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Norwich Business School Nuclear Power 1 NBSLM03E (2010) Low Carbon Technologies and Solutions: Sections 6 - 8 N.K. Tovey ( ) M.A, PhD, CEng, MICE, CEnv.

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Presentation on theme: "Norwich Business School Nuclear Power 1 NBSLM03E (2010) Low Carbon Technologies and Solutions: Sections 6 - 8 N.K. Tovey ( ) M.A, PhD, CEng, MICE, CEnv."— Presentation transcript:

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2 Norwich Business School Nuclear Power 1 NBSLM03E (2010) Low Carbon Technologies and Solutions: Sections N.K. Tovey ( ) M.A, PhD, CEng, MICE, CEnv

3 Norwich Business School 2 6. Nature of Radioactivity Structure of the Atom Radioactive Emissions Half Life of Elements Fission Fusion Chain Reactions Fertile Materials 7. Fission Reactors 8. The Nuclear Fuel Cycle 9. Fusion Reactors (in notes) Section 6: Nuclear Power:- The Basics 2 NBSLM03E (2010) Low Carbon Technologies and Solutions N.K. Tovey ( ) M.A, PhD, CEng, MICE, CEnv

4 Norwich Business School 3 Structure of Atoms. Matter is composed of atoms which consist primarily of a nucleus of: – positively charged PROTONS – and (electrically neutral) NEUTRONS. The nucleus is surrounded by a cloud of negatively charged ELECTRONS which balance the charge from the PROTONS. PROTONS and NEUTRONS have approximately the same mass ELECTRONS are about times the mass of the PROTON. A NUCLEON refers to either a PROTON or a NEUTRON p 4n Lithium Atom 3 Protons 4 Neutrons Section 6: Nature of Radioactivity (1)

5 Norwich Business School 4 Structure of Atoms. Elements are characterized by the number of PROTONS present – HYDROGEN nucleus has 1 PROTON – HELIUM has 2 PROTONS – OXYGEN has 8 PROTONS – URANIUM has 92 PROTONS. Number of PROTONS is the ATOMIC NUMBER (Z) N denotes the number of NEUTRONS. The number of neutrons present in any element varies. 3 isotopes of hydrogen all with 1 PROTON:- – HYDROGEN itself with NO NEUTRONS – DEUTERIUM (heavy hydrogen) with 1 NEUTRON – TRITIUM with 2 NEUTRONS. only TRITIUM is radioactive. Elements up to Z = 82 (Lead) have at least one isotope which is stable Symbol D Symbol T Section 6: Nature of Radioactivity (2)

6 Norwich Business School 5 Structure of Atoms. URANIUM has two main ISOTOPES 235 U which is present in concentrations of 0.7% in naturally occurring URANIUM 238 U which is 99.3% of naturally occurring URANIUM. Some Nuclear Reactors use Uranium at the naturally occurring concentration of 0.7% Most require some enrichment to around 2.5% - 5% Enrichment is energy intensive if using gas diffusion technology, but relatively efficient with centrifuge technology. Some demonstration reactors use enrichment at around 93%. Section 6: Nature of Radioactivity (3) 5

7 Norwich Business School 6 Structure of Atoms. Protons have strong nuclear forces to overcome the strong repulsive forces from the charges on them. This is the energy released in nuclear reactions Stable elements plot close to blue line. Those isotopes plotting away from line are unstable. For elements above Lead (Z = 82), there are no stable isotopes Section 6: Nature of Radioactivity (4)

8 Norwich Business School 7 Radioactive emissions. FOUR types of radiation:- 1) ALPHA particles ( ) -large particles consisting of 2 PROTONS and 2 NEUTRONS the nucleus of a HELIUM atom. 2) BETA particles (β) which are ELECTRONS 3) GAMMA - RAYS. ( ) – Arise when the kinetic energy of Alpha and Beta particles is lost passing through the electron clouds of atoms. Some energy is used to break chemical bonds while some is converted into GAMMA -RAYS. 4) X - RAYS. – Alpha and Beta particles, and gamma-rays may temporarily dislodge ELECTRONS from their normal orbits. As the electrons jump back they emit X-Rays which are characteristic of the element which has been excited. Section 6: Nature of Radioactivity (5)

9 Norwich Business School 8 - particles are stopped by a thin sheet of paper β – particles are stopped by ~ 3mm aluminium - rays CANNOT be stopped – they can be attenuated to safe limits using thick Lead and/or concrete β Section 6: Nature of Radioactivity (6)

10 Norwich Business School 9 Radioactive emissions. UNSTABLE nuclei emit Alpha or Beta particles If an ALPHA particle is emitted, the new element will have an ATOMIC NUMBER two less than the original. If an ELECTRON is emitted as a result of a NEUTRON transmuting into a PROTON, an isotope of the element ONE HIGHER in the PERIODIC TABLE will result. e Section 6: Nature of Radioactivity (7)

11 Norwich Business School 10 Radioactive emissions. 235 U consisting of 92 PROTONS and 143 NEUTRONS is one of SIX isotopes of URANIUM decays as follows:- URANIUM 235 U alpha THORIUM 231 Th PROTACTINIUM 231 Pa ACTINIUM 227 Ac Thereafter the ACTINIUM decays by further alpha and beta particle emissions to LEAD ( 207 Pb) which is stable. Two other naturally occurring radioactive decay series exist. One beginning with 238 U, and the other with 232 Th. Both also decay to stable (but different) isotopes of LEAD. beta alpha Section 6: Nature of Radioactivity (8)

12 Norwich Business School 11 HALF LIFE. Time taken for half the remaining atoms of an element to undergo their first decay e.g:- 238 U 4.5 billion years 235 U 0.7 billion years 232 Th 14 billion years All of the daughter products in the respective decay series have much shorter half - lives some as short as seconds. When 10 half-lives have expired, – the remaining number of atoms is less than 0.1% of the original. 20 half lives – the remaining number of atoms is less than one millionth of the original Section 6: Nature of Radioactivity (9)

13 Norwich Business School 12 HALF LIFE. From a radiological hazard point of view short half lives - up to say 6 months have intense radiation, but decay quite rapidly. Krypton-87 (half life 1.8 hours)- emitted from some gas cooled reactors - the radioactivity after 1 day is insignificant. For long half lives - the radiation doses are small, and also of little consequence For intermediate half lives - these are the problem - e.g. Strontium -90 – has a half life of about 30 years which means it has a relatively high radiation, and does not decay that quickly. Radiation decreases to 30% over 90 years Section 6: Nature of Radioactivity (10)

14 Norwich Business School 13 This reaction is one of several which might take place. In some cases, 3 daughter products are produced. n n n 140 Cs 93 Rb 235 U Some very heavy UNSTABLE elements exhibit FISSION e.g. 235 U Section 6: Nature of Radioactivity (11): Fission 13

15 Norwich Business School 14 Nucleus breaks down into two or three fragments accompanied by a few free neutrons and the release of very large quantities of energy. Free neutrons are available for further FISSION reactions Fragments from the fission process usually have an atomic mass number (i.e. N+Z) close to that of iron. Elements which undergo FISSION following capture of a neutron such as URANIUM are known as FISSILE. Diagrams of Atomic Mass Number against binding energy per NUCLEON enable amount of energy produced in a fission reaction to be estimated. All Nuclear Power Plants currently exploit FISSION reactions, FISSION of 1 kg of URANIUM produces as much energy as burning 3000 tonnes of coal. Section 6: Nature of Radioactivity (12): Fission

16 Norwich Business School 1524/04/2014 n 4 He 2H2H 3H3H Deuterium Tritium Deuterium – Tritium fusion (3.5 MeV) (14.1 MeV) In each reaction 17.6 MeV is liberated or 2.8 picoJoules (2.8 * J) Fusion of light elements e.g. DEUTERIUM and TRITIUM produces even greater quantities of energy per nucleon are released. Section 6: Nature of Radioactivity (13): Fusion 15

17 Norwich Business School 16 1)The energy released per nucleon in fusion reaction is much greater than the corresponding fission reaction. 2) In fission there is no single fission product but a broad range as indicated Atomic Mass Number Binding Energy per nucleon [MeV] Iron 56 Uranium 235 Range of Fission Products Fusion Energy release per nucleon Fission Energy release per nucleon 1 MeV per nucleon is equivalent to 96.5 TJ per kg Redrawn from 6 th report on Environmental Pollution – Cmnd Section 6: Nature of Radioactivity (14): Binding Energy

18 Norwich Business School 17 Developments at the JET facility in Oxfordshire have achieved the break even point. Next facility (ITER) will be built in Cadarache in France. Commercial deployment of fusion from about 2040 onwards One or two demonstration commercial reactors in 2030s perhaps No radioactive waste from fuel Limited radioactivity in power plant itself 8 litres of tap water sufficient for all energy needs of one individual for whole of life at a consumption rate comparable to that in UK. Sufficient resources for 1 – 10 million years Section 6: Nature of Radioactivity (15): Fusion

19 Norwich Business School 18 n n n 235 U n n n Slow neutron fast neutron Fast Neutrons are unsuitable for sustaining further reactions Section 6: Nature of Radioactivity (16): Chain Reactions

20 Norwich Business School 19 CHAIN REACTIONS FISSION of URANIUM yields free neutrons. If exactly ONE of these triggers a further FISSION, then a chain reaction occurs, and continuous power can be generated. UNLESS DESIGNED CAREFULLY, THE FREE NEUTRONS WILL BE LOST AND THE CHAIN REACTION WILL STOP. IF MORE THAN ONE NEUTRON CREATES A NEW FISSION THE REACTION WOULD BE SUPER-CRITICAL (or in layman's terms a bomb would have been created). Section 6: Nature of Radioactivity (17): Chain Reactions

21 Norwich Business School 20 IT IS VERY DIFFICULT TO SUSTAIN A CHAIN REACTION, Most Neutrons are moving too fast TO CREATE A BOMB, THE URANIUM MUST BE HIGHLY ENRICHED > 93%, Normal Uranium is only 0.7% U235 Material must be LARGER THAN A CRITICAL SIZE and SHAPE OTHERWISE NEUTRONS ARE LOST. Atomic Bombs are made by using conventional explosive to bring two sub-critical masses of FISSILE material together for sufficient time for a SUPER-CRITICAL reaction to take place. NUCLEAR POWER PLANTS CANNOT EXPLODE LIKE AN ATOMIC BOMB. Section 6: Nature of Radioactivity (18): Chain Reactions

22 Norwich Business School 21 FERTILE MATERIALS Some elements like URANIUM are not FISSILE, but can transmute:- n 238 U fast neutron 239 U 238 U Uranium U Uranium n ee 239 Np Neptunium Pu Plutonium beta 239 Np 239 Pu PLUTONIUM is FISSILE and may be used in place of URANIUM Materials which can be converted into FISSILE materials are FERTILE. Section 6: Nature of Radioactivity (19): Fertile Materials

23 Norwich Business School 22 URANIUM is FERTILE as is THORIUM which can be transmuted into URANIUM Naturally occurring URANIUM consists of 99.3% 238 U which is FERTILE and NOT FISSILE, and 0.7% of 235 U which is FISSILE. Normal reactors primarily use the FISSILE properties of 235 U. In natural form, URANIUM CANNOT sustain a chain reaction: free neutrons are travelling fast to successfully cause another FISSION, or are lost to the surrounds. MODERATORS are thus needed to slow down/and or reflect the neutrons in a normal FISSION REACTOR. The Resource Base of 235 U is only decades But using a Breeder Reactor Plutonium can be produced from non-fissile 238 U producing 239 Pu and extending the resource base by a factor of 50+ Section 6: Nature of Radioactivity (20): Fertile Materials

24 Norwich Business School 23 n n n 235 U n n n fast neutron Slow neutron fast neutron n Fast Neutrons are unsuitable for sustaining further reactions Slow neutron n Insert a moderator to slow down neutrons Sustaining a reaction in a Nuclear Power Station Section 6: Nature of Radioactivity (21): Chain Reactions

25 Norwich Business School 24 6.Nuclear Power – The Basics 7.Nuclear Power: Fission reactors a)General Introduction b)MAGNOX Reactors c)AGR Reactors d)CANDU Reactors e)PWRs f)BWRs g)RMBK/ LWGRs h)FBRs i)Generation 3 Reactors j)Generation 3+ Reactors 8.Nuclear Fuel Cycle 9.Fusion Reactors Section 7: Fission Reactors 24 NBSLM03E (2010) Low Carbon Technologies and Solutions N.K. Tovey ( ) M.A, PhD, CEng, MICE, CEnv

26 Norwich Business School 25 FISSION REACTORS CONSIST OF:- i) a FISSILE component in the fuel ii) a MODERATOR iii) a COOLANT to take the heat to its point of use. The fuel elements vary between different Reactors Some reactors use unenriched URANIUM – i.e. the 235 U in fuel elements is at 0.7% of fuel – e.g. MAGNOX and CANDU reactors, ADVANCED GAS COOLED REACTOR (AGR) uses 2.5 – 2.8% enrichment PRESSURISED WATER REACTOR (PWR) and BOILING WATER REACTOR (BWR) use around 3.5 – 4% enrichment. RMBK (Russian Rector of Chernobyl fame) uses ~2% enrichment Some experimental reactors - e.g. High Temperature Reactors (HTR) use highly enriched URANIUM (>90%) i.e. weapons grade. Fission Reactors (1)

27 Norwich Business School 26 PWR fuel assembly: UO 2 pellets loaded into fuel pins of zirconium each ~ 3 m long in bundles of ~200 Magnox fuel rod: Natural Uranium metal bar approx 35mm diameter and 1m long in a fuel cladding made of MagNox. AGR fuel assembly: UO 2 pellets loaded into fuel pins of stainless steel each ~ 1 m long in bundles of 36. Whole assembly in a graphite cylinder Burnable poison Fission Reactors (2): Fuel Elements

28 Norwich Business School 27 No need for the extensive coal handling plant. In the UK, all the nuclear power stations are sited on the coast so there is no need for cooling towers. Land area required is smaller than for coal fired plant. In most reactors there are three fluid circuits:- 1) The reactor coolant circuit 2) The steam cycle 3) The cooling water cycle. ONLY the REACTOR COOLANT will become radioactive The cooling water is passed through the station at a rate of tens of millions of litres of water and hour, and the outlet temperature is raised by around 10 o C. Fission Reactors (3)

29 Norwich Business School 28 REACTOR TYPES – summary 1 MAGNOX - Original British Design named after the magnesium alloy used as fuel cladding. Four reactors of this type were built in France, One in each of Italy, Spain and Japan. 26 units were built in UK. They are only in use now in UK. On December 31 st 2006, Sizewell A, Dungeness A closed after 40 years of operation leaving Oldbury with two reactors is now continuing beyond its original extended 40 year life. Wylfa (also with 2 reactors) will close this year or next. All other units are being decommissioned AGR - ADVANCED GAS COOLED REACTOR - solely British design. 14 units are in use. The original demonstration Windscale AGR is now being decommissioned. The last two stations Heysham II and Torness (both with two reactors), were constructed to time and have operated to expectations. Fission Reactors (4)

30 Norwich Business School 29 REACTOR TYPES - summary SGHWR - STEAM GENERATING HEAVY WATER REACTOR - originally a British Design which is a hybrid between the CANDU and BWR reactors. PWR - Originally an American design of PRESSURIZED WATER REACTOR (also known as a Light Water Reactor LWR). Now most common reactor.- BWR - BOILING WATER REACTOR - a derivative of the PWR in which the coolant is allowed to boil in the reactor itself. Second most common reactor in use. RMBK - LIGHT WATER GRAPHITE MODERATING REACTOR (LWGR)- a design unique to the USSR which figured in the CHERNOBYL incident. 16 units still in operation in Russian and Lithuania with 9 shut down. Fission Reactors (5)

31 Norwich Business School 30 REACTOR TYPES - summary CANDU - A reactor named initially after CANadian DeUterium moderated reactor (hence CANDU), alternatively known as PHWR (pressurized heavy water reactor). 41 currently in use. HTGR - HIGH TEMPERATURE GRAPHITE REACTOR - an experimental reactor. The original HTR in the UK started decommissioning in The new Pebble Bed Modulating Reactor (PBMR) is a development of this and promoted as a 3+ Generation Reactor by South Africa. FBR - FAST BREEDER REACTOR - 'breeds' PLUTONIUM from FERTILE 238U – extends resource base of URANIUM over 50 times. Mostly experimental at moment with FRANCE, W. GERMANY and UK, Russia and JAPAN having experimented with them. Fission Reactors (6)

32 Norwich Business School 31 FUEL TYPE - unenriched URANIUM METAL clad in Magnesium alloy MODERATOR - GRAPHITE COOLANT - CARBON DIOXIDE DIRECT RANKINE CYCLE - no superheat or reheat efficiency ~ 20% to 28%. ADVANTAGES:- LOW POWER DENSITY - 1 MW/m 3. Thus very slow rise in temperature in fault conditions. UNENRICHED FUEL GASEOUS COOLANT ON LOAD REFUELLING MINIMAL CONTAMINATION FROM BURST FUEL CANS VERTICAL CONTROL RODS - fall by gravity in case of emergency. DISADVANTAGES:- CANNOT LOAD FOLLOW – [Xe poisoning] OPERATING TEMPERATURE LIMITED TO ABOUT 250 o C o C limiting CARNOT EFFICIENCY to ~ %, and practical efficiency to ~ 28-30%. LOW BURN-UP - (about 400 TJ per tonne) EXTERNAL BOILERS ON EARLY DESIGNS. MAGNOX REACTORS (also known as Gas Cooled Reactors (GCR) 31

33 Norwich Business School 32 FUEL TYPE - enriched URANIUM OXIDE - 2.3% clad in stainless steel MODERATOR - GRAPHITE COOLANT - CARBON DIOXIDE SUPERHEATED RANKINE CYCLE (with reheat) - efficiency % ADVANTAGES:- MODEST POWER DENSITY - 5 MW/m 3. slow rise in temperature in fault conditions. GASEOUS COOLANT ( BAR cf 160 bar for PWR) ON LOAD REFUELLING under part load MINIMAL CONTAMINATION FROM BURST FUEL CANS RELATIVELY HIGH THERMODYNAMIC EFFICIENCY 40% VERTICAL CONTROL RODS - fall by gravity in case of emergency. DISADVANTAGES:- MODERATE LOAD FOLLOWING CHARACTERISTICS SOME FUEL ENRICHMENT NEEDED % OTHER FACTORS:- MODERATE FUEL BURN-UP - ~ 1800TJ/tonne (c.f. 400TJ/tonne for MAGNOX, 2900TJ/tonne for PWR). SINGLE PRESSURE VESSEL with pres- stressed concrete walls 6m thick. Pre- stressing tendons can be replaced if necessary. ADVANCED GAS COOLED REACTORS (AGR) 32

34 Norwich Business School 33 FUEL TYPE - unenriched URANIUM OXIDE clad in Zircaloy MODERATOR - HEAVY WATER COOLANT - HEAVY WATER ADVANTAGES:- MODEST POWER DENSITY - 11 MW/m3. HEAVY WATER COOLANT - low neutron absorber hence no need for enrichment. ON LOAD REFUELLING - and very efficient indeed permits high load factors. MINIMAL CONTAMINATION from burst fuel can - defective units can be removed without shutting down reactor. MODULAR: - can be made to almost any size DISADVANTAGES:- POOR LOAD FOLLOWING CHARACTERISTICS CONTROL RODS ARE HORIZONTAL, and cannot operate by gravity in fault conditions. MAXIMUM EFFICIENCY about 28% OTHER FACTORS:- MODERATE FUEL BURN-UP - ~ MODEST FUEL BURN-UP - about 1000TJ/tonne FACILITIES PROVIDED TO DUMP HEAVY WATER MODERATOR from reactor in fault conditions MULTIPLE PRESSURE TUBES instead of one pressure vessel. CANDU REACTOTS (PHWR) 33

35 Norwich Business School 34 FUEL TYPE - 3 – 4% enriched URANIUM OXIDE clad in Zircaloy MODERATOR - WATER COOLANT - WATER ADVANTAGES:- GOOD LOAD FOLLOWING CHARACTERISTICS - claimed for SIZEWELL B. - most PWRs are NOT operated as such. HIGH FUEL BURN-UP- about 2900TJ/tonne – VERTICAL CONTROL RODS - drop by gravity in fault conditions. DISADVANTAGES:- ORDINARY WATER as COOLANT - pressure to prevent boiling (160 bar). If break occurs then water will flash to steam and cooling will be less effective. ON LOAD REFUELLING NOT POSSIBLE - reactor must be shut down. SIGNIFICANT CONTAMINATION OF COOLANT CAN ARISE FROM BURST FUEL CANS - as defective units cannot be removed without shutting down reactor. FUEL ENRICHMENT NEEDED %. MAXIMUM EFFICIENCY ~ % latest designs ~ 34% OTHER FACTORS:- LOSS OF COOLANT also means LOSS OF MODERATOR so reaction ceases - but residual decay heat can be large. HIGH POWER DENSITY MW/m 3, and compact. Temperature can rise rapidly in fault conditions. NEEDS active ECCS. SINGLE STEEL PRESSURE VESSEL 200 mm thick. PRESSURISED WATER REACTORS – PWR (VVER) 34

36 Norwich Business School 35 FUEL TYPE - 3% enriched URANIUM OXIDE clad in Zircaloy MODERATOR - WATER COOLANT - WATER ADVANTAGES:- HIGH FUEL BURN-UP- about 2600TJ/tonne STEAM PASSED DIRECTLY TO TURBINE therefore no heat exchangers needed. BUT SEE DISADVANTAGES.. DISADVANTAGES:- ORDINARY WATER as COOLANT – but designed to boil: pressure ~ 75 bar. CONTROL RODS MUST BE DRIVEN UPWARDS - POWER NEEDED IN FAULT CONDITIONS. Water can be dumped in such circumstances. ON LOAD REFUELLING NOT POSSIBLE - reactor must be shut down. SIGNIFICANT CONTAMINATION OF COOLANT CAN ARISE FROM BURST FUEL CANS RADIOACTIVE STEAM WILL PASS DIRECTLY TO TURBINES. FUEL ENRICHMENT NEEDED. - 3%. MAXIMUM EFFICIENCY ~ 34-35% OTHER FACTORS:- LOSS OF COOLANT also means LOSS OF MODERATOR so reaction ceases - but residual decay heat can be large. HIGH POWER DENSITY MW/m 3, and compact. Temperature can rise rapidly in fault conditions. NEEDS active ECCS. SINGLE STEEL PRESSURE VESSEL 200 mm thick. 35 BOILING WATER REACTORS – BWR

37 Norwich Business School 36 FUEL TYPE - 2% enriched URANIUM OXIDE clad in Zircaloy MODERATOR - GRAPHITE COOLANT - WATER ADVANTAGES:- ON LOAD REFUELLING VERTICAL CONTROL RODS which can drop by GRAVITY in fault conditions. NO THEY CANNOT!!!! RMBK (LWGR): (involved in Chernobyl incident) DISADVANTAGES:- ORDINARY WATER as COOLANT - flashes to steam in fault conditions hindering cooling. POSITIVE VOID COEFFICIENT !!! - positive feed back possible in some fault conditions -other reactors have negative voids coefficient in all conditions. IF COOLANT IS LOST moderator will keep reaction going. FUEL ENRICHMENT NEEDED. - 2% PRIMARY COOLANT passed directly to turbines. This coolant can be slightly radioactive. MAXIMUM EFFICIENCY ~30% ?? OTHER FACTORS:- MODERATE FUEL BURN-UP - ~ MODEST FUEL BURN-UP - about 1800TJ/tonne LOAD FOLLOWING CHARACTERISTICS UNKNOWN POWER DENSITY probably MODERATE? MULTIPLE PRESSURE TUBES RMBK (LWGR): - involved in Chernobyl Incident

38 Norwich Business School 37 FUEL TYPE - depleted Uranium or UO 2 surround PU in centre of core. All elements clad in stainless steel. MODERATOR - NONE COOLANT - LIQUID METAL ADVANTAGES:- LIQUID METAL COOLANT - at atmospheric pressure. Will cool by natural convection in event of pump failure. BREEDS FISSILE FUEL from non-fissile 238U – increases resource base 50+ times. HIGH EFFICIENCY (~ 40%) VERTICAL CONTROL RODS drop by GRAVITY in fault conditions. DISADVANTAGES:- DEPLETED URANIUM FUEL ELEMENTS REPROCESSED to recover PLUTONIUM and sustain the breeding for future use. CURRENT DESIGNS have SECONDARY SODIUM CIRCUIT WATER/SODIUM HEAT EXCHANGER. If water and sodium mix a significant CHEMICAL explosion may occur which might cause damage to reactor itself. OTHER FACTORS:- VERY HIGH POWER DENSITY MW/m 3 but rise in temperature in fault conditions limited by natural circulation of sodium. FAST BREEDER REACTORS (FBR OR LMFBR)

39 Norwich Business School 38 Schematic of Reactor is very similar to later PWRs (SIZEWELL) with 4 Steam Generator Loops. Main differences? from earlier designs. – Output power ~1600 MW from a single turbine (cf 2 turbines for 1188 MW at Sizewell). – Each of the safety chains is housed in a separate building. Construction is under way at Olkiluoto, Finland. Second reactor under construction in Flammanville, France Possible contender for new UK generation Efficiency claimed at 37% But no actual experience and likely to be less GENERATION 3 REACTORS: EPR1300: PWR

40 Norwich Business School 39 24/04/2014 A development from SIZEWELL Power Rating comparable with SIZEWELL Will two turbines be used ?? Passive Cooling – water tank on top – water falls by gravity Two loops (cf 4 for EPR) Significant reduction in components e.g. pumps etc. Possible Contender for new UK reactors GENERATION 3: AP1000: PWR

41 Norwich Business School 40 A development from CANDU with added safety features less Deuterium needed Passive emergency cooling as with AP1000 See Video Clip of on-line refuelling GENERATION 3: ACR1000: Advanced Candu Reactor

42 Norwich Business School 41 A derivative of Boiling Water Reactor for which it is claimed has several safety features but which inherently has two disadvantages of basic design Vertical control rods which must be driven upwards Steam in turbines can become radioactive Generation 3 ESBWR: Economically Simple BWR

43 Norwich Business School 42 Pebble Bed Modulating Reactors are a development from Gas Cooled Reactors. Sand sized pellets of Uranium each coated in layers of graphite/silicon carbide and aggregated into pebbles 60 mm in diameter. Coolant: Helium Connected directly to closed circuit gas turbine GENERATION 3+ REACTORS: the PBMR Efficiency ~ 39 – 40%, possibility of CCGT?? Graphite/silicon carbide effective cladding very durable at high temperatures

44 Norwich Business School 43 Unlike other Reactors, the PBMR uses a closed circuit high temperature gas turbine operating on the Brayston Cycle for Power. This cycle is similar to that in a JET engine or the gas turbine section of a CCGT. Normal cycles exhaust spent gas to atmosphere. In this version the helium is in a closed circuit. Fuel In Air In Combustion Chamber Exhaust Compressor Turbine Generator PBM Reactor Heat Exchanger Open Brayston Cycle Closed Brayston Cycle GENERATION 3+ REACTORS: the PBMR

45 Norwich Business School 44 Efficiency of around 38 – 40%, but possibility of CCGT??? Helium passes directly from reactor to turbine Pebbles are continuously fed into reactor and collected. Tested for burn up and recycled as appropriate ~ typically 6 times GENERATION 3+ REACTORS: the PBMR

46 Norwich Business School 45 6.Nuclear Power – The Basics 7.Nuclear Power: Fission reactors 8.Nuclear Fuel Cycle 9.Fusion Reactors Section 8: Nuclear Fuel Cycle 45 NBSLM03E (2010) Low Carbon Technologies and Solutions N.K. Tovey ( ) M.A, PhD, CEng, MICE, CEnv

47 Norwich Business School 46 TWO OPTIONS AVAILABLE:- 1.ONCE-THROUGH CYCLE, 2.REPROCESSING CYCLE CHOICE DEPENDS primarily on:- 1.REACTOR TYPE IN USE (more or less essential for MAGNOX), 2.AVAILABILTY OF URANIUM TO COUNTRY IN QUESTION, 3.DECISIONS ON THE POSSIBLE USE OF FBRs. 4.DECISIONS ON HOW RADIOACTIVE WASTE IS TO BE HANDLED. Reprocessing leads to much less HIGH LEVEL radioactive waste, but more low level radioactive waste ECONOMIC CONSIDERATIONS done 10 years ago show little difference between two types of cycle except that for PWRs, ONCE-THROUGH CYCLE appeared MARGINALLY more attractive. Section 8: Nuclear Fuel Cycle

48 Norwich Business School 47 NUCLEAR FUEL CYCLE divided into two parts:- FRONT-END - includes MINING of Uranium Ore, EXTRACTION, CONVERSION to "Hex", ENRICHMENT, and FUEL FABRICATION. BACK-END - includes TRANSPORTATION of SPENT FUEL, STORAGE, REPROCESSING, and DISPOSAL. NOTE: 1.Transportation of Fabricated Fuel elements has negligible cost as little or no screening is necessary. 2.Special Provisions are needed for transport of spent fuel for both cycles. 3.For both ONCE-THROUGH and REPROCESSING CYCLES, the FRONT-END is identical. The differences are only evident at the BACK- END. Section 8: Nuclear Fuel Cycle

49 Norwich Business School 48 Liquid 5m 3 HL Waste Concentrate 0.5m m 3 solid Once Through Storage 0.9m 3 HL waste 0.4m 3 IL waste 0.8m 3 IL waste 0.7m 3 LL waste REPROCESSING 9 kg Plutonium 0.96 t Uranium U3O8U3O8 UF 6 Enrichment Cooling Ponds Reactor Ore Mining Spoil 1PJ Fuel Rods 1 T 0.9m m 3 ~ homes 60 x 2MW wind turbines Section 8: Simplified Fuel Cycle for a PWR (1)

50 Norwich Business School 49 MINING - ore > 0.05% by weight of U 3 O 8 to be economic. – Typically at 0.5%, 500 tonnes (250 m 3 ) must be excavated to produce 1 tonne of U 3 O 8 ("yellow-cake") which occupies about 0.1 m 3. URANIUM leached out chemically – resulting powder contains about 80% yellow-cake. The 'tailings' contain the naturally generated daughter products. PURIFICATION/CONVERSION - dissolve 'yellow-cake' in nitric acid and conversion to Uranium tetrafluoride (UF 4 ) UF 4 converted into URANIUM HEXAFLOURIDE (UF 6 ) or "HEX" if enrichment is needed. Section 8: Simplified Fuel Cycle for a PWR (2)

51 Norwich Business School 50 ENRICHMENT. proportion of URANIUM is artificially increased. GAS DIFFUSION - original method still used in FRANCE. "HEX" is allowed to diffuse through a membrane separating the high and low pressure parts of a cell. 235 U diffuses faster than 238 U through this membrane. Outlet gas from lower pressure is slightly enriched in 235 U (by a factor of ) and is further enriched in subsequent cells. HUNDREDS / THOUSANDS of such cells are required in cascade depending on the required enrichment. Pumping demands are very large as are the cooling requirements between stages. Section 8: Simplified Fuel Cycle for a PWR: Enrichment (1)

52 Norwich Business School 51 ENRICHMENT: GAS DIFFUSION. Outlet gas from HIGH PRESSURE side is slightly depleted URANIUM and is fed back into previous cell of sequence. AT BACK END, depleted URANIUM contains only % 235 U, – NOT economic to use this for enrichment. This depleted URANIUM is currently stockpiled, but could be an extremely value fuel resource should we decide to go for the FBR. Section 8: Simplified Fuel Cycle for a PWR: Enrichment (2)

53 Norwich Business School 52 ENRICHMENT. GAS CENTRIFUGE ENRICHEMENT similar to the Gas diffusion in that it requires many stages. "HEX" is spun in a centrifuge, and the slightly enriched URANIUM is sucked off near the axis and passed to the next stage. ENERGY requirements for this process are only ~10% of the GAS DIFFUSION method. All UK fuel is now enriched by this process at Capenhurst. Section 8: Simplified Fuel Cycle for a PWR: Enrichment (3)

54 Norwich Business School 53 FUEL FABRICATION - MAGNOX reactors: URANIUM metal is machined into bars using normal techniques. – CARE MUST BE TAKEN not to allow water into process as this acts as a moderator and might cause the fuel element to 'go critical'. – CARE MUST ALSO BE TAKEN over its CHEMICAL TOXICITY although this is not a much a problem as PLUTONIUM – URANIUM METAL bars are about 1m in length and about 30 mm in diameter. OXIDE Fuels for Other Reactors – Because of low thermal conductivity of oxides of uranium, fuels of this form are made as small pellets which are loaded into stainless steel cladding in the case of AGRs, and ZIRCALLOY in the case of most other reactors. TRANSPORT of FUEL Elements – Little screening is needed as URANIUM is an alpha emitter and even a thin layer of paper is sufficient to stop such particles. – No special precaution are needed as even enriched fuel is unsuitable for bomb making Simplified Fuel Cycle for a PWR: Fuel Fabrication (1)

55 Norwich Business School 54 PLUTONIUM Fuel fabrication presents much greater problems. Workers require more shielding from radiation. Chemically toxic. Metallurgy is complex. Can reach criticality on its own WITHOUT a MODERATOR. Care must be taken in manufacture and ALL subsequent storage that the fuel elements are not of size and shape which could cause a criticality. NOTE:- Transport of PLUTONIUM fuel elements a potential hazard, as a crude atomic bomb could be made without the need for a large amount of energy cf enriched URANIUM. DELIBERATE 'spiking' of PLUTONIUM with some fission products is considered to make the fuel elements very difficult to handle. Simplified Fuel Cycle for a PWR: Fuel Fabrication (2)

56 Norwich Business School 55 1 tonne of enriched fuel for a PWR produces ~1PJ of energy. 1 tonne of unenriched fuel for a CANDU reactor produces about ~0.2 PJ in a single pass. However, because of losses, about 20-25% MORE ENERGY PER TONNE of MINED URANIUM can be obtained with CANDU if the spent fuel is reprocessed. Simplified Fuel Cycle for a PWR: Fuel Fabrication (3)

57 Norwich Business School 56 BOTH ONCE-THROUGH and REPROCESSING CYCLES SPENT FUEL ELEMENTS from the REACTOR FISSION PRODUCTS mostly with SHORT HALF LIVES. heat is evolved – spent fuel elements are normally stored under water – at least in the short term. 100 days, the radioactivity reduced to about 25% of its original value, and after 5 years the level will be down to about 1%. Early reduction comes from the decay of radioisotopes such as IODINE and XENON half-lives (8 days and 1.8 hours respectively). CAESIUM decays to only 90% of its initial level even after 5 years. – accounts for less than 0.2% of initial radioactive decay, but 15% of the activity after 5 years. Simplified Fuel Cycle for a PWR: BACKEND (1)

58 Norwich Business School 57 BOTH ONCE-THROUGH and REPROCESSING CYCLES SPENT FUEL ELEMENTS stored under 6m of water – also acts as BIOLOGICAL SHIELD. – Water may become radioactive from corrosion of fuel cladding causing leakage - so water is conditioned – – kept at pH of (i.e. strongly alkaline in case of MAGNOX). Other reactor fuel elements do not corrode so readily. – Any radionucleides escaping into the water are removed by ION EXCHANGE. Subsequent handling depends on whether ONCE-THROUGH or REPROCESSING CYCLE is chosen. – Spent fuel can be stored in dry caverns, – drying the elements after the initial water cooling is a problem. – Adequate air cooling must be provided, and this may make air - radioactive if fuel element cladding is defective. WYLFA power station stores MAGNOX fuel elements in this form. Simplified Fuel Cycle for a PWR: BACKEND (2)

59 Norwich Business School 58 ADVANTAGES:- NO REPROCESSING needed - therefore much lower discharges of low level/intermediate level liquid/gaseous waste. FUEL CLADDING NOT STRIPPED - therefore less solid intermediate waste created. (although sometimes it is) NO PLUTONIUM in transport so no danger of diversion. DISADVANTAGES:- CANNOT RECOVER UNUSED URANIUM - 235, PLUTONIUM OR URANIUM Thus fuel cannot be used again. VOLUME OF HIGH LEVEL WASTE MUCH GREATER ( times) than with reprocessing cycle. SUPERVISION OF HIGH LEVEL WASTE needed for much longer time as encapsulation is more difficult than for reprocessing cycle. Simplified Fuel Cycle for a PWR: No Reprocessing

60 Norwich Business School 59 ADVANTAGES:- MUCH LESS HIGH LEVEL WASTE - therefore less problems with storage UNUSED URANIUM - 235, PLUTONIUM AND URANIUM can be recovered and used again, or used in a FBR thereby increasing resource base 50 fold. VITRIFICATION is easier than with spent fuel elements. Plant at Sellafield now operational although technical problems are preventing vitrification at full capcity. DISADVANTAGES:- Greater volumes of both Low Level and Intermediate Level Waste are created. Historically, routine emissions from reprocessing plants have been greater than storage of ONCE-THROUGH cycle waste. Simplified Fuel Cycle for a PWR: Reprocessing Cycle (1)

61 Norwich Business School 60 Dealing with liquid effluents At SELLAFIELD the ION EXCHANGE plant SIXEP (Site Ion EXchange Plant) – commissioned in early 1986, – substantially reduced the radioactive emissions in the effluent discharged to Irish Sea since that time by a factor of 500+ times Further improvements with more advance waste treatment have now been installed. PLUTONIUM is stockpiled or in transport if used in FBRs. (although this can be 'spiked'). Simplified Fuel Cycle for a PWR: Reprocessing Cycle (2)

62 Norwich Business School 61 **Pipes in this area are of small diameter to prevent CRITICALITIES. The Chemistry Fuel stored in cooling ponds to allow further decay Fuel decanned cladding to intermediate level waste storage Dissolve Fuel in Nitric Acid add tributyl phosphate (TBP) in odourless ketone (OK) further treatment with TBP/OK reduced with ferrous sulphamate High Level Waste medium level waste URANIUM – converted into UO 3 and recycled ** PLUTONIUM – converted for storage or fuel fabrication for MOX or FBR Simplified Fuel Cycle for a PWR: Reprocessing Cycle (3)

63 Norwich Business School 62 LOW LEVEL WASTE. CONTAINS MATERIALS CONTAMINATED WITH RADIOISOTOPES – either very long half lives indeed, – or VERY SMALL quantities of short lived radioisotopes. FEW SHIELDING PRECAUTIONS ARE NECESSARY DURING TRANSPORTATION. PHYSICAL BULK MAY BE LARGE as its volume includes items which may have been contaminated during routine operations. – Laboratory Coats, Paper Towels etc. – Such waste may be generated in HOSPITALS, LABORATORIES, NUCLEAR POWER STATIONS, and all parts of the FUEL CYCLE. Radioactive Waste Disposal – An Introduction

64 Norwich Business School 63 OPTIONS FOR DISPOSAL OF LOW LEVEL WASTE. BURYING LOW LEVEL WASTE SURROUNDED BY A THICK CLAY BLANKET IS A SENSIBLE OPTION. If clay is of the SMECTITE type acts as a very effective ion exchange barrier which is plastic and deforms to any ground movement sealing any cracks. IN BRITAIN IT IS PROPOSED TO BURY WASTE IN STEEL CONTAINERS AND PLACED IN CONCRETE STRUCTURES IN A DEEP TRENCH UP TO 10m DEEP WHICH WILL BE SURROUNDED BY THE CLAY. IN FRANCE, THE CONTAINERS ARE PILED ABOVE GROUND AND THEN COVERED BY A THICK LAYER OF CLAY TO FORM A TUMULUS. Energy Field Courses in 1999 and 2001 visited the site at ANDRA near Cherbourg. (Agence National de Déchets Radioactive) Radioactive Waste Disposal – An Introduction

65 Norwich Business School 64 INTERMEDIATE LEVEL WASTE. – contains HIGHER quantities of SHORT LIVED RADIOACTIVE WASTE, – or MODERATE QUANTITIES OF RADIONUCLEIDES OF MODERATE HALF LIFE – - e.g. 5 YEARS YEARS HALF LIFE. IN FRANCE SUCH WASTE IS CAST INTO CONCRETE MONOLITHIC BLOCKS AND BURIED AT SHALLOW DEPTH. IN BRITAIN, it was originally proposed to bury similar blocks at the SAME SITES to those used for LOW LEVEL WASTE. UNSATISFACTORY AS CONFUSION BETWEEN THE TWO TYPES OF WASTE WILL OCCUR. SEPARATE FACILITIES ARE NOW PROPOSED. Radioactive Waste Disposal – An Introduction

66 Norwich Business School 65 HIGH LEVEL WASTE. At Sellafield, high level waste is now being encapsulated and stored on site in specially constructed vaults. A building about the size of the UEA swimming pool house in area and about twice as high houses all the high level radioative waste from the UKs Civil Nuclear Program with space for decommissioning of all final fuel from MAGNOX. MOST RADIONUCLEIDES IN THIS CATEGORY HAVE HALF LIVES OF UP TO 30 YEARS, and thus ACTIVITY in about 700 years will have decayed to around natural background radiation level. PROPOSALS FOR DISPOSAL INCLUDE – burial in deep mines in SALT; – burial 1000m BELOW SEA BED and BACKFILLED with SMECTITE; – burial under ANTARCTIC ICE SHEET, – shot INTO SPACE to the sun! Radioactive Waste Disposal – An Introduction

67 Norwich Business School 66 UK processes waste from Overseas Countries. Should we send back exact quantities of each of: – High Level Waste – Intermediate Level Waste – Low Level Waste Or should we: – Send back same amount of radioactivity i.e. a larger amount of a small volume of High Level Waste and no Intermediate and Low Level Waste? Radioactive Waste Disposal – An Introduction – A Dilemma

68 Norwich Business School 67 Magnox fuel rod: Natural Uranium metal bar approx 35mm diameter and 1m long in a fuel cladding made of MAGNOX. Fission Reactors: Fuel Elements (MAGNOX)

69 Norwich Business School 68 AGR fuel assembly: UO 2 pellets loaded into fuel pins of stainless steel each ~ 1 m long in bundles of 36. Whole assembly in a graphite cylinder Burnable poison Fission Reactors: Fuel Elements (AGR)

70 Norwich Business School 69 PWR fuel assembly: UO 2 pellets loaded into fuel pins of zirconium each ~ 3 m long in bundles of ~200 Fission Reactors: Fuel Elements (PWR)


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