In MCNP6, a fixed, cell dependent, lattice source hangs.

Anomaly: | In a fixed, cell dependent, lattice
source without i, j, k, indices MCNP6 hangs. |

History: | Discovered in one of the example
problems in an MCNP6 workshop. |

Versions affected: | MCNP5 and MCNPX run,
MCNP6 hangs. |

Impact: | In MCNP6, must abort the run. |

Work Around: | Use i, j, k, lattice indices in the source description. |

Steps required to reproduce this anomaly:

Note: Run this example in the RSICC release of each of these codes.

About the Input file:

A three by three xz lattice with a pitch of 20 cm. Each lattice cell is filled with an 8 cm radius sphere of water. A fixed source is volumetrically distributed through each of the nine spheres.

The definition of the source in this file is:

sdef cel=d1 rad=d2 |

Note that the si1 definition does not have i, j, k, lattice indices

Click here to download the input file, iddt2 (2 kb).

Process to Produce Anomaly:

Run the input file in MCNP5 and/or MCNPX and verify the result.

Run the input file in MCNP6 and verify that MCNP6 hangs. Type Ctrl-C multiple times until the run aborts.

Work around:

The definition of the source in the new file is:

sdef cel=d1 rad=d2 |

Note that the si1 definition does have i, j, k, lattice indices.

Click here to download the input file, iddt2a (2 kb).

Process to Demonstrate Work Around.:

Run the input file in MCNP5 and/or MCNPX and verify the result.

Run the input file in MCNP6 and verify the results.

Results obtained from our test:

MCNPX ran to completion:

MCNP6 hangs and the run has to be terminated:

With the altered source, MCNP6 now runs to completion.