2019 ⦽ǎႊᔍᖒ⠱ʑྜྷ⦺⫭ ⇹ĥ⦺ᚁݡ⫭ םྙ᧞Ḳ
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Meso-scale Multi-physics Modeling of CRUD Layer With Water Radiolysis Reactions
Seungjin Seo1, Byunggi Park2, and Sungyeol Choi1,*
1
Korea Advanced Institute of Science and Technology, 291, Daehak-ro, Yuseong-gu, Daejeon, Republic of Korea
2
Soonchunhyang University, 22, Soonchunhyang-ro, Sinchang-myeon, Asan-si, Chungcheongnam-do, Republic of Korea
*
1. Introduction
During operation of nuclear power plant, axial shift of power distribution has occurred. CRUD (Chalk River Unidentified Deposit or Corrosion Related Unidentified Deposit) layer and boron hideout has been considered as one of the reason of the axial shift. Water radiolysis is one of main part within the CRUD layer due to its influence of chemical environment. This model treats the fully coupled multi-physics within the meso-scale CRUD layer by using COMSOL Multi-physics software for predicting the behavior of radiolysis products within the CRUD layer.
2. Method for Multi-physics Modeling
2.1 Geometry of Model
A meso-scale geometry of CRUD layer with uniform thickness and uniform porosity was used. The cell included the four boundary; cladding interface, coolant interface, steam chimney interface and symmetry line.
2.2 Each Physics Within CRUD Layer
In the CRUD layer, conductive heat transfer with evaporative heat on the surface of steam chimney considered. Due to evaporation, mass flux occurs on the surface of steam chimney, and to satisfy the mass
conservation capillary flow occurs through the porous layer. Mass transport occurs by diffusion and convection due to the capillary flow. Numerous chemical reactions occurs within the layer during mass transport, and they act as source/sink term of species.
Fig. 1. Geometry of CRUD layer.
2.3 Water Radiolysis
During the radiolysis of water, the molecular products are produced by alpha particles and neutrons. Also, the radical products are produced by gamma rays. With the G-valued related with these phenomena and dose rate data, radiolysis reaction rate for thirteen radiolysis products are calculated. These products are also undergone the overall 37 recombination and decomposition reactions and some of them contributes on the chemical reactions as source/sink term of concentration distribution.
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2019 ⦽ǎႊᔍᖒ⠱ʑྜྷ⦺⫭⇹ĥ⦺ᚁݡ⫭םྙ᧞Ḳ3. Results of Meso-scale CRUD Model
Radiolysis products undergo mass transport according to multi-physics. Especially, ܪା, and ܱܪି quietly contributes on chemical reactions, so they have special distribution behavior within the CRUD layer, as shown in Fig. 2. ܪଶ, ܱଶ undergo the partitioning volatilization on the surface of steam chimney, so their concentration near the surface of steam chimney is relatively low compared with CRUD layer.
Fig. 2. Concentration distribution of H2, O2, H +
, and OH-.
4. Conclusion
The behavior of radical and molecular products generated from radiolysis of water was analyzed by using meso-scale CRUD multi-physical model with COMSOL multi-physics software. Thirteen radiolysis products with 37 reactions are calculated with heat transfer, capillary flow, transport and five categories of chemical reactions.
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>@ - +HQVKDZ HW DO ³$ PRGHO RI FKHPLVWU\ DQG WKHUPDO K\GUDXOLFV LQ 3:5 IXHO FUXG GHSRVLWV´ Journal of Nuclear Materials, 353(1), 1-11 (2006). >@ - 'HVKRQ ³3:5 Axial Offset Anomaly (AOA)
*XLGHOLQHV5HYLVLRQ´(35,3DOR$OWR&$S 1008102 (2004).
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[4] D.D. 0DF'RQDOGHWDO³$FRXSOHGHQYLURQPHQW model for stress corrosion cracking in sensitized W\SH VWDLQOHVV VWHHO LQ /:5 HQYLURQPHQWV´ Corrosion Science, 32(1), 51-81 (1991).
>@ + &KULVWHQVHQ ³)XQGDPHQWDO $VSHFWV RI :DWHU &RRODQW5DGLRO\VLV´6., 2006).
