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What is the Future of our radioactive waste?. Gabrielle DUPR É, Professor University of Orléans, and CNRS - ICARE ORLÉANS, France E-mail : gabrielle.dupre@cnrs-orleans.fr. What is the Future of radioactive waste?.
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What is the Future of our radioactive waste? Gabrielle DUPRÉ, Professor University of Orléans, and CNRS - ICARE ORLÉANS, France E-mail : gabrielle.dupre@cnrs-orleans.fr
What is the Future of radioactive waste? Before thinking of the future of radioactive waste for the next centuries - and in some cases for the next millenaries -, we have to know: • some elements of atomic and nuclear physics • what is called « radioactive waste »? • the specific properties? • their origin? • their peculiar treatment? • their storing mode? • the long-term memory of their storing?
Some elements of atomic physics The ATOM is theultimate entity of a simple species constituted of a nucleus and electrons
Some elements of atomic physics Atomic Nucleus : • is positively charged (charge = multiple of |e|) • contains the most part of the atom mass in a tiny volume • has no influence on chemical reactions but is fundamental for nuclear reactions • contains A nucleons (nucleons = protons + neutrons) • with a “mass number”: A = Z + N • Z: number of protons • Mass = mp = 1,6726 x 10-27 kg > mp • Positive charge = |e| = + 1,602 x 10-19 C • N: number of neutrons • Mass = mn = 1,6749 x 10-27 kg • Electric charge = 0
Some elements of atomic physics Electrons are gravitating around the atomic nucleus • very low mass: me = 9,1094 10-31 kg • negative charge: e = - 1,602 x 10-19 C • number: equal to the number of protons = Z • essential for chemical reactions, but not for nuclear reactions Nucleus and electrons, equally but oppositely charged, provide the neutrality of the atom
Some elements of atomic physics Isotopes of a same chemical element are: nuclides with the same number of protons (identical Z) but with a different number of neutrons N and a different mass number A Examples: Isotopes AZX: same Z and different A and N 23892U, 23592U, 23492U constituting the natural U element 11H , 21H, 31U, 41H constituting the H element
Stability of the atomic nucleus • Electrons belonging to a given atom are relatively independent: • they can escape from the attractive force of the nucleus, giving a positive ion • or other electron(s) can be attracted by the positively charged nucleus, giving a negative ion • Protons and neutrons, main constituents of the nucleus, are linked by very strong interactions, making generally the atomic nucleus very stable, although the Z protons having the same positive charge should flee from each other because of repulsion forces. However, • Protons and neutrons stay together within the nucleus • Nucleus mass: mnucleus < Z mp + N mn for a stable nucleus
Stability of the atomic nucleus For a stable atom: mnucleus < Z . mp + N . mn Δm = mnucleus - (Z mp + N mn ) is the“mass deficit” withΔm < 0 • Δm is the equivalent of the formation energy of the nucleus from its constituents: Z protons + N neutrons → nucleus (ΔHf) • According to Einstein: ΔHf = Δm . c2 (c: speed of light) • Since Δm is < 0, ΔHf is also < 0 • The link energy inside the nucleus EL corresponds to the energy necessary for dissociating the nucleus into its nucleons: EL = - ΔHf > 0
Stability of the atomic nucleus • For a stable nucleus: Δm < 0 and EL > 0 • For a radioactive (thus unstable) nucleus: Δm = 0 and EL = 0 • For a radioactive nucleus with very short life-time: Δm > 0 and EL < 0 EL depends on the number of nucleons: • If Z ≤ 20, then Z # N stable nucleus (N, O, Cl…) • If Z > 20, then N must increase to get a stable nucleus • There is a curve N = f(Z) around which nucleus are stable Away from the curve N = f(Z), and for N/Z ≥ 1.6 unstable nucleus are able to disintegrate spontaneously
Different types of radioactive disintegration reactions Emission β-: emission of electrons (e-) Ex:126C → 147N + 0-1e- Emission β+: emission of positrons (e+) Ex:116C → 115B + 01e+ Emission γ: electromagnetic emission It accompanies almost all disintegration reactions Emission α: emission of hellions (He nucleus) For high Z and A (A ≥ 206 : 84206Po isotope), the nucleus breaks into 2 pieces: Ex:23892U → 23490Th + 42He
Different other types of nuclear reactions Emission of neutrons: as the result of the collision of a light atom with a: - α particule: Ex:94Be + 42He → 126C + 10n stable stable - γ photon: Ex:94Be + 00γ → 84Be + 10n stable radioactive Fusion reaction: needs T # 108 K (ITER International Program) Ex: 21H + 31H → 42He + 10n + E (17.6 MeV) Fission reaction: Ex: 23592U + 10n →(9438Sr + 14054Xe) + (2 or 3 10n) + hν + E Fission products Several n Radiation Energy (≥ 200 MeV)
Fusion energy • Fusion energy: in thermonuclear reactors • None operating at present in France (the two existing have been stopped) • Fundamental research carried out at an international level in the Atomic Energy Commissariat (CEA) in Cadarache, Provence, France (ITER Project for a very long term: 22nd century)
Advantages and difficulties of fusion energy D + T → He (E = 3.5 Mev) + n (E = 14.1 MeV) • Advantages • Abundant resources of D and Li (→ T) inside the sea • Very little risk of uncontrolled reaction • Constant production, at any time, in all seasons • Very few radioactive waste, with a short half-life time (T = 12,3 y) • Activated reactor materials but with rapid decrease (T < 100 y) • Very little impact on environment (no CO2, no dust…) • Difficulties • Very high temperature having to be reached (plasma of ≈ 108 K) • Problems due to rapid neutrons • Risk of Tritium proliferation (→ thermonuclear bomb or bomb H)
Fission energy • Fission energy: in REP (Reactors with Pressurized Water), based on the fission of natural Uranium enriched with U235 isotope • REP : the only operating reactors in France at present (58 units on 19 different sites): 2nd generation of reactors • EPR : 3rd generation (1 EPR under construction at Flamanville, Normandy; another decided also in Normandy; one being built in Finland; others to be built in India, China…) • 4th generation (being conceived for 2040-2050)
Advantages and difficulties of fission energy 23592U + 10n →(9438Sr + 14054Xe) + (2 or 3 10n) + hν + E • Advantages • Abundant resources of Uranium in stable countries • Constant production, at any time, in all seasons (900–1400 MWe/unit) • 58 French REP, on 19 sites, along rivers or Atlantic ocean • Low impact on environment (no CO2, nor dust…) • Most waste with short radioactive period (managed by ANDRA) • Difficulties • Some radioactive waste with very long period, and strong activity (fission products, actinides) • Risk of uncontrolled reactions: limited but real (cf Tchernobyl, Fukushima) • Risk of proliferation of U enriched with U235 and with Pu (→A bomb) • Finite resources of Uranium (may be towards 2100-2200)
Reaction of fission in a Pressurized Water Reactor called « REP » Fission reaction: Ex: 23592U + 10n →(9438Sr + 14054Xe) + (2 or 3 10n) + hν + E Fissile Neutron Fission products Several n Energy nucleus (≥ 200 MeV) Remaining after reaction: 23892U and 23592U: recycled Production of: - Fission products: harmful waste (200 different FP) - Minor Actinides (Np, Am, Cm): long-life heavy nuclei - All Plutonium isotopes: among them, 23994Pu, a fissile nucleus, being separated at La Hague re-treatment plant -23994Puoxide mixed with natural U oxide provides a new nuclear matter called MOX (Mixed OXides of U and Pu)
Definition of waste, of radioactive waste • A waste is officially “any residue from production, transformation, or utilization processes, any substance, material, product, or more generally any abandoned staff or staff the owner wants to abandon” • A radioactive waste contains radioactive isotopes that are characterized by: • the production of dangerous ionizing radiations of very short wavelength (thus of large energy) • their long term activity and life-time
Among industrial waste: radioactive waste In France: Global amount of industrial waste: 2500 kg / year.person among them: 100 kg of toxic chemical waste 380 kg of home waste And only1 kg of radioactive waste (0.04%)
Origin of radioactive waste (in France) • Electro-nuclear waste (85%): production of electricity via nuclear energy • Some waste from care activities, from hospitals (14%), for diagnostics and/or therapy: slightly radioactive • Waste from other industries: food sterilization, quality control in metallurgy… • Waste from nuclear research and from production of radioactive isotopes • Waste from nuclear armament (not included in the %)
Electro-nuclear sites in the world, United States has the most important potential in terms of MegaWatts installed (99.210 MWe*) France has the second one (63.363 MWe*), but the first one if compared to respective population between USA and France Japan (47.839 MWe*: 3rd one), Germany, United Kingdom… are well equipped Italy has no more operating nuclear plants since 1997, but a certain number of storage sites do exist * 1995 data
In Italy: 4 old nuclear plants (red points) and nuclear storage sites (black points and stars)
Classification of radioactive waste Ra → Rn + He (disintegration reaction) t = 0 n0 0 0 Any t>0 n < n0 Reaction rate: v = - dn / dt = λ n 1st order reaction Radioactive period: T = ln 2 / λ Classification according two criteria: • Radioactive activity: A = v = - dn / dt A provides the importance of protections to use for protection against ionizing radiations from waste • Radioactive period: T T defines the duration of waste potential nuisance
Classification of radioactive waste (in France) According to both criteria: A and T, several categories of waste are considered for storage: • very low radioactive waste coming from uranium mines and from deconstruction of some old nuclear plants (TFA) • waste of low and moderated activity with a short radioactive period (FMA) • waste of high activity (HA) and of moderated activity with a long radioactive period (MAVL) • waste containing graphite and/or radon
Classification of radioactive waste In France, for example: Global amount per year and per person: 1 kg of radioactive waste (0.04%) 900 g100 g « Short life-time »« Long life-time » (T<30 years, low or moderate A) (T>30 years or with high A) 80 g 20 g T>30 years high activity
Three barriers for the confinement of radioactive matter in the case of a « REP » • 1st barrier: the metallic pencils containing uranium oxide enriched with 235U isotope • 2nd barrier: the concrete envelope of the reactor core • 3rd barrier: the double concrete wall of the reactor or concrete wall + metallic envelope
The UO2 or MOX pastilles are pilled in a series of long tubes, made of “zircaloy” (alloy of Zirconium (Zr) and 2.5% Tin (Sn)), forming the so called « combustible pencils » and thefirst barrier between the combustible matter and the environment The first barrier: the combustible pencil
The second barrier: a thick concrete wall surrounding the reactor core
The third barrier : the double thick concrete wall enveloping the reactor
Several categories of radioactive waste (in France) with the purpose of storage According to both criteria: A and T, several categories of waste are considered for storage: • very low radioactive waste coming from uranium mines and from deconstruction of some old nuclear plants (TFA) • waste of low and moderated activity with a short radioactive period (FMA) • waste of high activity (HA) and of moderated activity with a long radioactive period (MAVL) • waste containing graphite and/or radon
Waste with very low activity (TFA)stored in Morvilliers center
Waste of low and moderated activity with a short radioactive period (FMA)
Waste of high activity (HA) and of moderated activity with a long radioactive period (MAVL)