Natural Uranium Consumption Research Articles

Attainment of Radiation Equivalency in Nuclear Power Radioactive Product Management

The conditions for future progress in Russian nuclear power include increasing the safety of reactors and of radioactive waste management. The principal proposals regarding radiation equivalent disposal of radioactive waste are as follows:1. extraction of long-lived radioactive decay products from ore together with uranium2. extraction of such actinides as neptunium, americium, and curium and of strontium and cesium from fuel during chemical reprocessing so that they can be used for useful purposes3. long-term controlled storage of radioactive waste in near-surface depositories.It takes ∼400 yr of controlled cooling for the activity of buried radioactive waste to reach radiation equivalency with the activity of uranium naturally occurring in the earth, assuming a natural uranium consumption level of ∼100 t/G W(electric). yr, and it takes ∼200 yr for strontium and cesium extracted from radioactive waste.In the limiting case of complete uranium burning and the consumption of ∼1 t natural uranium/GW(electric)·yr, to reach radiation equivalency, additional measures may be needed before burial of the radioactive waste, such as more complete extraction of actinides during chemical reprocessing of fuel, improvement of the physical and chemical forms of the radioactive waste packages, an increase in the duration of controlled storage to ∼500yr, and possibly, 129I and 99Tc transmutation.

Improvement of the design of the series-produced fuel element of the VV�R-440 reactor to increase burnup

The fuel elements for the VVER-440, which were developed for a 4-yr run, operate satisfactorily to an average burnup of 59 MW-day/kg of uranium in the most-stressed fuel element with average burnup of the unloaded fuel of 40 MW-day/kg. Through the introduction of end beveling of the pellets, the mobility of the fuel column is increased. Furthermore, the presence of bevels makes possible a reduction of the number of chips and elimination of process crumbs, and the high mobility of the fuel column makes it possible, during outfitting of the fuel element, to eliminate the axial gaps between pellets, which are unacceptable for safety reasons. The increase in the initial helium gage pressure has made possible substantial improvement of the thermomechanical characteristics of the fuel elements and avoidance of high fuel temperatures and large gas release. When the conversion is made to a 4-yr fuel run, the number of fuel assemblies refueled each year decreases from 117 to 90 per power-generating unit, natural uranium consumption is reduced by 11–12% [2], zirconium consumption is lowered, and the effective capacity of burned-up fuel stores is increased.

Experiment on the increase of the burn-up fraction of fuel assemblies in VV�R-440 reactor

The rated fuel lifetime in a standard VVER-440 reactor includes three partial fuel rechargings). One way of intensifying the fuel use is to increase the number of partial reactor rechargings with a simultaneous increase of the full fuel lifetime. This mode of fuel use makes it possible to raise the fuel burn-up fraction. Two conditions, however, should be met. First, the number of the recharged fuel assemblies (FA) should make it possible to retain a rated number of fuel rechargings during the calendar year of operation, and, second, operational reliability level of the fuel elements should not be exceeded as a result of an increase of the nuclear fuel lifetime. Theoretical studies of various fuel-use ways in the VVER-440 reactor were made. They involved an increased number of partial rechargings with a simultaneous increases of fuel lifetime and specified the quantitative parameters of a fuel cycle consistent with these conditions. The studies showed that for intensifying the fuel use in commercial NPS containing VVER-440 reactors it is appropriate to increase the number of partial reactor rechargings from three to four with a simultaneous decrease of the number of recharged FA from 102 to 78. The design duration of a fuelmore » cycle with the rated fresh fuel enrichment amounts to 255 eff. days. This fuel-use mode makes it possible to increase the burn-up fraction of unloaded fuel by 13.3% in comparison with the rated value and, as a result of this, to decrease the fuel component of electric power cost, to reduce natural uranium consumption, and to cut down separation man-hours in the external fuel cycle.« less

Some neutron-physics considerations of improving the fuel use in water-cooled thermal VV�R and RBMK power reactors

The exploitation of the fuel in water-cooled reactors can be improved by changing the design and the operational conditions of the reactor and also by replacing in those reactors the uranium dioxide by other types of fuel, e.g., by uranium fuel of increased density. In the modernization of reactors (without fuel replacement) one can reduce the consumption of natural uranium fed to the reactor in stationary operation by about 20%. A method is presented of calculating the conversion coefficient and the neutron balance. Results are presented.

Reactor Physics Calculations on Close-Packed Pressurized Water Reactor Lattices

The recycling of plutonium in close-packed pressurized water reactor (PWR) lattices, leading to a higher conversion ratio than recycling in a normal lattice, has been studied by calculations. These calculations were performed with the multigroup cell and assembly transport theory code CASMO. This code, widely used for normal light water reactor (LWR) lattices, was tested for close-packed ones by calculations on experiments. The outcome of these tests was reasonably good for the parameters of greatest importance in closepacked plutonium-recycle lattices. Subsequently, the code was applied to an LWR system containing PWRs with such lattices. The emphasis in this application was on the net consumption of natural uranium and separative work. In an asymptotic (steady-state) situation for the close-packed lattice case, these amounts turned out to be about35% below the corresponding ones for plutonium recycling in a normal lattice.

Optimization of nuclear power system integrated within COMECON

Calculations were carried out on an optimization model of a nuclear power system, integrated with respect to fuel connections, embracing the COMECON member-countries. A minimum demand for natural uranium in the entire forecast period was adopted as the optimization criterion. It was found that because of the integration the fraction of fast breeder reactors could be increased by 8-12% for COMECON as a whole by the end of the forecast period while the consumption of natural uranium would be reduced by 13-14%. A method is given for determining the Pareto-optimal strategies with implicitly expressed compromise properties and two strategies of equal relative losses and gains in which the sense of the compromises is obvious. 6 refs.

Economic aspects of the development of nuclear power and fuel cycle plants in the USSR

Plutonium breeding in fast reactors themselves will not have any significant effect in the next 20–25 years on growth rate of the capacity of nuclear power stations with fast reactors. The character of the distribution of the capital expenditures on nuclear power stations and on the fuel cycle shows that the bulk of the expenditures is spent on the construction of the nuclear power stations and only 20% on the development of the fuel-cycle plants. For this reason, greatest savings of capital expenditure are given by a reduction in the construction costs of nuclear power stations by means of improvements in the design and of the reactor and the thermal and mechanical equipment of the plant. In the fuel cycle the biggest economic effect is produced by measures that lead to a reduction in the specific consumption of natural uranium since the capital expenditure on the mining operations constitutes about one-half of the total capital expenditures on the fuel cycle. The natural uranium costs also make up roughly one-half of the fuel component of the cost of electricity generated by a nuclear power station. As the price of uranium rises, this fraction of costs will also increase.