James M. Mahar

Underground Nuclear Power Parks: Power Plant Design Implications

The siting of nuclear power plants underground, along with associated reprocessing, fuel manufacturing, and high level waste disposal facilities offer many advantages. Security costs are substantially less, radiative package transportation issues are eliminated, and political issues of high level waste storage and disposal are largely eliminated. Keeping the site preparation costs to a minimum requires that the underground facilities accommodate several power producing units (nominally 6 GW or more). However, significant redesign and placement of components can make it possible to accomplish most of the underground excavation with tunnel boring machines. These latter issues are addressed in this paper.© 2008 ASME

Potential Advantages of Underground Nuclear Parks

In this paper we argue that an underground nuclear park (UNP) could potentially lead to lower capital and operating cost for the reactors installed in the UNP compared to the traditional approach, which would be to site the reactors at the earth’s surface at distributed locations. The UNP approach could also lead to lower waste management cost. A secondary benefit would be the increased margins of safety and security that would be realized simply as a consequence of siting the reactors underground. Lowered capital and operating cost for a UNP relative to traditional reactor siting is possible through the aggregate effect of the elimination of containment structures, in-place decommissioning, reduced physical security costs, reduced weather-related costs, reduced cost of liability insurance and reduced unit-cost for the nth reactor made possible through the continuous construction of multiple reactors at the same underground location. Other cost reductions might be possible through the transfer of the capital cost for part of the underground construction from the reactor owners to the owners of the UNP. Lower waste management cost is possible by siting the UNP at a location where there are geological and hydrological conditions suitable for hosting both the reactors and the repository for the waste from those reactors. After adequate storage and cooling, and assuming direct disposal, this would enable the spent fuel from the reactors to be transported directly to the repository and remain entirely underground during the transport process. Community concerns and transportation costs would be significantly reduced relative to current situations where the reactors are separated from the repository by long distances and populated areas. The concept for a UNP in bedded salt is used to develop a rough order of magnitude cost estimate for excavation of the reactor array portion of a UNP. Excavation costs appear to be only a small fraction of the overall power plant costs for an UNP in salt. Many engineering, safety, environmental, regulatory and cost-benefit and technical issues related to the UNP concept need to be evaluated.Copyright

Underground Siting of Nuclear Power Plants: Insights From Fukushima

Siting of nuclear power plants in an underground nuclear park has been proposed by the authors in many previous publications, first focusing on how the present 1200 to 1600 MW-electric light water reactors could be sited underground, then including reprocessing and fuel manufacturing facilities, as well as high level permanent waste storage. Recently the focus has been on siting multiple small modular reactor systems. The recent incident at the Fukushima Daiichi site has prompted the authors to consider what the effects of a natural disaster such as the Japan earthquake and subsequent tsunami would have had if these reactors had been located underground. This paper addresses how the reactors might have remained operable — assuming the designs we previously proposed — and what lessons from the Fukushima incident can be learned for underground nuclear power plant designs.Copyright

Cost Advantages of Large Underground Nuclear Parks

Underground nuclear power plant parks have been projected to be economically feasible compared to above ground installations. This paper is a conceptual analysis of the cost savings, compared to surface facilities, which result from reduced costs in the aspects of construction, transportation of materials, security, and decommissioning. The paper also explores the cost burdens associated with underground nuclear power plant parks. Overall, the cost savings are projected to far outweigh the cost burdens if design and regulatory issues are reasonably managed. The cost savings for electricity generated over a 60 year life of a typical 1000 MWe nuclear power plant are projected to be 0.23 to 0.66 cents (2008 U.S. currency) per kWh.© 2009 ASME

Underground Siting of Nuclear Power Plants: Enhancing Safety and Reducing Construction Cost

It has been shown, in a number of papers presented by the authors, that the construction of a nuclear power park underground, involving a number (six or more) of conventional Generation III+ LWR units, plus reprocessing, fuel re-manufacturing, and waste storage facilities is cost effective (both capital construction cost and operating costs) compared to the construction of similar facilities above ground (even if all such facilities are co-located). These papers have addressed the protection provided for both security from domestic acts of terror and natural hazards, and the ultimate containment of nuclear contamination in the event of accidents. However, as a result of the Fukushima tsunami and its effect on the six reactors at that location, issues are raised concerning the worst possible accident scenarios that could occur as a result of siting of nuclear plants underground. This paper addresses those highly unlikely events, with extremely low probabilities of occurrence, and shows that the effect of underground siting has advantages has over at ground locations.Copyright

Underground Siting of Small Modular Reactors in Bedrock: Rationale, Concepts, and Applications

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

Underground Nuclear Energy Complexes: Technical and Economic Advantages

90 million to

Below the Horizon

45 million per reactor, respectively, and for a twelve-unit installation constructed by tunnel boring machine from

Advantages of co-located spent fuel reprocessing, repository and underground reactor facilities

25 to

Underground siting of small modular reactors:rationale, concepts and applications

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.Copyright