In the design of reactor core and fuel assemblies for most types of nuclear power reactors, it is important to conduct tests to characterize the thermal-hydraulic condition at which the departure from nucleate boiling (DNB) phenomenon occurs in the fuel assembly. The tests require identification of both lateral and longitudinal locations of the DNB events in a fuel assembly. The DNB phenomenon, sometimes referred to as Boiling Crisis, limits the operation margins of a particular reactor fuel design and must be well studied.
For decades, reactor component designers have used electrically heated rods as simulated nuclear fuel. The coolant for the simulated fuel bundles is water and large amounts of electricity are consumed. Other low boiling point refrigerants such as freon may be used as the simulated coolant to minimize the electrical consumption, while retaining the basic physical phenomenon. Each electrically heated rod consists of a thin wall tube of high resistivity metal, such as inconel or monel, as the heated section, an unheated upstream section, and an unheated downstream section for flow development. The unheated sections are made of a low resistivity metal, such as nickel. The rod diameter and inter-rod spacing are set to be the same as those in an actual fuel rod assembly.
In order to achieve a realistic thermal-hydraulic condition in the reactor fuel rod assembly, electrically heated rods are arranged into a configuration such as a 3.times.3, 4.times.4, 5.times.5, 6.times.6, 7.times.7 square, or other hexagonal bundles. A 5.times.5 square bundle requires a total of 25 rods. All 25 rods are commonly bused (or electrically tied together) at two electrodes, a cathode on one end and an anode on the other, to allow electric current to pass through the rod bundle. In addition to DNB studies, electrically heated rod bundles may also be used to investigate other thermal-hydraulic phenomena of a reactor core, such as multiphase instability and post-accident reflood heat transfer.
Due to longitudinal thermal expansion and potential buckling, the individual heater rods cannot be rigidly anchored to both electrodes at the same time. Normally, one end of all heater rods may be rigidly tied to a common electrode which is made of a highly conductive metal, such as nickel. The opposite ends of all rods are left free to enable expanding or sliding. As a consequence, the free expanding ends of the heater rods need to be individually connected to a braided/flexible cable. All braided cables are then joined to the other common electrode.
This approach, as traditionally practiced in most DNB or other rod bundle heat transfer test facilities to counter the buckling problem, suffers from the tedious electrical connection (and disconnection) procedure and crowded cabling, particularly when the number of rods is large. In addition, the consistency and reliability of electrical contact in this type of connection may be compromised, which can result in undesirable arcing and local fusing.
Accordingly, it is an object of this invention to provide an improved flexible electrical connection that exhibits a low resistance.
It is another object of this invention to provide an improved flexible electrical interconection that is easily configured and exhibits a consistent low resistance interconnection.