Comparison of the transient behaviour of LBE-and gas-cooled experimental accelerator-driven systems (original) (raw)
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Analyses of Unprotected Transients in the Lead/Bismuth-Cooled Accelerator Driven System PDS-XADS
Safety investigations for the lead/bismuth (Pb/Bi)-cooled experimental accelerator driven system (XADS) were performed with the computational code SIMMER-III. The code has been extended so as to describe the ADS configuration with heavy-metal coolant, sub-critical core and strong external neutron source. As transient scenarios, unprotected loss of flow (ULOF), unprotected subassembly blockage and unprotected transient over-power (UTOP) were simulated. The calculation results showed that the current Pb/Bi-cooled XADS design proposed in the framework program of the European Union has remarkable resistance against severe scenarios.
Transient analyses for accelerator driven system PDS-XADS using the extended SIMMER-III code
Nuclear Engineering and Design, 2005
Transient analyses for Preliminary Design Studies of an Experimental Accelerator Driven System (PDS-XADS) were performed with the reactor safety analysis code SIMMER-III, which was originally developed for the safety assessment of sodium-cooled fast reactors and recently extended by the authors so as to describe the XADS specifics such as subcritical core, strong external neutron source and lead-bismuth-eutectic (LBE) coolant. As transient scenarios, the following cases were analyzed in accordance with the PDS-XADS program: spurious beam trip (BT), unprotected beam overpower (UBOP), unprotected transient overpower (UTOP), unprotected loss of flow (ULOF) and unprotected blockage (UBL) in a single fuel assembly. In addition, to cover some core-melt situations and investigate the potential for recriticalities, so-called snap-shot analyses with ad hoc postulated severe blockage conditions were also investigated.
This paper deals with transients in a small scale accelerator driven system (ADS) caused by beam variations, reactivity changes and coolant blockages, namely, the beam trip (BT), unprotected transient over current (UTOC), protected and unprotected transient over power (PTOP and UTOP) and unprotected loss of flow (ULOF). The beam trip itself is of interest for investigating fuel temperature changes. The calculations of UTOC show that no severe fuel melting problems are encountered within the range of 100% increase of the source strength. The UTOP calculations predict that a 1$ reactivity increase does not cause any problem. For completeness also PTOP calculations have been performed. The ULOF calculations show that the natural convection remaining after the pump trip is sufficient to prevent any clad and fuel melting.
Safety Analyses of the Lead-Bismuth Eutectic Cooled Accelerator Driven System XT-ADS
18th International Conference on Nuclear Engineering: Volume 6, 2010
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.
Comparative safety analyses and investigations have been performed for a small scale ADS with conventional MOX fuel and 800 MWth power class ADTs with advanced fertile free fuels, both cooled by Pb/Bi. The analyses cover perturbations of the source, as e.g. unprotected transient over current (UTOC) and beam interruptions as well as perturbations on the core side, protected/unprotected transient over power (P/UTOP), induced by reactivity additions and unprotected loss of flow (ULOF) accidents. It shows that the small scale ADS has a very good safety performance, while for the 800 MWth ADTs with ZrO 2 and MgO matrix based fuels some safety problems are identified, mainly related to the large positive void feedback and high linear power rate. Further design and safety optimizations are under consideration.
In the framework of the IAEA project on "Studies of Advanced Reactor Technology Options for Effective Incineration of Radioactive Waste," a series of benchmarks is performed to investigate the transient behaviors of various transmuters. One benchmark analysis concerns the transients in Accelerator Driven Transmuters (ADTs) using several types of dedicated fertile-free fuels, such as CERCER fuels with a ZrO 2 matrix or with an MgO matrix. For this benchmark, a mid-size 580MWth ADT with a large fraction of minor actinides (MAs) and Pb/Bi cooling has been proposed and investigated using the SIMMER-III code. As a first step, the relevant safety parameters have been determined, e.g., Doppler constants, coolant worth and cladding worth. Several transient classes have been analyzed, mostly focusing on reactivity-driven perturbations with time-scales in the ms and s range: unprotected transient overpower (UTOP), unprotected loss of flow (ULOF) and the unprotected blockage accident (UBA). In the area of UBAs a case has been simulated which leads to local pin failure and fuel redistribution in the flowing PB/Bi. For completeness, a beam trip (BT) and an unprotected transient over current (UTOC) have also been calculated.
Thermal-hydraulic analysis of LBE spallation target for accelerator-driven systems
In an accelerator-driven subcritical system (ADS), a high-performance spallation neutron source is used to feed the subcritical reactor. Neutron generation depends on the proton beam intensity. If the beam intensity is increased by a given factor, the number of generated neutrons will increase. The mechanism yielding a high rate of neutron production per energy is the spallation process, and this mechanism produces very high-energy deposition in the spallation target material. Producing a high rate of neutrons is accompanied by creation of problems of decay heat cooling and radiological protection. As a first step in designing a full-scale industrial ADS, a small-scale experimental ADS, which is similar to the European experimental ADS (XADS) is analysed. The analysis presented in this paper is based on lead-bismuth eutectic (LBE) cooled XADS-type experimental reactors, designed during the European experimental (PDS-XADS) project. Computational fluid dynamics analysis has been carried out for the spallation target. Steady-state behaviour and shear stress transport turbulence model with the automatic wall treatment were applied in the present analysis.
Analyses of transients for an 800MW-class accelerator driven transmuter with fertile-free fuels
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006
In the FUTURE Program, the development and application of fertile-free fuels for Accelerator Driven Transmuters (ADTs) has been advanced. To assess the reactor performance and safety behavior of an ADT with so-called dedicated fuels, various transient cases for an 800MWth-class Pb/Bi-cooled ADT were investigated using the SIMMER-III code. The FUTURE ADT also served as vehicle to develop and test ideas on a safety concept for such transmuters. After an extensive ranking procedure, a CERCER fuel with an MgO matrix and a CERMET fuel with a Mo-92 matrix were chosen. The transient scenarios shown here are: spurious beam trip (BT), unprotected loss of flow (ULOF) and unprotected blockage accident (UBA). Since the release of fission gas and helium after cladding failure could induce a significant positive reactivity, the gas-blowdown was investigated for the transient scenarios. The present analyses showed that power excursions could be avoided by the fuel sweep-out from the core under severe accident conditions.