[논문]CFD Analysis of Natural Convection Flow Characteristics of Various Gases in the Spent Fuel Dry Storage System

Shin, Doyoung; Jeong, Uiju; Jeun, Gyoodong; Kim, Sung Joong

doi:10.5293/kfma.2016.19.4.019

[국내논문] CFD Analysis of Natural Convection Flow Characteristics of Various Gases in the Spent Fuel Dry Storage System 원문보기

한국유체기계학회 논문집 = The KSFM journal of fluid machinery, v.19 no.4, 2016년, pp.19 - 28

Shin, Doyoung (Department of Nuclear Engineering, Hanyang University) , Jeong, Uiju (Department of Nuclear Engineering, Hanyang University) , Jeun, Gyoodong (Department of Nuclear Engineering, Hanyang University) , Kim, Sung Joong (Department of Nuclear Engineering, Hanyang University)

Abstract ▼ AI-Helper

Objective of this study is to compare the inherent characteristics of natural convection flow inside the canister of spent fuel dry storage system with different backfill gases by utilizing computational fluid dynamics (CFD) code. Four working fluids were selected for comparison study. Helium currently used backfill gas for canister, air, nitrogen, and argon are frequently used as coolant in many heat transfer applications. The results indicate that helium has very distinct conductive behavior and show very weak natural convective flow compared to the others. Argon showed the strongest natural convective flow but also the worst coolability. Air and nitrogen showed similar characteristics to each other. However, due to difference in Prandtl number, nitrogen showed more effective natural convective flow. These results suggest that experimental validation for the nitrogen is needed to investigate the potential coolability other than currently commercially used helium.

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가설 설정

2) As for air and nitrogen cases, trend of results were very similar to each other. However, nitrogen shows the stronger natural convective flow with much lower PCT inside the canister and faster air movement outside the canister.
3) Argon showed the strongest natural convective flow. However, at the same time, PCT was the highest among the explored four fluids.
1) Helium gas showed low axial heat transfer efficiency and high PCT inspite of relatively high thermal conductivity and specific heat. Very weak flow was observed inside the sub-channel with Reynolds number less than 12 while fast air movement was observed at the outside of the canister.
2) Air and nitrogen showed very similar behaviors to each other. However, even though air mostly consists with nitrogen, difference in Prandtl number was observed and thus nitrogen showed more effective natural convection with higher Reynolds number and much lower PCT.

제안 방법

Thus, the objective of this study is to utilize CFD code to compare the inherent characteristics of natural circulation with four kinds of possible working fluids, helium, air, nitrogen, and argon gases inside the canister of spent fuel dry storage system. Peak cladding temperature (PCT), Reynolds number for each sub-channel, and z-vector velocity contour were compared for all explored cases.
0 simulation are shown in Table 3. All explored simulations were calculated under steadystate and gravitational condition. Flow was assumed as laminar flow because decay heat is small in terms of sub-channel.

대상 데이터

The reference fuel for the simulation was selected as typical PWR fuel, which was cooled in the spent fuel pool for 1,000 days after the discharge with burnup of 45 GWD/MTU. Resulting decay heat was calculated as 6.
Thickness of the canister was conserved and free air space was modeled to apply convective boundary condition at the outer wall of the canister. Stainless steel grade 304 (SS304) was adopted for canister material. Small circles inside the assembly are the locations indicating center of respective sub-channel in diagonal and radial direction named as FD 1, 2, 3 and FR 1, 2, 3, respectively to extract data set.

이론/모형

In this study, a commercial CFD analysis tool, ANSYS FLUENT 17.0 was employed to explore the natural convective flow characteristic in the canister of dry storage system and to investigate the dominant heat removal mechanism with various backfill gases. The comparison of maximum cladding surface temperature inside fuel assembly, Reynolds number distribution of flow inside the sub-channels and investigation of relationship between Rayleigh number (Ra) and Nusselt number (Nu) were major interest in this study.
In this study, natural convective flow simulations for the various backfill gases for the canister of dry storage system were carried out using ANSYS FLUENT code. Helium, air, nitrogen, and argon were selected for the working fluids.

성능/효과

1) Helium case showed the second highest PCT located under the plenum region with very low Reynolds number range and fastest air movement was observed at the free air space near the canister outside wall. These results indicate that most of the heat is transferred radially rather than axially by means of conduction.
3) Argon showed the strongest flow inside the canister but its coolability was the worst among four fluids explored. Due to low specific heat and thermal conductivity, argon showed small Prandtl number, from which effective natural convective flow could be observed.

참고문헌 (8)

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상세보기
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상세보기
Yoo, S. H., No, H. C., Kim, H. M., and Lee, E. H., 2010, "CFD-assisted scaling methodology and thermal-hydraulic experiment for a single spent fuel assembly," Nuclear Engineering and Design, Vol. 240, No. 12, pp. 4008-4020.

상세보기
In, W. K., Kwack, Y. K., Kook, D. H., and Koo, Y. H., 2014, "CFD Simulation of Heat and Fluid Flow for Spent Fuel in a Dry Storage," Transactions of Korean Nuclear Society Spring Meeting, Jeju, Korea.
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상세보기
Churchill, S. W. and Chu, H. H. S., 1975, "Correlating equations for laminar and turbulent free convection from a vertical plate," International Journal of Heat and Mass Transfer, Vol. 18, No. 11, pp. 1323-1329.

상세보기
Ishii, M. and Kataoka, I., 1984, "Scaling laws for thermal-hydraulic system under single phase and two-phase natural circulation," Nuclear Engineering and Design, Vol.81, No. 3, pp. 411-425.

상세보기
Ade, B. J. and Gauld, I. C., 2011, "Decay Heat Calculation for PWR and BWR Assemblies Fueled with Uranium and Plutonium Mixed Oxide Fuel Unsing Scale," ORNL/TM-2011/290.

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