Wire Wrap Research Articles

Characterization of heat transfer and temperature distributions in an electrically heated model of an LMFBR blanket assembly

Abstract This paper describes results of an experimental program to reduce uncertainties associated with the thermal-hydraulic design and analysis of LMFBR blanket assemblies. These assemblies differ significantly from fuel assemblies in design detail and operating conditions. In blanket assemblies, heat transfer occurs over a wide range of complex operating conditions. The range and complexity of conditions are the result of flux and power gradients which are an inherent feature of the blanket region and the power generation level in an assembly which can vary from 20 kW to ∼ 2 MW. To provide effective cooling of all assemblies and economical operation, coolant is metered to groups of assemblies in proportion to their ultimate power level. As a result, the assembly flow can be in the laminar, transition or turbulent range. Because of the wide range of heat generation rates and the range of coolant flow velocities, heat transfer from rods to coolant may take place in the forced, natural or mixed convection mode. Under low flow conditions, buoyancy affects the flow pattern in the bundle, and thus, alters the temperature distribution. The complexities are further compounded since, in addition to temperature gradients within an assembly, there are also significant temperature differences between adjacent assemblies. This results in heat transfer by conduction between adjacent assemblies, which tends to further distort flow and temperature patterns. Since these effects cannot be accurately predicted analytically, full-size radial blanket assembly heat transfer tests are being conducted using electrically heated fuel rod simulators in flowing sodium. A 61-rod electrically heated radial blanket assembly mockup of prototypic dimensions was designed, constructed and installed in a 200 gpm (45 m 3 /hr) sodium test loop. Heat transfer tests are being conducted over a wide range of power and sodium flow rates with this full-scale, vertical, electrical-resistance-heated rod bundle. The rod bundle is extensively instrumented by thermocouples located at six distinct elevations in the wire wrap and inside the heater cladding. Tests were conducted covering the flow range from fully turbulent to fully laminar with approximately constant power-to-flow ratio. The power input patterns included across bundle gradients of 2.8 to 1 and 2.0 to 1 maximum to minimum, uniform power input to all rods and a dished distribution with low power in the central row and high power in the two rows of rods adjacent to the duct walls. The test program provided experimentally measured axial and transverse temperature profiles for the test model over a range of anticipated plant operating conditions. The data were used to (a) determine the effect of Reynolds Number, power gradients and power-to-flow ratio on transverse and axial temperature profiles and particularly on peak and peripheral channel temperatures; (b) determine the effect of inter-assembly heat transfer on peak temperatures and temperature distributions; and (c) determine the effect of buoyancy on temperature profiles.

Pressure Drop in a Model of a Forced Cooled Pipe-Typr Electric Cable System with Cable Snaking

An experimental study was conducted of the pressure losses in a scale model of a high pressure oil filled (HPOF) pipe cable system with a wave-like snaking pattern of the cables inside the pipe. In HPOF systems, snaking can be caused by longitudinal thermal expansion of the cables between fixed points of support when the cables are placed under electrical load. Friction factors were determined for a Reynolds number range of 200 to 3800 and longitudinal expansion up to 13.2 percent for cables with and without wire wrap (skid wires).

Thermal-Hydraulic Analysis of Fuel Blockages Formed during Transient Overpower Accidents in Liquid-Metal Fast Breeder Reactors

Generally, the blockages that may form in the reactor core when molten fuel is ejected into the coolant channels during a transient overpower accident can be divided into two categories. The first type of blockage forms when semi-molten fuel particles hit a wire wrap and freeze on the wire wrap, whereas the second type of blockage forms when solid or semi-solid particles get stuck in the coolant channels. The thermal-hydraulic analysis of these proposed blockages indicates that under certain specific conditions, the blockages can lead to melting of the wire wrap and cladding and also to in-channel voiding. The second type of blockage, if formed as a plug, may remelt before being quenched by subcooled or saturated sodium.

A Single-Channel Printing Scaler for Photon Counting

A device is described which counts pulses and generates serial code to punch a paper tape and produce formatted count listings on a Teletype. The digital counting mode employed by the printing scaler makes it ideal for photon counting or other event recording applications in spectroscopy. The count capacity is 5 digits (99 999 if decimal; 1 048 575 if hexadecimal). Provision is made to record initialization and overflow flags and two optional external flags. A data latch is included to allow simultaneous counting and printing for minimum dead time; the maximum print rate is 1 data point per sec on a 110 baud terminal. “Initialize” and “enable” signals must be supplied by external circuitry, such as a spectrometer timing and stepping control system. A “done” pulse is supplied by the printing scaler for use in external circuitry if desired. The circuit can also be used with other serial recording devices including an on-line computer; the baud rate is easily adjustable. This device contains 32 TTL SSI and MSI integrated circuits and a few associated discrete components. Our version was constructed on a single 36-position wire wrap breadboard with edge connector and housed in an inverted 8 by 12 by 3 in. chassis box with perforated cover. The required power can be obtained from an inexpensive 5 V, 1 A power supply.

Velocity Measurements in the Subchannel of the Wire-Spaced Subassembly

Measurements of the flow velocity and direction in wire-spaced rod bundles were performed in air flow with a 37-rod subassembly that consisted of rods 31.6 mm in diameter, 3464 mm long, 6.0 mm in spacer wire diameter, and 1100 mm in wire wrapping pitch. The fine flow velocity and its direction were measured in both interior and wall subchannels in two sections of axial direction. Circular flow and decrease of axial flow velocity were observed in the subchannel containing the spacer wire. The variation of the transverse flow rate within one spacing wire pitch, which occurred between two adjacent subchannels, was obtained from the measured value to develop the computer program for the subchannel analysis.

Stress Relaxation in Press-Fitted Joints

When contact pins, wire wrap posts, etc., are press fitted into printed circuit boards, the contact force at the interface of a post and plate relaxes with time. Much of the relaxation of the contact force occurs immediately after the connection has been made. Theoretical estimates on the reduction in contact force until a steady state (a steady state is assumed to be reached when the stress rates become 1 percent of their initial values) is reached are presented. Since most of the relaxation of the radial stress component occurs in the vicinity of the hole, the effect of adjacent joints on the relaxation characteristics of a joint are neglected. And, therefore, only an idealized geometry of a thin circular plate with a single press-fitted hole is considered.

High burnup performance of LMFBR fuel rods—Recent GE experience

A series of tests designed to evaluate the high burnup irradiation performance of mixed oxide fuel rods has acheived substantial burnup in EBR-II without incidence of failure. Several stainless steel cladding alloys and fuel configurations were irradiated over a broad range of operating conditions up to 16.3 at. % burnup, 47 kW/m linear power, and 570°C cladding temperature. Extensive examination showed the rods to be in good condition after extended operation in both loose and tight wire wrap spaced assembly configurations. In fuel rods with typical near-term LMFBR design parameters, cladding inelastic strains in the range from 0.3 to 0.8% were commonly observed at about 10 atom % burnup. The inelastic strain appears to increase with burnup and fluence, with the possibility of threshold values for these variables. Preliminary analyses suggest that the cladding inelastic strain was not entirely caused by pressure from released fission gases. Microstructural examinations indicated good fuel-cladding chemical compatibility and comparable behavior for both physically-mixed and coprecipitated fuel. Significant results include: the observation of negligible fuel-cladding gap in low power fuel at ∼8 atom % burnup, and partial closure of the central void in annular fuel at ∼10 atom % burnup.

ORRIBLE–A Computer Program for Flow and Temperature Distribution in 19-ROD LMFBR Fuel Subassemblies

A computer program named ORRIBLE was written to predict the flow and temperature distribution for steady single-phase flow through a bundle of 19 heated rods spaced by helical wire wraps in a hexagonal duct. Any combination of flow subchannels can be blocked at the inlet. The section can have an unheated entrance length followed by a heated section and an unheated exit length. In the heated section, the linear heat rate of each of the rods can be individually specified. Turbulent interaction, sweeping crossflow due to the wire wrap, and transverse thermal conduction are considered. An approximate relationship for pressure-diversion crossflow in terms of local axial mass velocities is used to eliminate pressure as a variable. Hence, the computational procedure does not require iterative techniques.

Wire Wrapped Joints—A Review

The basic technique of wire wrapping is now well established as a simple and reliable method for joining conductor wires in a permanent, though easily replaceable, manner to more massive terminals. This paper describes the mechanical and the metallurgical basis of the joining technique and outlines the advantages. The scope of the technique as it has developed up to the present day is discussed in terms of the ranges of wrapping terminals and wrapping wires used and the types of wrapped joint that have been evolved. Finally the tools available for wire wrapping are briefly reviewed with particular emphasis on the wrapping bit.

Numerical Model of Heat Transfer in a Rod Bundle With Helical Wire Wrap Spacers

A practical solution to the problem of predicting operating temperatures for nuclear fuel assemblies contining wirewrapped fuel pins spaced in a triangular array is presented. It is shown that the flow field predictions for the subpitch length (below 12 in. for these data) agree with experimental data obtined from prototypic LMFBR model fuel assembly tests. (auth)

Coolant mixing in a fuel pin assembly utilizing helical wire wrap spacers

Coolant mixing in a helically wire-wrapped, 217 pin, full-scale model of an LMFBR fuel assembly is presented. Salt-injection-conductivity techniques were employed, using water as the coolant. Over four hundred probes were concentrated in a one-sixth sector of the assembly to exhaustively measure the salt distribution. The basic results are presented for use in the verification of thermal hydraulic computer codes and wire-wrap mixing models. Interior channel gross mixing rates were about 9%/cm (effectively 3% per cm per gap); this was more than three times the natural turbulence level. There existed only a small peripheral (swirl) flow around the bundle; its direction averaged only slightly greater than half helical wire wrap angle. The results were reduced into an effective turbulent mixing model, and a wire-wrap forced diversion cross flow model is also presented.

Fracture Resistance of Wire-Wrapped Cylinders

Steel cylinders wrapped with steel wire have the capability of offering not only an economical high-strength structure, but also a structure with improved fracture resistance compared with that of an unwrapped cylinder of equivalent strength. Accordingly, 2000-psi-pressure hydraulic burst tests were therefore conducted to determine the fracture resistance of 36-in-dia, 60-ksi yield-strength, 1000-psi-pressure wire-wrapped cylinders at different levels of shell notch ductility, which was varied by testing at different temperatures. The cylinders were prestressed with 1/4-in-dia cold-drawn wire, and the shells contained part-through-wall flaws. A similarly flawed unwrapped cylinder was tested for comparison. The working-stress level was 72 percent of the specified minimum yield strength in the shell and 60 percent of the minimum tensile strength in the wire. The results showed that at a pressure double that of the unwrapped shell, no crack extension occurred at a temperature at which the steel exhibited fully ductile shell behavior (+110 deg F). A 2-ft crack extension occurred at a temperature (+10 deg F) at which the steel was still in the transition temperature range from ductile-to-brittle behavior (about 20 percent shear fracture), but a brittle crack (−70 deg F) propagated to the end of the wire-wrapped shell. Except for the brittle propagating crack, wire wrapping appears to provide sufficient constraint of a shell defect or propagating crack to limit bulging and crack-opening displacement. A model based on the compatibility in displacements between the crack opening and the local wire strain is presented for calculating the arrest conditions of the propagating crack in the test at 10 deg F. The same flaw size was critical at the constant failure pressure for all test temperatures, and showed that, as predicted, ductile initiation occurs even at the −70 deg F temperature in both the wrapped and unwrapped-cylinder tests. A circumferential flaw was shown to be less critical than a longitudinal flaw of the same size.

Equipment and materials

The RB scries of bridge rectifiers in the 4, 5, 15 and 25amp current range are housed in a high conductivity alloy case with a durable nickel finish, and are designed for easy installation and maximum thermal conductivity. The 4amp version has tinned copper leads only (‘A’ outline) and the 5, 15 and 25amp versions have universal terminals (‘B’ outline) for push on connectors, wire wrapping or standard soldering. An avalanche version is available for critical applications. Maximum thermal impedance for junction/mounting surface is l·5°C/watt with maximum operating and storage temperature −55°C to 150°C. Overall dimensions of the ‘B’ outline bridge rectifiers are 29mm × 29mm × 10mm. Terminals are 13mm (maximum). Delivery date is 25 off ex stock, prices £1·15–2·14.

Micro-Mechanisms of Solderless Wrapped Joint Formation

The manner in which the various surfaces interact during wire wrapping, and the structure at the contact sites in the completed joint, have received only cursory attention. This paper describes an investigation designed to elucidate these phenomena using metallographic, scanning electron microscopic and electron microprobe analysis techniques. Series of joints made under known sets of parameters are examined to provide data on post-into-wire penetration, metal displacement and contact area :for different wrapping loads. It is shown that at high wrapping loads, the wrapping system tends towards an unstable state analogous to the onset of necking in tensile strain. Scanning electron microscopy and microprobe analysis of the surfaces of dismantled joints are used to show irrefutably that a substantial amount of cold welding occurs during the wrapping sequence. The transfer of metal from wire to post, and vice versa, by a welding-followed-by-fracture mechanism is clearly demonstrated for a variety of materials. This contradicts currently held views on the subject and indicates additional guide-lines for wrapped joint design. Above all, it is evident that the presence, and subsequent behaviour during wrapping, of thin plated layers on wire and terminal post cannot be ignored, and indeed plays a significant role in joint formation. A theoretical model is used to derive variation in contact area with wire diameter for typical joints. A change in wire diameter from 0.050 cm to a micro-wrap dimension of 0.017 cm is seen to reduce the area of individual contact sites by an order of magnitude, i.e. to approximately l0-4 cm2. It is argued that as the contact areas of wrapped joints tend towards this microscopic level, the phenomena discussed under the heading of "micro--mechanisms of wrapped joint formation" assume great significance.

Pressure tests of cylindrical steel pressure vessels reinforced with steel wire wrapping

To examine the bursting-strength and crack-arrest benefits that may be gained by adding circumferential wire wrapping on a cylindrical steel pressure vessel, four wire-wrapped steel vessels were pneumatically, internally pressurized to failure. Two of the vessels had intentional notch-type defects in the cylinder wall, one had notch-type defects in the wire, and one had no defects. The tests showed that circumferential wire wrapping limits the total extension and rate of extension of longitudinal cracks and restrains crack propagation. Also, the bursting pressure of a wire-wrapped cylinder is greater than that for a nonwrapped cylinder of similar wall thickness and approaches that for a nonwrapped sphere. Wire-wrapped cylindrical vessels may provide both cost and weight savings over a similar nonwrapped vessel of equal strength. The aspects of increased fracture toughness and increased bursting strength would certainly be beneficial concepts in reactor pressure vessels.

Miniaturized Wire Wrap

Miniaturization and micro-miniaturization are key words that are often heard in the electronic industry today. The increasing frequency of these terms reflects the growing importance attached to the reduction in size, of logic and power components used for data processing applications. In fact, miniaturization is now a primary project of many scientific research teams throughout the industry. The success of these projects is evidenced by the wide variety of small, smaller, and ultra-small computer components presently available. However, one aspect of the miniaturization program that has not kept pace with the primary effort, is the aspect of inter-component connections. There still exists in this area, a serious problem of developing and implementing an electrical communications scheme that can function between components of increasingly greater logical density. This paper proposes an effective connection scheme based on the "solderless wire wrap" technique.

The automation of topological layout

A computer system that will produce input data for an automatic wire wrap machine is an important extension of the automatic backboard wiring system. The essential task of the extended system is to translate data already present in the backboard wiring files into codes which are acceptable to the machine. The Electronic Data Processing (EDP) Division of Minneapolis-Honeywell Regulator Company has in operation a set of computer programs to accomplish this task.

Investigation of Production Requirements for Solderless Wire Wrapped Electrical Connections

A solderless wire wrapped electrical connection consists of tightly wrapping solid bare wire around a stationary terminal to produce a durable pressure connection. Properly made, the wrapped connection is a permanent, reliable electrical connection that can be produced faster than soldered connections. The elimination of solder and heat detriments are distinct advantages over the soldered connection. Wire wrapping lends itself to automation, and connections can be easily made on closely spaced terminals. While it is a mechanically strong connection, an individual connection is easily removed, simplifying modification and repair. However, this may be less of an advantage in multi-level wrapping. The increase in complexity of electronic equipment during the last decade has presented industry with some unique production problems. Not the least of these has been the great increase in the number of electrical connections. The need for speed in making this many connections, without decreasing quality, prompted IBM to expend considerable effort in identifying the variables that affect solderless wire wrapping connections in order to define the controls needed in production. At the present time, these connections are widely used by IBM in both commercial and military applications, and over 100 million solderless wrapped connections were made by IBM in 1960. The use of the solderless wrapped connection has grown steadily since the Bell System first made the new connection public in 1952. Extensive laboratory tests, performed principally byBell Laboratories, and field experience have verified the reliability of the connection. This paper describes the effect of the variables involved in the wire wrapping process which were determined from the results of laboratory tests and manufacturing experience and the process controls required to assure the quality and reliability of production connections. To meet process requirements consistently, the many variables inherent in the solderless wire wrapping process must be considered. These variables will be discussed under the major variable factors involved in the process.

Secondary Stresses in Parallel Wire Suspension Cables

Working stress in parallel wire cable is normally based on average stress across section of cable; paper analyzes variation of stress across section, caused by deflection of cable; influence of clamping bands and of tensioned wire wrapping are considered; numerical examples show that secondary stresses may be important part of effects of live loading.