Original scientific paper
Spent Fuel Pool Dose Rate Calculations Using Point Kernel and Hybrid Deterministic-Stochastic Shielding Methods
Mario Matijević
orcid.org/0000-0001-9775-5773
; University of Zagreb, Faculty of Electrical Engineering and Computing, Department of Applied Physics, Unska 3, 10000 Zagreb, Croatia
Radomir Ječmenica
; University of Zagreb, Faculty of Electrical Engineering and Computing, Department of Applied Physics, Unska 3, 10000 Zagreb, Croatia
Davor Grgić
; University of Zagreb, Faculty of Electrical Engineering and Computing, Department of Energy and Power Systems, Unska 3, 10000 Zagreb, Croatia
Abstract
This paper presents comparison of the Krško Power Plant simplified Spent Fuel Pool (SFP)
dose rates using different computational shielding methodologies. The analysis was performed to
estimate limiting gamma dose rates on wall mounted level instrumentation in case of significant
loss of cooling water. The SFP was represented with simple homogenized cylinders (point kernel
and Monte Carlo (MC)) or cuboids (MC) using uranium, iron, water, and dry-air as a bulk region
materials. The pool is divided on the old and new section where the old one has three additional
subsections representing fuel assemblies (FAs) with different burnup/cooling time (60 days, 1 year
and 5 years). The new section represents the FAs with the cooling time of 10 years. The time
dependent fuel assembly isotopic composition was calculated using ORIGEN2 code applied to the
depletion of one of the fuel assemblies present in the pool (AC-29). The source used in Microshield
calculation is based on imported isotopic activities. The time dependent photon spectrum with total
source intensity from Microshield multigroup point kernel calculations was then prepared for two
hybrid deterministic-stochastic sequences. One is based on SCALE6.2b3/MAVRIC (Monaco and
Denovo) methodology and another uses Monte Carlo code MCNP6.1.1b and ADVANTG3.0.1.
code. Even though this model is a fairly simple one, the layers of shielding materials are thick
enough to pose a significant shielding problem for MC method without the use of effective variance
reduction (VR) technique. For that purpose the ADVANTG code was used to generate VR
parameters for the MCNP fixed-source calculation using continuous energy transport. ADVATNG
employs a deterministic forward-adjoint transport solver Denovo which implements CADIS/FWCADIS
methodology. Denovo uses a structured, Cartesian-grid SN solver based on the Koch-
Baker-Alcouffe parallel transport sweep algorithm across x-y domain blocks. This was our first
application of ANDVANTG/MCNP hybrid sequence for this type of calculation and the results
where compared to SCALE/MAVRIC sequence which we regularly use for similar calculations.
The comparison of gamma dose rates on different point detector locations (central above pool and
at the top of pool periphery) showed a good agreement between Microshield (point-kernel) and
deterministic-stochastic shielding methodologies for the cylindrical approximation of the pool
geometry. More complicated cases for model with multi-source option and for cuboids showed very
good agreement between SCALE/MAVRIC and ANDVANTG/MCNP calculations.
Keywords
pool dose rate; point kernel; hybrid deterministic-stochastic; Microshield; SCALE/MAVRIC; MCNP; ADVANTG; FW-CADIS
Hrčak ID:
199634
URI
Publication date:
15.10.2017.
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