TM on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools IAEA Headquarters, Vienna, Austria 2 – 5 September 2019 Application of Modified ART Mod 2 2 Code to Fis ission Product Behavior Analysis for Spent Fuel Pool of Nuclear Power Plant Thailand Institute of Nuclear Chulalongkorn University Technology (Public Organization) W. Vechgama*, K. Silva, C. Kittasin, S. Rassame Corresponding author email*: wasin@tint.or.th 1
Overv rview ASEAN Network on Nuclear R&D activities Power Safety Research Regional strategy for accident management Fission product Severe accident of NPP behavior analysis 2
Background and Motivation ART Mod 2 Code TINT & CU Fission product behavior during Modified ART Mod 2 severe accident ☑ Containment vessel ✇ Spent fuel pool (SFP) ☑ Reactor vessel To help understand the overall consequences of fission product deposition 3 and release during severe accident of nuclear power plants
Objective The objective of this study is to assess fission product behavior in the SFP to fulfill the gap of fission product analysis. • The Robert Emmett Ginna Nuclear Power Plant ➢ Geometry conditions of the SFP ➢ Boundary conditions of the SFP • Compounds of Cs-137 ➢ Long term effect of Cs-137 ➢ Gas form of CsI ➢ Aerosol form of CsOH 4
Modified ART Mod 2 2 Code Brownian diffusion Gas Aerosol Condensation Diffusiophoresis Adsorption Gas remaining Aerosol remaining Thermophoresis Wall Floor Gravitational Settling Deposition on wall Gas deposition Deposition on floor Aerosol deposition Remaining 5
Sim imulation Conditions The SFP of the Robert Emmett Ginna NPP is selected as a representative accident because of; • PWR type which is the same type of the neighboring NPPs of ASEAN, • Publicly available reports on postulated accidents in case of LOCA or complete draining in the SFP. General information • Ontario, New York, USA • 2 loops PWR, Westinghouse • Capacity of 490 MW(e) https://en.wikipedia.org/wiki/R._E._Ginna_Nuclear_Power_Plant 6
Sim imulation Conditions • CsI in gas form and CsOH in aerosol form are dominant cesium compounds in the SFP analysis. • Cesium compounds in different forms can be evaluated behavior using existing models of modified ART Mod 2. • The study divided to two cases to understand release behavior differences between gas and aerosol. ➢ Case 1: CsI in gas form ➢ Case 2: CsOH in aerosol form Source term parameters Case 1 Case 2 Source term type CsI CsOH Form Gas Aerosol Size [µm] - 50-70 1.48×10 7 1.48×10 7 Amount [Ci] 7
Sim imulation Conditions Geometry parameters of the SFP Environment volume • Nodalization for modified ART Mod 2 code • The studies assumed that the SFP is open to the environment. Geometry parameters Data Length [ft] 43.0 Width [ft] 22.2 Hight [ft] 41.7 Volume [ft 3 ] 3.98×10 4 Source term volume SFP volume 8
Sim imulation Conditions • Thermal hydraulic parameters of the SFP in case of LOCA or complete draining in the SFP are selected because this is period of fission product release. Thermal hydraulic parameters Data Rate of temperature increase ~7 Complete Self- during boiling [°C/hr] draining oxidation of the reaction Self-sustaining oxidation ~900 SFP temperature [°C] Cutoff oxidation temperature [°C] ~1900 Pressure [MPa] 0.101 Starting point of release at 18,760 seconds Boil off rate [ft 3 /hr] 13 Temperature of heat decay and oxidation reaction of the SFP 9
Result and Dis iscussion Case 1: CsI in gas form • Majority of CsI is released from the Release into environment at 17 days SFP into environment in 17 days. • The release characteristic is consistence to measurement data set of Cs and I of the Fukushima nuclear accident. Remaining in • In the Fukushima accident, the major the SFP Adsorption part of the release is estimated to be within 19 days after the accident Case 1 starts. CsI release at 18,760 seconds 10
Result and Dis iscussion Case 2: CsOH in aerosol form Brownian diffusion • Almost no CsOH is released from the SFP into environment. • Brownian diffusion is dominant for CsOH at high temperature due to increases of turbulence flow. • There are no diffusiophoresis and thermophoresis due to assuming no Gravitational settling difference of wall temperature and Release into gas temperature because of the environment CsOH release at limitation of data of temperature. 18,760 seconds 11
Result and Dis iscussion • From experiment of fission product, CsOH can also exist in form gas because of reaction between CsI and steam. • Therefore, there is a potential of a larger release of CsOH into environment when compared to the simulation results. • Accuracy of the results can be further increased by considering the source term ratio of gas and aerosol, difference between wall and ambient temperatures, and chemical reactions appropriately. • From our previous study noted the possibility of having different cesium and iodine compounds due to chemical reactions, such as cesium molybdate (Cs 2 MoO 4 ), cesium telluride (Cs 2 Te), methyl iodide (CH 3 I), iodine pentoxide (I 2 O 5 ). 12
Conclusion Modified ART Mod 2 code was used to assess cesium compounds behavior of the LOCA or complete draining in SFP of the Robert Emmett Ginna Nuclear Power Plant. • Majority of CsI gas tend to be released into environment within 17 days which resembles the release characteristic of the Fukushima Nuclear Accident in early period. • Brownian diffusion is dominating CsOH aerosol deposition at high temperature because of increase of turbulence flow. • Modified ART Mod 2 code can capture the trend of release of CsI gas but not CsOH aerosols because of assuming no difference of wall and gas temperatures. • Total cesium compounds releases and retention can be more accurately estimated if source term ratio of gas and aerosol, difference between no difference of wall and gas temperatures, and chemical reactions are appropriately considered. 13
Future Pla lan • Modified ART Mod 2 code should be adjusted to accurately evaluate cesium compounds aerosol. • The combination of radioactive releases from the RPV and the SFP should be considered to identify mass balance and fission product release. 14
TM on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools IAEA Headquarters, Vienna, Austria 2 – 5 September 2019 Thank you for your kin ind attention Q & A W. Vechgama*, K. Silva, C. Kittasin, S. Rassame Corresponding author email*: wasin@tint.or.th 15
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