Operating experience with decommissioning of underground components, USA

In the USA there has over the years been widespread use of underground piping and tank storage systems, as well as use of other storage vaults and miscellaneous underground storage systems. In most instances these systems are associated with other operating facilities such as large nuclear facilities. There has been considerable experience over the last 60 years in the design, installation, operation and decommissioning of these radioactive waste handling and storage structures and systems. Legislation was enacted in the 1980s that required extensive upgrades to existing systems, with newly installed systems being required to meet stringent installation, operation and removal requirements. This has had an impact on the use of some of these underground systems. One major problem with many of these systems is to gauge the integrity of the systems after they have been in operation for many years and to accurately determine whether they have leaked or not. Depending on the results of these investigations, the next question is whether these systems even need to be excavated or if they can be dispositioned in place rather than expending a large amount of effort to excavate them and remove the materials in question to a disposal site for final dispositioning. In some areas this is possible while in others excavation is required. Over the years that nuclear facilities have been operational in the USA, advantage has been taken of the fact that the earth serves as a good location for emplacement of otherwise obtrusive (or even less aesthetically pleasing) structures. These structures are also still clearly able to support the useful mission they were always intended to fulfil. This arrangement also serves as a structural feature favourable to minimizing radiation exposure levels emanating from systems and components containing radioactive materials. In some cases, embedding of various components such as tanks, pits, vaults, pipes and ducting was an easy way to avoid these components becoming obstacles to performing maintenance or to operating the facility efficiently. In cases in which the system had leaked, embedding of components was a good way to capture the leaked material in the surrounding soil or basins until some action could be taken. This was especially true at many of the older USDOE facilities and other US Defense Department facilities during periods of wartime defence production activities or when other short lead time defence activities needed to be performed. Owing to many significant regulatory changes since then, the use of these systems is now much more closely scrutinized or even prohibited, to ensure that they are in full regulatory compliance and minimize damage to the environment. However, over time, the piping and the different structural materials of components will slowly degrade so that eventually leaks are likely to develop. Additionally, at some point in the future, these same facilities will need to undergo some process of final dispositioning. Inside the various research facilities it was a common practice to either, in a few instances, emplace the various items of waste system piping into trenches or, in most cases, embed them directly in the concrete floor of the facility. In other cases, such as at some USDOE research and production sites, these systems would also be used to move the various liquid wastes from individual facilities to a centralized collection and treatment location for dispositioning. In the latter case, much experience was gained over the years in replacing or decommissioning portions of these systems, which failed over time and for which there was still a need to keep the systems operational. In other cases, the systems or parts of the systems at the time of final shutdown or decommissioning would be entombed in place. The latter case occurred mainly in situations where long term institutional controls were to be continued at a site in order to ensure that no hazards would be presented to future use of the same area. The end result of these past practices is that these embed ded components in the environment begin to fail over time due to either corrosion or a combination of leaks and corrosion. In some cases, systems become no longer necessary and require removal, with the soil in the area being remediated as needed. Once many of these structures reach an advanced age, they do begin to become a greater liability - both in that they might fail and that if they do fail there may be anything from minor to major consequences as to the future cleanup needed at these sites. This has become a major problem at many US sites, for radioactive systems and even for non-radioactive systems. Another complicating factor in decommissioning many of these older nuclear facilities is the issue of record keeping. The fact that many of these facilities do not have accurate as-built drawings for their systems and components can make the removal of the facilities extremely difficult. This is especially relevant when the time comes to remove these components, and little that is accurate is known about the area in which this work is planned to take place. Operational records may not be available to support historical knowledge of what the systems and equipment were even used for in the past