### Iteration mode

Posted:

**Thu Aug 19, 2010 5:56 pm**Jaakko,

I tried to run a PWR assembly model in the B1 iteration mode. I got the following:

====================================================================

Starting the transport calculation cycle...

Sampling initial source...

OK.

Inactive cycle 1 / 25: k-eff = 1.11376 (DT thresh = 0.9000)

Inactive cycle 2 / 25: k-eff = 1.11677 (DT thresh = 0.9000)

Inactive cycle 3 / 25: k-eff = 1.11915 (DT thresh = 0.9000)

Inactive cycle 4 / 25: k-eff = 1.12349 (DT thresh = 0.9000)

Inactive cycle 5 / 25: k-eff = 1.12085 (DT thresh = 0.9000)

Inactive cycle 6 / 25: k-eff = 1.12095 (DT thresh = 0.9000)

***** Wed Aug 18 13:50:09 2010 (seed = 1282132193)

Fatal error in function NextCollision:

Total xs exceeds majorant (E = 1.225141E+00, f = 7.934123E-04)

Simulation aborted.

====================================================================

I was wondering if you have any explanations for such a behavior? Note that without iterations everything runs smoothly.

I tried to run a PWR assembly model in the B1 iteration mode. I got the following:

====================================================================

Starting the transport calculation cycle...

Sampling initial source...

OK.

Inactive cycle 1 / 25: k-eff = 1.11376 (DT thresh = 0.9000)

Inactive cycle 2 / 25: k-eff = 1.11677 (DT thresh = 0.9000)

Inactive cycle 3 / 25: k-eff = 1.11915 (DT thresh = 0.9000)

Inactive cycle 4 / 25: k-eff = 1.12349 (DT thresh = 0.9000)

Inactive cycle 5 / 25: k-eff = 1.12085 (DT thresh = 0.9000)

Inactive cycle 6 / 25: k-eff = 1.12095 (DT thresh = 0.9000)

***** Wed Aug 18 13:50:09 2010 (seed = 1282132193)

Fatal error in function NextCollision:

Total xs exceeds majorant (E = 1.225141E+00, f = 7.934123E-04)

Simulation aborted.

====================================================================

I was wondering if you have any explanations for such a behavior? Note that without iterations everything runs smoothly.