Nuclear-assisted hydrogen production presents a promising pathway for low-carbon hydrogen generation, leveraging the high energy density and consistent output of nuclear power. Two primary methods exist: electrolysis using nuclear-generated electricity and thermochemical water splitting, often via the sulfur-iodine cycle. A comprehensive lifecycle assessment must account for emissions from uranium mining, plant construction, operation, and waste management to evaluate its carbon footprint relative to renewable and fossil-based methods.

### Lifecycle Emissions Breakdown

#### Uranium Mining and Fuel Processing
Uranium mining contributes to the lifecycle emissions of nuclear hydrogen. Open-pit and underground mining emit between 1.5 to 50 kg CO2-equivalent per kg of uranium, depending on ore grade and extraction methods. Milling, conversion, and enrichment add another 5 to 15 kg CO2e per kg of uranium. Transport and fuel fabrication contribute minimally, typically under 1 kg CO2e per kg of uranium.

#### Nuclear Plant Construction
Constructing a nuclear power plant is material-intensive, with emissions primarily from steel, concrete, and other high-embodied-energy materials. Estimates suggest 10 to 30 g CO2e per kWh over the plant's lifetime, translating to approximately 1.5 to 4.5 kg CO2e per kg of hydrogen produced via electrolysis, assuming an energy requirement of 50 kWh per kg H2. Thermochemical cycles, being more efficient (requiring 30 to 40 kWh per kg H2), may reduce this to 1 to 3 kg CO2e per kg H2.

#### Operational Phase
Nuclear plants emit negligible CO2 during operation. Electrolysis using nuclear electricity typically results in 2 to 5 kg CO2e per kg H2, dominated by upstream emissions. Thermochemical cycles, which bypass electricity conversion losses, can achieve lower emissions—1 to 3 kg CO2e per kg H2—due to higher efficiency.

#### Waste Management and Decommissioning
Spent fuel handling, storage, and plant decommissioning contribute 0.5 to 2 kg CO2e per kg H2. Advanced reactors with fuel recycling could reduce this by 30-50%.

### Comparative Analysis with Other Methods

#### Fossil-Based Hydrogen
Steam methane reforming (SMR) emits 9 to 12 kg CO2e per kg H2 without carbon capture, dropping to 1.5 to 3 kg CO2e with CCS. Coal gasification emits 18 to 20 kg CO2e per kg H2, reduced to 3 to 5 kg CO2e with CCS. Both methods face scalability constraints due to finite feedstock and CCS infrastructure requirements.

#### Renewable Electrolysis
Wind-based electrolysis emits 0.5 to 2 kg CO2e per kg H2, while solar PV ranges from 1 to 4 kg CO2e per kg H2, depending on panel manufacturing and irradiance. Renewables face intermittency challenges, requiring storage or overcapacity, which increases system-level emissions.

#### Scalability and Emission Profiles
Nuclear-assisted hydrogen offers baseload capability, avoiding intermittency issues of renewables. A 1 GW nuclear reactor could produce 200,000 kg H2 daily via electrolysis or 300,000 kg via thermochemical cycles, comparable to large-scale SMR plants but with lower emissions. However, nuclear faces public acceptance and high capital cost barriers.

Renewables excel in decentralized applications but require significant land and storage solutions for large-scale hydrogen production. Fossil methods with CCS are transitional but depend on carbon storage viability.

### Conclusion
Nuclear-assisted hydrogen production exhibits a lifecycle carbon footprint of 3 to 8 kg CO2e per kg H2, competitive with renewables and superior to unabated fossil methods. Thermochemical cycles offer marginal efficiency gains over electrolysis. While scalability is technically feasible, economic and regulatory hurdles remain. In contrast, renewables provide lower emissions in ideal conditions but face intermittency limitations, while fossil-based methods with CCS offer a bridge at the cost of residual emissions. The optimal pathway depends on regional energy policies, resource availability, and technological advancements.