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Don't Do That BannerIn 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
si1 L (3<1<2)
sp1 1
si2 8

 

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
si1 L (3<1[0:2 0:0 0:2]<2)
sp1 1 8r
si2 8

 

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:

MCNPX OK

 

MCNP6 hangs and the run has to be terminated:

MCNP6 fail

 

 

With the altered source, MCNP6 now runs to completion.

 

MCNP6 OK