# Presentation: 927318

## Automated Variance Reduction for SCALE Shielding Calculations

*Douglas E. Peplow *
*and John C. Wagner*
**Nuclear Science and Technology Division**
**Oak Ridge National Laboratory**
**14th Biennial Topical Meeting of the ANS **
**Radiation Protection and Shielding Division **
**April 3-6, 2006 **
**Carlsbad, New Mexico, USA**

## Motivation

**Codes need to solve increasingly difficult problems**
**Need accurate and fast answers**
**Monte Carlo with importance sampling is the best variance reduction**
**Codes need to be simple and as automated as possible**

## Background

**SCALE (Standardized Computer Analyses for Licensing Evaluation) **
**Collection of codes for performing criticality safety, radiation shielding, spent fuel characterization and heat transfer analyses**
**Control modules or sequences automate the execution and data exchange of individual codes to perform various types of analyses**
**SAS4 – Shielding Analysis Sequence**
**Automated 1-D variance reduction capability for more than a decade, with limitations **
**Effective for cask midplane and top center dose**
**Not well suited to cask corners and very heterogeneous geometries**
**Hence, need for Monte Carlo tool with automated 3-D variance reduction (AVR) for general shielding applications**

## CADIS Methodology - Consistent Adjoint Driven Importance Sampling 

**Use Discrete Ordinates to find approximate adjoint flux**
**From the adjoint flux**
**Importance map for MC transport  (weight windows for splitting and roulette)**
**Biased source distribution**
**Biased source and importance map work together**

## SCALE Implementation of CADIS

**Cross sections**
**Multi-group SCALE libraries – many choices**
**Create adjoint and forward cross section sets**
**Find the approximate adjoint flux**
**GRTUNCL3-D – first collision code**
**TORT – three dimensional DO transport code**
**Monaco**
**Descendant of MORSE – still in progress**
**Uses SCALE general geometry (KENOVI)**
**Automate as much as possible**

## SCALE Sequence:  MAVRIC

**Monaco with Automated Variance Reduction using Importance Calculations**

**SCALE**
**Driver**
**and**
**MAVRIC**

- Input

**ICE**

**Monaco**

-  **End**

**Optional: TORT adjoint cross sections**

**Optional: 3-D discrete ordinates calculation**

**3-D Monte Carlo**

**Resonance cross-section **
**processing**

** ****BONAMI / NITAWL or**
**BONAMI / CENTRM / PMC**

**TORT**

**GRTUNCL-3D**

**Optional: first-collision source calculation**

## SCALE Sequence:  MAVRIC

**Monaco with Automated Variance Reduction using Importance Calculations**
**Input:**
**Physical Problem**
**Materials**
**Geometry**
**Source**
**Det. Positions**
**Det. Responses**
**Monte Carlo info**
**Histories, max time, etc**
**Adjoint DO info**
**Adjoint source**
**Spacial discretization**

## Example

**Simple cask with ventports**
**Spent fuel: **
**UO2 (20%), air**
**Uniform source**
**Steel, Concrete**

## Example

**Source: photons**
**Response: photon dose**

## Analog Monaco

## Example - Discretization

## Example – Adjoint Flux

## Example – Imp. Map/Biased Source

## Example – Biased source distribution

## Results

## Results

**Compare MAVRIC and Analog**

## Results

**Compare MAVRIC and SAS4**

## Results

**Compare MAVRIC and others: FOM ratios to analog Monaco**

## Results

**Compare MAVRIC and ADVANTG: FOM ratios to analog**

## Future Work

**MAVRIC Sequence**
**Automatic homogenization in importance map**
**Determine standard set of TORT parameters**
**Monaco **
**Flux tallies for regions**
**Mesh tally**
**Testing, Testing, then a bit more Testing**

## Discussion & Questions