SOUTHWEST EXPERIMENTAL FAST OXIDE REACTOR Research Articles

USE OF DIFFERENT LIBRARIES IN THE ANALYSIS OF THE DOPPLER MEASUREMENTS OF THE SEFOR REACTOR: ASSESSMENT OF THE DOPPLER EFFECT OF THE ASTRID CORE

For the next generation of fast reactors, global objectives are required in terms of safety, sustainability, waste minimization and non-proliferation issues. Concerning safety issues, particular efforts have been made in order to obtain core designs that can be resilient to accidental transients. In that frame, the CEA held R&D program toward a GEN-IV-like core concept that could meet those requirements: the ASTRID project. Based on heterogeneous core geometry (axial inner fertile layer, large upper sodium plenum) the ASTRID core shows improved behavior in case of unprotected loss of flow. It has been found that Doppler Effect plays a dominant role for the considered transients to deal with in the safety demonstration. The prediction of the Doppler Effect by neutronic simulation codes require experimental validation, the reason for which static tests conducted within SEFOR (South-West Experimental Fast Oxide Reactor) –a fast reactor fueled with mixed PuO2-UO2 and cooled with sodium –are being used. The SEFOR experimental tests are being analyzed with the ERANOS code package using nuclear data libraries of different evaluations: JEFF-3.1.1, JEFF-3.2, ENDF-B/VII.1 and JENDL4. The C/E values on the SEFOR Doppler Effect range from 1.01 to 1.07 with an experimental uncertainty of ±0.06. With the use of perturbation break down in energy and isotope, this paper identifies the reasons for such large C/E spread and identifies the differences and similarities of the SEFOR Doppler Effect with the ASTRID one.

Two-region analysis of pulsing data in fast critical systems

Pulsed neutron die-way experiments were performed in three fast critical systems assembled in the Argonne Zero Power Reactor-III (ZPR-III). These experiments were part of a comprehensive study of the mockups of the proposed fast reactors FARET (Fast Reactor Test) and SEFOR (Southwest Experimental Fast Oxide Reactor). The two FARET systems pulsed were Assembly 46-B, a 68 1 plutonium-uranium carbide core with stainless steel and sodium reflector; and Assembly 46-C, an 87 1 plutonium-uranium oxide core with the same reflector materials. The SEFOR mockup was a 528 1 plutonium-depleted uranium oxide core with a reflector of stainless steel, sodium and nickel. In all three cases, an acceptable analysis of the die-way curves required two exponentials plus background. From this data, we were able by a two-region transfer function analysis to assign a prompt neutron lifetime to core neutrons and to the system as a whole. Further, the transfer function model used predicts that the die-away curves in the reflector will contain two exponential terms having the same two exponential decay constants as were found in the core, and that the coefficient of the faster decay will be negative. This was found to be the case within experimental uncertainty.

The SEFOR Minimum Critical Core

The minimum critical core size for the Southwest Experimental Fast Oxide Reactor was predicted prior to the initial fuel loading using the results of a critical mockup in ZPR-3. The predicted minim...