Vitaly Mogulian

Monte Carlo Variance Reduction Research & Code Developing & Nuclear Engineering

Protvino concrete labyrinth benchmark (ALARM-CF-AIR-LAB-001)

A californium-252 neutron source of intensity $5.66 \cdot 10^8$ n/s is located at entrance to a 3-section concrete labyrinth [1]. The goal is computation of spatial distribution of a neutron flux linear functional which is determined via a fluence-to-energy response funtion and relates to the Bonner sphere detector count rates. Those are considered below just two of the most problematic cases among represented in the original work [1]: Case 5A (2 polyethylene plates in the 2nd section) and Case 6B (covered source and dead-end).

In this calculation, the following techniques are used:

Expected value estimators;
Simplified adaptive splitting.

The primary computational gain is achieved here thanks to the simplified adaptive splitting technique.

Computed flux functional - pulse rate by the detector response function is taken from the benchmark data for the case of 5 in. Bonner polyethylene sphere diameter.


Figure 1: Horizontal cross-section of Case 5A model


Figure 2: Horizontal cross-section of Case 6B model

Thicknesses of volumetric detectors are equal to 10 cm. Results of the two 11.2 hours long concurrently ran computations are presented in Figures 3-5 (see details in [2]).


Figure 3: Global plot of count rates spatial distribution for Case 5A, pulse/sec


Figure 4: Local plot of count rates spatial distribution for Case 5A, pulse/sec


Figure 4: Plot of count rates spatial distribution for Case 6B, pulse/sec

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References

Mark Nikolaev, Natalia Prokhorova, Tatiana Ivanova, “Neutron Fields in Three-Section Concrete Labyrinth from Cf-252 Source,” ALARM-CF-AIR-LAB-001, “International Handbook of Evaluated Criticality Safety Benchmark Experiments,” OECD Nuclear Energy Agency, NEA-1486/19, 2021 (DVD).
V.G. Mogulian. An approach to radiation shielding evaluations using estimators by expected scoring. 2025. doi:10.5281/zenodo.16781416.