Future_of_Nuclear_Energy

The future of Nuclear Energy Carlo Rubbia CERN 1 The demographic transition 1700;; 6008million 1800; 200 million 1350; 150 billion 1950;930 billion AD 2.4 1900; 1.6 2020; 1985; 5 An “explosive” population growth: 90 M/year ● World’s population is rising rapidly . ● It is generally expected that it may grow to some 10÷ 12 Billion people by 2100 and stay relatively stable after that. ● Most of the population will be in what are presently the so-called Developing Countries. ● Everybody will agree on the fact that no future progress of mankind will be possible without substantial amount of of energy, namely Sweden, June 2005 “Energy is necessary” . Slide# : 2 Energy growth: it may not be for ever ● The individual energy consumption of the most advanced part of And what And what after that '' after that mankind has grown about 100 fold from the beginning of history. ● The level is today about ➩ 0.9 GJ/day /person, ➩32 kg of Coal/day/ person, ➩continuous 10.4 kWatt/person. ● The corresponding daily emission rate of CO2 is about 100 kg Energy consumption/person increments by +2 %/y (fossil dominated) Slide# : 3 Sweden, June 2005 Energy and poverty ● A huge correlation between energy and poverty 1’600 Millions without electricity 1’600 Millions without electricity ➩Sweden: 15’000 kWh of ➩Tanzania: electricity/ person/year 100 kWhe /p/y ● 1.6 billion people - a quarter of the current world's population - are without electricity, ● About 2.4 billion people rely almost exclusively on traditional biomass as their principal energy source. 2’400 Millions with only biomass 2’400 Millions with only biomass ● Of the 6 billion people, about one half live in poverty and at least one Technologically advanced countries have the fifth are severely under nourished. responsibility of showing the way The rest live in comparative comfort to the most needy ones ! and health. Sweden, June 2005 Slide# : 4 New energies: how soon ' ● During this lecture of mine, one hour long, about 10’000 new people have entered the world, at the rate of 3/sec, most of them in the Developing Countries. ● At the present consumption level, known reserves for coal, oil, gas and nuclear correspond to a duration of the order of 230, 45, 63 and 54 years. ● The longevity of the survival of the necessarily limited fossil’s era will be affected on the one hand by the discovery of new, exploitable resources, strongly dependent on the price and on the other by the inevitable growth of the world’s population and their standard of living. ● Even if these factors are hard to assess, taking into account the long lead time for the massive development of some new energy sources, the end of the fossil era may be at sight. Sweden, June 2005 Slide# : 5 Climatic changes ' ● The consumption of fossils may indeed be prematurely curbed by unacceptable greenhouse related environmental disruptions. ● The climatic effect of the combustion of a given amount of fossil fuel produces one hundred times greater energy capture due to the incremental trapped solar radiation (if we burn 1 with a fossil, the induced, integrated solar heat increment is >100 !) ● Doubling of pre-industrial concentration will occur after roughly the extraction of 1000 billion tonnes of fossil carbon. We are presently heading for a greenhouse dominated CO2 doubling within roughly 50-75 years. ● It is generally believed (IPCC, Kyoto…) that a major technology change must occur before then and that in order to modify drastically the present traditional energy pattern a formidable new research and development would be necessary. ● New dominant sources are needed in order to reconcile the huge energy demand, growing rapidly especially in the Developing Countries, with an acceptable climatic impact due to the induced earth’s warming up. Sweden, June 2005 Slide# : 6 New energies: ● Only two natural resources have the capability of a long term energetic survival of mankind: 1.A new nuclear energy. Energy is generally produced whenever a light nucleus is undergoing fusion or whenever a heavy nucleus is undergoing fission. Practical examples are natural Uranium or Thorium (fission) and Lithium (fusion) both adequate for many thousand of years at several times the present energy consumption. energy. The world’s primary energetic consumption is only 1/10000 of the one available on the surface of earth of sunny countries. Solar energy may be either used directly as heat or PV or indirectly through hydro, wind, bio-mass and so on. If adequately exploited, solar energy may provide enough energy for future mankind. 2.Solar ● It is unlikely that any stable, long term development of mankind will be possible without both of them. Sweden, June 2005 Slide# : 7 Novel forms of energy from nuclei Sweden, June 2005 Slide# : 8 Nuclear proliferation and the developing countries ● The most important new energy demands will necessarily come from now fast growing developing countries. Is there a room for nuclear energy ' ● In the sixties,”atoms for peace” promised a cheap, abundant and universally available nuclear power, where the few “nuclear” countries would ensure the necessary know-how to the many others which have renounced to nuclear weaponry. ● Today, the situation is far from being acceptable: the link between peaceful and military applications has been shortened by the inevitable developments of nuclear technology: ➩ Uranium enrichment may be easily extended to a level sufficient to produce a “bomb grade” U-235 (f.i. see the case of Iran); ➩natural Uranium reactors (CANDU) generate a considerable amount of Pu, such as produce easily Pu-239 “bomb grade” (f.i. the case of India). ● The nuclear penetration in the developing countries could become acceptable only once the umbilical chord between energy and weapons production is severed. ● Some totally different but adequate nuclear technology must be developed. Sweden, June 2005 Slide# : 9 Nuclear energy without U-235 ● Today’s nuclear energy is based on U-335, 0.71 % of the natural Uranium, fissionable both with thermal and fast neutrons. A massive increase of this technology (5 ÷ 10 fold), such as to counterbalance effectively global warming is facing serious problems of accumulated waste and of scarcity of Uranium ores. ● But, new, more powerful nuclear reactions are possible. Particularly interesting are fission reactions on U-238 or Th-232 in which ➩the natural element is progressively converted into a readily fissionable energy generating daughter element ➩the totality of the initial fuel is eventually burnt ➩ the released energy for a given quantity of natural element is more than one hundred times greater than the one in the case of the classical, U235 driven nuclear energy. ● Natural reserves U-238 or Th-232 can become adequate for many tens of centuries at a level several times the today’s primary fossil production. Sweden, June 2005 Slide# : 10 Choosing a nuclear energy without proliferation ● Indeed energy is produced whenever a light nucleus is undergoing fusion or whenever a heavy nucleus is undergoing fission. Particularly interesting are fission reactions in which a natural element is bred into a readily fissionable energy generating process. [1] [2] ● The energies naturally available as ores by [1] and [2] are comparable to the one for the D-T fusion reaction: [3] ● While reaction [2] is again strongly proliferating, reactions [1] and [3] may be safely exploited in all countries. Sweden, June 2005 Slide# : 11 Closing the nuclear cycle with Th-232 and U-238 ● The fissile element (U-233 or Pu-239) is naturally produced by the bulk natural element progressively converted into fertile element. ● Two neutrons are required within the basic cycle, one for the breeding and the other for the fission, in contrast with the ordinary U-235 process, in which only one neutron is necessary. ● After a time the process has to be recycled since: ➩The fraction of the produced fission fragments has affected the operation of the system materials. ➩Radiation damage of the fuel elements requires reconstruction of the ● In practical conditions this correspond to the burning of about 10 ÷ 15 % of the metal mass of the natural element (Th-232 or U-238) and to a specific energy generation of 100 ÷ 150 GWatt x day/ ton. ● For practical conditions, this may correspond to some 5 ÷ 10 years of uninterrupted operation. Sweden, June 2005 Slide# : 12 Fuel reprocessing ● At this moment the fuel is reprocessed and ➩the only waste are Fission fragments Their radio-activity of the material is intense, but limited to some hundreds of years. Ordinary PWR ➩Actinides are recovered without separation and are the “seeds” of the next load, after being topped with about 10 ÷ 15 % of fresh breeding element (Th or U-238) in order to compensate for the losses of element. Th-based cycle ➩A small fraction of Actinides is not recovered and ends with the “waste” ● The cycle is “closed” in the sense that the only material inflow is the natural element and the only “outflow” are fission fragments. Sweden, June 2005 Toxicity of lost TH-232 Slide# : 13 “Breeding” equilibrium ● The process is periodically restarted as an indefinite chain of cycles. The fuel composition progressively tends to a ”secular” equilibrium between the many actinides composing the fuel, with rapidly decreasing amounts as a function of the rising of the atomic number. ● In the case of Th-232, the secular mixture is dominated by the various U isotopes with a fast decreasing function of the atomic number. ● Np and Pu (mostly the Pu-238) are at the level of grams/ton ! ● Proto-actinium (Pa-233) is the short lived precursory element to U-233 formation. Sweden, June 2005 Slide# : 14 Residual radio-toxicity of waste as function of time Comparing : PWR (1) ordinary reactor (PWR), Closed cycle U (2)Thorium based EA (closed cycle) (3)two T-D fusion models Closed cycle Th Relative amounts of leaked Actinide waste, excluding fission Fragments. In the case of a closed cycle the rejected fraction is x = 0.1% for U and Pu and of x = 1% for the other actinides [J.L. Bobin, H. Nifenecker, C. Stéphan : L'énergie dans le Sweden, June 2005 monde : bilan et perspectives] Slide# : 15 Prompt and delayed neutrons in a reactor ● Operation of a critical reactor is possible only because of the presence of some neutrons delayed up to minutes, which provide enough time to exercise mechanically the multiplication coefficient. ● The fraction of delayed neutrons is for a U=235 PWR, β ≈ 0.0070 ● This value of β is particularly favorable: it is only β ≈ 0.0020 for a U-238 breeder and β ≈ 0.0025 for a Th-232 breeder, ● For instance for a Th-232 breeder, an uncontrolled sudden reactivity change Δβ ≈ 0.0036 implies prompt criticality and a hundred fold power increase in 140 µs. ● Recently the possibility of operating the fission power generation as a sub-critical device with external supply of generating neutrons has been studied. ● These problems can be solved with the help of an external contribution of neutrons produced with a high energy proton beam hitting a spallation target. ● In the case of a sub-critical system with k = 0.99, the corresponding power increase will be a mere +50%. Sweden, June 2005 Slide# : 16 Critical(reactor) and sub-critical (energy amplifier) operation Sweden, June 2005 Slide# : 17 Principle of operation of the Energy Amplifier Sweden, June 2005 Slide# : 18 Benefits of the sub-critical operation ● A critical reactor operation with U-233 is far more delicate than an ordinary PWR. ● These problems are best solved with the help of an external contribution of neutrons produced with a high energy proton beam hitting a spallation target. ● In absence of the proton beam the assembly is sub-critical with an appropriate criticality parameter keff< 1 and no fission power is produced. ● With the beam on,the nuclear power is directly proportional to the beam power, namely the power gain G = [Fission thermal power]/[beam power] is related to the value of the multiplication coefficient keff by a simple expression: G= η 1− keff ;η ≈ 2.1÷ 2.4 for Pb − p coll. > 0.5 GeV ● For instance, in order to correct for the reduction in β ≈ 0.007- 0.002= 0.005 of the delayed neutrons, such as to operate with U-233 in the same delayed neutron conditions of ordinary U-235, keff ≈ 0.995 and G ≈ 480, namely the € controlling beam power is 2.1 MWatt for each GWatt of thermal power. For keff ≈ 0.99, G ≈ 240. Sweden, June 2005 Slide# : 19 Basic choices FUEL Depleted Uranium (U-238) Natural Thorium (Th-232) Same as Super-Phenix. Pu/U @ equilibrium ≈ 20 % It produces both Plutonium and minor Actinides (Cm, Am, etc). Positive void coeff. Both a critical reactor and sub-critical system (external neutron supply) are possible For critical reactor, very small fraction of delayed neutrons (