April 07, 2015
Electrical power from nuclear energy has always been understood as different and that will not change. While the focus of the world has been on renewable energy and the extraordinary progress it has made, nuclear energy remains a significant component of base-load electrical generation. While controversy remains it seems clear that choices and decisions are being made for a variety of reasons that favour fission as a source of electricity.
Capital costs are enormous but operating costs and consequences in human and environmental terms compare favourably with carbon-based alternatives. It is also true that attitudes towards nuclear energy vary greatly from country to country.
Beyond the news headlines, however, the evidence suggests that the amount of electricity from nuclear looks set to remain steady in percentage terms and may well increase. China and Saudi Arabia provide two examples.
There are two challenges for China. How to provide the energy it needs for its burgeoning economy, and how to manage its serious contributions to greenhouse gases. This is a particularly difficult situation given China’s very large and easily exploited reserves of coal.
While China has become closely identified with renewable energy, especially solar, there has clearly been a decision to use nuclear energy for a sizeable part of the base load (non-interruptible) supply of electricity. As of 2013, China’s 21 nuclear power plants provided only 2.1% of China’s electrical needs. However there are 26 new nuclear plants under construction, 64 in the planning stage and 123 proposed.
It is highly unlikely all of these will be realised but the scale of the commitment to nuclear energy is clear as are the reasons for doing so: breathable air for Chinese citizens and meaningful reductions in greenhouse gases.
The reasoning behind Saudi Arabia’s commitment to build 16 new reactors by 2030 (from zero at the moment) differs from that of China. In addition to the industrial aspirations of the government there is the understanding that burning hydrocarbons to make electricity—while cheap and logical in a country so well endowed—is an inefficient use of a finite resource that can be upgraded into so many value-added products.
The conclusion is clear. The “nuclear age” has not ended and that for the nuclear industry as for every other source of electrical energy, nickel-containing materials will remain essential.
Nickel in nuclear power
A nuclear power station is like any other power station: a heat source converts water (pressurised light or heavy in the case of nuclear) into steam in boilers that feed turbines which run generators. The nature of the fuel dictates, however, a very different treatment of the heat source.
Still, all the nickel you would expect to find in any power station will be there: nickel alloys in the boilers, boiler tubes, pumps, piping, turbines and generators. For power stations that use salt water for cooling, additional nickel will be found in materials for pipework, filters and heat exchangers. With a nuclear station there are special sensitivities and attention to service life including the storage and transport of spent fuel. Some of the additional nickel-containing elements prominent in the nuclear industry include:
Mechanical modules: machinery, pumps, valves, all contained in module units made of a sandwich of carbon steel, concrete and a lean duplex stainless steel 2101 (UNS S32101). The mechanical module for the Westinghouse-designed AP1000 nuclear facility uses approximately 500 tonnes of duplex.
Steam separator units: These allow dry (dewatered) steam to be fed to turbines. These specialised pressure vessels are typically made of 316L (S31603) stainless steel—35 to 50mm thickness—controlled for very low cobalt content
(<0.06% Co). Note that such units are not unique to the nuclear industry as dry steam is important to reduce and control erosion of turbine blades.
Accumulator tanks: Safety is paramount for nuclear and the protocols surrounding emergency shutdowns are especially demanding. Accumulator tanks, with their reservoirs of coolants in close proximity to the reactor chamber, are typically made of 304L (S30403) with similarly low cobalt content.
Short/medium term storage of spent nuclear fuel: Radioactivity declines over time but the most demanding situations arise in the early years. The containers (CASTORs: Containers for the Storage and Transport of Radioactive materials) vary in size and construction but a special variant of 304L with boron is often used, e.g., S30467 with 2% boron, an element known for its ability to moderate/absorb radiation.
Long term storage of spent nuclear material: various versions exist but most include the use of nickel-containing stainless steels.