Lecture on applications of the monte carlo adjoint shielding methodology
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Lecture on Applications of the Monte Carlo Adjoint Shielding Methodology. By Roger A. Rydin , University of Virginia, Consultant U.S. Army Craig R. Heimbach , formerly with Army Pulse Radiation Facility. Personnel. Rydin - University Expert, NGIC, VA

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Lecture on applications of the monte carlo adjoint shielding methodology

Lecture onApplications of the Monte Carlo Adjoint ShieldingMethodology

By

Roger A. Rydin, University of Virginia, Consultant U.S. Army

Craig R. Heimbach, formerly with Army Pulse Radiation Facility


Personnel
Personnel

  • Rydin - University Expert, NGIC, VA

    Computational Studies of Military Vehicles and Structures

  • Heimbach – Experimentalist, APG, MD

    Neutron and Gamma Ray Spectroscopy

  • APRF, Crane-Mounted Bare Fast Reactor

  • WWD, Munster, Germany, Movable Fallout Simulator

  • ETBS, Bourges, France, Fallout Simulator


Order of talk
Order of Talk

  • Generalities About Shielding Methodology

  • Available Computer Codes

  • Statement of Problem

  • Solution – Hybrid Method Called MASH

  • Examples Galore


Comments on mixed field neutron gamma ray shielding
Comments on Mixed FieldNeutron-Gamma Ray Shielding

  • Shielding is an Art

    Requires Skilled Modeling

  • Shielding Requires Transport Theory

    Highly Anisotropic Cross Sections

  • Discrete Ordinates Sn Methods

    Large Distances In Regular Geometry

  • Monte Carlo Methods

    Short Distances In Detailed Geometry


General mixed field neutron gamma ray shielding
General Mixed FieldNeutron-Gamma Ray Shielding

  • Shield Neutrons With Light Materials

    Water, Plastic, Boron

  • Shield Gamma Rays With Heavy Materials

    Lead, Iron

  • Beware of

    Holes and Gaps !


Shielding codes
Shielding Codes

  • ORNL (Shielding)

    ANISN, DORT, TORT, Discrete Ordinates

    MORSE, Multi-group Monte Carlo

  • LANL (Weapons Design)

    TRIDENT, etc, Discrete Ordinates

    MCNP, Continuous Energy Monte Carlo

  • Cross Section Libraries, Quadratures

    Incompatible! (2 l +1) / 2 Factor


Monte carlo codes
Monte Carlo Codes

  • MORSE

    Volumetric Primitives - SPH, RPP, ARB,

    ARS, TRC, BOX, ELL, etc

    Boulean Combinatorial Geometry

  • MCNP

    Define Surfaces, Make Volumes

    Easy Replication, Restart

    Can’t Do Adjoint Problem


Basic question
Basic Question

  • How Do You Accurately Calculate the Dose Inside a Geometrically Complicated Shield a Large Distance from a Mixed Source of Neutrons and Gamma Rays ?

  • Discrete Ordinates Can’t Handle The Shield Geometry (Stair Steps ?)

  • Monte Carlo Can’t Handle the Distance or a Small Size Dose Receiver


Air over ground problem
Air-Over Ground Problem

  • 2D Problem Covers 2+ Kilometers

    Large, Geometrically Increasing, Mesh Spaces in Air, Small Mesh in Ground

  • 42 Neutron, 17 Gamma Ray Groups

    Cover Inelastic Scattering

  • P6 Cross Sections

    Compton Scattering Anisotropy

  • S16 Forward – Biased Quadrature Set


Adjoint problem
Adjoint Problem

  • Every Integro – Differential Equation Has

    a Dual, Adjoint or Importance Counterpart

  • Equations Are Connected Through an

    Integral Variational Principle Functional

  • They Have the Same Boundary Conditions

  • The Operators Are Obtainable By

    Transpositions, Role Reversals, and

    Energy Direction Reversal


Solution mash methodology
Solution - MASH Methodology

  • Transport from Source = Discrete Sn Calculation with DORT (2D) or TORT (3D)

    NoDistance and Geometry Limitations to Vicinity of Shield

  • Dose in Complicated Shield = Stochastic Calculation with MORSE in Adjoint Mode

    Shield Geometry Complexity, Orientation, and All Particles Start from Detector Volume

  • Couple Over a Surface Around Shield


Mash methodology
MASH Methodology

  • Implied – The Presence of the Shield Doesn’t Perturb the Discrete Ordinates Solution

  • If Untrue, Add a Dummy Shield

  • Rotation of the Shield Before Coupling Doesn’t Affect the Answer – Not True for Big Shields


Theory
Theory

  • FLUX From Source Distribution

  • IMPORTANCE From Detector Response

  • L-Terms Cancel


Dose calculation

Need Flux at Detector or Importance at Source

Or Flux and Importance at a Coupling Surface

Dose Calculation


Definitions
Definitions

  • Neutron Reduction Factor NRF

    NeutronDose Outside (Gray) / Dose Inside Shield

  • Gamma Reduction Factor GRF

    Gamma Dose Outside (Gray) / Dose Inside Shield

  • Fallout Protection Factor FPF

    Fallout Gamma Dose Outside (Gray) / Dose Inside Shield


Further definitions
Further Definitions

  • Neutron Protection Factor NPF

    NeutronDose Outside (Gray) / N and γ Dose Inside Shield Caused by Neutron Source

  • Gamma Protection Factor GPF

    Gamma Dose Outside (Gray) / γ Dose Inside Shield Caused by γ Source


Applications
Applications

  • Boxes Near a Prompt Source

  • Vehicles Near a Prompt Source

  • BNCT Medical Therapy Room Design

  • Tank on a Fallout Field

  • Small Concrete Building

  • Foxhole

  • Buildings in an Urban Environment


Verification of methodology for simple geometries
Verification of Methodology for Simple Geometries

  • 1 Meter Box, Rotated, With Holes and Gaps

  • 2 Meter Box ORNL Calculation

  • RTK Angled Box From WWD


Detectors
Detectors

  • ROSPEC – 4 Spherical Proportional Counters, Unfolding

  • DOSPEC – Dose – Calibrated NaI

  • Calibrated GM Tubes

  • TE Ion Chambers

    International Intercalibration Effort – US, UK, Germany, France, Canada



Small lined iron box1
Small Lined Iron Box

  • Unlined, Polyethylene Liner,

    Boron Polyethylene Liner

  • 200 Meters From APRF

  • Calibrated GM Tubes, Tissue Equivalent Dosimeters

    Learned The Value of Source Energy Biasing

    Start More Particles That Give High Dose



Medical therapy room1
Medical Therapy Room

  • Dummy Head in DORT Problem Gives

    Scattering Source to Walls

  • Conclusions

  • Doesn’t Make Much Difference If Patient Is Prone In Beam, Seated Out Of Beam, Or Shadow Shielded

  • Dose To Rest Of Body Comes Through the Neck !


T72 russian tank model
T72 Russian Tank Model

>10000 Primitive Bodies:

ARS Arbitrary Surfaces;

ARB Arbitrary Polyhedrons; etc.

>6000 Material Regions by Combinatorial Geometry


T72 russian tank model1
T72 Russian Tank Model

  • The Model Came From BRL CAD – CAM

  • Required Graphical Debugging – ORGBUG

  • Required Tolerance Debugging

    Lost Particles !

  • Required a MORSE Modification !


Fallout field at bourges france using la 140
Fallout Field at Bourges, FranceUsing La-140

  • 80 by 80 Meter Dirt Field

  • At Corner, Rotated ~ 160 by 160 Meters

  • 30 by 30 Meter Concrete Pad

  • At Corner, Rotated ~ 60 by 60 Meters


Experiment vs calculation
Experiment vs. Calculation

  • Fallout simulated with Fission Products

  • Fallout Simulated with La-140

  • Comparison to ORNL Calculations



Observations
Observations

  • Strong Variation, Seat to Head

  • Concrete FPF >Dirt , in General

  • Conc. vs. Dirt Difference, Probably Real

  • Calculation ~in Middle

  • Agreement Generally Within Error Bars

  • Fallout Protection is Significant



General conclusions for t 72
General Conclusions for T 72

  • Fallout Protection Factor ~ 40

  • Driver Less Well Protected ~ 15

  • Some Differences for Source Type

  • Some Differences for Model Maker

  • Typical Accuracy, ~ 15 – 20 %






Concrete building conclusions
Concrete Building Conclusions

  • Reasonably Good Neutron Protection ~ 3

  • Fair Prompt Gamma Protection ~ 3.5

  • Good Fallout Protection ~ 9

    Stay Away From Doors and Windows




Foxhole conclusions
Foxhole Conclusions

  • Reasonably Good Neutron Protection ~ 3

  • Fair Prompt Gamma Protection ~ 2

  • Good Fallout Protection ~ 12

    Keep Head Down and Stay Inside




Large buildings
Large Buildings

  • We Can Make a Geometry Model

  • But - New Problem, Not Yet Solved !

  • NoExperimental Data !

  • TORT Had Computational Limits for 10 Story Building!

  • MASH Coupling Over Large Surface ?


Large buildings cont
Large Buildings, cont.

  • Alternate Method, QAD Point Kernel Gamma Code

  • QAD Uses MASH Model

  • Chinese Building Study near Reactor

  • QAD Point Kernel Buildup Factors ?

  • Effect of Extended Shadowed Source ?


Conclusions
Conclusions

  • MASH Works Very Well for Small Shields

  • C/E Typically 10 – 20 %

  • Large Buildings Represent an Unsolved Problem

  • More Research Needed


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