Question

The liquid fluoride thorium reactor (LFTR)
1. how will the LFTR provide benefits?
2. how might the LFTR produce harm?
3. will the LFRT be gendered?
4. what might be the malfunction risks?
5. how might the LFRT introduce cause and effects relationship?
please help me answer all questions.

Answer 1

a)LFTR have technological advantages in three particular areas: safety, fuel efficiency and lack of nuclear waste.

• Inherent safety. LFTR designs use a strong negative temperature coefficient of reactivity to achieve passive inherent safety against excursions of reactivity. The temperature dependence comes from 3 sources. The first is that thorium absorbs more neutrons if it overheats, the so-called Doppler effect. This leaves fewer neutrons to continue the chain reaction, reducing power. The second part is heating the graphite moderator, that usually causes a positive contribution to the temperature coefficient. The third effect has to do with thermal expansion of the fuel.If the fuel overheats, it expands considerably, which, due to the liquid nature of the fuel, will push fuel out of the active core region. In a small (e.g. the MSRE test reactor) or well moderated core this reduces the reactivity. However, in a large, under-moderated core (e.g. the ORNL MSBR design), less fuel salt means better moderation and thus more reactivity and an undesirable positive temperature coefficient.
• Stable coolant. Molten fluorides are chemically stable and impervious to radiation. The salts do not burn, explode, or decompose, even under high temperature and radiation. There are no rapid violent reactions with water and air that sodium coolant has. There is no combustible hydrogen production that water coolants have.However the salt is not stable to radiation at low (less than 100 C) temperatures due to radiolysis.
• Low pressure operation. Because the coolant salts remain liquid at high temperatures, LFTR cores are designed to operate at low pressures, like 0.6 MPa(comparable to the pressure in the drinking water system) from the pump and hydrostatic pressure. Even if the core fails[clarification needed], there is little increase in volume. Thus the containment building cannot blow up. LFTR coolant salts are chosen to have very high boiling points. Even a several hundred degree heatup during a transient or accident does not cause a meaningful pressure increase. There is no water or hydrogen in the reactor that can cause a large pressure rise or explosion as happened during the Fukushima Daiichi nuclear accident.
• No pressure buildup from fission. LFTRs are not subject to pressure buildup of gaseous and volatile fission products. The liquid fuel allows for online removal of gaseous fission products, such as xenon, for processing, thus these decay products would not be spread in a disaster.Further, fission products are chemically bonded to the fluoride-salt, including iodine,cesium, and strontium, capturing the radiation and preventing the spread of radioactive material to the environment.
• Easier to control. A molten fuel reactor has the advantage of easy removal of xenon-135. Xenon-135, an important neutron absorber, makes solid fueled reactors difficult to control. In a molten fueled reactor, xenon-135 can be removed. In solid-fuel reactors, xenon-135 remains in the fuel and interferes with reactor control.
• Slow heatup. Coolant and fuel are inseparable, so any leak or movement of fuel will be intrinsically accompanied by a large amount of coolant. Molten fluorides have high volumetric heat capacity, some such as FLiBe, even higher than water. This allows them to absorb large amounts of heat during transients or accidents.
• Passive decay heat cooling. Many reactor designs (such as that of the Molten-Salt Reactor Experiment) allow the fuel/coolant mixture to escape to a drain tank, when the reactor is not running (see "Fail safe core" below). This tank is planned to have some kind (details are still open) of passive decay heat removal, thus relying on physical properties (rather than controls) to operate.
• Fail safe core. LFTRs can include a freeze plug at the bottom that has to be actively cooled, usually by a small electric fan. If the cooling fails, say because of a power failure, the fan stops, the plug melts, and the fuel drains to a subcritical passively cooled storage facility. This not only stops the reactor, also the storage tank can more easily shed the decay heat from the short-lived radioactive decay of irradiated nuclear fuels. Even in the event of a major leak from the core such as a pipe breaking, the salt will spill onto the kitchen-sink-shaped room the reactor is in, which will drain the fuel salt by gravity into the passively cooled dump tank
• b)

  LFTRs are quite unlike today's operating commercial power reactors. These differences create design difficulties and trade-offs:

• Questionable economics – although proponents of LFTR technology list a wide variety of claimed economic advantages, a 2014 study of their economics from University of Chicago concluded there is no real advantage in overall terms. A number of the claims, like the ambient pressure operation and high-temperature cooling loops, are already used on a number of conventional designs and have failed to produce the economic gains claimed. In other cases, there is simply not enough data to justify any conclusion. When the entire development is considered, the report concluded: "... the difference in cost, given the current industry environment, remains insufficient to justify the creation of a new LFTR.
• Reaching break-even breeding is questionable – While the plans usually call for break-even breeding, it is questionable if this is possible, when other requirements are to be met. The thorium fuel cycle has very few spare neutrons. Due to limited chemical reprocessing (for economic reasons) and compromises needed to achieve safety requirements like a negative void coefficient too many neutrons may be lost. Old proposed single fluid designs promising breeding performance tend to have an unsafe positive void coefficient and often assume excessive fuel cleaning to be economic viable.
• Still much development needed – Despite the ARE and MSRE experimental reactors already built in the 1960s, there is still a lot of development needed for the LFTR. This includes most of the chemical separation, (passive) emergency cooling, the tritium barrier, remote operated maintenance, large scale Li-7 production, the high temperature power cycle and more durable materials.
• Startup fuel – Unlike mined uranium, mined thorium does not have a fissile isotope. Thorium reactors breed fissile uranium-233 from thorium, but require a small amount of fissile material for initial start up. There is relatively little of this material available. This raises the problem of how to start the reactors in a short time frame. One option is to produce U-233 in today's solid fueled reactors, then reprocess it out of the solid waste. An LFTR can also be started by other fissile isotopes, enriched uranium or plutonium from reactors or decommissioned bombs. For enriched uranium startup, high enrichment is needed. Decommissioned uranium bombs have enough enrichment, but not enough is available to start many LFTRs. It is difficult to separate plutonium fluoride from lanthanide fission products. One option for a two-fluid reactor is to operate with plutonium or enriched uranium in the fuel salt, breed U-233 in the blanket, and store it instead of returning it to the core. Instead, add plutonium or enriched uranium to continue the chain reaction, similar to today's solid fuel reactors. When enough U-233 is bred, replace the fuel with new fuel, retaining the U-233 for other startups. A similar option exists for a single-fluid reactor operating as a converter. Such a reactor would not reprocess fuel while operating. Instead the reactor would start on plutonium with thorium as the fertile and add plutonium. The plutonium eventually burns out and U-233 is produced in situ. At the end of the reactor fuel life, the spent fuel salt can be reprocessed to recover the bred U-233 to start up new LFTRs.
• Salts freezing – Fluoride salt mixtures have melting points ranging from 300 to 600 °C (572 to 1,112 °F). The salts, especially those with beryllium fluoride, are very viscous near their freezing point. This requires careful design and freeze protection in the containment and heat exchangers. Freezing must be prevented in normal operation, during transients, and during extended downtime. The primary loop salt contains the decay heat-generating fission products, which help to maintain the required temperature. For the MSBR, ORNL planned on keeping the entire reactor room (the hot cell) at high temperature. This avoided the need for individual electric heater lines on all piping and provided more even heating of the primary loop components.One "liquid oven" concept developed for molten salt-cooled, solid-fueled reactors employs a separate buffer salt pool containing the entire primary loop. Because of the high heat capacity and considerable density of the buffer salt, the buffer salt prevents fuel salt freezing and participates in the passive decay heat cooling system, provides radiation shielding and reduces deadweight stresses on primary loop components. This design could also be adopted for LFTRs.
• Beryllium toxicity – The proposed salt mixture FLiBe contains large amounts of beryllium, which is toxic to humans (although nowhere near as toxic as the fission products and other radioactives). The salt in the primary cooling loops must be isolated from workers and the environment to prevent beryllium poisoning. This is routinely done in industry.Based on this industrial experience, the added cost of beryllium safety is expected to cost only $0.12/MWh.After start up, the fission process in the primary fuel salt produces highly radioactive fission products with a high gamma and neutron radiation field. Effective containment is therefore a primary requirement. It is possible to operate instead using lithium fluoride-thorium fluoride eutectic without beryllium, as the French LFTR design, the "TMSR", has chosen This comes at the cost of a somewhat higher melting point, but has the additional advantages of simplicity (avoiding BeF
  2 in the reprocessing systems), increased solubility for plutonium-trifluoride, reduced tritium production (beryllium produces lithium-6, which in turn produces tritium) and improved heat transfer (BeF
  2 increases the viscosity of the salt mixture). Alternative solvents such as the fluorides of sodium, rubidium and zirconium allow lower melting points at a tradeoff in breeding.
• C) I can no understand the meaning of will LfRT be genedered.