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I2S-LWR Activation Analysis of Heat Exchangers Using Hybrid Shielding Methodology With SCALE6.1

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
Dubravko Pevec orcid.org/0000-0002-1991-5193 ; 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

Sažetak

The Integral Inherently Safe Light Water Reactor (I2S-LWR) concept developed by a team
lead by Georgia Tech is a novel PWR reactor delivering electric power of 1000 MWe while
implementing inherent safety features typically reserved for Generation III+ small modular reactors.
The main safety feature is based on an integral primary circuit configuration, bringing together a
compact core design with 121 fuel assemblies (FA), control rod drive mechanism (CRDM), 8
primary heat exchangers (PHE), 4 passive decay heat removal systems (DHRS), 8 pumps, and other
integral components. A high power density core based on uranium silicide fuel (U3Si2) is selected to
achieve high thermal power which is extracted with PHEs placed in the annular region between the
barrel and the vessel. The compact and integrated design of I2S-LWR leads to activation of integral
components, mainly made from stainless steel, so accurate and precise Monte Carlo (MC)
simulations are needed to quantify potential dose rates to personnel during routine maintenance
operation. This shielding problem is therefore very challenging, posing a non-trivial neutron flux
solution in a phase space. This paper presents the performance of the hybrid shielding
methodologies CADIS/FW-CADIS implemented in the MAVRIC sequence of the SCALE6.1 code
package. The main objective was to develop a detailed MC shielding model of the I2S-LWR reactor
along with effective variance reduction (VR) parameters and to calculate neutron fluence rates
inside PHEs. Such results are then utilized to find the neutron activation rate distribution via 60Co
generation inside of a stack of microchannel heat exchangers (MCHX), which will be periodically
withdrawn for the maintenance. 59Co impurities are the main cause of (n,γ) radiative gamma dose to
personnel via neutron activation since 60Co has half-life of 5.27 years and is emitting high energy
gamma rays (1.17 MeV and 1.33 MeV). The developed MC model was successfully used to find
converged fluxes inside all 8 stacks of PHEs with respect to MC statistics using the FW-CADIS
methodology. For that purpose the SN module Denovo, based on forward-adjoint transport theory,
was used to find VR parameters (importance map and biased source) to effectively bias MC
simulation. Further research is required to account for other activation pathways, i.e. isotopes of
iron which may generate 59Co through neutron activation and beta decay.

Ključne riječi

I2S-LWR; PWR; shielding; Monte Carlo; activation; SCALE6.1; FW-CADIS

Hrčak ID:

199633

URI

https://hrcak.srce.hr/199633

Datum izdavanja:

15.10.2017.

Posjeta: 531 *