What is the Future of our radioactive waste?

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

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 > m_p

– 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: m_e = 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: m_nucleus < Z m_p + N m_n for a stable nucleus

Stability of the atomic nucleus

For a stable atom:

m_nucleus < Z . mp + N . mn

Δm = m_nucleus - (Z m_p + N m_n ) is the “mass deficit”

with Δm < 0

– Δm is the equivalent of the formation energy of the nucleus from its constituents:

Z protons + N neutrons → nucleus (ΔHf) – According to Einstein: ΔH_f = Δm . c^{2 (}c: speed of light)

– Since Δm is < 0, ΔH_f is also < 0

– The link energy inside the nucleus E_L 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 E_L > 0

– For a radioactive (thus unstable) nucleus:

Δm = 0 and E_L = 0

– For a radioactive nucleus with very short life-time:

Δm > 0 and E_L < 0

E_L 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 + _0-1

e

Emission β

: emission of positrons (e

)

Ex: ₁₁₆C → ₁₁₅B + ₀₁

e

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 + 14054}Xe) + (2 or 3 ₁₀n) + hν + E Fission products Several n Radiation Energy

(≥ 200 MeV)

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: 22

century)

Fusion energy

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: 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): 2^nd

generation of reactors

• EPR : 3^rd 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…)

• 4^th generation (being conceived for 2040-2050)

Fission energy

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:

-

- All Plutonium isotopes: among them, ₂₃₉₉₄Pu, a fissile nucleus, being separated at La Hague re-treatment plant

- ₂₃₉₉₄Pu oxide 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 only

1 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

Location of nuclear sites in the world

Location of nuclear sites in Europe

Location of nuclear sites in France

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 1^st 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 g 100 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

Retreatment of used combustible

Three barriers for the confinement of radioactive matter

in the case of a « REP »

• 1^st barrier: the metallic pencils containing uranium oxide enriched with ²³⁵U isotope

• 2^nd barrier: the concrete envelope of the reactor core

• 3^rd barrier: the double concrete wall of the reactor or concrete wall + metallic envelope

The first barrier: the combustible pencil

• 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 the first barrier between the

combustible matter and the environment

The second barrier: a thick concrete

wall surrounding the reactor core

The third barrier : the double thick

concrete wall enveloping the reactor

Storage of nuclear

(and other radioactive) waste

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)

Memory of the storage of

radioactive waste

Possible visits of ANDRA

radioactive waste sites in France

• TFA: in Morvilliers (east of Troyes)

• FA/MA and VC: in Soulaines-Dhuys (east of France), in activity since 1992

Another site exists (the 1^st one) in Normandy, at La Hague, near Cherbourg, but it is full, covered, thus not so interesting

• HAVC, HAVL: in Bure (east of France) a 490 m-deep

laboratory inside special clay has been built and is operating.

It can be visited only for a limited number of persons.

A reproduction on surface of a part of it can be visited, so as an interesting technical area and museum shows the different machines, tools, containers… they are making for a future

adequate deep storing

They are now searching for a proper site in the region of Bure for building the real site for a deep storage within 15-20 years and for at least 100 years or much more