goyal paper

7/28/2019 Goyal Paper

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Thermal Analysis of J oule Heated Ceramic Melter

P. Goyal*, Vishnu Verma, R. K. Singh and K. K. Vaze

Reactor Safety DivisionBhabha Atomic Research Centre

Trombay, [email protected]

Abstract

High level radioactive waste (HLW) generatedby nuclear fuel cycle is immobilized using glassmelters. In Glass melters such as Joule Heated

Ceramic Melter (JHCM) electrodes immersed inthe glass generates heat by the joule heating dueto electric current passing between electrodesthrough glass. For melter performance it isrequired to evlaute temperature distribution inthe melter. Thermal analysis of the melter hasbeen carried out with the help of COMSOL.

1.0 IntroductionThermal analysis of a joule heated ceramicmelter (JHCM) has been carried out at Tarapur.In the melter, concentrated high level liquid

waste and glass former (in the form of granules)is fed into Joule Heated Ceramic Melter, whereelectrodes immersed in the glass generates heatby the joule heating due to electric currentpassing between electrodes through glass. Glasshas the property of conducting current at atemperature above approx. 600 C becauseresistivity of glass decreases with increase in thetemperature. The vitrified product glass meltedin the furnace is withdrawn periodically by usinga bottom freeze valve (central or side drain)consisting of joule heated section followed byinduction heated section into the stainless steel

canister.

In ceramic melter, glass is contained in a ceramiclined refractory AZS (Alumina Zirconia Silica).Bubble Alumina as backup refractory is providedto reduce molten glass migration. Standardinsulation materials like insulation brick, fibreboard and fibre wool were used [1] ( Fig. 1).Overall dimension of JHCM is 1516 x 1466 x1874 mm.

Thermal analysis has been carried out with thehelp of COMSOL [2] by taking boundarycondition such as glass pool temperature of950 C and cold cap temperature of 150 Cas

shown in Fig 2. Due to symmetry in X-Z and Y-Zplane only quarter geometry has been modeled.Steady state temperature are reported at selectedlocations from the overall thermal field obtainedfrom the present analysis.

Fig. 1 Section View of J HCM

2.0 MATHEMATICAL MODEL

The temperature distribution in AVS can beobtained by solving the following 3-D

Outer Shell (steel)

Bubble Alumina

AZS

Fibre B

Fibre W

Insulation Bricks

Central Drain

Excerpt from the Proceedings of the COMSOL Conference 2010 India
http://www.comsol.com/conf_cd_2011_in


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conduction equation in Cartesian coordinates forall the materials.

( ) QTkt

TCp +=

.

(1)

Where, T T (x, y, z, t)

In addition to conduction, radiation plays animportant role in heat transfer from glass pool toAZS.

2.1 AssumptionsFixed temperature of 950 C of glass pool hasbeen assumed i.e. glass and AZS interfacetemperature also will be at 950 C but in actualcondition due to convection effect in the cavitythere will be some temperature drop and glass-

AZS interface temperature will be less than 950C. By assuming same temperature of interface(950 C) it will predict higher temperature in themelter then actual case which is conservative.Material properties of the material which is takenin the analysis is shown in Table-1.

Table-1 Material Properties

S.N. Material ThermalConductivity(W/m-k)

1 AZS (AluminaZirconia Silica)

2.88

2 Bubble Alumina 0.83 Fibre Board 0.174 Fibre Wool 0.175 Insulation Brick 0.286 Steel 15.07 Inconel 100 C - 14.1

200 - 14.3300 - 14.5400 - 14.8500 - 15.2600 - 15.7700 - 16.2800 - 16.6900 - 17.01000 - 17.4

8 Upper layer ofglass and glass indrain pipe

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2.2 Boundary Conditions

(i) Fixed temperature of 950 C ofglass pool up to 10 mm above topsurface of main electrode has beenassumed ( Fig.-2).

(ii) Cold cap temperature of 150 Cwith radius of 90 % of glass poolcavity radius.

(iii) Upper layer thickness of glass poolabove molten glass is taken as 100mm.

(iv) Radiation heat transfer within thecavity (emissivity 0.8).

(v) Radiation (emissivity of 0.3) andconvection heat transfer from outersurface of melter to the ambient.

(vi) Outside ambient temperature of air35 C.

(vii) Convective cooling due to air in thechannel of bottom electrode hasbeen considered

Fig. 2 Section View of J HCM with glass pool

and cold cap

Result and Discussion

The computational mesh considered for theanalysis is shown in Fig. 3. The mesh consists ofapproximately 1.7 million cells to adequatelycapture the temperature distribution in variouscomponents of JHCM.

Cold cap (150

Glass Pool (95



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Fig. 3 : Computational Mesh for ThermalAnalysis of JHCM

Temperature Contour plot and slice plot forJHCM are shown in Fig. 4. and Fig. 5respectively

.

Fig.4 Temperature contour plot of JHCM(glass pool temperature of 1223 K)

Fig. 5 Slice plot of Temperature contour plotof JHCM (glass pool temperature of 1223 K)

Steady State temperature variations at mid heightlocation of main electrode (for no glass draining)from inside glass pool to themelter outer surfacefor AVS is shown in Figure 6.

Fig.6 Temperature variation at mid heightlocation of main electrode of JHCM

Acknowledgement

Authors thank Shri P. K. Wattal, Head, PSDDand Chairman of the working group (review ofthe Joule Heated Ceramic Melter related issues)and all the members of working group fordiscussion and input provided for the analysis.



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References

1. Umesh Dani, Y . Kulkarni, K. Banerjee andR. D. Changrani, Industrial ScaleVitrifiaction of High Level RadioactiveLiquid Waste experince at AdvancedVitrifiaction System, Tarapur, IndianNuclear Society, Anushaktinager, Mumbai-94, Vol.5, No.3 July-Sept. 2008.

2. COMSOL Multiphysics, version 4.03. Shri Umesh Dani, Shri Sangam Gupta and

Shri K. Banarjee, NRG- Privatecommunication, 2010.


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