## 1 Introduction  
The United States of America have more nuclear power plants (NPPs) than any other country in the world. Currently a total of 99 NPPs are operating while another 35 have already been shut down [1]. The scale of the industry results in great amounts of nuclear waste: The commercial production of electricity has also produced over 70,000 metric tons of spent nuclear fuel (SNF), meaning high-level waste (HLW), over the last decades [2]. For the time being, the majority of the SNF is stored at reactor sites in wet pools where HLW is to be stored for the first few years to cool off and have the radiation shielded. However, the absence of a long-term repository for HLW results in these pools reaching capacity [3]. To cope with this, independent storage installations were built at the reactor site, where the waste is stored in dry casks. Hence, although this way of storage seems to work more or less for the present, both means of storage are meant to be only temporary as they harbor various risks ([3], pp. 70-71). Therefore, a new storage solution has to be found in order to deal with the continuously increasing amount of waste [4]. The main source of HLW is SNF which is used fuel from a reactor whose fission process has slowed too much to be able to create electricity efficiently, but is still thermally hot, highly radioactive and therefore potentially harmful [2] (the International Atomic Energy Agency (IAEA) distinguishes three main kinds of nuclear waste that are mainly distinguished by their radiation and half-life: low-levelwaste, intermediate-level waste and HLW. The latter one is the one dealt with in this paper because firstly, special problems and thus costs are connected to it and secondly, a permanent storage solution for low-level waste (LLW) as well as for most parts of intermediate-level waste (ILW) exists at this time). As a decay heat greater than 2 kW/m\({}^{3}\), radioactivity that varies between \(5\times 10^{4}\) and \(5\times 10^{5}\) TBq/m\({}^{3}\) and a long decay are characteristic for HLW [5] a deep geological disposal is needed for storage in order to contain the danger arising from these features. Due to long decay that can take hundreds of thousands of years, any solution thought of must be long-term [2]. However, the current situation in the U.S. is anything but long-term. There are two stages of on-site storage of SNF (After the fuel rods are extracted from the reactors, they are put into steel-lined, seismically designed concrete storage pools, under about 40 feet of water, which serve by cooling down the fuel rods with pumps, that supply continuously flowing water, and shielding the radiation the SNF emits [2]. The SNF must be stored in those pools for several years until it has cooled down enough to be removed. Afterwards, if the pools reach capacity, the SNF must be moved into so-called dry-cask storage. The dry casks are metal canisters filled with inert gas and welded shut after being filled with SNF. They are usually stored above ground in one-car-garage-sized concrete containers on a flat field [2]. Those storage sites are called independent spent fuel storage installations and exist at the reactor sites as well as away-from-reactor at decommissioned reactor sites). Currently around 78% of all SNF is stored in pools, whereas the remaining 22% is stored in dry casks [2]. Due to an increasing number of reactors that exceed their pool capacity, the amount stored in dry casks storage increases continuously. The reason why this method of storing can only be seen as a short-term solution is that the casks are exposed to the weather and they are also potential terror targets. In addition both ways of on-site storage are very expensive [3]. There is a permanent storage solution for LLW and ILW (Except for the so-called \"greater than class C\" waste i.e., ILW with high concentrations of radio-nuclides) in the U.S., but none for HLW.