FIGURE G-8 Estimated thermal-to-hydrogen efficiency (η_H) of the sulfur-iodine (SI) process and thermal energy required to produce a kilogram of hydrogen from the modular high-temperature reactor-SI technology. SOURCE: Brown et al. (2003).

tions have been undertaken. One of the main advantages of this process is that construction materials and corrosion-resistance are more tractable at 500°C than at higher temperatures. Another advantage is that, owing to its relatively low operating temperature, it can become compatible with several current and advanced nuclear reactor technologies.

Steam methane reforming (SMR) is currently the main commercial technology for hydrogen production in the United States. The SMR process requires high temperature, and the most common means of providing the heat for the process is through the burning of natural gas in the reforming furnaces, as described in the section “Hydrogen from Natural Gas,” earlier in this appendix.

The SMR process can be coupled to a high-temperature helium-cooled reactor, such as the MHR. The MHR can function as the heat source operating at about 850°C, to replace the natural gas burning. The high operating temperature can enable the process to take place at about 80 percent efficiency. This approach (which might be called N [nuclear]-SMR) reduces the CO₂ emissions to the atmosphere by large quantities. Elimination of the natural-gas-burning furnace in this process reduces the CH₄ consumption by about 40 percent (Spath et al., 2000), which is parallel to the amount of CO₂ emission reduction.

The cost of hydrogen produced by electricity generated from existing nuclear power through water electrolysis is equivalent to using the electricity supplied by the grid for hydrogen production. Today this cost is about a factor of 3 higher than what is achievable by conventional SMR, with natural gas prices at $4.5/million Btu, even when the cost of hydrogen distribution is taken into account. The improved power-cycle efficiencies of the advanced nuclear power plants may bring this cost differential in the future down to a factor of 1.5.

The cost of hydrogen production using the MHR-SMR option is dependent on the cost of natural gas feedstock to the reforming process. However, the cost from MHR-SMR is less sensitive to the cost of natural gas than is conventional