## MCNP Macrobodies and Other Solid Bodies

Moritz recognizes and properly decomposes MCNP4C and MCNP4C2 macrobodies (Table 3 and Figure 1) and Sabrina solid bodies (Table 4 and Figure 2) when reading an MCNP input or Sabrina command file. MCNP4C cell descriptions referencing the macrobodies are converted to the equivalent surface geometry descriptions. Sabrina cell descriptions using the QCELL command are recognized, but the Sabrina (and ITS ACCEPT) CELL command is not yet supported. The GIFT5 geometry format defines several additional bodies and uses different names or definitions for bodies equivalent to the MCNP and Sabrina solid bodies.

Sense Conventions.Sabrina/ACCEPT solid bodies and MCNP macrobodies use different sense conventions when used in cell descriptions. Space inside the body is denoted by a positive sense for the former and negative sense for MCNP. Moritz uses the MCNP convention when displaying body based cell descriptions. These are shown in theOriginal Cell Descriptionfield of the Cell Description property page. The body-based descriptions are rearranged to place bodies with inside sense before any bodies with outside sense.

Facets.For some plane facets of macrobodies, MCNP uses a general plane equivalent to an aligned plane (PX, PY, or PZ) to preserve a preordained sense for the facets. For example, P -1 0 0 5 may be used instead of PX -5. The general plane usage causes problems in some of Moritz algorithms. Unlike MCNP, Moritz always uses an aligned plane where possible and defines the sense accordingly. We have yet to investigate whether this usage will cause problems when a cell description references one of the affected facets directly.

The bodies are converted to surfaces. The individual surfaces may be modified, either interactively or on the Surface dialog. The surfaces resulting from the decomposition of a body are labeled asn.f, wherenis the body's ID number andfis a facet number that is consistent among bodies of the same type. For example, the cylindrical surface of an RCC will always be facet 1. Because surfaces may be deleted in favor of existing identical surfaces, all surfaces from the decomposition of a body may not be present. Surfaces from bodies enclosed by a single surface (SPH, ELL, TX, TY, TZ, and TOR) do not carry a facet number.

Variable References.Variable references in body coefficients are applied to the surface coefficients when there is a direct relation between the two coefficients, such as the radii of an RCC and its cylinder surface.

The surface coefficients inherit variable references from the solid body if it is possible to do so without complicated expressions. For example, if the coefficient of the plane corresponding to the maximum Y face of an RPP carries the same reference as the RPP Ymax coefficient. Consider a Right Circular Cylinder (RCC) parallel to the X axis. It is defined by an origin vector, height vector, and radius with possible references such as

and generates three surfaces:`%Vx %Vy %Vz %H 0 0 %R`

Among the references that are not propagated due to complex expressions are the opening angle of the cone from a Truncated Right Angle Cone (TRC) and the planes from BOX, Right Angle Wedge (WED), and Arbitrary Polyhedron (ARB) bodies.

- Cylinder parallel to the X axis of radius %R centered at (Y, Z) = (%Vy, %Vz)
- Plane perpendicular to the X axis defined by X = %Vx
- Plane perpendicular to the X axis defined by X = %Vx+%H

ELL Differences.The Accept ELL is defined by the coordinates of the 2 foci and the diameter of the major axis. The MCNP ELL (in the R > 0 variant) is defined by the 2 foci and the radius of the major axis. Moritz may not handle both cases consistently; we will sort out the different treatments.

Expanding Bodies.The MCNP Output property page contains options whether or not to expand the macrobodies. When bodies are expanded, the individual surfaces, with ID numbers generated by the program, that define the body are written in the surface block and the cell descriptions referencing the bodies are written in terms of these surfaces. When not expanded, the macrobody definition is written in the surface block, and cell descriptions contain references to the macrobody; if the cell description was originally entered in terms of the individual macrobody facets, that notation will be repeated.

Sabrina Cutter Bodies.Sabrina input files can contain cutter bodies that are used to expose the interior of a model. Bodies that appear as an argument to the Sabrina ICUT command are set to invisible in both 2D and 3D. Because Moritz uses the same numbering sequence for surfaces and bodies, the number of a cutter body may change if it conflicts with an existing surface number.

Figure 2. Sabrina Solid Bodies

Macrobody

Origin

Description

Color in Figure 1

RCC

4C

Right Circular Cylinder

Magenta

RHP

4C

Right Hexagonal Prism

Cyan

RPP

4C

Right Parallelepiped

Brown

SPH

4C

Sphere

Orange

BOX

4C

Box

Dark Blue, Light Green

REC

4C2

Right Elliptical Cylinder

Pink, Red

TRC

4C2

Truncated Right-angle Cone

Light Blue

ELL

4C2

Ellipsoid

Yellow, Gold

WED

4C2

Right Angle Wedge

Green

ARB

4C2

Arbitrary Polyhedron of up to 6 Sides

Grey

Solid Body

Description

Color in Figure 2

RCC

Right Circular Cylinder

Pink

RPP

Right Parallelepiped

Blue

SPH

Sphere

Light Blue

BOX

Box

Yellow

WED

Wedge (aligned with coordinate axes)

Yellow

REC

Right Elliptical Cylinder

not shown

TRC

Truncated Right Cone

Red

ELL

Ellipsoid

Purple

ARB

Arbitrary Polyhedron of up to 6 sides

Gold

TX, TY, TZ

Aligned Torus

not shown

TOR

Nonaligned Torus

not shown

TABSF

Tabular Surface of Revolution

Dark Gray, Light Gray

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