Re: [Vo]:Thorium breeding now?
In reply to bobcook39...@hotmail.com's message of Thu, 2 May 2019 17:36:47 +: Hi Bob, [snip] >With such a reactor, I would hope a scale-up in size with several prototype >reactors is in the card to demonstrate validation of the design concept. That would certainly be the prudent thing to do. Note that much of the initial work has already been done in various places. Google "Aqueous Homogeneous Reactor". >Controlling the concentration of dissolved fuelU-235 in the thorium breeder >reactor concept would be difficult to assure a reasonably steady power with >good reactivity control IMHO. Possibly, though reprocessing is "designed in", and changes can be made in very small increments to "test the waters". ;) [snip] Regards, Robin van Spaandonk local asymmetry = temporary success
Re: [Vo]:Thorium breeding now?
wrote: Some points. > > 1) The fuel is dissolved in the water, so initially there is no fuel in the > reactor until water is added, then criticality is achieved at startup by > pulling > control rods somewhat once the water (and fuel) has been added. > At this point, the negative temperature coefficient is already in effect. > . . . All in all, this sounds much better than a conventional uranium reactor. I have heard that the people at BARC are enthusiastic about this kind of reactor.
RE: [Vo]:Thorium breeding now?
With such a reactor, I would hope a scale-up in size with several prototype reactors is in the card to demonstrate validation of the design concept. Controlling the concentration of dissolved fuel—U-235 in the thorium breeder reactor concept would be difficult to assure a reasonably steady power with good reactivity control IMHO. Bob Cook From: mix...@bigpond.com Sent: Wednesday, May 1, 2019 2:08:49 PM To: vortex-l@eskimo.com Subject: Re: [Vo]:Thorium breeding now? In reply to bobcook39...@hotmail.com's message of Wed, 1 May 2019 02:47:34 +: Hi Bob, Some points. 1) The fuel is dissolved in the water, so initially there is no fuel in the reactor until water is added, then criticality is achieved at startup by pulling control rods somewhat once the water (and fuel) has been added. At this point, the negative temperature coefficient is already in effect. 2) If all the water were to rapidly evaporate, and leave a solid salt (impossible by the way), the reactor would long have shut down because only fast neutrons with a too small fission cross section would remain (i.e. no moderator). If the water were all to leak out, then the fuel would go with it leaving an empty reactor. Leakage should probably be caught in a flat tray with an area large enough to ensure that only a thin layer could exist even with all the water from the reactor in it. The large area thin layer would ensure that too many neutrons would be lost to sustain a chain reaction in the pan. This is a passive safety measure. Furthermore anything leaking into the pan under normal use could be pumped back into the reactor ensuring that it could keep running normally even with a leak. 3) Because fission products are constantly being removed during operation (liquid fuel cycle), there would be few left to produce decay heat, so a melt-down could not happen. 4) If all external systems fail at once, and there is no leak, then the water boils off (pressure release valve) and the reactor shuts down (no moderator). 5) Another advantage of a liquid fuel reactor is that the total fuel load in the reactor at any one time can be kept small, and fuel constantly added as required. I.e. it doesn't need to have years worth of fuel in the reactor at all times. This is another safety feature. >Without water—lost in the steam production—the negative temperature coeff. Is >diminished or lost completely. ...but while this is happening the reaction stops (loss of moderator). > > > >The rate at which reactivity is added to the reactor is important in startup >to avoid super criticality and an uncontrolled –run-away—reaction. Any >positive temperature coeff. resulting in an increase in fast neutron flux is >unacceptable and needs to be avoided. Loss of liquid water would be a >problem if it happened fast and added reactivity and loss of the negative >temperature coeff. > > > >Bob Cook [snip] Regards, Robin van Spaandonk local asymmetry = temporary success
Re: [Vo]:Thorium breeding now?
In reply to bobcook39...@hotmail.com's message of Wed, 1 May 2019 02:47:34 +: Hi Bob, Some points. 1) The fuel is dissolved in the water, so initially there is no fuel in the reactor until water is added, then criticality is achieved at startup by pulling control rods somewhat once the water (and fuel) has been added. At this point, the negative temperature coefficient is already in effect. 2) If all the water were to rapidly evaporate, and leave a solid salt (impossible by the way), the reactor would long have shut down because only fast neutrons with a too small fission cross section would remain (i.e. no moderator). If the water were all to leak out, then the fuel would go with it leaving an empty reactor. Leakage should probably be caught in a flat tray with an area large enough to ensure that only a thin layer could exist even with all the water from the reactor in it. The large area thin layer would ensure that too many neutrons would be lost to sustain a chain reaction in the pan. This is a passive safety measure. Furthermore anything leaking into the pan under normal use could be pumped back into the reactor ensuring that it could keep running normally even with a leak. 3) Because fission products are constantly being removed during operation (liquid fuel cycle), there would be few left to produce decay heat, so a melt-down could not happen. 4) If all external systems fail at once, and there is no leak, then the water boils off (pressure release valve) and the reactor shuts down (no moderator). 5) Another advantage of a liquid fuel reactor is that the total fuel load in the reactor at any one time can be kept small, and fuel constantly added as required. I.e. it doesn't need to have years worth of fuel in the reactor at all times. This is another safety feature. >Without waterlost in the steam productionthe negative temperature coeff. Is >diminished or lost completely. ...but while this is happening the reaction stops (loss of moderator). > > > >The rate at which reactivity is added to the reactor is important in startup >to avoid super criticality and an uncontrolled run-awayreaction. Any >positive temperature coeff. resulting in an increase in fast neutron flux is >unacceptable and needs to be avoided. Loss of liquid water would be a >problem if it happened fast and added reactivity and loss of the negative >temperature coeff. > > > >Bob Cook [snip] Regards, Robin van Spaandonk local asymmetry = temporary success
RE: [Vo]:Thorium breeding now?
No. I meant fast neutrons. Without the water there will be only a spectrum of fast neutrons. Add water and the reactor will go critical just as it would if rods were pulled. FRC Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10 From: mix...@bigpond.com Sent: Tuesday, April 30, 2019 3:51:31 PM To: vortex-l@eskimo.com Subject: Re: [Vo]:Thorium breeding now? In reply to bobcook39...@hotmail.com's message of Tue, 30 Apr 2019 20:57:40 +: Hi Bob, [snip] >As suggested, steam would reduce the flux of thermalized neutrons in the >reactor and shut it down. To maintain criticality, reactivity would need to >be added, probably by the movement of control rods to increase the flux of >fast neutrons upon which criticality depended. Did you mean "...to increase the flux of [slow] neutrons"? >Control systems, including the mechanical portion of the system for insertion >of negative reactivity—the control rods, need to be very fast to avoid super >critical conditions. I think that would only be true is the feedback were positive, however negative feedback is by definition self-regulating. IOW a power increase leads to more boiling reducing the slow neutron flux and therefore slowing the reactor down again. Inversely, a power decrease reduces the number & size of steam bubbles, resulting in more moderation, and an increase in thermal neutron triggered fission events and the power increases. IOW a boiling water reactor would be self-regulating and tend to stabilize at a fixed power level. The actual level at which it stabilized could be regulated by control rods, the degree of insertion thereof determining the current stable power level. Of course the maximum power level would be determined by the overall size of the reactor and the concentration of fuel nuclei in the solution. Radiolysis is a potential problem, though I think that can largely be overcome by using recombiners. Note that bubbles created by radiolysis have the same negative feedback characteristic that steam bubbles have. > The design of fast control systems with high reliability is a problem IMHO > given the complex analysis associated with knowing the local variety of > materials at any given place. > > > >The “nice” thing (RELATIVELY SPEAKING) about normal fission reactors is the >reliable knowledge of the location of the various isotopes in a dynamic >reactor with pressure, temperature and dimensional change occurring rapidly. > I think such variability "might" be reduced to acceptable levels by pumping the working fluid through a many densely packed parallel tubes in the reactor core, rather than having it is a single large container. Individual tubes tend to minimize convection currents, especially if they run horizontally. A rapid fluid flow also helps. Control rods can be inserted between the tubes, and parallel with them. Regards, Robin van Spaandonk local asymmetry = temporary success
RE: [Vo]:Thorium breeding now?
Without water—lost in the steam production—the negative temperature coeff. Is diminished or lost completely. The rate at which reactivity is added to the reactor is important in startup to avoid super criticality and an uncontrolled –run-away—reaction. Any positive temperature coeff. resulting in an increase in fast neutron flux is unacceptable and needs to be avoided. Loss of liquid water would be a problem if it happened fast and added reactivity and loss of the negative temperature coeff. Bob Cook Bob Cook Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10 From: mix...@bigpond.com Sent: Tuesday, April 30, 2019 3:51:31 PM To: vortex-l@eskimo.com Subject: Re: [Vo]:Thorium breeding now? In reply to bobcook39...@hotmail.com's message of Tue, 30 Apr 2019 20:57:40 +: Hi Bob, [snip] >As suggested, steam would reduce the flux of thermalized neutrons in the >reactor and shut it down. To maintain criticality, reactivity would need to >be added, probably by the movement of control rods to increase the flux of >fast neutrons upon which criticality depended. Did you mean "...to increase the flux of [slow] neutrons"? >Control systems, including the mechanical portion of the system for insertion >of negative reactivity—the control rods, need to be very fast to avoid super >critical conditions. I think that would only be true is the feedback were positive, however negative feedback is by definition self-regulating. IOW a power increase leads to more boiling reducing the slow neutron flux and therefore slowing the reactor down again. Inversely, a power decrease reduces the number & size of steam bubbles, resulting in more moderation, and an increase in thermal neutron triggered fission events and the power increases. IOW a boiling water reactor would be self-regulating and tend to stabilize at a fixed power level. The actual level at which it stabilized could be regulated by control rods, the degree of insertion thereof determining the current stable power level. Of course the maximum power level would be determined by the overall size of the reactor and the concentration of fuel nuclei in the solution. Radiolysis is a potential problem, though I think that can largely be overcome by using recombiners. Note that bubbles created by radiolysis have the same negative feedback characteristic that steam bubbles have. > The design of fast control systems with high reliability is a problem IMHO > given the complex analysis associated with knowing the local variety of > materials at any given place. > > > >The “nice” thing (RELATIVELY SPEAKING) about normal fission reactors is the >reliable knowledge of the location of the various isotopes in a dynamic >reactor with pressure, temperature and dimensional change occurring rapidly. > I think such variability "might" be reduced to acceptable levels by pumping the working fluid through a many densely packed parallel tubes in the reactor core, rather than having it is a single large container. Individual tubes tend to minimize convection currents, especially if they run horizontally. A rapid fluid flow also helps. Control rods can be inserted between the tubes, and parallel with them. Regards, Robin van Spaandonk local asymmetry = temporary success
Re: [Vo]:Thorium breeding now?
In reply to bobcook39...@hotmail.com's message of Tue, 30 Apr 2019 20:57:40 +: Hi Bob, [snip] >As suggested, steam would reduce the flux of thermalized neutrons in the >reactor and shut it down. To maintain criticality, reactivity would need to >be added, probably by the movement of control rods to increase the flux of >fast neutrons upon which criticality depended. Did you mean "...to increase the flux of [slow] neutrons"? >Control systems, including the mechanical portion of the system for insertion >of negative reactivitythe control rods, need to be very fast to avoid super >critical conditions. I think that would only be true is the feedback were positive, however negative feedback is by definition self-regulating. IOW a power increase leads to more boiling reducing the slow neutron flux and therefore slowing the reactor down again. Inversely, a power decrease reduces the number & size of steam bubbles, resulting in more moderation, and an increase in thermal neutron triggered fission events and the power increases. IOW a boiling water reactor would be self-regulating and tend to stabilize at a fixed power level. The actual level at which it stabilized could be regulated by control rods, the degree of insertion thereof determining the current stable power level. Of course the maximum power level would be determined by the overall size of the reactor and the concentration of fuel nuclei in the solution. Radiolysis is a potential problem, though I think that can largely be overcome by using recombiners. Note that bubbles created by radiolysis have the same negative feedback characteristic that steam bubbles have. > The design of fast control systems with high reliability is a problem IMHO > given the complex analysis associated with knowing the local variety of > materials at any given place. > > > >The nice thing (RELATIVELY SPEAKING) about normal fission reactors is the >reliable knowledge of the location of the various isotopes in a dynamic >reactor with pressure, temperature and dimensional change occurring rapidly. > I think such variability "might" be reduced to acceptable levels by pumping the working fluid through a many densely packed parallel tubes in the reactor core, rather than having it is a single large container. Individual tubes tend to minimize convection currents, especially if they run horizontally. A rapid fluid flow also helps. Control rods can be inserted between the tubes, and parallel with them. Regards, Robin van Spaandonk local asymmetry = temporary success
RE: [Vo]:Thorium breeding now?
As suggested, steam would reduce the flux of thermalized neutrons in the reactor and shut it down. To maintain criticality, reactivity would need to be added, probably by the movement of control rods to increase the flux of fast neutrons upon which criticality depended. Control systems, including the mechanical portion of the system for insertion of negative reactivity—the control rods, need to be very fast to avoid super critical conditions. The design of fast control systems with high reliability is a problem IMHO given the complex analysis associated with knowing the local variety of materials at any given place. The “nice” thing (RELATIVELY SPEAKING) about normal fission reactors is the reliable knowledge of the location of the various isotopes in a dynamic reactor with pressure, temperature and dimensional change occurring rapidly. Bob Cook From: mix...@bigpond.com Sent: Tuesday, April 30, 2019 12:34:22 PM To: vortex-l@eskimo.com Subject: Re: [Vo]:Thorium breeding now? In reply to JonesBeene's message of Tue, 30 Apr 2019 06:42:54 -0700: Hi Jones, [snip] >Robin, > >On first glance, one obvious thermodynamic problem is steam – in that every >fission fragment capable of knocking off a neutron is also able to boil off >several hundred million molecules of heavy water in the process of >thermalizing. As you can see, from the second message I posted in this thread, this type of reactor was in fact among the first reactors ever built. They do work. Furthermore, I think steam production would probably be a negative feedback mechanism which helps control the reactor. I.e. steam bubbles are less dense, which reduces the amount of moderation available between nuclei, resulting in faster neutrons with a lower fission cross-section. That means that steam formation reduces the power generated and results in a self stabilizing reactor. In fact they (google AHR), were known to be very easy to control, see the second message I posted. See also http://large.stanford.edu/courses/2012/ph241/tilghman2/ There were corrosion problems when uranyl sulphate was used, but these were largely overcome when they switched to uranyl nitrate in a stainless-steal vessel. I suspect that corrosion could be further reduced by lining the metal parts with teflon. However what I was really wondering is whether or not fission fragments can contribute significantly to the neutron efficiency by splitting D nuclei, in a heavy water base? I'm guessing they do, because the AHR is known for a high neutron flux, which would appear to make it a reasonable choice for a thorium based breeder. > > Consequently maintaining a liquid state with uniformly dissolved salt > becomes impossible even under high pressure.. A molten salt would be feasible > but not a dissolved salt in the liquid state. > > > > >? Please see http://rvanspaa.freehostia.com/Thorium_breeder_in_solution.html > >Regards, Robin van Spaandonk > > Regards, Robin van Spaandonk local asymmetry = temporary success
Re: [Vo]:Thorium breeding now?
In reply to JonesBeene's message of Tue, 30 Apr 2019 06:42:54 -0700: Hi Jones, [snip] >Robin, > >On first glance, one obvious thermodynamic problem is steam in that every >fission fragment capable of knocking off a neutron is also able to boil off >several hundred million molecules of heavy water in the process of >thermalizing. As you can see, from the second message I posted in this thread, this type of reactor was in fact among the first reactors ever built. They do work. Furthermore, I think steam production would probably be a negative feedback mechanism which helps control the reactor. I.e. steam bubbles are less dense, which reduces the amount of moderation available between nuclei, resulting in faster neutrons with a lower fission cross-section. That means that steam formation reduces the power generated and results in a self stabilizing reactor. In fact they (google AHR), were known to be very easy to control, see the second message I posted. See also http://large.stanford.edu/courses/2012/ph241/tilghman2/ There were corrosion problems when uranyl sulphate was used, but these were largely overcome when they switched to uranyl nitrate in a stainless-steal vessel. I suspect that corrosion could be further reduced by lining the metal parts with teflon. However what I was really wondering is whether or not fission fragments can contribute significantly to the neutron efficiency by splitting D nuclei, in a heavy water base? I'm guessing they do, because the AHR is known for a high neutron flux, which would appear to make it a reasonable choice for a thorium based breeder. > > Consequently maintaining a liquid state with uniformly dissolved salt > becomes impossible even under high pressure.. A molten salt would be feasible > but not a dissolved salt in the liquid state. > > > > >? Please see http://rvanspaa.freehostia.com/Thorium_breeder_in_solution.html > >Regards, Robin van Spaandonk > > Regards, Robin van Spaandonk local asymmetry = temporary success
RE: [Vo]:Thorium breeding now?
Liquid salt is a bad idea for fissioin reactors IMHO. When it cools it becomes a solid and needs some heating to bring it back to a liquid. In general it does not afford good corrosion protection to reactor containment materials—like metal alloys---and is a difficult waste product to manage, assuming fission products remain associated/entrained. Reactor maintenance is nearly impossible.It’s very costly compared to a reactor with water as its coolant and neutron moderator. Bob Cook From: JonesBeene<mailto:jone...@pacbell.net> Sent: Tuesday, April 30, 2019 6:43 AM To: vortex-l@eskimo.com<mailto:vortex-l@eskimo.com> Subject: RE: [Vo]:Thorium breeding now? Robin, On first glance, one obvious thermodynamic problem is steam – in that every fission fragment capable of knocking off a neutron is also able to boil off several hundred million molecules of heavy water in the process of thermalizing. Consequently maintaining a liquid state with uniformly dissolved salt becomes impossible even under high pressure.. A molten salt would be feasible but not a dissolved salt in the liquid state. * Please see http://rvanspaa.freehostia.com/Thorium_breeder_in_solution.html Regards, Robin van Spaandonk
RE: [Vo]:Thorium breeding now?
Robin, On first glance, one obvious thermodynamic problem is steam – in that every fission fragment capable of knocking off a neutron is also able to boil off several hundred million molecules of heavy water in the process of thermalizing. Consequently maintaining a liquid state with uniformly dissolved salt becomes impossible even under high pressure.. A molten salt would be feasible but not a dissolved salt in the liquid state. ➢ Please see http://rvanspaa.freehostia.com/Thorium_breeder_in_solution.html Regards, Robin van Spaandonk
Re: [Vo]:Thorium breeding now?
In reply to mix...@bigpond.com's message of Tue, 30 Apr 2019 15:49:17 +1000: Hi, [snip] See also https://en.wikipedia.org/wiki/Aqueous_homogeneous_reactor Regards, Robin van Spaandonk local asymmetry = temporary success
