Future Power Production System 1M. I. Al-Jarallah

Presentation by:M. I. Al-Jarallah

Department of PhysicsKing Fahd University of Petroleum & Minerals

Dhahran-Saudi Arabia

Contact: 009 663 860 2281Email: mibrahim@kfupm.edu.sa

Homepage: http://faculty.kfupm.edu.sa/phys/mibrahim

Future Power Production System

Future Power Production System 2M. I. Al-Jarallah

Future Power Production System

1. Introduction

2. Advantages & Disadvantages

3. Available ADSs and Those in The Design Stages

4. Diagrams of the Facilities

5. Target, Fuel, Coolant and Accelerator Types

6. The Physics of Spallation

7. Applications of ADSs

8. Conclusion

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Neutrons resulting from interaction of relativistic projectiles with extended targets [e.g. protons on lead], can be used for energy production and nuclear waste transmutation, in sub-critical nuclear assemblies. These systems are known as Accelerator Driven Systems [ADS], and are also called AD Sub-critical Reactors [ADSR]. They are designed to replace or supplement conventional nuclear reactors as neutron sources.

– In such system, an accelerator produces an energetic and intense proton beam [several hundred MeV to a few GeV, 5 – 100 mA], which is made interact with a cooled target consisting of lead or other high mass nuclei to produce fast neutrons through Spallation Process. Spallation Process is the nuclear reaction of high energy protons with nuclei.

– These neutrons can then be moderated and used for some of the same purposes as the neutrons that are produced in a reactor through the fission process. Similar ideas were first proposed more than fifty years ago !

1. Introduction

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A) Advantages of an ADS over conventional reactors:

1. Greater efficiency in neutron production2. Greater safety in operation3. Less production of unwanted radioactive materials in

particular, Pu or other transuranium actinides by using thorium fuel. Thorium is more abundant than Uranium, it generates much less transuranic actinides among the radioactive waste and the risk of nuclear proliferation is negligible. Thorium based thermal reactor cannot operate in a satisfactory way on a self sufficient 232Th – 233U cycle. Evidently an external supply of neutrons remove the above mentioned limitations.

2. Advantages and Disadvantages of ADS

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B) Disadvantages of ADS compared with existing reactors:

1. The need to construct accelerators that are considerably more powerful than existing one.

2. The need to accurately determine many as yet unknown or poorly known nuclear data for the target and other material used in the system

3. The need to develop chemical separation and partitioning methods that are specific to the process in an ADS.

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• Because of the mentioned problems, only a few ADS are in use or have been designed to some degree of details at the present time.

These are:• The SING facility at the Paul Scherror Institute [PSI] in

Villigen, Switzerland, makes uses of the 590 MeV, 1.5 mA proton beam from PSI cyclotron: (nth = 1013 cm-2 s-1,)

• Russian facility in the Joint Institute for Nuclear Research, Dubna, Russia (GeV).

• MYRRHA: A multipurpose ADS being developed jointly by Belgian Nuclear Research Center and Ion Beam Applications [350 MeV, 5 mA proton beam].

• The Spallation neutron facility to be built at Oakridge National Laboratory [ORNL] in cooperation with several other U.S. national laboratories, will have about twice the neutron flux in, SING facility

• the European Spallation Neutron Source [ESS] and a Japanese facility with similar design features, will have an order of magnitude higher thermal neutron flux of SING facility.

3. Available ADS and those in the Design Stage

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Fig. 1 Schematic View of the Target System

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Fig. 2 Schematic Diagram of a Separate High Energy Target

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Fig. 3 Scheme of the Target and Fuel Spheres

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Fig. 4 Diagram of a Beam Driven Liquid Cooled ADS Without Separate Target.

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Fig. 5 Diagram of the Fuel Assembly

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Fig. 6 Diagram of Spherical Fuel Pellets in a Fluidized Bed Configuration

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Fig. 8 MYRRHA in a confinement building that is inaccessible during operation

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A) Target Types:

Solids or liquids can be used as fuel. The requirement for both is high neutron yields and for solids they should have high fusion temperature:

• Lead [fusion 327o] heavy target is considered practical

• Solid Tungsten• Solid [metallic, oxides, nitrides, carbides, etc.]• Lead – Bismulth liquid targets

5. Target, Fuel, Coolant and Accelerator Types:

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1. Higher heat removal capability due to the fact that the heated material is transported rather than the heat.

2. Higher spallation material density in the volume due to absence of cooling channels which tend to dilute the target the more the higher the power density.

3. No or minimum amount of water with its associated problems in the proton beam.

4. No life time limit caused by radiation damage in the target material.

5. Significantly lower specific radioactivity in the target material due to the target mass used and perfect mixing, making an emergency cooling system unnecessary.

6. The inside pressure in the target can be significantly lower than in water cooled system, putting less stringent requirements on the ca`sing wall.

The advantages of liquid metal targets over volume cooled solid targets:

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B) Fuel Types:

• Solids [metallic, oxides, nitrides, carbides, etc.]• Molten Salt [Fluorides or Chlorides]

C) Cooling Agent• Gas• Molten Metal [Sodium, Lead, or Lead, Bismulth]• Molten Salts [Transparent to visible light, and thus allow visual

inspection]

D) The Accelerator System• Cyclotron: more compact and thus require less space and more

economical. However there is current limitation: 5 – 10 mA.• LINACS: Current 100 mA

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6. The Physics of Spallation

• The physics of spallation is in fact rather complex because of the large range of energies involved, and efforts are still going on in various locations to develop models that reproduce all the pertinent experimental observations.

• During the spallation process not only n’s but also protons and other light nuclei are emitted from the excited nuclei. As a consequence, the residual nuclei are not only neutron–poor isotopes of the parent nucleus that decay, mainly by internal p n conversion and + emission, into lower Z elements, but these elements are also created directly in the spallation process.

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About 90% of the n’s released from thick targets in a spallation reaction can be described by characteristic energies around 1 – 2 MeV and are emitted more or less isotopically. Their spectral and angular distributions thus resemble closely to thoseof fission n’s [Figure 9 ].

The small fraction cascade n’s whose energy can reach up tothat of the primary particles driving the reaction, are emittedmainly in the forward hemisphere relative to the proton beam.They are difficult to moderate and thus constitute the mainproblem in shielding and activation in a spallation neutronsource.

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Fig. 9 Calculated neutron spectra for fission and for spallation in a tungsten target

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Fig. 10 Chain of Possible Reactions Starting from Initial 232Th fuel. Cross Sections are for Thermal Neutrons in Barns.

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Fig. 11 Time Evolution of the Composition of an Initial, Thin Thorium Slab Exposed to a Constant Thermal Neutron Flux of 1.0 x1014 cm-2 s-1.

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Fig. 12 Chain of Possible Reactions Starting from initial 238U fuel.

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Fig. 13 The Evolution of the Composition of an Initially Slightly Depleted Uranium Fuel.

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1. Production of Energy: a credible alternative to fast breeder and fusion reactors. They give a unique opportunity to improve the social acceptability of fission energy.

2. Nuclear Waste Processing: • Transmutation, which by neutron capture, transforms a

radioactive nucleus into a stable one.• Incineration which amount to nuclear fission following neutron

capture [transuranic elements such as Pu and minor actinides: Np, Am, Cn. They have high radiotoxicities due to this dominant decay. They have long lifetimes, up to 25000 years for 239Pu]. At least one incineration reactor for four PWRs would be needed if one wants to incinerate completely plutonium and minor actinides.

3. Production of radioisotopes for medical and industrial purposes.

4. Production of tritium

7. Applications of ADSs:

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• It is evident that ADS are now accepted by sponsoring agencies and by members of the nuclear community as valuable new tools in basic research and in applications.

• This will require new technologies of immediate relevance for ADS development. A first demonstration prototype of several tense of MW could be build within 5 – 7 years.

• An industrial realization would probably require at lest 15 years.

8. Conclusion:

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Thank You