d. struwe, w. pfrang forschungszentrum karlsruhe institut für reaktorsicherheit

EUROTRANS DESIGN WP 1.5 Meeting May 22nd/23rd 2007 Stockholm, Sweden

Recommendations for the MOX fuel conductivity and heat transfer correlations

to be used in the XT-ADS design and safety calculations

D. Struwe, W. PfrangForschungszentrum Karlsruhe

Institut für Reaktorsicherheit

D. Sruwe, W. Pfrang: “Recommendation for the fuel conductivity of the MOX fuel to be used for the XT-ADS

core design” (December 2006)

W. Pfrang, D. Struwe:” Assessment of correlations for the heat transfer to the coolant necessary for heavy

liquid metal cooled core designs” (May 2007)


Correlations for the MOX fuel conductivity

MOX fuel conductivity is dependent on - temperature, - porosity, - oxygen to metal ratio and - burn-up

Correlations of special interest here are the following ones

- the Duriez-correlation with the LUCUTA model for burn-up - the Duriez-NFI correlation used in the FRAPCON-3 code, - the mod. Martin correlations used in the CABRI project - the correlations of Philipponneau used in the EFR project. (Fast Reactor Data Manual, issue 1, Nov. 1990 consistent with Del 3.4 Version 1.0 of the AFTRA project)



Burn-up dependence

Burn-up correction factor of the fuel thermal conductivity correlations ofLucuta and Duriez-mod NFI mod (FRAPCON) for different temperatures over burn-upqualified for LWR fuels



Burn-up dependence

Burn-up correction factor of the fuel thermal conductivity correlations of SAS4A mod. Martin and Duriez-mod NFI mod (FRAPCON) for different temperatures over burn-up qualified forfast reactor or LWR fuels respectively



Porosity dependence

Porosity correction factor of the fuel thermal conductivity correlations SAS4A mod. Martin, Lucuta and Philipponneau over porosity qualified for fast reactor andAnd LWR fuels respectively



Temperature dependence of green fuel

Fuel thermal conductivity correlations SAS4A mod. Martin and Duriez-mod NFI mod (FRAPCON) for 0.025 2-O/M, 0 at% burnup and 5% porosity




• In Duriez et.al. it is explicitly stated on basis of experimental data evaluations for green fuel that the behaviour difference between FBR and LWR mixed oxide fuels is to be taken as a fact

• Equations recommended for the determination of the light water reactor fuels should not be used to calculate the conductivity of hypo- stoichiometric oxide fuels if the Pu- concentration is higher than 15 %.



Fuel thermal conductivity correlations of SAS4A mod. Martin and Philipponneau for different 2-O/M-ratios, 0 at% burn-up and 5% porosity



Burn-up correction factor of the fuel thermal conductivity of correlations SAS4A mod. Martin and Philipponneau for different temp. over burn-up



• Theoretical interpretation of the CABRI projects at FZK i.e. pre-test and post test calculations revealed that use of the re-commendations according to mod. Martin led to the relatively best agreement between experimental observations and calculated results especially in case of low power pre-irradiations. • The international fuels specialists group of the EFR project came to the conclusion that the recommendations provided by Philipponneau should be taken as reference for the EFR project evaluations.

• Differences between mod. Martin and Philipponneau are small except for low power operation conditions.



• Correlations for determination of the influence of burn-up on the fuel conductivity as proposed by Lucuta leads partly to curious results of correction factor dependencies from burn-up which cannot be accepted. • The modified approach followed in the FRAPCON-3 code was investigated in view of experimental results obtained within the CABRI – programs. It could be demonstrated that application of this recommendation leads to an over-estimation of the fuel temperatures by up to 350 K especially for high burn-up conditions and thus to erroneous results concerning fission gas release and clad loading in case it is applied to fast reactor fuel pins.• To maintain consistency with the EFR project recommendation it is appropriate to apply the set of correlations developed by Philipponeau for the fast reactor fuels of the XT-ADS project



Philipponneau’s correlation [T in K]

Thermal conductivity: λ = (1/(A+BT) + CT ** 3 )* FP

A = 1.320 √(x+0.0093) – 0.0911 + 0.0038 τ

B = 2.493 10 -4 m W -1 (constant)

C = 88.4 10 -12 W m -1 K -4 (constant)

FP – correction factor representing the effect of porosity

FP = (1 – P) / (1 + 2P)

P – porosity; x – deviation from stoichiometry; τ – burn-up in at%


Review of heat transfer correlations for HLM

Evaluated dependencies:

- Correlations for tube flows

- Correlations for flows in triangular rod bundles

(influence of P/D - ratio)

- Correlations for flow in square rod bundles

(influence of P/D - ratio)

- Influence of spacers and axial power profiles



Triangular arraysP/D = 1.409



Triangular arraysP/D = 1.563



• Experimental investigations to study the heat transfer in liquid metals have preferably used mercury (Hg) and sodium–potassium alloy (NaK), sometimes also sodium (Na) and, for tube flows, also a lead-bismuth alloy (LBE) has been used.

• The Prandtl numbers of lead and LBE are in the same range as those of Hg and NaK .

• Some developers of correlations assessed experimental data from campaigns using different coolants and none of the respective publications reported on differences which could be attributed to the differences of the fluids.

• Therefore, correlations considered here, which are not explicitly dependent from the Prandtl number, can be used for lead and LBE without restriction.



• The correlation of Subbotin/Ushakov recommended for P/D ratios between 1.2 and 2.0 appears to be the one with the best experimental qualification

• The data base for rod bundles with triangular rod arrange-ments, which has been used to adjust the correlations, is relatively extended, but it has to be noted, that the respective experiments for triangular arrays have all been performed before 1975.

• It has been shown that spacers can enhance the heat transfer substantially, especially in the vicinity of the spacer. This has to be kept in mind if spacers are used which alter the local coolant flow considerably.



• The consequences of possible oxide layers on the cladding should not be covered by the Nusselt number correlations but modelled separately in the computer codes.

1 / alpha total = 1 / alpha conv + 1 /alpha cond

alpha conv – convective heat transfer

alpha cond = lambda / layer thickness

lambda - thermal conduction of the layer, f (density,

temperature)

layer thickness – f (temperature, residence time, etc.)


SAS4A/Ref05R0LBE calculation for XT-ADS hot pin

Peak linear rating: 252 W/cmHTF-corr. LBE => clad: Subbotin/UshakovCoolant inlet temperature: 300 °C

Standard calculation:corrosion layer / GESA treatment not taken into account.

Modified calculation:

Oxide layer with λ = 1 W/(mK) and variable thickness added.(Thermal conductivity of steel in the respective temperature

range is about 28 W/(mK)). Only thermal aspects considered here.


XT-ADS Hot Pin: Axial profiles of clad and coolant temperature


XT-ADS Hot Pin: Axial profiles of the clad inner temperature(Modified calculation with different additional oxide layers)

d. struwe, w. pfrang forschungszentrum karlsruhe institut für reaktorsicherheit

Documents

sweden correlations

martin correlations

mox fuel conductivityburn

correlations of philipponneau

assessment of correlations

duriezmod nfi mod frapcon

heat transfer correlations

porosityeurotrans design