monte carlo simulation of nuclear reactions
TRANSCRIPT
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Monte Carlo Simulation of Nuclear
Reactions Dr Albrecht Kyrieleis MCnet, August 2014
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Content
After particle physics
AMEC
Nuclear fission: Shielding and criticality
Nuclear Fusion and ITER
Conclusion
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PhD (2003) in Hamburg / DESY
Small-x Physics: Diffractive DIS, BFKL
Topic: Calculation of the γ* impact factor at NLO with the aim to make
prediction using NLO BFKL.
PhD: Calculation of the real corrections and combination with virtual
corrections.
Collaboration with S. Gieseke
Many discussions with A. Sabio-Vera and J. Anderson
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Postdoc at Manchester (2003-2006)
pQCD - Gaps between jets – resummation – BFKL
Mainly analytical calculations.
Collaboration with Jeff Forshaw and Mike Seymour
Discovery of a new tower of super-leading logarithms in gaps-
between-jets cross sections (J. Forshaw, A Kyrieleis, M Seymour,
2006)
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Into industry ..
NNC: Company specialised on providing technical consultancy in the
area of nuclear technology and physics.
Using specialised software: simulation of different aspects a of a
nuclear power plant, e.g.:
Interplay of heat production from nuclear fission, cooling by
gas/water, fission rate variation in presence of water/steel/graphite
Statistical analysis of failure of engineering parts due to
heat/irradiation/mechanical stress
Consequences analysis for faults occurring in a nuclear plant
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University of Manchester / Diamond light source (Oxforshire)
Project: develop a prototype x-ray tomography station for material
science at a Synchrotron and
Develop new algorithms for image reconstruction and analysis and for
artefact suppression.
Analysis of nuclear materials
... and back
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Since 2009: at AMEC
Developing Monte Carlo based software to model radiation transport
(neutron, photon)
Using simulation software for radiation analysis
Leading projects involving development/testing/application of
simulation software.
Developing (deterministic) simulation software for crack initiation and
evolution in materials.
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AMEC at a glance
FTSE 100 company
Operating in over 40 countries worldwide
Serving oil & gas, mining, clean energy and environment & infrastructure markets across the world
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Over 29,000 employees in:
Europe 10,000 Americas 16,000 Growth Regions
3,000
Revenue some £4.2 billion
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Sectors
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Oil & Gas
Unconventional Oil & Gas
Nuclear
Renewables/ Bioprocess
Transmission & Distribution
Power
Water
Transportation/ Infrastructure
Government Services
Industrial/ Commercial
Mining
Oil & Gas Mining Clean Energy Environment & Infrastructure
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Our offices around the world
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Our 29,000 employees operate in 40 countries
AMEC office locations
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Key nuclear markets
Decommissioning
Waste Management
Environmental
Radiological
Lifetime Extension
Operational
Performance
Reactor Servicing
NUCLEAR
CLEAN UP
REACTOR
SUPPORT
NEW
BUILD
Strong renaissance in
Europe, potentially
>30 new reactors in
next two decades
10 GW new capacity
planned for UK at
£20bn by 2020.
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Nuclear – UK locations
Westlakes
Warrington
Knutsford
Gloucester
Winfrith
Thatcham
Harwell
Regional Office
Site Presence Hinkley
Dungeness
Torness
Hunterston
Heysham
Aldermaston
Faslane
Dounreay
Sizewell
Wylfa
Trawsfynydd
Oldbury
Barnwood
Chapelcross
Hartlepool
Culham
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Physics & Performance technical
disciplines
Nuclear Physics
Reactor Core Physics
Criticality
Shielding analysis
Radiological
Health Physics
Radiological Protection,
Dosimetry
Transport
Radiological safety
Environmental
Environmental control, pollution
prevention and control,
sustainability, contaminated land
Environmental safety
Plant Performance
Performance optimisation
Dynamic analysis of system
behaviour
Simulation-based analysis of
operational and control problems
Thermal hydraulics
CFD
Heat transfer & Fluid Flow
Transient analysis
Nuclear reactor behaviour during
faults
Gas Cooled Reactors
Water Cooled Reactors
(PWR/LWR)
Fast Reactors
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Nuclear Fission
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Nuclear fission
MeV192.9 fragments fission4.2235 nnU
decay
α, β, γ radiation
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Resulting physics problems:
Fuel elements are produced by enriching with U235. Protection
against neutron radiation in production process of fuel.
During operation: ensure shielding against any radiation and
containment of radioactive substances (e.g. coolant) under a variety
of possible fault conditions.
‘spent’ fuel contains various fission products; highly radioactive; most
importantly radiating gammas (from nuclear decay). Ensure protection
against this radiation during extraction from reactor, transport,
processing, storage.
Material may be activated by Neutrons becoming a gamma source
In a nuclear chain reaction the number of Neutrons rapidly increases.
Only if balanced by neutron absorption (e.g. in the control rods) and
loss can a controlled nuclear reaction be maintained. When does the
n-production rate exceeds the absorption rate (criticality) ?
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The Shielding Problem
Neutrons/photons/electrons emitted from the source move through a
geometry undergoing:
• Capture
• Scatter
• Escape
Given a specified source: What is the particle flux in a specified
area?
Source Scatter Capture
Escape
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The Criticality Problem
Neutrons emitted from the source undergo a sequence of events:
• Fission
• Capture
• Scatter
• Escape
Fission events are sources of further neutrons. For given geometry
and materials: what is the ratio of produced and lost neutrons ?
Source Fission Scatter Capture
Escape
Source’
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Estimating K
A neutron generation starts with the emergence of a neutron
from a fission event and ends with it escaping from the system or
being captured or initiating a further fission event.
k = neutrons produced in one generation
neutrons lost in the same generation
Therefore in a simple Monte Carlo calculation we can calculate
the value of k for a large number of sample neutrons and then
compute an average value.
In civil nuclear applications we want k<=1 !
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Monte Carlo solution (shielding and
criticality problem)
Model the system and simulate the tracking of a sample of particles.
Sample position, energy and direction of a particle emitted from the source.
Sample distance to be travelled in the current material before a collision
occurs (using total cross section)
Sample nuclide with which a collision occurs (using specified material
composition)
Now (and here is most of the physics) :
– Sample type of reaction with the collided nucleus
– For scattering events: the energy and direction of the scattered particle(s)
– For fission events: the number of emergent neutrons, their energies and
directions.
Compute tally
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Main particle reactions
(x, y): x in, y out
Neutrons
Elastic, inelastic scattering, (n, n), (n,n’)
Fission
Radiative capture (n, γ)
Alpha decay
(n, p), (n, 2n)
Photons:
Compton scattering (tracking of electron)
Photo-electric effect (tracking of electron)
Pair production (e+e- may be tracked)
Cross section available in library shipped with software
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Monte Carlo software by AMEC
MCBEND : A generalised 3D Monte Carlo code for Neutron, Gamma
and Electron transport in sub-critical systems
– acknowledged standard UK Monte Carlo computer code for radiation
shielding and dose assessments.
MONK: A 3D Monte Carlo code for nuclear criticality safety and
reactor physics analysis.
Both codes are licensed by ANSWERS Software Service, AMEC
http://www.answerssoftwareservice.com/
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Elements of a Monte Carlo Calculation
A specification of the geometry of the system.
The description of the materials.
The location and characteristics of the neutron, photon or electron
source.
The scores or tallies required.
Any variance reduction techniques to improve efficiency.
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Geometry Modelling in MCBEND
The MCBEND geometry modelling and tracking package
comprises:
A simple body component (Fractal Geometry or FG) using conventional
‘ray tracing’
The additional power of hole geometries employing Woodcock tracking
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Fractal Geometry
Fractal Geometry is a system of solid geometry modelling.
The problem geometry is subdivided into ZONES of uniform material.
These zones are defined as the intersections and differences of
simple mathematical BODIES such as cuboids, cylinders and
spheres. Any body can be rotated from
its alignment with the part axes
+1 -2
2 1
+1 +2
1 2
+1 OR+2
1 2
Difference
Intersection
Union
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Selection of Simple Body Types
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Fractal Geometry PARTS
The bodies are assembled into structures called PARTS. Parts are
self contained to simplify the construction and to take advantage of
any replication which may be present.
Parts may be included within other parts to any depth of nesting and
a given part may be included more than once within the geometry.
The ability to break down complex models into parts, each separately
described in its own local co-ordinate system, simplifies the
preparation and checking of the input data.
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Part Types
+4 +3 +1 +2
+2 -1
+1 -2
3 2
1
4 Container body
General FG part
Cluster part
1 2 3
5
4 6
Container body
Nest part
6
Container body
Overlap part
1
Container body
7 1
2 3
4
2
3
4
Array part
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Subsidiary Parts
Each subsidiary part is defined separately as a normal part
but then it is placed inside a zone of another part.
Reactor Segment
Core Segment
Fuel Assembly
Safety Assembly
Control Assembly
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Hole Geometries in MCBEND
Woodcock tracking: Introduce fictitious material to make free path
length the same in all materials: No need to solve equation to
check in which zone particle is.
Additional geometric complexity
Used in conjunction with simple body geometries by placing a
hole geometry inside a zone (taking the place of a physical
material or a subsidiary part)
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Hole Material Types
SPIRAL TETMESH
CONE LATTICE
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Hole Material Types
PLATE
POLY
PIPES
QUADRIC
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Hole Material Types
RANDOM
RZMESH
RANDRODS
VOXELA
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CAD Interfaces
Two CAD interfaces are being developed for use with MCBEND.
Either convert a CAD file into tetrahedral mesh and import as a
Hole Geometry. Or directly convert into MCBEND geometry.
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A given material is defined by VOLUME or WEIGHT or ATOM
fractions of the following constituents:
Elements referenced by their chemical symbol -
e.g. Fe
A standard mixture from a library -
e.g. STAINLESS STEEL
A user-defined mixture of elements -
e.g. a mixture of sodium, chlorine, hydrogen and oxygen
defining a particular saltwater.
Material Specification
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Elements of a Monte Carlo Calculation
A specification of the geometry of the system.
The description of the materials.
The location and characteristics of the neutron, photon or
electron source.
The scores or tallies required.
Any variance reduction techniques to improve efficiency.
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Source Specification
The Source Variables are :
The nature of the source - neutron, photon or electron.
The position of the source defined by its x, y and z coordinates.
The geometrical extent of the source (e.g. using bodies as above)
The energy of the source particle.
The initial direction of the source particle.
The weight of the source particle (source strength).
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Energy Variation
A range of options are available for defining the energy
variation.
group
Histogram
P(G)
Energy
P(L)
Lines
Energy
Continuous spectrum:
U235 Fission and/or
U238 Fission
Am/Be
1/E
P(E)
q
P(q)
Angular spectrum
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Elements of a Monte Carlo Calculation
A specification of the geometry of the system.
The description of the materials.
The location and characteristics of the neutron, photon or electron
source.
The scores or tallies required.
Any variance reduction techniques to improve efficiency.
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Scoring
Need to specify :
The scoring quantity (i.e. what we want to score), e.g. Flux
Response, e.g. Gamma dose rate
Sensitivity of Flux or Response
Pulse Height Distribution
The scoring energy group scheme MCBEND has standard energy group schemes
The scoring region (i.e. where we want to score it)
one or more FG regions or surfaces
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MCBEND: Example Input File
& EXAMPLE B1 - FUEL TRANSPORT FLASK, NEUTRON CASE
& Variation using structured parts and holes.
BEGIN CONTROL DATA
SAMPLE LIMIT 100000
Seeds 12345 54321
END
& Using SQUARE and PLATE Holes for fuel assemblies
BEGIN MATERIAL GEOMETRY
PART 1 NEST ! Flooded container
BOX BH1 1.0 0.5 75.0 24.0 24.0 400.0
BOX M3 0.5 0.5 75.0 25.0 25.0 400.0
BOX M4 0.0 0.0 75.0 26.0 26.0 400.0
...
Etc.
...
END
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Elements of a Monte Carlo Calculation
A specification of the geometry of the system.
The description of the materials.
The location and characteristics of the neutron, photon or electron
source.
The scores or tallies required.
Any variance reduction techniques to improve efficiency.
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Variance Reduction
A realistic shielding problem may involve attenuation by a factor of
106 or more.
Typically, to provide acceptable results at least 100 particles must
reach the scoring region.
Thus, a direct analogue Monte Carlo calculation would involve
simulating 108 or more particles.
Techniques for getting round this problem are known as:
Variance reduction techniques
Particle weights:
Each particle carries a weight, W, which is a measure of the number of physical particles it represents.
It is possible to alter the normal probability of an event as long as the particle weight is adjusted to compensate.
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Variance Reduction: Splitting and Russian
Roulette
score
Splitting mesh
• Define splitting mesh covering model geometry
• Define importance values in each cell
• When particle crossing boundary with increasing importance
double particle number but half their weight
• When crossing boundary with decreasing importance: sample
particle death or survival. Double weight if survival.
• Importance values can be calculated automatically in
MCBEND
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Variance Reduction: Source Weighting
Particles from some parts of the source or emitted in certain directions
or with certain energies are more likely to contribute to the detector
response than others.
Sample particles more frequently which are more likely to reach the
scoring area. Compensate by adjusting the weights.
Angular source weighting:
Polar axis
Particle Track
Bin of highest importance
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Variance reduction: Forced Flight
Forced Flight Interface
Track of real particle
created at the interfaceTrack of Forced Flight Particle
Track of
original
part ic le
Detector
Collis ion
Collis ion
Collimator
• Particles are forced into a particular direction towards a geometric interface located near the detector.
• At each collision, a ‘forced flight particle’ is created and transported directly to the interface without further collision.
• The weight of the particle is adjusted accounting for the true probability of a particle scattering in that direction and travelling uncollided to the interface.
• The original particle is also tracked onwards and can produce further forced flight particles.
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Visual Workshop
Software offered by ANSWERS
Visualise model
Check model
Run calculation
View results
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Visual Workshop: Real time interactive
3D ray trace
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Visual Workshop: 2D ray trace with
rulers and overlays
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Visual workshop: results display
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Nuclear Fusion
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ITER / France
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Gamma radiation after shut-down
Materials activated
by n-irradiation act
as gamma source
150Mio °C hot
plasma in here
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CONGA (COupled Neutron Gamma Analysis)
Bespoke software suite currently under development at AMEC
Couples MC code MCNP and nuclear activation code FISPACT
MCNP
Neutron
fluxes
FISPACT
MCNP Photon
spectra
Photon
fluxes
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ANSWERS Software Service
High quality software and consultancy services for customers world-
wide in the areas of reactor physics, radiation shielding, dosimetry,
nuclear criticality, well logging and nuclear data.
Based in Dorset /UK
Close collaboration with various universities
Codes:
MCBEND, MONK
WIMS (General purpose reactor physics program for core physics
calculations, deterministic and Monte Carlo)
PANTHER (Advanced 3D nodal code for reactor core analysis)
FISPIN (calculates the changes in the numbers of atoms of the nuclides as
a result irradiation and cooling)
...
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Conclusions
Nuclear renaissance in Europe; New build in UK
Shielding and Criticality problem Monte Carlo solution MCBEND
/ MONK
Elements of a Monte-Carlo Calculation
Geometry
Source
Scoring
Variance Reduction
Visual workshop: Visualisation, Checking, Results
Fusion/ITER: CONGA for gamma radiation from activated materials
We are always on the watch out for enthusiastic highly skilled new
people.
Contact: [email protected]