A containment of a nuclear power plant is a final barrier against the release of radioactive materials and withstands internal pressure due to an accident. Buckling is a critical failure mode of an ellipsoidal head of steel containment vessel under internal pressure. First, a vessel was designed to measure buckling pressure and shape of the ellipsoidal head. Second, an experiment was successfully performed on an ellipsoidal head which has a diameter of 4797 mm, a radius-to-height ratio of 1.728, and a thickness of 5.5 mm. The initial shape and deformations of the ellipsoidal head were measured by using three-dimensional (3D) laser scanners. The detailed buckling characteristics including shapes, deformations, strains of buckles, and buckling pressures were obtained. Finally, initial buckling pressures were predicted by nonlinear finite element analysis considering the initial measured and the initial perfect shapes of the ellipsoidal head, respectively. The agreement between the initial experimental buckling pressure and that predicted by the analysis considering the initial measured shape is good.

Due to its high maturity and low cost, alkaline water electrolysis (AWE) technology has been widely integrated with large-scale renewable energy systems (RESs) for green hydrogen (H₂) production. Here, to evaluate the operational performance of a 50 kW AWE electrolyzer under different operation conditions, we developed an empirical modeling and experimental validation approach. The model particularly focuses on the polarization curve and the hydrogen to oxygen ratio (HTO). The relevant parameters of the empirical model were obtained by fitting the experimental data with MATLAB. The validity and accuracy of the established model and parameters were verified by comparing the fitted values with experimental values, and a good correlation was found. Since the experiments were performed in the sub-cell of 5 MW scale AWE electrolyzers, this model can also predict the performance of industrial MW-scale AWE electrolyzers and serve as a tool for the optimal design and control of industrial AWE electrolyzers. The results demonstrated that the models can achieve an accuracy with an R² value exceeding 0.95 across a range of operational conditions.

High-pressure hydrogen storage systems (up to 100 MPa) require advanced materials for safety and reliability, particularly for rubber seals, which are prone to degradation under extreme conditions. This study explores the use of cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs) as sustainable nanofillers for nitrile butadiene rubber (NBR) latex nanocomposites. CNFs and CNCs were evaluated for their effects on mechanical properties, crosslink density, and resistance to high-pressure hydrogen exposure in rubber O-rings. A life cycle assessment (LCA) was carried to assess the environmental impact of these nanocomposites. The results showed that CNF-filled NBR composites exhibited better resistance to bubble formation under hydrogen exposure compared to CNC-filled ones. However, the LCA indicated relatively high environmental impacts for both, reaching up to 2.5 kg CO₂ eq. in Global Warming Potential (GWP), highlighting the need for further optimization of production processes. This study demonstrates the potential of cellulose nanofillers to improve NBR performance while advancing sustainable hydrogen storage materials.

Ellipsoidal and torispherical heads, whose geometric shapes are close, are usually used as end closures of internally pressurized vessels. In pressure vessel codes, for example, ASME BPVC Section VIII and EN13445-3, ellipsoidal heads are designed as torispherical heads using geometric equivalency approaches. However, the difference between ellipsoidal and equivalent torispherical heads has not been studied in detail. In this paper, we first investigate shape deviation between the two types of heads. Then we compare elastic–plastic behaviors between ellipsoidal and equivalent torispherical heads as well as their failure modes, i.e., buckling and plastic collapse (bursting). It is found that ellipsoidal heads have more buckling resistance than equivalent torispherical heads, indicating that the current design rules for buckling of ellipsoidal heads based on the geometric equivalency approaches result in uneconomical design. In addition, experimental and numerical results show that such heads experience geometric strengthening. The finite element (FE) method considering the effect of geometric strengthening provides a good prediction of plastic collapse pressure. However, the current design equation for bursting does not consider the effect of geometric strengthening, also leading to uneconomical design. Therefore, in order to avoid uneconomical design, we recommend that (1) with respect to buckling of ellipsoidal heads, a new design equation be proposed rather than implementing the geometric equivalency approaches, and (2) the current design equation for bursting be deleted, and a new design equation, considering the effect of geometric strengthening, be proposed for bursting of ellipsoidal and torispherical heads.

Rubber materials undergo continuous wear in high-pressure seal applications. To address the risk of adhesive wear and consequent leakage of rubber seals operating under reciprocating sliding in high-pressure hydrogen storage and refueling systems, this study employed high-pressure hydrogen tribology testing. Ball-on-disk reciprocating tests were conducted using a 316L stainless-steel ball against silica-filled nitrile butadiene rubber (NBR), and the friction response and wear-morphology evolution were compared under ambient air, 1 MPa hydrogen (H₂), 50 MPa H₂, 50 MPa nitrogen (N₂), and grease-coated conditions. Under dry sliding, the coefficient of friction (COF) of NBR in air and hydrogen ranged from 1.34 to 1.44, whereas it decreased markedly to 0.942 in 50 MPa N₂. The wear volume under the four dry conditions was concentrated in the range of ~0.292–0.320 mm³. After grease coating, the steady-state COF in air and at 50 MPa H₂ dropped to 0.099 and 0.105, respectively, and the wear features changed from ridge-like wear patterns/tear pits to regular, smooth indentations with slight running marks. The results demonstrate that a lubricating film can effectively separate direct metal–rubber contact and suppress stick–slip, enabling a low-friction, low-wear, and highly stable interface in high-pressure hydrogen, and providing a practical engineering route for reliable operation of rubber seals in hydrogen service.