In this paper a novel alternative for bulk electromagnetic separation working at high pressures is proposed. It is shown that if a self-induced Hall potential is stimulated in the boundaries, the system will be able to take advantage of the collisions process, boosting the isotopic separation and resulting in a linear-spectrometer with a higher spatial separation per unit length than a traditional calutron. Although originally the concept was devised for the production of medical isotopes where the minority isotope to be separated is produced by neutron capture and is the heavier isotope, if the Hall potential is replaced by an external electrical field, the concept is equally applicable for situations where the minority isotope is the lighter one, as for example in the enrichment of uranium. Additional R&D is required to explore further the possibilities of this concept and to identify optimal values for several of the system design variables.
In this paper the utility of using fission gas plenums in a lead-bismuth-cooled fast reactor (LBR) is called into question. It is shown that the primary coolant radiological activity levels due to the generation of 210Po from the neutronic activation of bismuth clearly overshadow the total radiological impact from the fission gas products even if only a tiny fraction of available unbound elementary polonium is considered, and then it does not make any difference if fission gases are collected in a gas plenum or if they are vented directly into the coolant. Moreover, the use of fission gas plenums in a LBR is not only futile from a radiological viewpoint but can neutralize the passive safety mechanism of capture and retention of the majority of polonium captured as lead-polonide (PbPo): the outrush of highly pressurized fission gases during a cladding rupture can act as a spray-like mechanism, and then could vaporize and disperse the retained PbPo in the form of a superfine dust or aerosol. The elimination of fission gas plenums will also result in direct mechanical benefits such as a reduction in pumping power requirements, potentially a smaller reactor vessel and related vessel internal components, deep burnups, a reduction in cladding failures, as well as an important reduction in the amount of high-level waste generated. All these benefits will translate into better reactor management and both social and economic benefits.
In this paper the possibility of stimulated self-induced electrostatic fields in radioisotope heat sources for power enhancement is discussed. Because electrons have higher mobility than the positively charged fragments from radioactive decay, a build-up of positive charges can be promoted, leading to an internal induced electrostatic field. This, in turn, results in a repulsive force acting on positive charges, endowing them with additional kinetic energy, and heat release after these charged particles are stopped by inelastic collisions with the boundary wall. Utilizing a simplified geometrical model, an analytical expression for the attainable power enhancement is derived. It is shown that the proposed concept could result in power enhancements of 5–10% for beta sources but enhancements are negligible for alpha sources.
The use of zirconium hydride (Th–ZrH1.6) blankets in a thorium-fuelled sodium-cooled reactor for void reactivity control with particular reference to UK's plutonium disposition problem is proposed and considered. It is shown that, with the use of such blankets, a mild moderation effect is produced during voiding which compensates for the general hardening of the spectrum, enabling a net negative void coefficient at pin level to be attained without the need to rely on traditional neutron leakage enhancement techniques or neutron poisons, and with negligible impact on transmutation capabilities. One important difference in comparison with the traditional methods is that the void coefficient is obtained at the pin level, eliminating or mitigating substantially the spatial dependencies on the location of the void. Combining the use of such blankets with a suitable n-batch fuelling scheme yields a negative void reactivity coefficient throughout the life of fuel. Additional research and development are required to explore further this concept's potential.
Criticality and recriticality considerations in heavy liquid metal fast reactors (HLMFRs) after a hypothetical core meltdown accident are discussed. Although many aspects of system behaviour in such scenarios can be deduced directly from the classical theory of sodium-cooled fast reactors (SFRs), certain ideas that have been accepted as true for SFRs cannot be extrapolated to HLMFRs without sufficiently careful thought. In this paper, we are concerned, as in SFRs, with fuel compaction, but with one important difference: there would be no boiling of the surrounding heavy liquid metal pool. Utilizing a Bethe–Tait model, it is shown that, due to the power flattening effect of the heavy liquid metal, explosive excursions at least an order of magnitude higher than for SFRs in similar situations are conceivable.
The handling of recovered Th-232 is perhaps the most important problem in thorium breeder reactors due to the presence of the undesirable nuclide U-232 and its daughter Th-228. In advanced multirecycling reactors with high conversion ratios, the amount of this nuclide might reach 5000 ppm after several rounds of recycling, an amount that is almost 50-fold higher than that in conventional PWRs resulting in very high remote reprocessing costs. A reduction of U-232 via a reduction of the fast neutrons available for the (n,2n)(n,2n) reaction by increasing the moderator is not a feasible option in advanced reactors because of the loss in conversion. In this paper the possibility to minimize U-232 by blanket fragmentation while maintaining both the fuel-to-volume moderator volume ratio and amount of material is analyzed. The result show that reductions of up to 10% are feasible with an associated -reduction of the reprocessing cost.
Film boiling heat transfer from a horizontal non-isothermal surface is formulated with due consideration to thermocapillary and thermal expansion where thermocapillary convection has been largely ignored in film boiling. The study is particularity important in nuclear reactor technology where non-isothermal heater is practically the general situation due to unavoidable non-axisymmetric neutronic flux in the fuel geometries (cylindrical geometries). Utilizing a simplified geometrical model, an analytical expression was derived. The above equation applied in a sigmoidal temperature profile results in a central stratification for film boiling along the heater's length.