Description
Table of contents: Contents ………………………………………………………………………………………………………………………… 4 Introduction ……………………………………………………………………………………………………………………. 8 Section 1: Basic Concepts ………………………………………………………………………………………………… 8 1.1 Geometry ………………………………………………………………………………………………………………. 8 1.1.1 Simplest possible input file………………………………………………………………………………… 8 1.1.2 Running MCNP – Simplest Case ……………………………………………………………………….. 9 1.1.3 Simple Input File ……………………………………………………………………………………………. 12 1.1.4 Running and plotting MCNP geometries …………………………………………………………… 14 1.1.5 Surfaces and Complicated Cells: Intersections and Unions ………………………………….. 17 1.1.6 Duplicate Cells, Compliments and Translations: LIKE BUT and TRCL ……………….. 22 1.1.7 Filled Cells: Universes…………………………………………………………………………………….. 26 1.1.8 Lattice Geometries ………………………………………………………………………………………….. 32 1.1.9 Fully Specified Lattice Geometries …………………………………………………………………… 40 1.2 Materials and Cross Sections …………………………………………………………………………………. 45 1.2.1 Specifying Materials ……………………………………………………………………………………….. 45 1.2.2 Neutron cross sections …………………………………………………………………………………….. 46 1.2.3 Low-energy neutron problems – thermal free gas treatment …………………………………. 49 1.2.4 Low-energy neutron problem data – S(a,) thermal treatment ……………………………… 50 1.2.5 Photon cross sections ………………………………………………………………………………………. 53 1.2.6 Electron stopping powers for coupled photon and electron problems ……………………. 57 1.2.7 Data and models for Ions and Charged Particles …………………………………………………. 61 1.2.8 Additional data diagnostics and recommendations ……………………………………………… 62 1.3 Sources ……………………………………………………………………………………………………………….. 63 1.3.1 SDEF Fixed Sources ……………………………………………………………………………………….. 63 1.3.2 SDEF Source Distributions ……………………………………………………………………………… 66 1.3.3 SDEF Dependent Distributions: DS ………………………………………………………………….. 69 1.3.4 Criticality Sources ………………………………………………………………………………………….. 71 1.3.5 Surface Source Read and Write (SSR, SSW) ………………………………………………… 77 1.3.6 Checking sources ………………………………………………………………………………………. 87 1.4 Output and Tallies ………………………………………………………………………………………………… 87 1.4.1 Output Files …………………………………………………………………………………………………… 87 1.4.2 MCNP Estimators and Tally Types …………………………………………………………………… 93 DRAFT 5 1.4.3 Basic Tally Format …………………………………………………………………………………………. 95 1.4.4 Special Tally Treatments ……………………………………………………………………………….. 111 1.4.5 Pulse-Height Tallies ……………………………………………………………………………………… 128 1.4.6 Point Detectors and Next-Event Estimators ……………………………………………………… 134 1.5 Plotting ……………………………………………………………………………………………………………… 143 1.5.1 Geometry Plotting and Command Files …………………………………………………………… 143 1.5.2 Cross Section plotting ……………………………………………………………………………………. 145 1.5.3 Tally Plotting ……………………………………………………………………………………………….. 150 1.5.4 Mesh, Radiography, and Ring Tallies ……………………………………………………………… 167 1.6 Statistics and Convergence …………………………………………………………………………………… 186 Section 2: Examples for nuclear safeguards applications ………………………………………………….. 198 2.1 Example 1: Fuel Assembly in Water Tank …………………………………………………………….. 198 2.1.1 Description…………………………………………………………………………………………………… 198 2.1.2 Geometry description ……………………………………………………………………………………. 203 2.1.3 Other data: sources, materials, tallies, and more ……………………………………………….. 204 2.1.4 MCNP Output ………………………………………………………………………………………………. 206 2.2 Example 2: Coincidence Counter with F4 and F8 Tallies for Coincidence and Multiplicity Counting Rates ………………………………………………………………………………………………………… 207 2.2.1 Description…………………………………………………………………………………………………… 207 2.2.2 Materials ……………………………………………………………………………………………………… 212 2.2.3 Source …………………………………………………………………………………………………………. 212 2.2.4 Tallies …………………………………………………………………………………………………………. 213 2.2.5 Warning Messages ………………………………………………………………………………………… 214 2.2.6 Results ………………………………………………………………………………………………………… 216 2.2.6A: From the Point Model ………………………………………………………………………………… 216 2.2.6B: Rates Calculated without Point Model assumptions……………………………………….. 221 2.3 Gamma pulse height (to be completed) …………………………………………………………………….. 227 2.4 Active Neutron Example: Cf Shuffler ……………………………………………………………………. 231 2.4.1 Description and input file ………………………………………………………………………………. 231 2.4.2 Results ………………………………………………………………………………………………………… 234 Section 3: Examples of Advanced Concepts …………………………………………………………………… 240 Section 3.1 Variance Reduction …………………………………………………………………………………. 240 3.1.1 Introduction …………………………………………………………………………………………………. 240 DRAFT 6 3.1.2 Multigroup Weight Windows and Time Splitting: Lead Slowing Down Spectrometer …………………………………………………………………………………………………………………………… 242 3.1.2.1 Input File Notes …………………………………………………………………………………………. 253 3.1.2.2 Variance Reduction Step 1: simplify problem and add weight window generator . 256 3.1.2.3 Iteration 2 ………………………………………………………………………………………………….. 261 3.1.2.4 Additional iterations …………………………………………………………………………………… 263 3.1.2.5 Cylindrical Mesh Weight Window Summary ………………………………………………… 267 3.1.3 Cell-based weight windows for the Lead Slowing Down Spectrometer ……………….. 271 3.1.4 Time splitting ……………………………………………………………………………………………….. 277 3.1.5 Variance Reduction for the Cf Shuffler ………………………………………………………………. 280 3.1.5.1 Cf Shuffler modified input ………………………………………………………………………….. 280 3.1.5.2 Particle production bias, time splitting, and windows ……………………………………… 285 3.1.5.3 Analysis of Cf Shuffler Variance Reduction ………………………………………………….. 288 3.2 DXTRAN and Other Capabilities for Distributed Source Problems ……………………………… 288 3.2.1 UF6 Cask Model ……………………………………………………………………………………………… 290 3.2.2 DXTRAN ……………………………………………………………………………………………………….. 300 3.2.3 Source Position Biasing ……………………………………………………………………………………. 307 3.2.4 Best Single Detector Solution ……………………………………………………………………………. 310 3.3 Neutron Detector Operation in More Detail ………………………………………………………………. 318 3.3.1 Introduction …………………………………………………………………………………………………….. 318 (i) Make reaction products (model, data) and recoil nuclei ……………………………………………. 318 (ii) Track created particles in real gas composition ………………………………………………………. 321 (iii) Tally energy deposition of particles in active volume (F8 CAP EDEP for coincidence/multiplicity counting) ……………………………………………………………………………… 322 Examples ………………………………………………………………………………………………………………… 322 3He detector Pulse Height ……………………………………………………………………………………… 322 3He Detector Coincidence Calculation …………………………………………………………………….. 324 10B-lined detectors ………………………………………………………………………………………………… 325 References ………………………………………………………………………………………………………………. 332 Section 4: Additional Topics ………………………………………………………………………………………… 332 4.1 Troubleshooting or “How can I be confident in the results?” ……………………………….. 332 4.1.1 Geometry and Materials ………………………………………………………………………………… 333 4.1.2 Detector modelling ……………………………………………………………………………………….. 334 DRAFT 7 4.1.3 Source modelling ………………………………………………………………………………………….. 334 4.1.4 Sample modelling …………………………………………………………………………………………. 335 4.1.5 Tracking limitations ………………………………………………………………………………………. 335 4.1.6 Nuclear Data ………………………………………………………………………………………………… 335 4.1.7 Statistics ………………………………………………………………………………………………………. 336 4.1.8 User …………………………………………………………………………………………………………….. 337 4.1.9 Summary and Conclusions – What to do?………………………………………………………… 337 4.2.1 Analysis of Delayed Neutron Production …………………………………………………………….. 338 4.2.2 Comparison of Table Physics vs Model Physics ………………………………………………….. 342 5 References and Bibliography ……………………………………………………………………………………… 354 6 Table of Figures ……………………………………………………………………………………………………….. 355
