Abstract for the Creation of a New Class of Nuclear Microreactors

This document introduces a theoretical and engineering framework for a novel class of compact nuclear energy generators based on direct conversion of decay energy into electricity using advanced piezoelectric materials. The core innovation lies in the proposed composite material "PZT-X", engineered to withstand high temperatures, intense neutron flux, and mechanical stress over decades of operation, with no need for moving parts or external fluids.

The reactor system is designed to operate continuously for over 20 years without maintenance, making it ideal for remote, inaccessible, or extreme environments such as polar stations, deep-sea installations, and disaster-response infrastructure. Particular attention is given to space exploration: the compactness, autonomy, and reliability of the piezo-nuclear generator make it a viable alternative to traditional RTGs for lunar bases, robotic landers, and Martian habitats.

The report also presents a detailed analysis of economic viability. Despite an initially higher cost per kilowatt-hour compared to conventional grid electricity, the system proves highly competitive in scenarios where energy continuity, resilience, and autonomy are strategic priorities. The document outlines the compositional strategies for the fabrication of the "PZT-X" material, including doping methods, multilayer architectures, and ceramic nanocomposites, along with proposed test protocols for performance validation under radiative and thermal stress.

This study aims to lay the groundwork for prototyping a resilient, modular and long-life nuclear generator class suitable for next-generation space missions and off-grid critical infrastructure.

This document is bilingual (English–Italian). The first part is the English version, followed by the original Italian text in the second part.

Note on Version 2 – This updated release is presented exclusively in English and incorporates corrections to certain fuel mass sizing calculations. It also introduces new design strategies for adaptive power management, aimed at maintaining constant output while reducing initial heat production, including variable particle capture mechanisms, graded-Z shielding for bremsstrahlung mitigation, scalable thermal dissipation modules, and automated derating controls linked to real-time dose and material performance monitoring.

Note on Version 3 - Compared to Version 2, this edition includes an additional appendix simulating a wafer-based modular geometry, detailing its impact on fuel mass reduction, thermal management, and overall reactor architecture.

Note on Version 4 – This release adds a dedicated Monte Carlo appendix (Appendix C) documenting the first particle-transport validation of the wafer–lamella geometry. The simulations, performed with Geant4, confirm a high geometric capture efficiency (~93%) independent of applied magnetic fields, thus establishing that the baseline wafer architecture alone ensures near-complete beta energy deposition in the active PZT-X layers. The results shift the critical design focus onto the engineered piezoelectric conversion efficiency, quantitatively requiring ~36% mechano-electrical transduction to achieve a global ηtot ≈ 30%. This edition therefore consolidates the technical feasibility of the 50 W modular cell and provides the first physics-based confirmation of its capture assumptions, while outlining future work on full ^90Sr/^90Y spectra, bremsstrahlung treatment, and multiphysics coupling.

Note on Version 5 – Compared to Version 4, this edition clarifies the fundamental conversion mechanism of PZT-X, explicitly distinguishing between negligible momentum-transfer pressure from β particles and the actual transduction pathway via localized energy deposition, transient strain fields, and domain wall motion. Appendix A has been fully revised to reflect this understanding, introducing a balanced doping strategy that combines donor dopants (La, Ce, Nb, Sm) for high d_{33} sensitivity with acceptor dopants (Mn, Fe, Sb) for thermal and irradiation stability, supported by partial Pb substitution and BN/AlN nanocomposite reinforcement. This update resolves potential inconsistencies in the original doping hypotheses and establishes PZT-X as a “radiation-coupled transducer” material. The new formulation and accompanying schematic provide a coherent framework for material engineering, highlighting that the viability of the reactor depends on achieving stable mechano-electrical conversion under continuous β-energy deposition.

Note on Version 6 – Compared to Version 5, this edition introduces a new appendix (Appendix D) dedicated to advanced thermal management and cogeneration strategies. The added section reframes thermal output not as waste but as a critical resource, detailing how heat can be safely extracted through high-conductivity insulating materials while ionizing radiation remains confined within the graded-Z shielding. It outlines architectures for transporting and utilizing this heat via heat pipes, loop heat pipes, or pumped loops, and presents strategic applications such as habitat warming, greenhouse support, regolith processing, and system preservation. A specific water-based cogeneration loop is analyzed, showing how domestic hot water and space heating can be provided for extraterrestrial outposts, complete with equations for conduction and convection, flow sizing, and a worked numerical example. By integrating this dimension, Version 6 establishes the reactor not only as a source of electricity but as a combined power and thermal hub for long-duration missions, thereby reducing radiator mass and eliminating redundant heating systems while approaching near-total energy utilization.

Note on Version 7 – Compared to Version 6, this edition introduces a new appendix (Appendix E) outlining the proposed procedures for the first laboratory-scale experiments. The section defines proof-of-concept tests aimed at verifying whether measurable piezoelectric signals can be correlated with ionizing energy deposition, and whether doped or multilayer PZT-X compositions exhibit enhanced performance and stability. It specifies sample preparation (standard PZT, modified PZT-X, ZnO, AlN), irradiation methods (Sr-90 source or low-energy linac), and electronic setups (electrometers, charge amplifiers, lock-in detection). An experimental matrix is provided, together with evaluation metrics for reproducibility, efficiency threshold (ηloc ≥ 10⁻⁴), and material degradation tolerance. The appendix also includes a comparative outcome table, describing best-, intermediate-, and worst-case scenarios with their implications for further development. This update therefore marks the transition from theoretical modeling to the definition of practical validation protocols, positioning the project for the critical step of experimental verification.

Note on Version 8 – Compared to Version 7, this edition consolidates the theoretical framework by formally discarding the pure piezoelectric pathway as a viable conversion mechanism, establishing through bounding calculations that its efficiency is intrinsically limited to η ≲ 10⁻⁶, i.e. many orders of magnitude below practical thresholds. The document therefore redefines the concept of PZT-X not as a standalone piezoelectric material, but as a composite lamella integrating a semiconductor betavoltaic junction (SiC, GaN, or diamond) with an ultrathin ferroelectric assist layer (HfZrO₂, thin PZT-X). This hybrid BV+FE architecture is shown, via Monte Carlo capture efficiency (~93.3%), present BV junction performance (8–10%), and realistic ferroelectric boost (+20–50%), to already enable ~10% global efficiency, with a credible roadmap to 20–25%. The update includes revised sizing of the 50 W elementary cell and the 3 kWe modular array, complete with detailed tables of isotope mass, thermal output, surface/volume requirements, radiator areas, and efficiency scaling. The economic analysis has been fully rewritten to reflect the hybrid approach: while not competitive with terrestrial grid electricity, the reactors prove strategically valuable in space, polar, underwater, and remote deployments where autonomy outweighs €/kWh. This version thus marks the transition from speculative piezoelectric-only concepts to a physically consistent, hybrid betavoltaic–ferroelectric generator class, with clear experimental signatures, validated capture assumptions, and an articulated pathway from laboratory validation to system-scale deployment.