In the name of Allah the

beneficent ,the merciful

CONTINUANCE of reactor topics

Presentation by Rasul Shamohamady

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Principles of Classification

1. Energy spectrum utilized for fission

2. Prime purpose

3. Fuel

4. Coolant

5. Coolant system

6. Moderator

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Energy

Thermal (0.5 eV) Intermediate (103 eV) Fast (105 eV)

Power reactors: BWR, PWR, VVER, RBMK; Thermal breeder,…

Spaceship reactors (accident in Can.)

BN350, BN600, Super Fenix , Naval reactors

Energy Spectrum Classification

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Purpose

Power Ship propulsion

Production Research Specialized

LWR PHWR (CANDU) HTGRAGRLMRLGR (RBMK)

Submarines Navy Aircarrier Icebreakers PWR-cargo

Plutonium Tritium

WPR TRIGA

Studsvik

Isolated areas Space propul. Heat for chem

PurposeClassification

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Fuel

UO2 (3-4%)sintered pellets zirconium alloy

Nat. Upelletstubes

UO2

spherical part.carbon, silicon

U-Pu-Zr alloy pellets

steel cladding

U-Al alloyplates

Al cladding + Al-Si

LWR CANDU HTGR LMR TRIGA

Fuel Classification

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Coolant

Light WaterH2O

Heavy Water D2O

Gas air, CO2, He

Liquid MetalNa, Na-K, Pb-Bi

LWR CANDU HTGRPebble bed

LMR

Coolant Classification

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Moderator

Light WaterH2O

Heavy Water D2O

GraphiteC

LWR CANDU LGR (RBMK)

GCRHTGR

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Commonly Accepted Classification

PWRBWR

German

USA

Na

Pb-Bi

NuclearReactors

PowerReactors

SpecializedReactors

ResearchReactors

Ship PropulsionReactors

ProductionReactors

CANDU AGR Other

PWR Fast

LMR

HTGR LWR

UnatC+H2O

UnatC+Gas

WPR

TRIGA

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Light-Water Reactors

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Light-Water Reactors

1.The most widely used reactor in the world today for producing electric power is the thermal reactor.

2.Is moderated, reflected, and cooled by ordinary (light) water.

3.Uranium in water reactors must always be enriched.

Light-Water Reactors

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water properties.

1. In addition, its thermodynamic properties are well understood

2. It is readily available at little cost.

3. Water has a high vapor pressure.

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Type of reactor

There are basically two types of light-water reactors now in use:

1. the pressurized-water reactor (PWR)

2. the boiling-water reactor (BWR).

PWR REACTORThe Pressurized-Water Reactor The PWR was one of the first types of power reactors developed commercially in the United States.

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1. water enters the pressure vessel at a temperature of about 290°C or 554°F,

2. flows down around the outside of the core where it serves as a reflector,

3. passes upward through the core where it is heated

4. then exits from the vessel with a temperature of about 325°C or 617°F.

The water in a PWR is maintained at a high pressure-approximately 15 MPa

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Breeder Reactor

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Breeder reactorOverview

Def.: A breeder reactor is a nuclear reactor that generates more fissile material in fuel than it consumes.

These reactors were initially (1940s and 1960s) considered appealing due to their superior fuel economy.

A normal reactor consumes less than 1% of the natural uranium that begins the fuel cycle, while a breeder can burn almost all of it (minus re-processing losses), also generating less waste for equal amounts of energy. Breeders can be designed to use thorium.

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TYPES

Four type of breeder reactor have been developed to date:

1. The liquid metal cooled fast breeder reactor(LMFBR)

2. The gas cooled fast breeder reactor(GCFR)

3. The molten salt breeder reactor (MSBR)

4. The light-water breeder reactor(LWBR)

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The Liquid Metal cooled Fast Breeder Reactor

(LMFBR)

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LMFBR

Overview1. The fundamental principles underlying the fast breeder reactor

concept were discovered before the end of World War II

2. The potential impact of breeder reactors was immediately recognized.

3. The first experimental breeder reactor was a small plutonium-fueled, mercury-cooled device, operating at a power level of 25 kW, that first went critical in 1946 in Los Alamos, New Mexico.

4. A 1.3 MW breeder, cooled with a mixture of sodium and potassium Was placed in operation in 1951 at the Argonne National Labora tory in Idaho. Experimental Breeder Reactor-I (EBR-I)

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Properties 1. The LMFBR operates on the uranium-plutonium fuel.

2. The number of fission neutrons emitted per neutron absorbed by 239pu, increases monotonically with increasing neutron energy for energies above 100 ke V

3. It follows that the breeder ratio and breeding gain increase with the average energy of the neutrons inducing fission in the system. Therefore, insofar as possible, every effort must be made to prevent the fission neutrons in a fast reactor from slowing down. This means, in particular, that

4. Lightweight nuclei must largely be excluded from the core

5. Sodium has been universally chosen as the coolant for the modern LMFBR

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Pro. Of sodium 1. With an atomic weight of 23

2. Sodium does not appreciably slow down neutrons by elastic scattering

3. Sodium is also an excellent heat transfer agent

4. Sodium has high boiling point (882°C at 1 atm)

5. The high coolant temperature also leads to high-temperature , high-pressure steam, and high plant efficiency

6. Sodium unlike water , is not corrosive to many structural materials.

7. Sodium is also highly reactive chemically.

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Con. Of Pro. Of sodium

Unfortunately

1. Its melting point, 98C

2. Sodium absorbs neutrons, even fast neutrons, leading to the formation of the beta-gamma emitter 24Na, with a half-life of 15 hours.

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Loop type

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Pool type

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1. Of the two types of LMFBRs, the loop-type appears based on the simpler concept.

2. This makes inspection, maintenance, and repairs easier than when these components are immersed in hot, radioactive, and opaque sodium, as they are in pool-type systems.

3. Substantial amounts of shielding are required around all the primary loops in a loop-type plant which makes these plants resemble large, heavily built fortresses.

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4. The core of an LMFBR consists of an array of fuel assemblies, which are hexagonal stainless steel cans between 10 and 15 cm across and 3 or 4 m long that Contain the fuel and fertile material in the form of long pins.

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5. An assembly for the Central region of the reactor contains fuel pins at its center and blanket pins at either end. Assemblies for the outer part of the reactor contain only blanket pins.

6. The fuel pins are stainless steel tubes 6 or 7 mm in diameter, containing pellets composed of a mixture of oxides of plutonium (PUo2) and uranium (Uo2).

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7. The pins in the blanket, which contain only U02 , are larger in diameter, about 1.5 cm, because they require less cooling than the fuel pins.

8. The liquid sodium coolant enters through holes near the bottom of each assembly and passes upward around the pins, removing heat as it goes and then exiting at the top of the core.

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9. Although virtually all present-day LMFBRs operate with uranium-plutonium oxide fuel, there is considerable interest in the future use of fuel composed of Uranium-plutonium carbide since larger breeding ratios are possible with this kind of fuel .

10. The control rods for LMFBRs are usually stainless steel tubes filled with Boron carbide, although other materials have also been used.

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11.Steam from an LMFBR plant is delivered superheated to the turbines at about 500°C and between 16 and 18 MPa.

12.The overall plant efficiency is in the neighborhood of 40%.

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GCFRREACTOR

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The GCFR

1. This reactor concept is a logical extrapolation from HTGR(already VHTR) technology.

2. It is a helium-cooled reactor fueled with a mixture of plutonium and uranium.

3. The core of the GCFR is similar to that of an LMFBR, with mixed Puo2 and Uo2 pellets in stainless steel pins

4. The pins are not as close together as they are in the LMFBR.

5. The pins in the GCFR have a roughened outer surface

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6. The GCFR, unlike the LMFBR, requires no intermediate heat exchangers

7. Since the coolant in a GCFR does not become overly radioactive, it is possible to work on any part of the coolant loops soon after the reactor is shut down.

8. The economics of a power reactor are determined by many factors, including the availability of the plant-the fraction of time during which the plant can, operated.

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Cont.

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9. The reactor is provided with auxiliary circulators and heat exchangers for use in case of a failure of the main cooling loops.

10. The steam generators produce superheated steam at 485°C and 10.5 MPa.

11. Being a gas , helium is essentially a void in the reactor and it has almost no effect on the neutrons in the reactor. The neutron spectrum is therefore harder than in the LMFBR

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MSBRREACTOR

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1.The MSBR this is a thermal breeder that operates on the 233U-thorium cycle.2.The MSBR concept is a unique design among reactors in that the fuel, fertile material, and coolant are mixed together in one homogeneous fluid. 3.This is composed of various fluoride salts that, at an elevated temperature, melt to become a clear, no viscous fluid. 4.The composition of a typical molten salt mixture exception of the thorium and uranium, have very small thermal neutron absorption cross-sections.

PRO..

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5. The fluoride salts have a high solubility for uranium 6. They are among the most stable of all chemical

compounds 7. They have very low vapor pressure at high temperature 8. They have reasonably good heat transfer properties. 9. These salts are not damaged by radiation10. Do not react violently with air or water

CONT..

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Advantages1.The fuel inventory of an MSBR is very small-about 1.0 to 1.2 kg of FISSILE material per MWe of plant output compared with about 3 kg per MWe for an LWR or 3 to 4 kg per MWe for the LMFBR.2. Because of the low vapor pressure of the molten salts, the MSBR operates at just a little above atmospheric pressure and thus no expensive pressure vessel is required.3.Since high temperatures are possible with the molten salts, the MSBR can produce superheated steam at 24 MPa and 540°C, which leads to a very high OVERALL PLANT EFFICIENCY of about 44%.

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Drawbacks 1.as the fuel flows out of the reactor, it carries the delayed neutron precursors with it2.Maintenance and repairs to any component in the system may therefore require extensive reactor downtime and extensive automatic, remotely operated equipment. 3.The breeding ratio of the MSBR is in the 1.05 to 1.07 range, much smaller than for the LMFBR or GCFR. Doubling times are expected to be from 13 to 20 years. Finally, the need to handle and process the radioactive mixture limits the commercial application of this s technology.

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LWBR REACTOR

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LWBR It was thought that : large absorption cross-section of water

To many neutrons would be lost at thermal Energies

BUTReducing the amount of water relative to fuel in the core It was recognized that this problem could be avoided

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UNFORTUNATELY

larger fraction of the neutrons would be absorbed in the 233U at intermediate energies (l eV : E : 10 keV)

AND

ƞ fell to a value only slightly greater than 2. SO

reactor would not breed.

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1960s:new experiments showed that ƞ is, in fact larger than 2 in the intermediate energy range to make breeding possible. Even when a special effort is made in the design of the LWBR to reduce neutron losses, its overall breeding gain will be very small-too small to make the reactor a net producer of 233U for other reactors of this type.

AND

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enough excess 233U (namely, from 1%-2%) would be obtained over the life of a core to compensate for the loss of 233U accompanying the chemical reprocessing of the fuel. Thus, once an LWBR is put into operation, it presumably could be fueled indefinitely with 232Th, of which there are abundant sources. The system operated well, producing a breeding ratio between 1.01 and 1.02 as designed.

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A cross-section through the LWBR core is given in Fig. 4.32. As indicated in the figure, The core consists of hexagonal modules arranged in a symmetrical array surrounded by a reflector blanket region. Each module contains an axially movable seed region-that is, a region having a multiplication factor greater than unity and a stationary, annular hexagonal blanket with k < 1. Each of these regions, in turn, consists of arrays of tightly packed, but not touching, fuel rods containing pellets of thorium dioxide (Th02) and 233UC2 , the latter in varying amounts from 0 to 6 W /0 in the seed and from 0 to 3 W /0 in the blanket region.

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Mobile Power

Reactors

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One of the widest 'Applications of nuclear power is in its use for propulsion of ships. This idea was fostered by the legendary Admiral Hyman G. Rickover who also played a key role in development of the commercial nuclear power program. Starting with the Nautilus, the U.S. Navy and later the British, French, and former Soviet Union all adopted nuclear propulsion as the primary power source for sub marines .

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U.S. and former Soviet Union Navies :::::::: use nuclear power for the propulsion of surface ships. The requirements of a mobile power reactor differ somewhat from those of a commercial central power station, in that the reactors and associated systems must be compact and long lived.

1.

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• As a result, the designs are different from those of the larger commercial reactors.2. Initially, two competing concepts were developed PWR and a liquid metal-cooled design. The PWR reactor concept was used in the Nautilus AND the liquid metal-cooled reactor in the Seawall l The Nautilus went operational in January 1955 and demonstrated its capabilities by sailing underneath the North Pole in August 1958.

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Because of maintenance and reliable it problems, the liquid metal Sign was abandoned in favor of the PWR concept, and the Seawall reactor was removed and replaced with a reactor similar to that of the Nautilus. Later reactors were designed for the propulsion of surface ships.The success of nuclear power is clear. All submarines are nuclear powered, and eventually all U.S. aircraft carriers Will be as well. With its nearly unlimited undersea endurance and its ability to provide a compact high power source without the need for oxygen, the nuclear reactor en ables submarines to stay submerged for months at a time. The designs are similar to those found in commercial reactors, but they use a much higher classified level of enrichment.

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Reference

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BOOKS

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ARTICLE:

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WEBSITE:

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END