Hydrogen production is rapidly becoming a central pillar of industrial decarbonization, yet its economic viability remains 

strongly constrained by electricity price volatility and system inefficiencies. While pressurized solid oxide electrolysis cell 

(SOEC) operation is often promoted as a performance enhancement strategy, its practical value at full system scale especially

under nuclear small modular reactor (SMR) heat integration has not been rigorously quantified. In this context, this 

study delivers a unified cross-configuration assessment that directly compares atmospheric SOEC (Case 1), PSOEC (Case 

2), and an SMR-PSOEC (Case 3) within one internally consistent thermodynamic and economic platform. By embedding 

electrochemical behavior, pressure effects, nuclear heat utilization, and capital-operational cost interactions into a single 

steady-state model, the present work reveals how pressure and nuclear coupling of an 80 MWₜₕ pressurized water reactor 

(PWR-20) SMR reshape overall SOEC plant efficiency and cost structure. The results reveal that operation of a SOEC 

yields moderate system-level efficiency gains; however, significantly higher improvements are achieved when high-grade 

SMR nuclear heat integration is utilized for steam generation. This integration increases the SMR-PSOEC efficiency to 

76.9 %, with a hybrid system efficiency of 50.1 % when both nuclear heat and electricity inputs are considered. Economically,

integration lowers the LCOH from 8.74 to 7.93 $/kg, highlighting the advantage of coordinated thermal-electrical 

coupling. Steam utilization and heat-power split emerge as key thermodynamic drivers, while capacity factor, electricity 

price, CAPEX, and taxation dominate economic sensitivity. Overall, SMR-assisted PSOEC integration presents a structurally

superior configuration for large-scale low-carbon hydrogen production.