Lecture on Applications of the Monte Carlo Adjoint Shielding Methodology

1. 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

2. 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

3. Order of Talk • Generalities About Shielding Methodology • Available Computer Codes • Statement of Problem • Solution – Hybrid Method Called MASH • Examples Galore

4. 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

5. 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 !

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. Theory • FLUX From Source Distribution • IMPORTANCE From Detector Response • L-Terms Cancel

14. Need Flux at Detector or Importance at Source Or Flux and Importance at a Coupling Surface Dose Calculation

15. 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

16. 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

17. 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

18. Verification of Methodology for Simple Geometries • 1 Meter Box, Rotated, With Holes and Gaps • 2 Meter Box ORNL Calculation • RTK Angled Box From WWD

19. 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

20. Small Lined Iron Box

21. 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

22. Medical Therapy Room

23. 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 !

24. T72 Russian Tank Model >10000 Primitive Bodies: ARS Arbitrary Surfaces; ARB Arbitrary Polyhedrons; etc. >6000 Material Regions by Combinatorial Geometry

25. T72 Russian Tank Model • The Model Came From BRL CAD – CAM • Required Graphical Debugging – ORGBUG • Required Tolerance Debugging Lost Particles ! • Required a MORSE Modification !

26. 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

27. Experiment vs. Calculation • Fallout simulated with Fission Products • Fallout Simulated with La-140 • Comparison to ORNL Calculations

28. FPF Comparisons

29. 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

30. FPF Comparison, ORNL

31. 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 %

32. Concrete Building Photo

33. Concrete Building Model

34. Concrete Building, Neutrons

35. Concrete Building, Gammas

36. Concrete Building Conclusions • Reasonably Good Neutron Protection ~ 3 • Fair Prompt Gamma Protection ~ 3.5 • Good Fallout Protection ~ 9 Stay Away From Doors and Windows

37. Foxhole Model

38. Foxhole Protection Factors

39. Foxhole Conclusions • Reasonably Good Neutron Protection ~ 3 • Fair Prompt Gamma Protection ~ 2 • Good Fallout Protection ~ 12 Keep Head Down and Stay Inside

40. Tall Buildings

41. Buildings in an Urban Environment

42. 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 ?

43. 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 ?

44. Conclusions • MASH Works Very Well for Small Shields • C/E Typically 10 – 20 % • Large Buildings Represent an Unsolved Problem • More Research Needed