PROCESS HEAT TRANSFER. BY. DONALD Q. KERN. D. Q. Kern Associates, and. Professorial Lecturer in Chemical Engineering. Case Instiiute of Technology . PROCESS HEAT TRANSFER. BY. DONALD Q. KERN. D. Q. Kern Associates, and. Professorial Lecturer in Chemical Engineering. Case Institute of Technology . Process Heat Transfer - D.Q. Kern - Ebook download as PDF File .pdf) or read book online.
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Process Heat Transfer - By D. Q. Kern - Free ebook download as PDF File .pdf), Text File .txt) or read book online for free. HE,Evaporator, heat transfer. PROCESS HEAT TRANSFER. BY. DONALD Q. KERN. D. Q. Kern Associates, and. Professorial Lecturer in Chemical Engineering. Case Institute of Techowlogy . A heat transfer textbook / John H. Lienhard IV and. John H. Lienhard V — 3rd ed. — Cambridge, MA: J.H. Lienhard V, c Includes bibliographic references.
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Andy Vallee. This energy must be removed to avoid overheating the graphite.
The rest of the heat is removed by the control rod channel coolant channels. The gas circulating in the reactor plays the role of enabling the heat transfer to the coolant channels.
There are fuel channels and control rod channels in the first generation RBMK reactor cores. Second generation reactor cores such as Chernobyl-4 have fuel channels and control rod channels. The fuel assembly is suspended in the fuel channel on a bracket, with a seal plug. The seal plug has a simple design, to facilitate its removal and installation by the remotely controlled refueling machine.
The fuel channels may, instead of fuel, contain fixed neutron absorbers, or be empty and just filled with the cooling water. The small clearance between the pressure channel and the graphite block makes the graphite core susceptible to damage. If the pressure channel deforms, e. The fuel pellets are made of uranium dioxide powder, sintered with a suitable binder into barrels The material may contain added europium oxide as a burnable nuclear poison to lower the reactivity differences between a new and partially spent fuel assembly.
The rods are filled with helium at 0. Retaining rings help to seat the pellets in the center of the tube and facilitate heat transfer from the pellet to the tube. The pellets are axially held in place by a spring. Each rod contains 3. The fuel rods are 3. The fuel assemblies consist of two sets "sub-assemblies" with 18 fuel rods and 1 carrier rod.
The fuel rods are arranged along the central carrier rod, which has an outer diameter of 1. The two sub-assemblies are joined with a cylinder at the center of the assembly; during the operation of the reactor, this dead space without fuel lowers the neutron flux in the central plane of the reactor.
The total mass of uranium in the fuel assembly is The total length of the fuel assembly is In addition to the regular fuel assemblies, there are instrumented ones, containing neutron flux detectors in the central carrier. In this case, the rod is replaced with a tube with wall thickness of 2. The refueling machine is mounted on a gantry crane and remotely controlled.
The fuel assemblies can be replaced without shutting down the reactor, a factor significant for production of weapon-grade plutonium and, in a civilian context, for better reactor uptime. When a fuel assembly has to be replaced, the machine is positioned above the fuel channel, mates to it, equalizes pressure within, pulls the rod, and inserts a fresh one. The spent rod is then placed in a cooling pond. The capacity of the refueling machine with the reactor at nominal power level is two fuel assemblies per day, with peak capacity of five per day.
The total amount of fuel under stationary conditions is tons. Most of the reactor control rods are inserted from above; 24 shortened rods are inserted from below and are used to augment the axial power distribution control of the core.
With the exception of 12 automatic rods, the control rods have a 4. The role of the graphite section, known as "displacer," is to enhance the difference between the neutron flux attenuation levels of inserted and retracted rods, as the graphite displaces water that would otherwise act as a neutron absorber, although much weaker than boron carbide; a control rod channel filled with graphite absorbs fewer neutrons than when filled with water, so the difference between inserted and retracted control rod is increased.
When the control rod is fully retracted, the graphite displacer is located in the middle of the core height, with 1. The displacement of water in the lower 1. This "positive scram" effect was discovered in at the Ignalina Nuclear Power Plant. The narrow space between the rod and its channel hinders water flow around the rods during their movement and acts as a fluid damper , which is the primary cause of their slow insertion time nominally 18—21 seconds for the RCPS rods, or about 0.
After the Chernobyl disaster, the control rod servos on other RBMK reactors were exchanged to allow faster rod movements, and even faster movement was achieved by cooling of the control rod tubes by a thin layer of water while letting the rods themselves move in gas.
The division of the control rods between manual and emergency protection groups was arbitrary; the rods could be reassigned from one system to another during reactor operation without technical or organizational problems.
Additional static boron-based absorbers are inserted into the core when it is loaded with fresh fuel. About absorbers are added during initial core loading. These absorbers are gradually removed with increasing burnup. The reactor's void coefficient depends on the core content; it ranges from negative with all the initial absorbers to positive when they are all removed. The moisture and temperature of the outlet gas is monitored; an increase of them is an indicator of a coolant leak.
The reactor has two independent cooling circuits, each having four main circulating pumps three operating, one standby. The cooling water is fed to the reactor through lower water lines to a common pressure header one for each cooling circuit , which is split to 22 group distribution headers, each feeding 38—41 pressure channels through the core, where the feedwater boils.
The mixture of steam and water is led by the upper steam lines, one for each pressure channel, from the reactor top to the steam separators , pairs of thick horizontal drums located in side compartments above the reactor top; each has 2.
The resulting feedwater is led to the steam separators by feedwater pumps and mixed with water from them at their outlets. From the bottom of the steam separators, the feedwater is led by 12 downpipes from each separator to the suction headers of the main circulation pumps, and back into the reactor. The turbine consists of one high-pressure rotor and four low-pressure ones.
Five low-pressure separators-preheaters are used to heat steam with fresh steam before being fed to the next stage of the turbine. The uncondensed steam is fed into a condenser, mixed with condensate from the separators, fed by the first-stage condensate pump to a chemical purifier, then by a second-stage condensate pump to four deaerators where dissolved and entrained gases are removed; deaerators also serve as storage tanks for feedwater.
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From the deaerators, the water is pumped through filters and into the bottom parts of the steam separator drums. Each pump has a flow control valve and a backflow preventing check valve on the outlet, and shutoff valves on both inlet and outlet.
Each of the pressure channels in the core has its own flow control valve so that the temperature distribution in the reactor core can be optimized. Each channel has a ball type flow meter. With few absorbers in the reactor core, such as during the Chernobyl accident, the positive void coefficient of the reactor makes the reactor very sensitive to the feedwater temperature.
Bubbles of boiling water lead to increased power, which in turn increases the formation of bubbles. After absorbers were introduced in the fuel assembly, permanently assuring a negative void coefficient at the cost of higher enrichment requirements of the uranium fuel. If the coolant temperature is too close to its boiling point, cavitation can occur in the pumps and their operation can become erratic or even stop entirely.
At low reactor power, therefore, the inlet temperature may become dangerously high. The water is kept below the saturation temperature to prevent film boiling and the associated drop in heat transfer rate. The reactor is tripped in cases of high or low water level in the steam separators with two selectable low-level thresholds ; high steam pressure; low feedwater flow; loss of two main coolant pumps on either side.
These trips can be manually disabled. The level of water in the steam separators, the percentage of steam in the reactor pressure tubes, the level at which the water begins to boil in the reactor core, the neutron flux and power distribution in the reactor, and the feedwater flow through the core have to be carefully controlled. The level of water in the steam separator is mainly controlled by the feedwater supply, with the deaerator tanks serving as a water reservoir.
The reactor is equipped with an emergency core cooling system ECCS , consisting of dedicated water reserve tank, hydraulic accumulators, and pumps.
Process Heat Transfer, DQ Kern.pdf
ECCS piping is integrated with the normal reactor cooling system. In case of total loss of power, the ECCS pumps are supposed to be powered by the rotational momentum of the turbogenerator rotor for the time before the diesel generators come online. The Chernobyl disaster occurred during a botched test of this system. The ECCS has three systems, connected to the coolant system headers. In case of damage, the first ECCS subsystem provides cooling for up to seconds to the damaged half of the coolant circuit the other half is cooled by the main circulation pumps , and the other two subsystems then handle long-term cooling of the reactor.
The third group is a set of electrical pumps drawing water from the deaerators. The short-term pumps can be powered by the spindown of the main turbogenerators. ECCS for long-term cooling of the damaged circuit consists of three pairs of electrical pumps, drawing water from the pressure suppression pools; the water is cooled by the plant service water by means of heat exchangers in the suction lines.
Each pair is able to supply half of the maximum coolant flow. ECCS for long-term cooling of the intact circuit consists of three separate pumps drawing water from the condensate storage tanks, each able to supply half of the maximum flow. Some valves that require uninterrupted power are also backed up by batteries. The distribution of power density in the reactor is measured by ionization chambers located inside and outside the core.
The physical power density distribution control system PPDDCS has sensors inside the core; the reactor control and protection system RCPS uses sensors in the core and in the lateral biological shield tank. The external sensors in the tank are located around the reactor middle plane, therefore do not indicate axial power distribution nor information about the power in the central part of the core.
There are over radial and 12 axial power distribution monitors, employing self-powered detectors. Reactivity meters and removable startup chambers are used for monitoring of reactor startup. Total reactor power is recorded as the sum of the currents of the lateral ionization chambers. The moisture and temperature of the gas circulating in the channels is monitored by the pressure tube integrity monitoring system. The RCPS system consists of movable control rods.
Both systems, however, have deficiencies, most noticeably at low reactor power levels.
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Below those levels, the automatic systems are disabled and the in-core sensors are not accessible. Without the automatic systems and relying only on the lateral ionization chambers, control of the reactor becomes very difficult; the operators do not have sufficient data to control the reactor reliably and have to rely on their intuition.
During startup of a reactor with a poison-free core this lack of information can be manageable because the reactor behaves predictably, but a non-uniformly poisoned core can cause large nonhomogenities of power distribution, with potentially catastrophic results. The reactor emergency protection system EPS was designed to shut down the reactor when its operational parameters are exceeded.
However, the slow insertion speed of the control rods, together with their design causing localized positive reactivity as the displacer moves through the lower part of the core, created a number of possible situations where initiation of the EPS could itself cause or aggravate a reactor runaway.
The computer system for calculation of the reactivity margin was collecting data from about 4, sources. Its purpose was to assist the operator with steady-state control of the reactor. Ten to fifteen minutes were required to cycle through all the measurements and calculate the results.
Kern, D. Q. 1950 Process Heat Transfer
The operators could disable some safety systems, reset or suppress some alarm signals, and bypass automatic scram , by attaching patch cables to accessible terminals. This practice was allowed under some circumstances. The reactor is equipped with a fuel rod leak detector.
A scintillation counter detector, sensitive to energies of short-lived fission products, is mounted on a special dolly and moved over the outlets of the fuel channels, issuing an alert if increased radioactivity is detected in the steam-water flow. The RBMK design was built primarily to be powerful, quick to build and easy to maintain. Full physical containment structures for each reactor would have more than doubled the cost and construction time of each plant, and since the design had been certified by the Soviet nuclear science ministry as inherently safe when operated within established parameters the Soviet authorities assumed proper adherence to doctrine by workers would make any accident impossible.
Additionally, RBMK reactors were designed to allow fuel rods to be changed without shutting down as in the pressurized heavy water CANDU reactor , both for refueling and for plutonium production for nuclear weapons. This required large cranes above the core. In the Chernobyl accident , the pressure rose to levels high enough to blow the top off the reactor, breaking open the fuel channels in the process and starting a massive fire when air contacted the superheated graphite core.
After the Chernobyl accident, some RBMK reactors were retrofitted with a partial containment structure in lieu of a full containment building , which surround the fuel channels with water jackets in order to capture any radioactive particles released. The bottom part of the reactor is enclosed in a watertight compartment. There is a space between the reactor bottom and the floor. In the event of an accident, which was predicted to be at most a rupture of one or two pressure channels, the steam was to be bubbled through the water and condensed there, reducing the overpressure in the leaktight compartment.
The flow capacity of the pipes to the pools limited the protection capacity to simultaneous rupture of two pressure channels; a higher number of failures would cause pressure buildup sufficient to lift the cover plate "Structure E", after the explosion nicknamed "Elena" , sever the rest of the fuel channels, destroy the control rod insertion system, and potentially also withdraw control rods from the core. The leaktight compartments around the pumps can withstand overpressure of 0. The distribution headers and inlets enclosures can handle 0.
The reactor cavity can handle overpressure of 0. The pressure suppression system can handle a failure of one reactor channel, a pump pressure header, or a distribution header. Leaks in the steam piping and separators are not handled, except for maintaining slightly lower pressure in the riser pipe gallery and the steam drum compartment than in the reactor hall.
These spaces are also not designed to withstand overpressure.From the bottom of the steam separators, the feedwater is led by 12 downpipes from each separator to the suction headers of the main circulation pumps, and back into the reactor. The RBMKP is rectangular instead of cylindrical, and it was intended to be made in sections at a factory for assembly in situ. To solve initial and boundary Kern D. Paolo Gochingco. This "positive scram" effect was discovered in at the Ignalina Nuclear Power Plant.
At low reactor power, therefore, the inlet temperature may become dangerously high. Man-made Catastrophes and Risk Information Concealment: The leaktight compartments around the pumps can withstand overpressure of 0. Cicero Gomes de Souza. The 7A, 7B, and 8B boards are also connected to the three essential power lines namely for the coolant pumps , each also having its own diesel generator.
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