There is much debate currently taking place on the issue of whether or not the UK should build a new generation of nuclear power plant. The debate focuses on two issues: is nuclear (fission) safe and do we actually need nuclear power in the first place.
In this article I will set aside the safety question and instead address why we need nuclear power enough, so much so that the safety question has to be seriously considered and cannot just be dismissed on principle.
Types of technology
When considering power-generating technology the debate mainly revolves around renewable vs non-renewable technologies. However, from a practical perspective another distinction is important: dispatchable vs non-dispatchable.
Dispatchable generation plant (D) is that which can be turned on when desired by the operator, regardless of external conditions. As will be obvious, the main renewable technologies, wind, marine and solar, fall into the non-dispatchable (ND) category as they cannot guarantee that the conditions they need in order to generate power will be present at any given time.
The reason this distinction is important is because of the nature of electricity and the National Grid. At any given instant the amount of power being put onto, and being taken off, the Grid must be in balance.
A regular supply
If there is an excess of supply or an excess of demand (a shortage of supply) this can manifest in phenomena such as a deviation from the target (50Hz) Grid voltage frequency, power surges and flickering lights. If left unchecked, it can lead to localised blackouts and in the worse case scenario a complete crash of the Grid. An excess of supply can be solved by simply switching off plant. Excess demand can either be addressed by reducing demand (asking factories to close, triggering controlled localised blackouts) or by turning on extra plant.
Ensuring the Grid remains balanced is vital, as modern electrical devices are built to run on a regulated supply and have only a limited ability to withstand power surges. More importantly though, if the Grid were to ever completely crash it is an enormous exercise to restart it.
The best estimate for how long it would take to restore the Grid to full national coverage, assuming no significant damage to the infrastructure was caused when it crashed, is 2-3 days. That would mean 2-3 days of large parts of the country going without electricity. Incidentally, in order to restart the Grid, large D-plant would be required.
ND power plant is problematic in two ways with respect to keeping the Grid balanced. Firstly, ND-plant cannot be relied upon to generate at any given time. For example, in the event of a large anti-cyclone (a prolonged period of very low wind) the entire UK wind fleet (plus a significant part of Europe) could be unavailable for a period of weeks.
More troublesome though is that ND-plant can turn off, or at least reduce output, at any time and without warning. Weather prediction and spreading ND-plant over a wide geographical area can help to mitigate this risk. However for every MW (1 million Watts) of ND power being put onto the Grid a certain amount of D-plant must be kept warm as backup, able to come on-stream quickly in the event that output from the ND-plant drops (the exact amount of backup D power needed for every MW of ND power on the Grid is currently being researched and refined).
Capping the proportion of non-dispatchable generation
As a consequence of this, research indicates that there is a limit to how much power on the Grid at any one time can come from ND sources. A study in Ireland, which can be thought of as a reasonable approximation to mainland UK in terms of electricity infrastructure, indicated that an upper limit of ~40% of power could come from ND sources.
If ND power makes up too high a percentage of the total power on the Grid and there is a sudden drop in its output, it will not be possible to bring backup power on-stream quickly enough and there is a higher risk of total Grid failure.
It should be pointed out that National Grid has not yet set a limit on the amount of ND power it will accept. This is most likely because the penetration of ND-plant into the UK market is currently 10% and thus not yet approaching the level where it may need to be limited.
If the proportion of ND power on the Grid at any one time is capped then this will necessarily also cap the amount of energy that ND sources can contribute to the annual UK total. In principle the cap would be at the same percentage, but in practice the intermittent nature of ND generation means that the effective energy cap would be significantly lower than the actual power cap. This is because it would be uneconomical to build ND capacity much greater than the cap level and the capacity that was built would not be running at full output all the time (e.g. in the UK wind turbines only generate electricity for around 3,000 hours a year).
Having established that there will still be a need for significant dispatchable generation in the future UK energy mix we must now consider the types of D-gen available. Technologies proven at large scale are: coal, gas, nuclear, biomass and geothermal.
Of these, biomass and geothermal would also be classed as renewable, however they are also likely to only contribute minimally (<10% of annual energy output combined) in the UK. This leaves the UK needing to generate ~50%+ of its energy from some combination of coal, gas and nuclear even in a scenario where we are heavily exploiting the available renewable resource.
Additionally the Climate Change Committee, a key body for informing UK government policy, has recommended that in order to tackle global warming, by 2030 the carbon intensity of UK electricity generation should be reduced to 50 grams of CO2 emitted per kilowatt hour of electricity generated (g/kWh). The table below shows the typical carbon intensities for various energy generation technologies.
Emissions (g CO2 /kWhe)
|Solar Thermal||80MW Parabolic Trough||13|
|Solar PV||Polycrystalline Silicon||32|
|Geothermal||80MW Hot Dry Rock||38|
|Nuclear||Various Reactor Types||66|
|Natural Gas||Combined Cycle||443 (50 with CCS)|
|Coal||Various Types with Scrubbing||960 (100 with CCS)|
If we assume that 50% of UK electricity in 2030 is generated by ND, renewable sources plus biomass and geothermal, at an average CO2 intensity of 15g/kWh, this means the remaining 50% has to be generated by D-gen sources with an average carbon intensity of <85g/kWh.
As can be seen from the table above, this will require a significant proportion of D-gen energy to be generated by either carbon capture and storage (CCS) equipped gas plant or nuclear.
Carbon Capture and Storage
CCS, and especially CCS on gas, is not yet a commercially-proven technology. There are planned demonstration projects aimed at proving the capture technology, however these are unlikely to be operational before 2015.
Additionally, there is a large amount of uncertainty surrounding actually storing the CO2 after it has been captured, with questions remaining over exactly how much storage capacity there is, how sure we can be that the CO2 wont escape and least importantly, though most prominently at present, the rules and regulations governing the storage sites.
All this means that it is highly unlikely that gas-equipped CCS plant will be ready for commercial deployment until 2020, and maybe not until 2025.
With a large amount of older coal, gas and nuclear plant due to close before 2023 the construction program to replace them needs to start well before the 2020-2025 window. Large power plant typically have a lifetime of 25+ years, thus anything we build from now onwards will still be operational in 2030.
Even if we could afford to wait, and gas CCS is technically proven, we would not want to rely on gas as our sole D-gen electricity source as this would expose the UK to a high level of risk from either high gas prices, or worse, an interruption in supplies.
Drawing the arguments presented above to a conclusion, it is clear that, from a technical perspective, the UK needs a new generation of nuclear plant to provide energy security and meet its climate change targets.
There is still a debate to be had over the safety of nuclear power, however that debate must be properly framed by the understanding that there is not a direct trade-off between renewable (ND) technologies and nuclear.
If we choose not to build a new generation of nuclear plant then we will by default be pushed onto a path that, while avoiding the nuclear safety issue, will likely compromise our attempts to tackle global warming.
 It is important to properly distinguish between electrical power and energy. Electrical power is the rate at which electrical energy is transferred by a circuit. It is a product of the current and voltage and is measured in Watts (W). Electrical energy measures the power delivered over a period of time. For example, a power of 1 Watt sustained for 1 hour produces an energy of 1 Watt-hour(Wh). In this article when power and energy are referred to it can be assumed that it refers to electrical power and energy.
[3 ]National Grid
 DCENR report
 NIRS report