The following presentation was created by me (Paul Callaghan) in order to demonstrate learning on the Physics and Technology of Nuclear Reactors Course I attended from Autumn 2007 to Spring 2008 at The University of Birmingham.
- 1. Physics and Technology of Nuclear Reactors Paul Callaghan Consultant Engineer
2. A bit about me
- (2008 Present)Consultant Engineer Atkins (Glasgow/Epsom/Bristol)
- (2006-2008)Stress Engineer Rolls-Royce Submarines (Derby)
- (2005-2006)Planning/Manufacturing Engineer Rolls-Royce Submarines (Derby)
- (2004)Undergraduate Engineer Rolls-Royce AR&O (East Kilbride)
- (2003)Undergraduate Engineer Rolls-Royce AR&O (East Kilbride)
- (2002)Undergraduate Engineer Rolls-Royce AR&O (East Kilbride)
- (2000 2004) B.Eng (Hons) Aeronautical Engineering (University of Glasgow)
- The following presentation was created by me (Paul Callaghan) in order to demonstrate learning on the Physics and Technology of Nuclear Reactors Course I attended from Autumn 2007 to Spring 2008 at The University of Birmingham.
- I delivered this presentation to a selection of my peers to satisfy the requirements of Further Learning (Engineering and Science Deepening) for the IMechE.
- The presentation was created in order to demonstrate my understanding of nuclear physics and the physics which underpins the operation of Nuclear Reactors.
- Interactions of neutrons with matter
- U 235Absorption Cross Section vs Energy
- Importance of Xenon transients
Learning Outcomes: 6. Interactions of Neutrons with matter (1)
- The energy released from a nuclear reaction is much higher than from a chemical reaction e.g. burning coal, oil or gas
- Burning coal releases 4 eV per reaction whereas a (nuclear) fission reaction produces 200 million eV (MeV).
Prompt Energies Daughter nuclei of fission fragments ~169 MeV K.E of (2.5) neutrons ~5 MeV Gamma ray photons ~7 MeV Delayed Energies Beta (from decay) ~6.5 MeV Anti-neutrinos ~8.8 MeV Delayed Gamma Emission ~6.3 MeV 7. Interactions of neutrons with matter (2)
- Nuclear reactionsinvolve collisions of a nucleus with a particle
- Neutrons are ideal for use as incident particle as they areelectrically neutral
- According to theCompound Nucleusmodel - a nuclear reaction occurs in 2 stages:
- Incident particle absorbed by target nucleus creating a compound nucleus
- Compound nucleus disintegrates expelling a particle (or photon) leaving a recoil nucleus.
- Radiative Captureis the process whereby a particle is captured and the excess energy is emitted as radiation
8. Cross-sections (1)
- Definition:A measure of the probability of occurrence of a particular nuclear reaction under prescribed conditions i.e. the probability of collision
- Applies to a particular process on a single nucleus
- Macroscopi c Cross-Section-
- Is volumetric and is for a collection of nuclei
- Where N = Number of nuclei per cm 2
- Nuclear cross-sections commonly of the order 10 -22to 10 -26cm 2per nucleus
- Unit of measurement is the barn
- 1 barn = 10 -24cm 2per nucleus
- Different types of macroscopic cross-section for different nuclear processes
- Absorption Cross-Section( a ) - neutrons lost to the system
- Fission Cross-Section( f ) behaviour of incident particle leads to generation of new particles
- Scatter Cross-Section( s) transfer of energy from one particle to another
9. Cross-Sections (2) Typical Reactor Material Values Source: The Elements of Nuclear Reactor Theory 2 ndEdition- Glasstone and Edlund Element Total - t (barns) Absorption - a (barns) Scatter - s (barns) H 20-80 0.32 20-80 D 2 0 15.3 0.00092 15.3 B 722 718 3.8 Zr 8.4 0.4 8.0 10. Fast and Slow Neutrons
- Fast Neutron -a free neutron with a kinetic energy level of about 1 MeV (100 TJ/kg), hence a speed of 14,000 km/s.
- Slow Neutron - a free neutron with a kinetic energy of about 0.03 eV (2.4 MJ/kg) (1/40) hence a speed of 2.2 km/s
- Slow neutrons are often referred to asThermal Neutrons astheir energy corresponds to the most probable velocity at a temperature of 290 K/17C (Room Temperature)
- Thermal neutronshave a different and often much larger effective neutron absorption cross-section for a given nuclide than fast neutrons, and can therefore often be absorbed more easily by an atomic nucleus
11. Resonance Effects (1)
- Experimental studies have shown that bombarding different target elements with projectiles of specific energy values causes a sharp increase in reaction rate.
- For certain energy values the probability that the incident particle will be captured and a compound nucleus formed is exceptionally large.
- This phenomenon is attributed toresonance.
12. Absorption Cross-Section vs Neutron Energy for U 235(1) 13. Scattering (1)
- Definition:The process in which the overall result is transfer of energy from one particle to another
- ElasticScatter Kinetic energy and momentum conserved
- InelasticScatter Kinetic energy not conserved, momentum conserved.
- Fast neutrons may be deprived of their kinetic energy and slowed down to become slow neutrons with an energy of ~0.03eV at room temperature.
- The slowing down is performed by inelastic scatter in a process known as moderation
14. Scattering (2)
- The medium used in this process is the moderator
- Typically involves atoms of low mass number e.g. H 2 0 or D 2 0
- Efficient moderators reduce the speed of fast neutrons in as few collisions as possible
- After a number of scattering collisions, the kinetic energy of the neutrons is reduced such that it is similar to the moderator medium.
- The new energy depends on the temperature of the medium and is thethermal energy .
- Neutrons of this energy arethermal neutrons .
- The process is thermalisation .
15. Importance of Xenon Transients (1)
- Xenon-135 is a fission product poison produced during fission of U 235and U 238
- Xenon-135 is formed from successive beta decays of its fission product precursors
- 51 Sb 13552 Te 13553 I 13554 Xe 13555 Cs 13556 Ba 135
- 135 Xe is of particular concern in a reactor as it has a half-life of 9.1 hrs compared with a 6.6 hr half-life of its precursor53 I 135
- Thus53 I 135decays quicker to54 Xe 135than54 Xe 135can decay
- Leads to increased concentration of54 Xe 135
16. Importance of Xenon Transients (2)
- On restart after a shutdown, the Xenon transient becomes important as the reactivity must be greater than the absorbing effect of the Xenon to establish criticality.
- Increases to reactivity are achieved by withdrawing the control rods
- If the absorbing effect of Xenon concentration in core is greater than the reactivity that can be achieved by withdrawing the control rods criticality cannot be achieved!
- Number of neutrons per fission
- Prompt and delayed neutrons
- Delayed neutrons from fission products
- Importance of reactor poisons
Learning Outcomes: 18. Binding Energy Curve 19. Number of Neutrons per fission
- U 235undergoes fission with thermal neutrons as well as those of higher energies.
- It has been observed that fission of U 235with slow neutrons produces 2.5 0.1 neutrons per fission
- Not an integer as U nucleus splits in a number of different ways
- Mean may not be whole number
20. Prompt and Delayed Neutrons (1)
- Two categories of neutron emitted from fission:promptanddelayed .
- account for 99% of total fission neutrons
- energies cover considerable range c.f Watt Spectrum
- Delayedneutrons are emitted by one of the fission products anytime from a few milliseconds to a few minutes later
21. Prompt and Delayed Neutrons (2)
- Delayed neutrons make it possible to run a r