Modeling Impact-Induced Reactivity Changes Using DAG-MCNP5
- University of Wisconsin, Madison, WI (United States)
There is a long literature studying the criticality of space reactors immersed in water/sand after a launch accident; however, most of these studies evaluate nominal or uniformly compacted system configurations. There is less research on the reactivity consequences of impact, which can cause large structural deformation of reactor components that can result in changes in the reactivity of the system. Predicting these changes is an important component of launch safety analysis. This paper describes new features added to the DAG-MCNP5 neutronics code that allow the criticality analysis of deformed geometries. A CAD-based solid model of the reactor geometry is used to generate an initial mesh for a structural mechanics impact calculation using the PRONTO3D/PRESTO continuum mechanics codes. Boundary conditions and material specifications for the reactivity analysis are attached to the solid model that is then associated with the initial mesh representation. This geometry is then updated with the deformed finite element mesh to perturb node coordinates. DAG-MCNP5 was extended to accommodate two consequences of the large structural deformations: dead elements representing fracture, and small overlaps between adjacent volumes. The dead elements are removed during geometry initialization and adjustments are made to conserve mass. More challenging, small overlaps where adjacent mesh elements contact cause the geometric queries to become unreliable. A new point membership test was developed that is tolerant of self-intersecting volumes, and the particle tracking algorithm was adjusted to enable transport through small overlaps. These new features enable DAG-MCNP5 to perform particle transport and criticality eigenvalue calculations on both deformed mesh geometry and CAD geometry with small geometric defects. Detailed impact simulations were performed on an 85-pin space reactor model. In the most realistic model that included NaK coolant and water in the impact simulation, the eigenvalue was determined to increase 2.7% due to impact.
- Research Organization:
- Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); University of Wisconsin, Madison, WI (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP)
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 1030306
- Report Number(s):
- SAND2010-7696C
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
97 MATHEMATICS AND COMPUTING
ALGORITHMS
BOUNDARY CONDITIONS
COOLANTS
CRITICALITY
DEFECTS
DEFORMATION
Detailed impact simulations
EIGENVALUES
GEOMETRY
Impact Reactivity Consequences
Launch Accident
Launch Safety Analysis
Models
New Features
Nuclear Criticality Safety Program (NCSP)
POTASSIUM ALLOYS
PRONTO3D/PRESTO
REACTOR COMPONENTS
REACTORS
SAFETY ANALYSIS
SIMULATION
SODIUM ALLOYS
SPECIFICATIONS
Space Reactors Criticality
TRANSPORT
WATER