Yigal Ronen

A novel method for energy production using 242mAm as a nuclear fuel

A novel system for energy production is presented. This system has a modular composition of homogeneous reactors with H2O and 242mAm as a fuel. These reactors are spheres of 0.11-m radius and 1-MW(thermal) power and with a critical mass of 0.0201 kg of 242mAm. The advantages of homogeneous reactors are constant fuel reprocessing and constant refueling. As a result, there is a reduction of fission products, which improves the ratio of natural cooling to heat production with respect to a loss-of-control accident (LOCA) and other safety aspects. Homogeneous reactors also have a large negative temperature coefficient and small inherent excess reactivity during operation. The reactor concept we have presented for a very small, homogeneous reactor, further enhances the safety aspects in the case of a LOCA, because of a large surface-to-volume ratio. The improved safety, the simplicity, and the small volume should compensate for the use of an unconventional nuclear fuel.

Effect of 95 241 Am(n, γ) reaction branching ratio on fuel cycle and reactor design characteristics

Abstract The growing interest in innovative reactors and advanced fuel cycle designs requires more accurate prediction of various transuranic actinide concentrations during irradiation or following discharge because of their effect on reactivity or spent-fuel emissions, such as gamma and neutron activity and decay heat. In this respect, many of the important actinides originate from the 241Am(n, γ) reaction, which leads to either the ground or the metastable state of 242Am. The branching ratio for this reaction depends on the incident neutron energy and has very large uncertainty in the current evaluated nuclear data files. This study examines the effect of accounting for the energy dependence of the 241Am(n, γ) reaction branching ratio calculated from different evaluated data files for different reactor and fuel types on the reactivity and concentrations of some important actinides. The results of the study confirm that the uncertainty in knowing the 241Am(n, γ) reaction branching ratio has a negligible effect on the characteristics of conventional light water reactor fuel. However, in advanced reactors with large loadings of actinides in general, and 241Am in particular, the branching ratio data calculated from the different data files may lead to significant differences in the prediction of the fuel criticality and isotopic composition. Moreover, it was found that neutron energy spectrum weighting of the branching ratio in each analyzed case is particularly important and may result in up to a factor of 2 difference in the branching ratio value. Currently, most of the neutronic codes have a single branching ratio value in their data libraries, which is sometimes difficult or impossible to update in accordance with the neutron spectrum shape for the analyzed system.

Correlations of the independent fission product yields of different isotopes

The independent fission product yields obtained from the fast fissions of {sup 232}Th, {sup 233}U, {sup 235}U, {sup 238}U, {sup 239}U, {sup 240}Pu, and {sup 241}Pu were found to be correlated to the 2Z-N values of these isotopes. Examples of these correlations are presented. In these examples, the chain yields of {sup 135}Xe and {sup 149}Sm, the important isotopes in the dynamics of nuclear reactors, are included. The correlations obtained can serve to predict the independent fission product yields from important actinides that have no experimental results so far. These correlations can also serve to point out errors in current evaluated yields.

High converter pressurized water reactor with heavy water as a coolant

There is an increasing interest in water breeder and high converter reactors. The increase in the conversion ratio of these reactors is obtained by hardening the neutron spectrum achieved by tightening the reactors lattice. Another way of hardening the neutron spectrum is to replace the light water with heavy water. Two pressurized water reactor fuel cycles that use heavy water as a coolant are considered. The first fuel cycle is based on plutonium and depleted uranium, and the second cycle is based on plutonium and enriched uranium. The uranium ore and separative work unit (SWU) requirements are calculated as well as the fuel cycle cost. The savings in uranium ore are about40 and 60% and about40% in SWU for both fuel cycles considered.

A nonproliferating nuclear fuel for light water reactors

In this paper a nonproliferating fuel for light water reactors is proposed. The nonproliferating aspects of the fuel are obtained by increasing the {sup 238}Pu/Pu ratio to 5% and above. This limit is maintained during the entire fuel cycle and, in particular, at low burnup values. The high value of the {sup 238}Pu/Pu ratio is obtained by introducing {sup 237}Np into the fuel. Some waste disposal aspects associated with {sup 237}Np are also discussed.

Inverse Perturbation Theory

Perturbation theory is a collection of methods for determining the effect of a known perturbation on a given physical system. Inverse perturbation theory is defined as a collection of methods for determining the nature of the perturbation itself. One method related to inverse perturbation theory is presented, where calculated and measured parameters in one system bound the expected measured parameters in a related system subject to the same uncertainties as in the first system. The method is applied to reactor theory problems. 1 table.

Breeding of 242mAm in a Fast Reactor

Abstract There is growing interest in the use of 242mAm as a nuclear fuel. Since the thermal absorption cross section of 242mAm is very high (σa = 8950 b), the best way to obtain 242mAm is by the capture of fast or epithermal neutrons in 241Am. As a result, we have considered replacing the radial blanket of a fast reactor, which is usually depleted uranium, with 241AmO2. We chose a 714-MW(thermal) MONJU reactor, and we replaced some of the radial blanket and the outer core assemblies with 10 676 kg of 241AmO2 fuel. We calculated the reactor core by using the MCNP Monte Carlo code. The total amount of 242mAm becomes stabilized after 16 yr, but the enrichment does not. In our calculation, ~7.2% enrichment is obtained after 18 yr. Obtaining higher enrichments might indicate that 242mAm nuclear fuel can be used without further enrichment in many cases. The results presented in this paper are considered an upper limit scenario. In particular the target 241Am loading is not likely to be available soon, but 242mAm production from lesser amounts is easily scaled down proportional to the actual mass irradiated.

Modified Fuel Assembly Design for Pressurized Water Reactors with Improved Fuel Utilization

A method for reactivity control through variation of the moderator content in the reactor core was proposed. The main idea is to adjust the amount of water in the core from a low value at beginning of cycle to a high value at end of cycle, so as to compensate for fissile material burnup and buildup of fission products. The possible implementation of this idea may be carried out by introducing a number of hollow tubes into the fuel assembly between the fuel rods. Then variation of the moderator content in the core may be managed through a change of the water level in these tubes. A preliminary neutronic and economic analysis indicated a potential savings in the fuel cycle requirements and costs. Preliminary steady-state thermal-hydraulic calculations indicate the possibility of implementing the proposed method in the existing pressurized water reactor plants. Feasibility of the proposed design may be finally established after rigorous thermal hydraulics as well as safety analysis calculations. Furthermore, there is need to elaborate the mechanical design of the pressure vessel internals together with cost benefit analysis.

A note on the adjoint function in time dependent reactor theory

Abstract The integral over time of some local density is found. The method is based on solving stationary regular and adjoint equations. It is applied to a problem from time dependent reactor theory and tested by a numerical example.

Combination of Two Spectral Shift Control Methods for Pressurized Water Reactors with Improved Power Utilization

Two methods for spectral shift control have been proposed for pressurized water reactors. The first method is a mechanical spectral shift where the moderator-to-fuel volume is changed. The second method is a chemical one in which the D/sub 2/O/H/sub 2/O ratio is changed. Utilization of a combination of the two methods has been suggested and analyzed. It was found that the advantage of the combined method is better than the sum of the advantages of the two methods separately. Emphasis was on using the spectral shift controls for one-batch reloads in order to increase the fuel cycles length and thus the electricity production. It was found that it is possible to increase electricity production during the plants lifetime by about 6 to 9% compared to three and fou