The Myers-Mahar paper offers important insights into the future of nuclear power station siting, nuclear cost reduction and nuclear safety. The "Underground Siting" abstract reads,
Small modular reactors (SMRs) sited 100 to 300 meters deep in underground chambers constructed in bedrock having favorable geotechnical properties could be both cost effective and provide superior levels of safety and physical security. The bedrock adjacent to and enclosing the reactor chamber would become the functional equivalent of a conventional containment structure, but one with increased margins of safety for design- basis accidents, reduced risks for beyond-design-basis accidents, and a high level of inherent physical protection against external threats. In addition, seismic safety could be enhanced at lower cost because seismic waves are generally attenuated with depth in bedrock. Nominal steel and concrete around the reactor would be required as would sealing of tunnels and other penetrations into the reactor chamber. Nonetheless, the net result in capital cost savings could potentially more than offset the cost of underground excavation. For a hypothetical granitic bedrock site with SMRs at a nominal depth of 100 meters, preliminary excavation cost estimates for single- and four-unit installations constructed by drill-and-blast range from around $90 million to $45 million per reactor, respectively, and for a twelve-unit installation constructed by tunnel boring machine from $25 to $15 million per reactor. Specialized applications for bedrock-sited SMRs include collocation at underground hydropower stations, test and demonstration facility for prototype SMR designs, and deployments in regions at risk of terrorist or military attack.One of the long term objections to underground reactor siting has been that it would increases reactor siting and housing costs, but advances in excavation technology and Alvin Weinberg's idea of building large numbers of multi reactor parks could potentially lower nuclear costs, while dramatically increasing nuclear safety. The Myers-Mahar paper makes clear exactly how dramatic the cost savings of underground reactor housing might turn out to be. They argue,
1) Reduce per-reactor capital cost of underground construction by siting multiple reactors in a single location, thereby allowing the cost of the common access shafts and tunnels to be shared among more than one reactor.In addition,
2) Reduce capital cost by restricting siting to those locations in bedrock of such high quality that excavated openings would be largely self-supporting and the rock overlying and enclosing the reactor chamber would act as a low-cost, passive, natural containment structure---and in addition would attenuate seismic motion and protect against aircraft impact, bombs and related threats.
3) Reduce capital cost and shorten the schedule for underground construction by taking advantage of advances in equipment, technology, and techniques for underground construction that have occurred since the 1970s such as underground excavation using hard-rock tunnel boring machines.
4) Reduce life-cycle cost by using in-place decommissioning.
5) Collocate waste management and other fuel cycle facilities underground in proximity to the reactors as a means to both reduce waste management cost and provide a new concept for nuclear waste management.Myers and Mahar reference a paper. "Cost Advantages of Large Underground Nuclear Parks," by K.M. Giraud, J.F. Junze, and J.M. Mahar, to argue that a 10% reduction of electrical generation costs from large single unit reactors is possible through underground siting with an even larger savings possible through multi-unit nuclear parks.
Public concerns about nuclear safety may have their irrational components, but nuclear power will not be acceptable until the public is sure that nuclear power plants do not pose a threat to their safety and well being. Once the public feels confident about nuclear safety, the case against nuclear power will weaken significantly. It is not enough to build safer reactors, an accomplishment which reactor manufactures have already accomplished, the public must be assured by the designed in safety improvements. Underground reactor siting hold the potential of boosting public confidence in reactor safety, to the point where opposition to nuclear power is no longer acceptable. If underground housing of power reactors increases confidence in nuclear safety, while lowering nuclear housing costs, then we will improve the likelihood of a nuclear powered future.