Effect of CASMO-5 Cross-Section Data and Doppler ... - Studsvik

Effect of CASMO-5 Cross-Section Data and Doppler Temperature Definitions on LWR Reactivity Initiated AccidentsThe Doppler reactivity effects are linear with the perturbation in the square root of the fuel temperature.Therefore, k-effective values for any fuel temperature can be well approximated using the Table I flattemperature data. Performing this procedure, the Doppler reactivity worth can be evaluated for thedifferent effective Doppler temperature definitions mentioned above, i.e. ‘BE1’, ‘NEA’ and ‘GDTL’.Another effective Doppler temperature, namely ‘BE2’, will be defined by Eq. (4) below. Results for allfour effective Doppler temperatures are compared in Table II against the exact reactivity computed usingthe non-uniform temperature profiles.Table II: Doppler reactivity for different definitions of effective Doppler temperature.DescriptionDoppler Reactivity (Delta-K/K)Error (%)FromCaseToCaseExact BE1 NEA GDTL BE2 BE1 NEA GDTL BE21 4 -981 -1056 -675 -975 -981 7.7 -31.2 -0.6 0.01 5 -1828 -1935 -1247 -1732 -1802 5.8 -31.8 -5.3 -1.41 6 -1989 -1935 -2392 -1915 -2000 -2.7 20.3 -3.7 0.6Note that, the use of the ‘BE1’ effective temperature over-estimates the Doppler reactivity for quadraticprofiles, and under-estimates the Doppler reactivity for the inverted temperature profile. The ‘NEA’temperature under-estimates the Doppler reactivity for quadratic temperature profiles. The opposite is truefor inverted temperature profiles. The ‘GDTL’ always underestimates the Doppler reactivity, thusrendering conservative results for LWR reactivity initiated accidents. ‘GDTL’ performs very well for atypical HFP quadratic temperature profile; the improvement with respect to ‘BE1’ is noticeable. Forhigher quadratic temperature profiles, the Doppler feedback is under-estimated by ~5%; and for theinverted temperature profile ~4%.Using the k-effective values of Table II, one can define another effective Doppler temperature, namely‘BE2’. The ‘BE2’ effective Doppler temperature is defined such that its Doppler reactivity matches theexact reactivity for the non-uniform cases. The ‘BE2’ Doppler temperature (T BE2 ) is written as a weightedaverage of the volume-averaged temperature (T BE1 ), and the fuel surface temperature (T S ), TT)1 ((4)BE 2 BE1where the value of is empirically adjusted to match the reactivity between the case 1 (representative ofHZP) and case 4 (representative of HFP). Effective Doppler temperatures computed using Eq. (4) with0.92, for the pin cell problem are presented in Table VI on Appendix A. Last column in Table IIcompares the ‘BE2’ Doppler reactivity worth. Note that error introduced by the ‘BE2’ approximation, forall cases presented here, is lower than 1.5%.SPHYSOR 2010 – Advances in Reactor Physics to Power the Nuclear RenaissancePittsburgh, Pennsylvania, USA, May 9-14, 20105/13

Gerardo Grandi et.al.4. DESCRIPTION OF THE ROD EJECTION ACCIDENT SCENARIOThe problem consists in analyzing a rod ejection in a PWR MOX/UO 2 core at Hot Zero Power conditions:10 -4 rated power, core inlet temperature 560 K, core pressure 15.5 MPa. The model was constructed basedon the OECD “PWR MOX/UO2 Core Transient Benchmark [12].” It is important to remark that: Cross sections were generated using CASMO-4 / ENDF/B IV and CASMO-5 / ENDF/B VII.0. The known state of the core (history data) was assumed to be the same regardless of the crosssectionset used in the transient calculations. The 3D fuel temperature distribution is evaluated by solving the one-dimensional, radial heatconduction equation for the average pin of each node. For safety evaluations, all the pins for eachnode may be modeled [2]. The closed channel thermal hydraulics module provides thetemperature of the coolant surrounding the pin which serves as the boundary condition for thefuel temperature calculation. Fuel thermal conductivity for UO 2 and MOX are computed using the Nuclear Fuel Industriescorrelations as reported in reference [14]. The gap conductance model is taken from the INTERPIN-4 code [15] and it is functionalizedversus exposure and temperature. The intra-pellet power profiles are a function of the fuel type (MOX/UO 2 ) and burnup. Valueswere taken from INTERPIN-4. Fig. 2 illustrates those profiles for 0.0 GWd/T, 20 GWd/T and 40GWd/T.All the control rod banks are fully inserted and all the shutdown banks are fully withdrawn. The initialboron concentration is determined to make the reactor critical in steady state. Note that in the OECDbenchmark; only one of the four rods in position E5 is ejected. However, in the present work all four rodsare ejected. The rod ejection starts at time 0 seconds and the rods are ejected in 0.1 s. The transient isfollowed for 5 s. The chosen spatial discretization is: radial mesh of 2x2 nodes per assembly (x=10.7cm) and 24 axial nodes (z=15.24 cm). The fuel pellet is divided in nine equal volume rings, and thecladding in two rings. Following the recommendation from Grandi [16], solutions were obtained with asmall time step (0.1 ms) to avoid any spurious effect from the numerical integration.5. RESULTSResults for two different exercises will be discussed in what follows. The objective of the first exercise isto assess the effect of the CASMO-5 nuclear data on the rod ejection accident key parameters, namely:peak power, time of peak power, peak power width, and peak fuel enthalpy. The objective of the secondexercise is to assess the influence of the Doppler temperature definition on the previously mentionedparameters.5.1. Effect of the CASMO-5 Cross-Section DataIn this subsection, all the calculations are performed using the ‘BE1’ effective Doppler temperaturedefined by Eq. (1). For simplicity, the S3K results obtained using CASMO-4 nuclear data will be referredas ‘CASMO-4’ case or solution; the results computed using CASMO-5 data will be labeled ‘CASMO-5’;and finally, the results computed using CASMO-5 data with the asymptotic scattering kernel (i.e. withoutthe CASMO-5 resonance elastic scattering model active) will be labeled ‘CASMO-5 Asymptotic’. TableIII presents relevant static -fraction, the static rod worthPHYSOR 2010 – Advances in Reactor Physics to Power the Nuclear RenaissancePittsburgh, Pennsylvania, USA, May 9-14, 20106/13

Effect of CASMO-5 Cross-Section Data and Doppler Temperature Definitions on LWR Reactivity Initiated Accidents(SRW)-re average Doppler. The main observations derived from Table III are: Relative differences in rod worth between ‘CASMO-5’ and ‘CASMO-4’ are less than 1%. Nosignificant differences are observed in the core- * . A difference of ~10% is observed in the Doppler coefficient. This result is consistent with thelattice results presented in Fig. 1. Differences in Doppler coefficient between ‘CASMO-5’ and ‘CASMO-4’ due to differences inthe nuclear data (i.e., ENDF/B VII.0 vs. ENDF/B IV) are less than 1.5%. The difference inDoppler coefficient is mainly due to the 238 U resonance elastic scattering treatment. It is expected, that the rod ejection accident computed with CASMO-5 cross-sections will bemilder. The total energy released during the power burst is proportional to the ratio of the promptreactivity and the Doppler coefficient. This ratio is ~11% smaller if CASMO-5 data is usedinstead of CASMO-4 data.Table III: Steady state REA parameters. Effect of CASMO-5 cross-section data.ParameterCASMO-4CASMO-5CASMO-5Exact kernelAsymptotic kernelValue Diff (%) Value Diff (%)Critical Boron (ppm) 1737 1738 0.1 1740 0.2SRW (pcm) 870 863 -0.8 864 -0.7 (pcm) 544 544 0.0 545 0.2 (1.E-05 s) 1.46 1.48 1.4 1.48 1.4 ($) 1.60 1.59 -0.8 1.59 -0.9 (pcm) 326 319 -2.1 319 -2.1 (pcm/K) -2.93 -3.24 10.6 -2.97 1.4Fig. 3 compares the power evolution for the ‘CASMO-4’ and ‘CASMO-5’ cases. Note that the ‘CASMO-5’ solution has a lower power peak, and a smaller peak width, and the energy release during the powerexcursion is smaller.Relative Power (% Rated Power)1.E+041.E+031.E+021.E+011.E+001.E-011.E-021.E-031.E-040.00 0.50 1.00 1.50 2.00Time (s)CASMO-4CASMO-5(a) Period 0.0 s to 2.0 s. Logarithmic scale.(b) Period 0.1 s to 0.2 seconds. Linear scaleFigure 3. Power evolution. Effect of CASMO-5 cross-section data.Relative Power (% Rated Power)60005000400030002000100000.10 0.12 0.14 0.16 0.18 0.20Time (s)CASMO-4CASMO-5* CASMO-5 delayed neutron fractions are not based on ENDF/B VII.0 data, but on the ENDF/B IV data used by CASMO-4.PHYSOR 2010 – Advances in Reactor Physics to Power the Nuclear RenaissancePittsburgh, Pennsylvania, USA, May 9-14, 20107/13

Gerardo Grandi et.al.Fig. 4 compares the Doppler reactivity feedback and the (core average) Doppler temperature evolutionduring the rod ejection accident.Doppler Reactivity ($)0.200.00-0.20-0.40-0.60-0.80CASMO-4CASMO-5Doppler Reactivity ($)-0.80-0.85-0.90-0.95-1.000.0 1.0 2.0 3.0 4.0 5.0Time (s)Doppler Temperature (K)750700650600550CASMO-4CASMO-5-1.000.0 0.5 1.0 1.5 2.0 2.5 3.0Time (s)5000.0 0.5 1.0 1.5 2.0 2.5 3.0Time (s)Figure 4. Doppler reactivity and Doppler temperature. Effect of CASMO-5 cross-section data.Note that the Doppler reactivity is the same in the ‘CASMO-4’ and ‘CASMO-5’ cases. This result iscounter intuitive due the more negative fuel temperature coefficient reported in Table III. However, sincethe external positive reactivity inserted in both cases differ only ~7 pcm; the Doppler reactivity tocompensate the inserted reactivity must be approximately the same. Due to the ~10% difference in theDoppler coefficient (see Table III), the Doppler temperature increase in the ‘CASMO-5’ case is ~10%smaller.Table IV summarizes the rod ejection accident results, in terms of power and fuel enthalpy, for ‘CASMO-4’, ‘CASMO-5’, and ‘CASMO-5 Asymptotic’ cases.The main observations derived from Table IV are: The energy release in the ‘CASMO-5’ case is 88 % of the energy release in the ‘CASMO-4’ case. Since the energy release is smaller in ‘CASMO-5’ and the peaking factors during the transient arealmost identical (not shown), the enthalpy rise in the ‘CASMO-5’ case is approximately ~88% ofthe enthalpy rise in the ‘CASMO-4’ case. The resonance treatment implemented in ‘CASMO-5’ is the key element for the fuel enthalpyreduction during this transient.PHYSOR 2010 – Advances in Reactor Physics to Power the Nuclear RenaissancePittsburgh, Pennsylvania, USA, May 9-14, 20108/13

Effect of CASMO-5 Cross-Section Data and Doppler Temperature Definitions on LWR Reactivity Initiated AccidentsTable IV: REA transient parameters. Effect of CASMO-5 cross-section data.ParameterCASMO-4CASMO-5Exact kernelCASMO-5Asymptotic kernelValue Diff (%) Value Diff (%)Peak power (MW) 196400 168700 -14.1 183800 -6.4Peak power time (s) 0.144 0.146 1.4 0.147 2.1Pulse width (ms) 17.7 18.2 2.8 18.2 2.8Pulse energy release (MJ) 3476 3070 -11.7 3345 -3.8Peak power part time (s) 0.1617 0.1642 1.5 0.1652 2.2Prompt fuel enthalpy (cal/g) 44.94 41.81 -7.0 44.24 -1.6Prompt enthalpy rise (cal/g) 27.84 24.71 -11.2 27.14 -2.5Peak fuel enthalpy (cal/g) 47.39 44.49 -6 46.63 -2Peak enthalpy rise (cal/g) 30.29 27.39 -10 29.53 -35.2. Effect of the Doppler Temperature DefinitionIn this subsection, all the results are obtained using CASMO-5 cross-section data. All four differenteffective Doppler temperature definitions will be used: ‘BE1’, the volume-averaged effective Dopplertemperature defined by Eq. (1); ‘NEA’, the weighted average of the surface and centerline temperaturesdefined by Eq. (2), ‘GDTL’ defined by Eq. (3) and ‘BE2’ the weighted average defined by Eq. (4). Fig. 5compares the power evolution for the Doppler temperatures definition mentioned above. The ‘BE1’,‘BE2’ and ‘GDTL’ solutions show a similar behavior. The ‘NEA’ solution shows a smaller power peak,but reaches a higher after-burst power level.Relative Power (% Rated Power)1.E+041.E+031.E+021.E+011.E+001.E-011.E-021.E-031.E-040.00 0.50 1.00 1.50 2.00Time (s)NEABE1BE2GDTLRelative Power (% Rated Power)5000400030002000100000.10 0.12 0.14 0.16 0.18 0.20Time (s)NEABE1BE2GDTL(a) Period 0.0 s to 2.0 s. Logarithmic scale.(b) Period 0.1 s to 0.2 seconds. Linear scaleFigure 5. Power evolution. Effect of the Doppler temperature definitions.PHYSOR 2010 – Advances in Reactor Physics to Power the Nuclear RenaissancePittsburgh, Pennsylvania, USA, May 9-14, 20109/13

Gerardo Grandi et.al.Fig.6 shows the evolution of the Doppler reactivity and the Doppler temperature during the transient.During the initial rapid power increase the problem is almost adiabatic, and the pin fuel temperature peaksnear the pellet surface due to the intra-pellet power shape (see Fig. 2). As the transient progresses, the heatconduction in the pin gradually reduces the surface temperature with respect to the centerline temperature.This behavior is illustrated in Fig. 7 for a pin in a fresh MOX assembly close to the ejected rod, and a pinin the UO 2 assembly where the rod is ejected.Doppler Reactivity ($)0.200.00-0.20-0.40-0.60-0.80NEABE1BE2GDTLDoppler Reactivity ($)-0.80-0.85-0.90-0.95-1.000.0 1.0 2.0 3.0 4.0 5.0Time (s)-1.000.0 0.5 1.0 1.5 2.0 2.5 3.0Time (s)Doppler Fuel Temperature (K)7006506005505000.0 0.5 1.0 1.5 2.0 2.5 3.0Time (s)NEABE1BE2GDTLFigure 6. Doppler reactivity and Doppler temperature. Effect of Doppler temperature definitions.MOX Fuel - Burnup 0.15 GWd/TUO2 Fuel - Burnup 37.5 GWd/TTemperature (K)1200110010009008007006005000 0.2 0.4 0.6 0.8 1Relative radiusTime (s)0.0000.1400.1450.1500.1600.2040.5041.0042.0045.000Temperature (K)1200110010009008007006005000 0.2 0.4 0.6 0.8 1Relative radiusTime (s)0.0000.1400.1450.1500.1600.2040.5041.0042.0045.000Figure 7. Evolution of the intra-pellet fuel temperature for 2 representative fuel pins.Table V summarizes the rod ejection accident results, in terms of power and fuel enthalpy, for the fourdifferent effective Doppler temperature cases. Differences with respect to the ‘BE1’ solution are alsoprovided. The main observations derived from Table V and Figs. 5-7 are: The ‘NEA’ effective Doppler temperature may predict a lower power peak depending on the corelife. However, the power generated in the after-burst computed using by the ‘NEA’ Dopplertemperature will always be the highest because the heat conduction in the pin gradually increasesthe centerline temperature with respect to the surface temperature.PHYSOR 2010 – Advances in Reactor Physics to Power the Nuclear RenaissancePittsburgh, Pennsylvania, USA, May 9-14, 201010/13

Effect of CASMO-5 Cross-Section Data and Doppler Temperature Definitions on LWR Reactivity Initiated AccidentsThe ‘NEA’ definition produces larger pulse widths as noted by other researchers [4]. This effectpartially compensates the lower power peak, and the energy generated during the powerexcursion differs only 1% with respect to the ‘BE1’ case.The prompt enthalpy rise is barely affected by the choice of the Doppler temperature definition.However, the maximum fuel enthalpy could be affected. The under-prediction of the Dopplerreactivity by the ‘NEA’ temperature results in a conservative estimate of the peak fuel enthalpy.Table V: Transient parameters: effect of the Doppler temperature definitionParameterBE1NEABE2GDTLValue Diff (%) Value Diff (%) Value Diff (%)Peak power (MW) 168700 162500 -3.7 167600 -0.7 170200 0.9Peak power time (s) 0.146 0.146 0.0 0.146 0.0 0.146 0.0Pulse width (ms) 18.2 18.7 2.7 18.2 0.0 18.1 -0.5Pulse energy release (MJ) 3070 3039 -1.0 3050 -0.7 3081 0.3Peak power part time (s) 0.1642 0.1647 0.3 0.1642 0.0 0.1641 -0.1Prompt fuel enthalpy (cal/g) 41.81 41.63 -0.4 41.73 -0.2 41.97 0.4Prompt enthalpy rise (cal/g) 24.71 24.53 -0.7 24.63 -0.3 24.87 0.6Peak fuel enthalpy (cal/g) 44.39 51.32 15.6 45.48 2.5 43.72 -1.5Peak enthalpy rise (cal/g) 27.29 34.22 25.4 28.38 4.0 26.62 -2.56. CONCLUSIONSThe effect of the cross-section data generated by CASMO-5, as well as the impact of different effectiveDoppler temperature definitions on LWR RIA was investigated. Key parameters of a PWR rod ejectionaccident scenario for a MOX/UO 2 core assuming the known core state have been compared.The main conclusions are: The LWR Doppler coefficient predicted using CASMO-5 cross-section data is ~10% morenegative at typical HZP conditions. The proper treatment of the 238 U resonance elastic scattering is the main contributor to the morenegative Doppler coefficient. The use of the volume-averaged Doppler temperature, Eq. (1), may overestimate the Dopplerreactivity. The ‘NEA’, Eq. (2), effective Doppler temperature definition leads to very conservativeresults because the Doppler worth is underestimated ~30% for quadratic profiles. Temperature distribution effects for Doppler could be accurately accounted by the empiricalweighting scheme described by Eq. (4). LWR RIA calculated using CASMO-5 cross-section data should be milder. This means that thefuel safety parameters computed with CASMO-5 core-section data show more margin than thesame parameters computed using CASMO-4 data for PWR rod ejection accidents and BWR roddrop accidents. The prompt enthalpy rise is barely affected by the choice of the Doppler temperature definition.The under-prediction of the Doppler reactivity by the ‘NEA’ Doppler temperature results in aconservative estimate of the peak fuel enthalpy. Results computed with the ‘BE1’, ‘BE2’, and‘GDTL’ effective Doppler temperatures, differ only a few percent.PHYSOR 2010 – Advances in Reactor Physics to Power the Nuclear RenaissancePittsburgh, Pennsylvania, USA, May 9-14, 201011/13

Gerardo Grandi et.al.Further investigation of the CASMO-5 cross-section effects shall be performed using realistic UO 2 /MOXcore designs in which the core state depends on the cross-section data set. Also, the CASMO-5 crosssectioneffects will be conducted for two other S3K mainstream applications, namely: BWR stability andfast operational transients.REFERENCES1. J. Borkowski, J. Rhodes, P. Esser, K. Smith, “Three Dimensional Transient Capability inSIMULATE-3,” Trans. Am. Nucl. Soc., 71, 456, (1994).2. G. Grandi and K. Smith, “SIMULATE-3K Explicit Fuel Pin Modelling in RIAs,” Trans. Am. Nucl.Soc., 96, 627, (2007).3. J. L. Eller, “Application of SIMULATE-3K To PWR Reactivity Insertion Accident,” Advances inNuclear Fuel Management (ANFM 2009), Hilton Head Island, South Carolina, April 12-15, on CD-ROM, (2009).4. H. Ferroukhi, M.A. Zimmermann, “Study of the PWR REA Pulse Width for Realistic UO2 and MOXCore Designs using 3-D Kinetics,” Annals of Nuclear Energy, 36, pp.274-280 (2009).5. K. Smith and J. Rhodes, “CASMO-4 Characteristic Methods for Two Dimensional PWR and BWRCore Calculations,” Trans. Am. Nucl. Soc., 83, 322, (2000).6. J. Rhodes, K. Smith and D. Lee, “CASMO-5 Development and Applications,” Advances in NuclearAnalysis and Simulation (PHYSOR 2006), Vancouver, BC, Canada, September 10-14, (2006).7. D. Lee, K. Smith and J. Rhodes, “The Impact of 238 U Resonance Elastic Scattering Approximationson Thermal Reactor Doppler Reactivity,” Annals of Nuclear Energy, 36, pp.274-280 (2009).8. D. Lee, J. Rhodes, K.Smith, “Quadratic Depletion Model for Gadolinium Isotopes in CASMO-5,”Advances in Nuclear Fuel Management IV (ANFM 2009), South Carolina, April 12-15, on CD-ROM,(2009).9. A. Yamamoto, M. Tabuchi, N. Sugimura, T. Ushio And M. Mori, “Derivation of Optimum PolarAngle Quadrature Set for the Method of Characteristics Based on Approximation Error for theBickley Function,” J. Nucl. Sci. Technol., 44, pp. 129-136 (2007).10. B. Becker, R. Dagan, and G. Lohnert, “Proof and Implementation of the Stochastic Formula for IdealGas, Energy Dependent Scattering Kernel,” Annals of Nuclear Energy, 36, pp.1170-1183 (2009).11. Y. Danon, E. Liu, D. Barry, and T. Ro, “Benchmark Experiment of Neutron Resonance ScatteringModels In Monte Carlo Codes,” International Conference on Mathematics, Computational Methodsand Reactor Physics (M&C 2009), Saratoga Springs, New York, May 3-7, on CD-ROM, (2009).12. T. Kozlowski, T. J. Downar, “The PWR MOX/UO2 Core Transient Benchmark, Final Report”,NEA/NSC/DOC(2006)20.13. A. O. Goltsev et al, “The Influence of a Non-Uniform Radial Temperature Distribution in the Fuel onthe Results of Calculations of Transients,” Annals of Nuclear Energy, 30, pp.1135-1153 (2003).14. D.D. Lanning, et al., “FRAPCON-3 Updates,” NUREG/CR-6534, Vol. 4, PNL-11513, (2005).15. G. Grandi and D. Hagrman, “Improvements to the INTERPIN Code for High Burnup and MOXFuel,” Trans. Am. Nucl. Soc., 96, 614-615, (2007).16. G. Grandi, “Effect of the Discretization and Neutronic Thermal Hydraulic Coupling on LWRTransients,” Proceedings of the 13 th International Topical Meeting on Nuclear Reactor ThermalHydraulics (NURETH-13), Kanazawa, Ishikawa-Ken, Japan, September 27-October 2, on CD-ROM,(2009).PHYSOR 2010 – Advances in Reactor Physics to Power the Nuclear RenaissancePittsburgh, Pennsylvania, USA, May 9-14, 201012/13

Effect of CASMO-5 Cross-Section Data and Doppler Temperature Definitions on LWR Reactivity Initiated AccidentsAPPENDIX A: EFFECTIVE DOPPLER TEMPERATURE PROBLEMThe geometry consists of a single pin-cell in a square lattice. The fuel is UO 2 fuel, 3.527 % enriched,density 10.2 g/cm 3 . The cladding is Zirconium, density 6.550 g/cm 3 . The coolant is water, density 0.7116g/cm 3 . The outer fuel pellet radius is 0.410 cm, the outer clad radius 0.475 cm and the pin pitch 1.26 cm.The fuel pellet was divided into 9 equal volume rings.Six cases were examined using this geometry. Case 1 consists of flat temperature profile within a pin athot zero power conditions. Cases 2 and 3 are flat temperature profiles at normal and high powerconditions respectively. Cases 4 and 5 represent quadratic temperature profiles at normal and high powerconditions. Finally, in case 6, the temperature resembles the intra-pellet power distribution in a highburned pellet. In all cases the cladding and coolant temperatures are assumed to be 450 K. Table VIsummarizes the conditions for each of the test cases. The alternative effective Doppler temperatures,computed using the equations in section 3, are also provided for completeness.Table VI: Fuel Temperature DefinitionsAverage Temperature (K)DopplerTemperatures(K)Surface Temp. (K)Average Temp. (K)Centerline Temp. (K)Ring 1 450 900 1350 1300 2150 1200Ring 2 450 900 1350 1200 1950 1200Ring 3 450 900 1350 1100 1750 1200Ring 4 450 900 1350 1000 1550 1260Ring 5 450 900 1350 900 1350 1300Ring 6 450 900 1350 800 1150 1350Ring 7 450 900 1350 700 950 1400Ring 8 450 900 1350 600 750 1440Ring 9 450 900 1350 500 550 1800BE1 (Eq. 1)NEA (Eq. 2)GDTL (Eq. 3)BE2 (Eq. 4)Case 1 Case 2Case 3 Case 4 Case 5 Case 6450 900 1350 450 450 1800450 900 1350 900 1350 1350450 900 1350 1350 2250 1200450450450900900450 9009001350135013509007201350 86086313509901276135016201238 13391387The results are used to determine the effect of including the temperature profile across the pin, and todetermine an appropriate weighting scheme in a steady state or transient nodal simulator. By comparingthe differences between Cases 2 and 4, Cases 3 and 5, and Cases 3 and 6 one can determine the impact ofcorrectly modeling the temperature distribution.PHYSOR 2010 – Advances in Reactor Physics to Power the Nuclear RenaissancePittsburgh, Pennsylvania, USA, May 9-14, 201013/13