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IAEA/ICTP Workshop on: Technology and Applications of Accelerator Driven Systems (ADS). Y. Kadi and A. Herrera-MartÃnez CERN, Switzerland October 17-28 2005, ICTP, Trieste, Italy. LECTURES OUTLINE. LECTURE 1: Physics of Spallation and Sub-critical Cores: Fundamentals
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Y. Kadi and A. Herrera-Martínez
October 17-28 2005, ICTP, Trieste, Italy
(Monday 17/10/05, 16:00 – 17:30)
17 October 2005, ICTP, Trieste, Italy
First demonstrated by Rutherford in 1919 who transmuted 14N to 17O using energetic a-particles (14N7 + 4He217O8 + 1p1)
I. Curie and F. Joliot in 1933 produced the first artificial radioactivity using a-particles (27AL13 + 4He230P15 + 1n0)
use of high power accelerators to produce large numbers of neutrons
The accelerator bombards a target with
high-energy protons which produces a
very intense neutron source through the
These neutrons can consequently be
multiplied in the sub-critical core which surrounds the spallation target.
p The idea of producing neutrons by spallation with an accelerator has been around for a long time:
+ In 1950, Ernest O. Lawrence at Berkeley proposed to produce plutonium from depleted uranium at Oak Ridge. The Material Testing Accelerator (MTA) project was abandoned in 1954.
+ In 1952, W. B. Lewis in Canada proposed to use an accelerator to produce 233U from thorium, in an attempt to close the fuel cycle for CANDU type reactors.
Concept of accelerator breeder : exploiting the spallation process to breed fissile material directly soon abandoned.
Ip ≈ 300 mA
+ Renewed interest in the 1980's and beginning of the 1990's, in particular in Japan (OMEGA project at Japan Atomic Energy Research Institute), and in the USA (Hiroshi Takahashi et al. proposal of a fast neutron hybrid system at Brookhaven for minor actinide transmutation and Charles Bowman a thermal neutron molten salt system based on the thorium cycle at Los Alamos).
p In November 1993, Carlo Rubbia proposed, in an exploratory phase, a first Thermal neutron Energy Amplifier system based on the thorium cycle, with a view to energy production. As it became clear that in the western world the priority is the destruction of nuclear waste (other sources of energy are abundant and cheap), the system evolved towards that goal, into a Fast Energy Amplifier.
Subcritical system driven by a proton accelerator:
p Classification of existing ADS concepts according to their physical features and final objectives:
neutron energy spectrum
fuel form (solid/liquid)
p Several nuclear reactions are capable of producing neutrons
However the use of protons minimises the energetic cost of the neutrons produced
p There is no precise definition of spallation this term covers the interaction of high energy hadrons or light nuclei (from a few tens of MeV to a few GeV) with nuclear targets.
It corresponds to the reaction mechanism by which this high energy projectile pulls out of the target some nucleons and/or light particles, leaving a residual nucleus (spallation product)
Depending upon the conditions, the number of emitted light particles, and especially neutrons, may be quite large
This is of course the feature of outermost importance for the so-called ADS
p At these energies it is no longer correct to think of the nuclear reaction as proceeding through the formation of a compound nucleus.
Fast Direct Process:
Intra-Nuclear Cascade (nucleon-nucleon collisions)
Evaporation (mostly neutrons)
Low-Energy Inelastic Reactions
p The relevant aspects of the spallation process are characterised by:
+ Spallation Neutron Yield (i.e. multiplicity of emitted neutrons)
determines the requirement in terms of the accelerator power (current and energy of incident proton beam).
+ Spallation Neutron Spectrum (i.e. energy distribution of emitted neutrons)
determines the damage and activation of the structural materials (design/lifetime of the beam window and spallation target, radioprotection)
+ Spallation Product Distributions
determines the radiotoxicity of the residues (waste management).
+ Energy Deposition
determines the thermal-hydraulic requirements (cooling capabilities and nature of the spallation target).
p The number of emitted neutrons varies as a function of the target nuclei and the energy of the incident particle saturates around 2 GeV.
p Deuteron and triton projectiles produce more neutrons than protons in the energy range below 1-2 GeV higher contamination of the accelerator.
p The spectrum of spallation neutrons evaporated from an excited heavy nucleus bombarded by high energy particles is similar to the fission neutron spectrum but shifts a little to higher energy <En> ≈ 3 – 4 MeV.
p The spallation product distribution varies as a function of the target material and incident proton energy. It has a very characteristic shape:
At high masses it is characterized by the presence of two peaks corresponding to(i) the initial target nuclei and (ii) those obtained after evaporation
Three very narrow peaks corresponding to the evaporation of light nuclei such as (deuterons, tritons, 3He and a)
An intermediate zone corresponding to nuclei produced by high-energy fissions
pExample of the heat deposition of a proton beam in a beam window and a Lead target
which takes into account not only the electromagnetic interactions, but all kind of nuclear reactions induced by both protons and the secondary generated particles (included neutrons down to an energy of 20 MeV) and gammas.
Increasing the energy of the incident particle affects considerably the power distribution in the Lead target. Indeed one can observe that, while the heat distribution in the axial direction extends considerably as the energy of the incident particle increases, it does not in the radial direction, which means that the proton tracks tend to be quite straight. Lorentz boost
Heat deposition is largely contained within the range of the protons. But while at 400 MeV the energy deposit is exactly contained in the calculated range (16 cm), this is not entirely true at 1 GeV where the observed range is about 9% smaller than the calculated (rcalc = 58 cm, robs ~ 53 cm). At 2 GeV the difference is even more relevant (rcalc = 137 cm, robs ~ 95 cm). This can be explained by the rising fraction of nuclei interactions with increasing energy, which contribute to the heat deposition and shortens the effective proton range.
Authors: A. Fasso1, A. Ferrari2,3, J. Ranft4, P.R. Sala2,5
1 SLAC Stanford, 2 INFN Milan, 3 CERN, 4 Siegen University, 5 ETH Zurich
Interaction and Transport Monte Carlo code
Web site: http://www.fluka.org
Inelastic Nuclear Interactions
All models: Evaporation / Fission / Fermi break-up /g-deexcitation of the residual nucleus
Total and elastic cross section for p-p and p-n scattering, together with experimental data
Isospin decomposition of p-nucleon cross section in the T=3/2 and T=1/2 components
Hadronic interactions are mostly surface effects hadron nucleus cross section scale with the target atomic mass A2/3
PreEquilibrium Approach to NUclear Thermalization
Sophisticated Generalized IntraNuclear Cascade
Smooth transition (all non-nucleons emitted/decayed + all secondaries below 30-50 MeV)
Standard Assumption on exciton number or excitation energy
Common FLUKA Evaporation model
Hadron-Nucleus interactions above 3-5 GeV/c
No other model available for energies above the pion threshold production (except QMD models)
No other model for projectiles other than nucleons
Easily available for on-line integration into transport codes
Every target-projectile combination without any extra information
Particle-to-particle correlations preserved
Valid on light and on heavy nuclei
Capability of computing cross sections, even when it is unknown
Low projectile energies E<200MeV are badly described
Quasi electric peaks above 100MeV are usually too sharp
Coherent effect as well as direct transitions to discrete states are not included
Nuclear medium effects, which can alter interaction properties are not taken into account
Multibody processes (i.e. interaction on nucleon clusters) are not included
Composite particle emissions (d,t,3He,a) cannot be easily accommodated into INC, but for the evaporation stage.
Backward angle emission poorly described (Corrected for FLUKA)Advantages and Limitations of GINC
ADS operates in a non self-sustained chain reaction mode
minimises criticality and power excursions
ADS is operated in a sub-critical mode
stays sub-critical whether accelerator is on or off
extra level of safety against criticality accidents
The accelerator provides a control mechanism for sub-critical systems
more convenient than control rods in critical reactor
safety concerns, neutron economy
ADS provides a decoupling of the neutron source (spallation source) from the fissile fuel (fission neutrons)
ADS accepts fuels that would not be acceptable in critical reactors
High Pu content
There is a spectacular difference between a critical reactor and an ADS (reactivity in $ = r/b; r = (k–1)/k) :
n = neutron density [n/cm3]; F = neutron flux [n/cm2/s]
n = neutrons emitted per fission; Sf = macroscopic fission cross section
= external neutron source (spallation neutrons for instance)
Sa = macroscopic absorption cross section(capture + fission)
= neutron current [n/cm2] according to Fick’s Law
where the diffusion length Lc is defined as :
where B2M is referred to as the « material buckling » (measure of the curvature). B2M being positive means that the solution is of oscillatory nature.
with the following eigenvalues :
Using the divergence theorem one can rewrite the first term :The relation between leakage and absorptionrate is given by:This illustrates the role of B2i: for a given volume the leakage probability increases with the mode.
It is of interest to note the Amplification factor 1/(1-ki) specific to every single mode.
the first term of the numerator corresponds to the rate of absorption whereas the second term is related to the leakage of neutrons, for the harmonic mode l,m,n. In other words, the total number of neutrons produced is equal to the sum of the neutrons absorbed (capture + fission) and those which have leaked out of the system.
the flux can then be expressed as :
it is apparent that C must be zero, for otherwise the flux would become infinite as r ∞, so that only A remains to be determined. The neutron current density at a point r is given by: upon inserting the value for A, it follows that
(1/ ~ 21 cm)
EXPERIMENTAL DETERMINATION OF THE ENERGY GENERATED BY NUCLEAR CASCADES FROM A PARTICLE BEAM
CEN, Bordeaux-Gradignan, France
CIEMAT, Madrid, Spain
CSNSM, Orsay, France
CEDEX, Madrid, Spain
CERN, Genève, Switzerland
Dipartimento di Fisica e INFN, Università di Padova, Padova, Italy
INFN, Sezione di Genova, Genova, Italy
IPN, Orsay, France
ISN, Grenoble, France
Sincrotrone Trieste, Trieste, Italy
Universidad Autónoma de Madrid, Madrid, Spain
Universidad Politecnica de Madrid, Madrid, Spain
University of Athena, Athens, Greece
Université de Bâle, Bâle, Switzerland
University of Thessalonic, Thessalonique, Greece
p Highly specified experiments have been carried out to verify the fundamental physics principle of Accelerator-Driven Sub-Critical Systems:
The First Energy Amplifier Test (FEAT): S. Andriamonje et al. Physics Letters B 348 (1995) 697–709 and J. Calero et al. Nuclear Instruments and Methods A 376 (1996) 89–103;
The MUSE Experiment (MUltiplication de Source Externe): M. Salvatores et al., 2nd ADTT Conf., Kalmar, Sweden, June 1996;
The YELINA Experiment (ISTC-B-70): S. Chigrinov et al., Institute of Radiation Physics & Chemistry Problems, National Academy of Sciences, Minsk, Belarus.
MASURCA facility (courtesy of CEA)
The Pulsed Neutron Source
« GENEPI »
General view of the YALINA fuel subassembly.
Experiment & calculations:keff vs. fuel load
Neutron pulses measured by 3He-counters in different experimental channels.
Layout of the Yalina core
CONFIG SOURCE KINETICS POWER EFFECTS
FEAT SPALL THERMAL NO
MUSE DD/DT FAST NO
YALINA DD/DT THERMAL NO
YALINA DD/DT FAST NO
TRADE SPALL THERMAL YES
RACE g-NUCLTHERMAL NO
SAD SPALL FAST NO
EA SPALL FAST YES