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