Thermal aspects of alternative fuels for use in nuclear reactors

SuperCritical Water- cooled nuclear reactors are a 4^th generation reactors that use light water coolant at temperature higher than its critical level. Uniform and non-uniform axial heat flux profiles applied with a range of alternative fuels such as thorium dioxide, uranium dicarbide, uranium nitride etc.

There are two reactor basic arrangements for SuperCritical Water cooled Nuclear Reactors(SCWRs)-A fuel was deemed fit it the fuel centerline temperature remained lower than 1850oC. 

Uranium dioxide was the main choice for its wide and traditional use as a nuclear fuel. Although several studies have concluded that fuel centerline temperature can significantly exceed the industry acceptable limit. Unconventional fuels like mixed oxide, thoria, uranium dicarbide, uranium nitride and uranium carbide. Uniform and non-uniform axial heat flux profiles were applied, non-uniform profiles included- upstream cosine, cosine and downstream cosine. The sheath materials chosen were Inconel 600, Inconel 718 and stainless steel 304. A shielding material is acceptable if the outer sheath temperature is below 850oC.

SCWR is using SuperCritical Water as a reactor coolant. It is a light water and above its critical point. Various fossil fuel based plants are using this water as a working fluid for the turbine. Major thermodynamic cycle options for direct cycles SCWR are with no-reheat and single reheat. Direct cycles are allowed with increased coolant factors such as high temperature and pressure. The no-reheat cycle SCW exits the channel and enters into the turbine. The single reheat cycle is obtained by using Steam-Reheat channels.

Significance of Sheath materials

Sheath material is suitable for SCWR use if the temperature remains below the design limit specified at 850oC. The main choice for sheath material is zirconium alloy for its high mechanical strength and outstanding neutron transparency. Although when the temperature increases to 500oC, it is steeply corroded. Therefore zirconium alloy is unfit as a sheath material because the coolant temperature vary from 350oC to 625oC.

Other sheath materials are- alloy Inconel 600, Inconel 71 and stainless steel 304. Inconel alloys are nickel based high temperature materials offering high mechanical strength, hot and cold workability and supreme corrosion resistance. With increase in temperature above 750oC, alloy 718 attains significant reduction in its yield stress and tensile strength. Stainless steel 304 is selected for offering good corrosion resistance but its structural strength is very low and wall thickness needs considerable increase. It is not fit as the thermal efficiency and neutron economy would be significantly reduced. Following the review, Inconel 600 is the main sheath material.

For fuel supply, MOX is the perfect option as it is developed from irradiated UO2 and Thoria is special because it is a non-uranium based fuel. The fuel centerline temperature industry limit goes beyond only by MOX fuel. To make this fuel suitable for advanced reactors, fuel bundle design changes are required or channel power should be reduced. Thoria, uranium nitride and uranium carbide are possible SCWR nuclear fuels because their fuel centerline temperatures remain lower than 850oC. Thoria offers an additional benefit due to reduced dependence on uranium reserves.

Tailored Window screens for your house and commercial unit

We focus on adventurous architectural ideas unfolding into exciting reality. We are passionate in shaping the structures that are valuable to people. We are recognized as leading mesh screen manufacturer bringing strong design element to the business that continues to reflect the industry.

Our name translates Energy, Spirit and Vitality- the basic values that encourage us to consistently discover new solutions for our valuable customers. We are dedicated to the regular enhancement of quality.

We manufacture insect screen offering a screening solution to any window or door applications with its innovative design. Made for flexibility and tested for durability, the screens are popular across the world. We produce small to large size single action mesh screens that can cover any size of opening.

The window screen supplier assembles screens with the finest quality materials to offer outstanding service. Our purpose built screens offer accuracy and efficiency as they undergo rigorous testing before delivery. We produce durable and stabilized screens for easy handling and seamless performance. The screens can slide smoothly with a low service force. Using precision bearings can increase screen’s life. The tensioning cords also prevent the mesh from blowing out in windy conditions. The screens are tested to withstand wind gusts about 20mph before the mesh leaves the channel. This protection feature helps to prevent damage and if the screen displaces from the channel, it can be easily packed back.

Our screens are made for any size and design of window and door system and can work easily with folding, sliding and advanced doors and window types. This freedom allows the screen to be used in numerous applications. The smart design is fully integrated in the windows and doors discretely while in service. It is obtained with low profile frame sections and plated, UV resistant mesh. We produce tailor made mesh for window screen and security. They can be easily used with straight sliding systems single run and timberoll.

We produce the screens that have an ability to be added to pre-installed window and doors that have suitable outer frames. The screens are adept to allow for face fix operations that can be easily configured by wood trim casing.

A simple yet effective solution to conditions where a door is already placed without adequate insect screening. The flexible screens can now protect these systems and transform them into a full exterior door way system. The retrofit screens are also made that can be easily integrated with existing systems.

The benefit of using screens is the potential to screen the openings without corner post, offering outstanding uninterrupted views. Corner applications are feasible with our exterior mesh systems for self draining and easy configuration. We also offer tailored mesh to discreetly incorporate screens directly in sliding doors to offer aesthetic and economic benefits.

Width screen reduces in width to the size of the smallest screen and the screens can be cut down to fit in your structure.

Behavior of Nickel-Copper Alloys in Sulfuric Acid

Monel 400 is commonly used in sulfuric acid based applications in reducing environments. So, this material is the best alternative to stainless steels and other materials when the sulfuric acid solutions are not highly oxidizing in nature. Monel 400 attains nominal corrosion rates in air-free sulfuric acid about 85% concentration at 30oC and about 60% concentration at 95oC. Even alloy 400 offers suitable corrosion resistance at the boiling temperature of about 20% sulfuric acid.

In saturated air the attack on Monel 400 increases, although in most applications the corrosion rate is equivalent to rates at air-free conditions because air saturation occurs rarely.

The rate at which air can be renovated at a quiet solution air interface is nominal in comparison to the rate at which oxygen is eradicated through corrosion. As a result, in a tank open in air, a large level of aeration would occur only at the liquid line, and if this level is constant, corrosion would occur at the fast rate at this level. Attention should be given to the nitrogen layer in these media. Most organic compounds containing proteins for example milk albumin, fats, sugars etc will interact with dissolved oxygen to eradicate from solution and may also contribute in the development of a more secured layer on the alloy surface.

In air-free sulfuric acid about 5 to 6% content, temperature has nominal influence, although in air saturated acid, the increasing temperature results into increased corrosion. The highest corrosion rate in air saturated media is noticed at 82oC. The corrosion rate decreases with increasing temperature until the boiling temperature when the corrosion rate is same as in air-free acid.

With the drastic increase in corrosion rate at high magnitudes of sulfuric acid, the limit of protection may be practical. Actually Monel 400 shows suitable resistance in the storage of 80% sulfuric acid at room temperature however it should not be used constantly at higher acid concentration before testing.

Alloy Monel 400 bar also offers god corrosion resistance to boiling sulfuric acid solutions about 15% concentration. Oxidizing salts like cupric and ferritic salts when dissolved in considerable magnitudes in sulfuric acid solutions increase the corrosivity of the solutions to the large scale. To show the corrosive effect of ferritic ion, lab tests were performed with Monel 400 in dilute, air saturated sulfuric acid solutions at 30oC in presence or absence of ferritic sulfate. Variations in ferric sulfate concentrations have also increased the corrosion rates more than variations in acid magnitudes.

Ferrous and cuprous based salts in application solution often do not have any effect on the corrosion rate of Monel 400 however it is crucial in dealing with solutions to prevent oxidation that would result into transforming these salts to higher valence form. Practically, it has been noticed that specific impurities will also prevent corrosion for example milk albumen, amines, ketones and meracptans prevent corrosion to some level.

By increasing the velocity of acid the corrosion rate of Monel alloy 400 also increases. 

How Stress corrosion cracking occurs in chloride environments

Austenitic stainless steels receive stress corrosion cracking in hot solutions comprising of chloride. A solution containing concentrated chloride should be present, however comparatively nominal magnitudes of chloride are adequate in heated surfaces where chloride content can occur or where chloride is concentrated by pitting or crevice attack and troubles may occur in tap water.

The factors resulting in SCC are different for those causing hydrogen embrittlement. The temperature often requires to be more than 70oC however stress corrosion cracking may occur at lower temperatures in some conditions, significantly higher acid solutions.  The cracking occurs at low stresses and usually due to residual stresses caused welding or fabrication. The cracking is usually transgranular, however it may switch to an intragranular path due to steel sensitization.

Carbon and low alloy steels can experience stress corrosion cracking in diverse environments that develop a security passivating layer of oxide or other materials. Cracking doesn’t occur even at noticeable corrosion rate which is not in case of hydrogen embrittlement. Diverse cases have been noticed to cause stress corrosion cracking such as strong caustic solutions, phosphates, nitrates, carbonates and hot water. The issues are considerable for economic and safety reasons. Caustic cracking of steam production boilers was a severe problem in the past century and boiler blasts took several lives.

Recently gas transmissions pipelines damaged due to carbonate solutions production in security layers. In such case the crack runs along the pipe length and may propagate for long distances by quick fracture. If a gas cloud that is released ignites, the resultant fireball is damaging.

Hydrogen embirttlement processes are often not firmly affected by the environment and that is needed is conditions that permit hydrogen to be developed by cathodic corrosion reaction and to penetrate the steel.

Other SCC mechanisms are much more specific and particular conditions are required for cracking to occur. It is because cracking is based on the feasibility of specific corrosion reactions at the crack edge with other reactions occurring on the crack walls and the sample surface. With just nominal variations in the environment one or other these needs may not be met and cracking will not occur.

While the need for a particular condition is advantageous in that it refers that stress corrosion cracking is relatively uncommon, it also makes life complicated for the materials engineer as it makes the occurrence of cracking instead unpredictable with slight differences in service environments causing remarkable changes in behavior.

The specific alloy chemistry, microstructure and heat processing of Hastelloy C22 bar can have a remarkable effect on stress corrosion cracking performance.

There are some general rules leading the effect of material strength on SCC sensitivity. For hydrogen embrittlement processes a strength usually increases the susceptibility, additionally higher strength materials have low K(ic) and hence damage by quick fracture with a nominal SCC crack. Processes that depend on plastic strain at the crack edge will be easier for lower strength materials. So various SCC systems like caustic cracking of carbon steels will become more vulnerable with reduction in strength. 

Importance of using super alloys in rigorous screening applications

Heanjia has established its business by accepting individual manufacturing orders that was hard to do for others. We are structured to efficiently produce both standard and customized mesh clothes for filter and strainer elements. Specially machines and non standard requirements are common to us. We have several special equipments and in-house CNC equipments to receive desired solutions. No order is small to us. Just give us a call so we can help you with orders that others cannot make. Special orders and custom projects need engineering effort. We can invest the energy to make custom design possible for you.

With over three decades of custom and element interchanges for filter elements, we are specialized in understanding what do you need exactly. We manufacture mesh fabrics in house so you are ensured to receive high quality products. The patent design reduces potential hazardous waste with substantial cost-effectiveness. Our quality management system has ISO certification with design and test specialization for both manufacturing and designing.

We have a complete range of mesh material options with plain steel, stainless steel and special alloys that are made to deal with high temperature and high pressure applications.

We manufacture Inconel mesh filter elements by using durable construction methods to offer adequate strength for variety of high pressure applications and are ideal for numerous fluid applications. Our mesh screens are easy to clean and are easy to restore to service by back flush, ultrasonic and other nonabrasive cleaning methods. This is specifically valuable and economical in various applications that deal with hazardous fluids. As our elements are easy to clean, the maintenance costs are nominal.

We also offer crimped construction, a process specifically feasible for industrial process cartridges that are usually pleated or cylindrical with a lightweight core and a support ring. The heavy duty cartridges are fit with all temperature and compatibility limits as they are made of stainless steel by crimping. Fully made of Stainless steel 304 or 316 steel type, our mesh screens for cartridges are cleanable, reusable and can handle various pressure limits up to 60 PSI. They also serve satisfactorily up to 500oF rather 250oF and are remain intact of diverse corrosive media. Fine particle retention up to 5 micro-m. Element media can be pleated to increase surface area. Cartridges rates at 100 micro-m or finer with hidden support layer of coarsed stainless steel mesh to avoid pleat damage.

The woven Hastelloy wire mesh cleanable elements feature rugged Hastelloy mesh components for a great range of applications in severe application environments including high temperature, high pressure and corrosive chemicals. These mesh screens are easy to clean to restore their significant life through backflushing or other methods.

The woven wire mesh elements feature the stainless steel components such as end caps, center tube, and woven wire mesh screen. The precision mesh pleat packs offer suitable particle size cutoff and fully prevent media movement that otherwise causes downstream contamination. 

How anodic protection is valuable to prevent corrosion in sulfuric acid

Sulfuric acid is produced more than any other chemical in this world for use in fertilizer, chemical, pigment, paint, petroleum, textile and film, iron and steel and other applications. Besides of these major applications, sulfuric acid is specifically used in producing dyes, drugs, rayons, cellulose, alkylation of petroleum products to increase octane rating, pickling of ferrous and nonferrous alloys, production of uranium from ore, develop hydrogen fluoride from fluorospar, application use in copper, zinc and nickel refining and treatment of organics in the development of alcohols and treatment of organics in the production of alcohols and detergents. Sulfuric acid is also used to add sulfur content that offer special characteristics to the finished product like surfactants.

Corrosion by sulfuric acid

Stainless steel series 300 specifically 316/316l are widely used in sulfuric acid solutions for particular applications. The applications include dilute or concentrated solutions at medium or low temperatures. Austenitic stainless steel 300 series show active passive behavior in sulfuric acid solutions.

Corrosion in sulfuric acid conditions is electrochemical in nature and the total magnitude of metal loss is associated with total corrosion current. The corrosion current is in proportion to current density of the corroded metal if the corrosion is symmetrical on the metal. With increase in temperature or chloride ion concentration, the critical current density increases, the area of passivity decreases and pitting occurs.

Corrosion of stainless steel 316 is observed in 93% sulfuric acid from a metallurgical plant stack gas. The acid comprised of contaminants that made it more severe. The corrosion potential was noticed to be stable passive at 25oC, rarely active at 75oC and at 95oC, the steel became active for a short duration.

Anodic Protection

Anodic protection is a significant way of increasing the service life of stainless steels and other materials in various corrosion media and it has been successfully used to reduce corrosion level of carbon steel and stainless steel in sulfuric acid application.

Austenitic stainless steels like SS 304, 304l, 316 and 316l can be anodically secured at actually all concentrations of sulfuric acid up to boiling temperature. The corrosion rate can be minimized by moving from freely corrosive active zone to secured passive zone.

A misconception about the passive state is that lowers the corrosion rates. It is feasible to find very corrosion rates in the passive state and hence there are practical limitations with respect to anodic protection. Stainless steel type 316 is observed in the acid content of 3 – 92% at temperatures 34 to 121oC and it is found that anodic protection is useful for the whole acid concentrations at temperatures up to 75oC.

Another factor considered is cathode current density that will be limited by content polarization. The cathode to anode surface area should be sufficiently big to passivate the anodic surface at genuine rate. Hastelloy C276 wire and platinum were used as cathodes for anodic protection. The harmful effect of chlorides in sulfuric acid can be overcome by anodic protection. For example stress corrosion cracking of Stainless steel type 304 in  5 to 50% sulfuric acid at 30oC was prevented by anodic protection. Hence it is a success.

How Mesh screens are key of industrial screening processes?

Woven wire screen filter clothes are fit for sieving, straining and filtration of diverse liquids, gases, powders and sludges. Every thread of the screen is a solid strand that is woven in to the material. They are perfect, precise and have uniform diameter.

Benefits

·         With their uniformity, they can be woven with extreme precision to offer an exact and regular aperture

·         The woven screen has a smooth surface to easily eliminate the filtered particles

·         Screen has excellent strength and elasticity

Subsequent to weaving, the mesh undergoes a finishing process to add the characteristics needed for specific applications. During the finishing process, the fabric is scoured to eliminate the contaminants and the mesh is then stabilized.

Woven wire screens are an outstanding material for their supreme strength, versatility, prolong life and resistance to wear and abrasion. The mesh materials offer supreme resistance to numerous solvents and serve regularly at different temperatures. Mesh screens made from super alloys are preferred for working at high temperatures.  They are fit for multiple screening applications.

Heanjia produces a great range of mesh products, catering our customer’s specific needs and standard designs. They are made from a good quality and high performance materials. The screens are specifically made to be used in a great range of applications in various industries – spanning chemicals, wine and juice production, waste water and sewage treatment, ceramics and food.

Screens are made in a wide range of weave constructions and permeabilities. Their great selection makes it feasible to serve in a range of applications. We manufacture screens in close cooperation with our end users particularly for applications in liquid-solid separation and dewatering if suspended solids. These applications are product extraction in chemical industry, metallurgy and mineral mining. Our filter screens are fit for extraction of phosphoric acid and fertilizers, filtration of aluminum hydroxide, coal wash and individual filtration in flue gas desulphurization. They can be used in vacuum filter belt units, gravity belt thickeners, pan filters, belt presses and fluid bed driers and several others.

We produce a full range of mesh screens that are fit for use as filter belts. They are available in different forms and materials varying from plain steel to Super alloys. They can be made to serve in specific set of environments for use in lighter to vigorous applications and processes. Stainless steels are used in a wide range of applications where physical strength is the key factor.

Insect Screens

We produce fly screens for use throughout the earth and are used in several ways to prevent the passage of different type of insects and reptiles and allow users to meet the stringent protocols on health, safety, food hygiene and environment regulations.  Steel based China window screens are easy to work with as they are rust free and wear resistant and easy to cut. The screens are made almost transparent so it is easier to see from the inside. It is an inexpensive material although specific applications may need other materials. Stainless steel is a durable material and is an expensive material that offers long lasting performance.