Overview and progress in the European project: “Supercritical Water Reactor – Fuel Qualification Test”

Advances and perspectives of actinide chemistry from ex situ high pressure and high temperature chemical studies

High pressure high temperature (HP/HT) studies of actinide compounds allow the chemistry and bonding of among the most exotic elements in the periodic table to be examined under the conditions often only found in the severest environments of nature. Peering into this realm of physical extremity, chemists have extracted detailed knowledge of the fundamental chemistry of actinide elements and how they contribute to bonding, structure formation and intricate properties in compounds under such conditions. The last decade has resulted in some of the most significant contributions to actinide chemical science and this holds true for ex situ chemical studies of actinides resulting from HP/HT conditions of over 1 GPa and elevated temperature. Often conducted in tandem with ab initio calculations, HP/HT studies of actinides have further helped guide and develop theoretical modelling approaches and uncovered associated difficulties. Accordingly, this perspective article is devoted to reviewing the latest advancements made in actinide HP/HT ex situ chemical studies over the last decade, the state-of-the-art, challenges and discussing potential future directions of the science. The discussion is given with emphasis on thorium and uranium compounds due to the prevalence of their investigation but also highlights some of the latest advancements in high pressure chemical studies of transuranium compounds. The perspective also describes technical aspects involved in HP/HT investigation of actinide compounds.

Further Details of a Numerical Analysis on the Thermal Hydraulic Effect of Wrapped Wire Spacers in Fuel Bundle

The application of relatively simple and cheap wrapped wire spacer in the European supercritical water-cooled reactor (SCWR) (high-performance light water reactor (HPLWR)) has been proposed in order to provide enhanced heat transfer in the fuel assembly without unacceptable penalty in pressure loss. The wires cause twisting flow in the fuel assembly, which means the coolant not only flows straight in the axial direction but also has a significant transverse velocity component, and strong mixing between neighboring subchannels occurs. The aim of this ongoing research is to numerically investigate the effect of wrapped wire spacers on thermal hydraulics of the turbulent coolant flow and its heat transfer in a small bundle of four fuel rods. One bare and six-wired geometries with varying wire pitches (1–6 turn(s) of wires) have been studied. It was found that the wires generate significant amount of transverse velocity, decrease the wall temperature, and increase the heat transfer coefficient mostly in corner subchannels which were the hottest in bare geometry. Thus, the presence of wires enhances heat transfer where it is most needed. Temperature hot spots with moderate values have been identified on the cladding wall of fuel rods. Based on the results, a technically optimal choice of number of wire turns from thermal hydraulic sense has been proposed.

Control Rod Withdrawal Analysis of the Supercritical Water Reactor-Fuel Qualification Test Facility in the LVR-15 Research Reactor

The aim of the supercritical water reactor-fuel qualification test (SCWR-FQT) Euratom-China collaborative project is to design an experimental facility for qualification of fuel for the supercritical water-cooled reactor. The facility is intended to be operated in the LVR-15 research reactor in the Czech Republic. The pressure tube of the FQT facility encloses four fuel rods that will operate in similar conditions to the evaporator of the HPLWR reactor. This article deals with the three-dimensional (3D) coupled neutronic-thermohydraulic steady-state and transient analysis of LVR-15 with the fueled loop. Conservatively calculated enveloping parameters (e.g., reactivity coefficients) were determined for the safety analysis. The control rod withdrawal analysis of the FQT facility with and without reactor SCRAM was carried out with the KIKO3D-ATHLET-coupled dynamic code.

Design of an In-Pile SCWR Fuel Qualification Test Loop

In the development of the supercritical water-cooled reactor (SCWR), an in-pile fuel assembly test loop has been designed within the framework of the joint Chinese–European project, called SCWR-FQT (Fuel Qualification Test). This paper presents the basic design of the loop with its auxiliary and safety systems, which has been examined in detail by thermal-hydraulic analyses in order to achieve operation of the loop above the thermodynamic critical point of water (374°C, 22.1 MPa) and checked by stress analyses to assure safe operation. The designed experimental loop for fuel qualification in supercritical water consists of a closed pressurized water circuit with forced circulation of the coolant through the test section—the active channel which is intended to be installed into the existing research pool-type reactor LVR-15. The active channel will be operated at temperatures and pressures which are typical for the high-performance light water reactor (HPLWR). A thick-walled pressure tube made from austenitic stainless steel, which is able to withstand the high system pressure, encloses the active channel. It contains four fuel rods with UO2 (enrichment of 19.7% U235) with a total heating power of ∼64  kW and a recuperator in order to achieve hot channel conditions as they are expected to occur in the evaporator of the HPLWR. The internal flow is realized so as to prevent the creep condition of the pressure tube. An internal U-tube cooler serves as heat sink and is connected to the secondary circuit. The entire active channel is isolated from water of the reactor pool by an air gap between the pressure tube and an aluminum displacer. The test section with fuel is connected to a 300°C closed loop and to a primary pump located outside the reactor building as well as safety systems and auxiliary systems, such as purification and measurement circuits, which are all connected with the primary circuit.

Expected Safety Performance of the Supercritical Water Reactor Fuel Qualification Test

The supercritical water reactor (SCWR) fuel qualification test is an in-pile test of a four-rod fuel assembly at supercritical pressure inside a research reactor, which is operated at atmospheric pressure. The risk of radioactive release from this new test facility should not exceed the accepted risk of the existing research reactor. A large number of safety analyses have been performed to assess this risk, which are summarized in this paper. Among them are studies of design basis accidents, assuming different failure modes of the high-pressure system, as well as an assessment of consequences of postulated accidents beyond the design basis. Results show that the safety objectives can be met.