Xue-Nong Chen

Theoretical Modeling of Radial Standing Wave Reactor

This paper is a theoretical study of a radial standing wave, which can be applied in the so-called traveling wave reactor (TWR). Two-dimensional cylindrical core geometry is considered and the fuel is assumed to drift radially, which corresponds to a radial fuel shuffling scheme in practice. A one-group diffusion equation coupled with burn-up equations is set up, where the burn-up solution is obtained numerically. The uranium-plutonium (U-Pu) conversion cycle with pure 238U as fresh fuel is considered under conditions of a typical sodium cooled fast reactor with metallic uranium fuel loaded. The asymptotic problem is solved by a time-stepping iteration scheme and the radial standing wave solution is obtained together with certain eigenvalue keff.The neutron flux, the neutron fluence and the net neutron generation cross section are presented and discussed for the inward fuel drifting motion.

SAFETY ANALYSES OF THE LEAD-BISMUTH EUTECTIC COOLED ACCELERATOR DRIVEN SYSTEM XT-ADS

Safety analyses for the XT-ADS were performed with the reactor safety code SIMMER-III. Besides a brief description of the numerical model, three typical transients are presented in this paper, namely, the unprotected loss of flow (ULOF), unprotected transient over-current (UTOC), and the unprotected coolant flow blockage accident (UBA). Because of the important phenomenon of mass flow rate undershooting in the ULOF case, an integral equation model was set up for a further theoretical study of ULOF. The model confirms the numerical simulation results for various cases and gives a deeper understanding of this phenomenon. The faster the pump shut down, the larger is the undershooting of the mass flow rate. On the other hand a larger coolant cold leg area leads to a weaker undershooting. The stability analysis shows that the natural convection state is in the region of the damped oscillation for the current XT-ADS design.

Optimization of Safety Parameters and Accident Mitigation Measures for Innovative Fast Reactor Concepts

Traditionally the analysis of the evolution of severe core disruptive accidents (CDA) is broken down into different phases. This is mainly done for a better focussing on the key phenomena of the accident phase and also allows the application of specific codes for the analysis. In the current paper we mainly deal with the initiating phase and the transition phase of an accident as the ULOF (unprotected loss of flow). The key phenomenon of the initiating phase is the start of boiling and the development of voiding; key phenomena of the transition phase are the progression of core melting and the occurence of recriticalities by fuel compaction. The first level of optimizing safety is oriented to the initiating phase by reducing the positive void worth in order to avoid that a ULOF accident would enter a severe development. If accident prevention is not achieved the transition phase, characterized by a progressive core degradation leading to the occurrence of recriticalities, can be mitigated by dedicated features that enhance and guarantee a sufficient and timely fuel discharge – e.g. by a controlled material relocation (CMR) - and influence and ‘brake’; the recriticality path. In the paper both phases are analyzed. The results presented are in agreement with the activities performed within the European Collaborative CP-ESFR project.

Numerical Studies of Axial Fuel Shuffling

The concept of traveling wave reactor (TWR) applies the mechanism of self sustainable and propagation nuclear fission traveling waves in fertile media of 238U and 232Th to achieve very high fuel utilization. However, the long wave length of such fission traveling wave puts a limit on the applicability of the TWR concept. The axial fuel shuffling strategy is proposed based on the mechanism of asymptotic nuclear fission traveling wave, and is applied to a sodium-cooled fast reactor (SFR) loading metallic 238U fuel. The multi-group deterministic neutronic code ERANOS with JEFF3.1 data library is used as a basic tool to perform the neutronics and burn-up calculations. The calculations are firstly performed in a 1-D case for parametric understanding, and further extended to a 2-D R-Z case. The shuffling calculations for the 1-D and 2-D SFR model described in this paper brought about some interesting results. The results indicate that keff parabolically varies with the shuffling period, while the burn-up increases linearly. The highest burn-up achieved in 2-D case is 46at%. The power shape distortion in 2-D case is observed, and the power peaking factor is much higher than that in 1-D case, but it decreases with the shuffling period increasing.

Accelerator Driven Systems for Transmutation: Safety Considerations and Analyses of EFIT Type Cores

European R&D for Accelerator Driven System (ADS) design and fuel development in the 6th EC Framework Programme is driven by the Intgrated Project EUROTRANS. In EUROTRANS two ADS design routes are followed, the XT-ADS and the EFIT. The XT-ADS is designed to provide the experimental demonstration of transmutation in an. The longer-term EFIT development (European Facility for Industrial Transmutation) aims at a generic conceptual design of a full transmuter. Within EUROTRANS, the domain 3 (DM3) named ‘AFTRA’, is responsible for a deeper assessment of the behavior of the dedicated fuels and for development of the fuel database for the EFIT core design. To test and assess the behavior of the currently chosen CERCER (MgO-matrix) and CERMET (Mo-matrix) fuels under normal operation and transient conditions, the AFTRA domain has performed some preliminary core design studies on an EFIT (coined AFTRA-EFIT). In this paper, design data and transient analyses of multi-zone high/lower power density cores are presented and important safety phenomena are analyzed.

Nuclear solitary wave

This paper gives an overview of our recent work on the fission solitary wave reactor concept. In order to gain an insight into this problem a simple but appropriate model, namely a one-group diffusion equation coupled with simplified burn-up equations, is studied. It is shown that this coupled system is analytically solvable in its one-dimensional case and a permanent plane solitary wave exists in a fertile medium. Moreover, a multidimensional solitary wave pattern can also be achieved theoretically by adjusting the initial transverse fuel distribution. This mechanism makes a nuclear reactor obviously stable. More importantly it can improve significantly utilization of nuclear fuel.