Abstract This work presents an experimental analysis of single-event upset (SEU) vulnerability in the program counter (PC) of the LEON3 soft-core processor and evaluates triple modular redundancy (TMR) as a hardware-level mitigation strategy. Using FPGA-based emulation with the NETFI+ fault injection framework, SEUs are injected into the 30 most significant bits of the PC across all active pipeline stages. Results reveal that vulnerability is highly stage-dependent: the Fetch (FE) and Decode (DE) stages exhibit 100% sensitivity, as any bit-flip immediately disrupts control flow, while later stages (RA, EX, ME) are fully masked due to natural overwriting of PC values. The Exception (XC) stage shows only marginal sensitivity (0.02%). To address this localized fragility, TMR is applied to the entire integer unit (IU), triplicating pipeline logic. Under single-replica SEU injection, TMR achieves 0% sensitivity, fully masking all faults. Even in pessimistic multi-replica fault scenarios, where two or all three replicas are simultaneously corrupted, the system demonstrates strong resilience, reducing observable error sensitivity by up to 10× compared to the unprotected baseline. Resource overhead includes a 56% increase in LUTs and 28% in registers on a Xilinx Virtex-5 FPGA. These results confirm that the PC is the dominant source of SEU-induced control-flow failure in LEON3 and that TMR provides complete protection in realistic singlefault conditions while maintaining robustness under rare multi-fault events. The study establishes TMR as a highly effective countermeasure for LEON3-based systems operating in radiation-prone aerospace and space environments.

Abstract Affected by strong ground motions, the severe damages on main tunnel in tunnel portal zone were observed in several seismic events. To reveal the dynamic response characteristics of main tunnel in high-intensity seismic zone, a fabricated three-dimension numerical model considering the end wall tunnel portal, open tunnel, and main tunnel as an entire system was established in this paper to investigate the aseismic characteristics under transverse excitation and three-component earthquake excitation based on a tunnel engineering in high-intensity earthquake zone. Subsequently, the aseismic ability of tunnel was estimated. The dynamic features of main tunnel along longitudinal direction and the corresponding damage status were ascertained and then aseismic fortification length of the main tunnel in the tunnel entrance zone was suggested furtherly. Finally, the shock absorbing effect of foam concrete, its effects in mitigation was investigated. The results showed that the dynamic response of the tunnel in the entrance zone gradually decayed to a relatively stable status with the increasing of the distance from the tunnel portal. Compared with the tunnel dynamic response under transverse excitation, it maintains a significant effect in vertical component under three-component earthquakes. An optimal mitigation layer thickness for a special tunnel engineering will be presented according to the mitigation effect of main tunnel. When the tunnel site area is located at high-intensity earthquake area and the near-field seismic effect is obvious. The research result can provide reference for seismic performance evaluation and seismic isolation technology of portal part of mountain tunnel in the high-intensity earthquake areas.