors during refueling
k-effective < 1 critical supercritical subcritical check all that apply to delayed neutrons a. emitted at the time of fission b. constitute only less than 1% of all fission neutrons c. constitute over 99% of fission neutrons b What is the difference between k-effective and k-infinite? options: -takes into account geometry of the reactor core -characterizes the multiplication properties of material in the reactor -characterizes both multiplication properties of the material in the reactor and geometry of the reactor core -k-effective: takes into account the geometry of the reactor core -k-infinite: characterizes the multiplication properties of material in the reactor Why the Doppler feedback is strongly negative in the thermal reactor systems? a. because their effective fissile content (U-235) is low b. because coolant is water c. because their effective fissile content (U-238) is low a Name the PWR auxiliary system that is used for adding soluble boron to the reactor coolant system in the form of boric acid a. low-pressure turbine b. refueling system c. high-pressure turbing
d. chemical volume control system (CVCS) or chemical shim d compare k-infinite and k-effective k-infinite > k-effective why do we have burnable and soluble poisons? Check all that are true a. they gradually burn out as the U burns out b. to make reactivity swing larger over the cycle c. to lower the initial reactivity d. we keep adding them during the reactor operation to make sure that concentration of burnable poison stays the same a, c match reactivity effects with description (positive and negative reactivity feedback) options: -decreases the condition that produced it -enhances the condition that produced it -positive reactivity feedback: enhances the condition that produced it -negative reactivity feedback: decreases the condition that produced it Why soluble poison can be added and dissolved in the coolant in the form of boric acid only into the coolant of PWR, but not in BWR? Check all that is true a. it is impossible to add soluble poison to BWR coolant by design b. boiling can result in boron plating out on the fuel rods c. plating can effect hear transfer as well as reactivity d. soluble poisons lose property at higher temperature and won't work with boiling water b, c increases reactivity leads to a greater rate of power increase. increased power raises core temperatures. higher temperatures increase reactivity.
What is max possible angle for neutron scattered from hydrogen a. 90 degrees b. 180 degrees c. 45 degrees d. 0 degrees a for an inelastic scattering the incident neutron kinetic energy must exceed a certain threshold energy. true or false? true kinetic energy is conserved for an inelastic scattering true or false? false in elastic scattering, the kinetic energy of the scattered neutron is _________________ (smaller/larger) than the energy of the incident neutron by an amount equal to the energy acquired by the recoiling nucleus. smaller the disintegration process of a compound nucleus is dependent on the original mode of formation true or false? false the good moderator has low alfa (the collision parameter) true or false? true calculate the average energy loss for a neutron in elastic scattering with stationary nucleus with A=28, if the initial neutron energy is E=285 in keV
match lethargy and neutron energy -at high energy, a neutron's lethargy is _______________ -as neutrons slow down and neutron's energy decreases, its lethargy _________________ -low -increases the first energy excited state of an atom is increasing with atomic mass number A true or false? false what is the collision parameter (alfa) for nuclide with A-
Why is the scattering of neutrons by hydrogen unique? because the masses of neutron and hydrogen nucleus (proton) are essentially equal
