Other nuclear reactor systems

The remainder of the nuclear plant is similar to any other power plant whether the steam is generated using coal, oil, natural gas or nuclear fuel. There will be issues with cooling tower decay, turbine corrosion, generator moisture, condenser corrosion, buried piping, etc. There are some issues that will be unique to nuclear power generation, however. For instance, decay of cable insulation in cable trays due to irradiation and high temperature is an important issue. Replacement of cabling in a nuclear plant is very expensive and takes a very long time and therefore should be avoided if at all feasible. The effects of soil and groundwater on buried cabling and the miles of bur­ied piping on any nuclear plant site are also at issue (INL, 2009).

Another issue that arises comes from the use of secondary sources of water. For instance, so-called gray water (sewage that has been through a waste treatment plant) has been used and is being looked at as cooling water to reduce overall water use by large power plants. This water has the poten­tial for higher and different salt concentrations than drinking water sources and can therefore cause unexpected corrosion or SCC issues (EPRI, 2007). Corrosion and decay of materials in the spent fuel pools, such as the boron containing structures that allow tighter packing of the spent fuel but which suffered unexpected degradation, also needs to be considered.

Outside of the nuclear plant itself but within the nuclear cycle, materials issues arise in such varied areas as zirconium metal production (the graphite receptors, ceramic gas injection nozzles, and ceramic linings in the chlorina­tion of either ZrO2 or zircon sand); the manufacture of nuclear fuel due to the common handling of mixtures of HF and nitric acid for UO2 dissolution; solvent extraction systems; and incineration of radioactive waste materials. For the most part, material issues have been solved in other portions of the cycle, but the ones listed above continue to be very resistant to reasonable materials solutions.

In summary, the issues outside of the nuclear island that require research and development are:

• The effects on cable insulation decay of temperature and radiation inside the containment and due to groundwater or soil for buried cable outside the containment.

• Methods to monitor and repair buried piping and cabling.

• Understanding of the interaction between older materials used in the initial construction of the plant and newer materials that may be used to repair or upgrade current plant systems including spent fuel pools.

• Components in the zirconium conversion from oxide or silicates to chlorides.

• Systems that handle mixed HF and HNO3 in the UO2 fuel manufacture area.

• Development of phenomenological understanding of the behavior of these materials in their respective environments that can be used to pre­dict their behavior over time.

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