Nuclear power is a mature, proven technology which is strongly regulated and controlled, making it among the safest available. It is also the lowest cost while its fuel supply is abundant, sustainable, secure, clean and reliable.

The existing reactor designs have been improved so they now offer even better performance. Many of the reactors built in the 1970s have proven so reliable they have had their license to operate extended to 60 years.

Any reactor built in Ireland would have all of these improvements. Because Ireland has a relatively small grid, we would most likely build a series of small, modular reactors (SMRs) rather than a single large reactor. Here is a good overview of the many types of SMR currently in development.

Reactors that would be suitable for Ireland include the 180 MWe B&W mPower™. A modular, passively safe, advanced light water reactor, it will be available in 2022. See this technical update from December 2011.

Westinghouse are also developing a small reactor to “provide licensing, construction and operation certainty that no other small reactor can match with competitive economics”. See this Bloomberg TV interview or this technical update from December 2011 on this 225 MWe reactor.

Below is a brief summary (mostly taken from the World Nuclear Association page on advanced reactors, but also from a really informative site at of the different types of new and existing reactors licensed in the OECD.

Read this excellent article by James Chater on the history of nuclear power

Different types of Nuclear Reactors

Quick references

Advantages of nuclear

Find out more about the advantages of nuclear power in Ireland:

Nuclear is the cheapest

Nuclear is the cleanest

Nuclear power is the safest electricity

New nuclear power is ideal for Ireland

Supporters of nuclear in Ireland

Many Irish organisations have called for nuclear power to be considered here. (These links to external sites open in a new window).




Irish Academy of Engineering



Political supporters of a debate

Calls for a national nuclear debate have come from (external sites open in a new window):

Minister for Energy, Eamon Ryan

Dáil Joint C’tee on Climate Change

Exploded myths about nuclear

These facts may surprise you:

Reactors would fit the Irish grid

There is a solution for nuclear waste

We can afford nuclear power

Nuclear fuel is plentiful

Other information

General items of interest about nuclear:

Types of reactors

History of nuclear power

IRIS - a suitable reactor for Ireland

Nuclear power is illegal in Ireland

Can we not just use Renewables?

Hydrogen - fuel of the future?

Who is BENE?

I want to be a Supporter

EPR : The EPR is a large pressurized water reactor of evolutionary design, with design output of approximately 1,600 MWe. Design features include four 100% capacity trains of engineered safety features, a double-walled containment, and a "core catcher" for containment and cooling of core materials for severe accidents resulting in reactor vessel failure. The design does not rely on passive safety features. The first EPR is currently being constructed at the Olkiluoto site in Finland. Framatome also hopes to build EPR's at the Flammanville site in France, and has submitted a bid for EPR construction in China.

ESBWR: The Economic and Simplified Boiling Water Reactor (ESBWR) is a 1,390 MWe, natural circulation boiling water reactor that incorporates passive safety features. This design is based on its predecessor, the 670 MWe Simplified BWR (SBWR) and also utilises features of the certified Advanced Boiling Water Reactor (ABWR). Natural circulation was enhanced in the ESBWR by using a taller vessel, a shorter core, and by reducing the flow restrictions. The ESBWR design utilises the isolation condenser system for high-pressure water level control and decay heat removal during isolated conditions. After the automatic depressurization system operates, low-pressure water level control is provided by the gravity-driven cooling system. Containment cooling is provided by the passive containment cooling system.

IRIS: The International Reactor Innovative and Secure is a pressurized light water cooled, medium-power 335MWe reactor that has been under development for several years by an international consortium. IRIS is a pressurized water reactor that utilizes an integral reactor coolant system layout. The IRIS reactor vessel houses not only the nuclear fuel and control rods, but also all the major reactor coolant systems components including pumps, steam generators, pressurizer and neutron reflector. The IRIS integral vessel is larger than a traditional PWR pressure vessel, but the size of the IRIS containment is a fraction of the size of corresponding loop reactors.

PBMR: The Pebble Bed Modular Reactor is a modular HTGR that uses helium as its coolant. PBMR design consists of eight reactor modules, 165 MWe per module, with capacity to store 10 years of spent fuel in the plant (there is additional storage capability in onsite concrete silos). The PBMR core is based on the German high-temperature gas-cooled reactor technology and uses spherical graphite elements containing ceramic-coated fuel particles.

System 80+: This standard plant design uses a 1,300 MWe pressurized water reactor. It is based upon evolutionary improvements to the standard CE System 80 nuclear steam supply system and a balance-of-plant design developed by Duke Power Co. The System 80+ design has safety systems that provide emergency core cooling, feedwater and decay heat removal. The new design also has a safety depressurization system for the reactor, a combustion turbine as an alternate AC power source, and an in-containment refuelling water storage tank to enhance the safety and reliability of the reactor system.

IRIS  A US-origin but international project which is a few years behind the AP1000 is the IRIS (International Reactor Innovative & Secure). 

International universities continue to develop it as an advanced 3rd Generation project. 
IRIS is a modular 335 MWe pressurised water reactor with integral steam generators and primary coolant system all within the pressure vessel.  It is nominally 335 MWe but can be less, eg 100 MWe.  Fuel is initially similar to present LWRs with 5% enrichment and burnable poison, in fact fuel assemblies are "identical to those ...  in the AP1000".  These would have burn-up of 60 GWd/t with fuelling interval of 3 to 3.5 years, but IRIS is designed ultimately for fuel with 10% enrichment and 80 GWd/t burn-up with an 8-year cycle, or equivalent MOX core.  The core has low power density.  IRIS could be deployed in the next decade, and US design certification is at pre-application stage.  Estonia has expressed interest in building a pair of them.  Multiple modules are expected to cost US$ 1000-1200 per kW for power generation, though some consortium partners are interested in desalination, one in district heating.

Here’s a technical update on the IRIS from December 2011.


OVERVIEW OF REACTOR TYPES There are many different ways of using nuclear fission to generate electricity, but all of them use the heat produced during the nuclear reaction to get a turbine and generator to turn and produce electricity. Most reactor types turn water into steam and use a steam turbine while others heat up a gas and use a gas turbine.

Light Water Reactors

Of those that use water, the two most common types use a purified form of regular water (H2O), sometimes called “light water”, and are either Boiling Water Reactors (BWRs) or Pressurized Water Reactors (PWRs). PWRs are by far the most popular reactors built in the past few decades. Some reactors, such as the CANDU (Canada Deuterium Uranium), employ natural Uranium, which is not enriched, and use “heavy water”.

Pressurized Water Reactors PWR

In the more common PWR, the water that cools the nuclear fuel is at a higher pressure and does not turn into steam. However, because of the higher pressure, this primary water can reach higher temperatures and is used to convert a secondary water supply into steam and from there to the steam turbine. This is the type shown in the graphic at the top of this page and includes reactors such as the EPR, AP1000, IRIS and most of the Small Modular Reactors including Westinghouse’s 225 MW SMR described above, B+W’s 180 MW mPower, Holtec’s 145 MW HI-SMUR and NuScale’s 45 MW SMR.

Boiling Water Reactors BWR

In a BWR, the water that cools the nuclear fuel is boiled, turns into steam and drives a steam turbine. This is the type of reactor that was used at Fukushima Daiichi and is quite common in Japan, Europe and the US.  In the diagram on the left, dark blue represents water while light blue represents steam. The green circuit represents cooling water (usually from a nearby river or the sea) which is used to condense the purified steam back into water so that it can be reused in the reactor.

The Fukushima Daiichi (Daiichi is Japanese for “number one”) reactors were among the first BWRs to be constructed by General Electric, the design for which dates from the 1950’s although the first unit went into operation in 1971. Five of the reactors at this station were Mark I GE BWRs while unit 6 is a Mark II BWR.

Newer designs in widespread use are called Advanced BWRs (ABWR), of which more details below. A further improvement, incorporating “passive safety”, is the Economic Simplified BWR (ESBWR), also described below, which received final design approval from the US Nuclear Regulatory Commission in March 2011.

Heavy Water Reactors

Other reactors use water in which the Hydrogen contains an extra neutron and is called Deuterium (so heavy water is described as D2O). This heavy water is used in various types of Canada Deuterium-Uranium (CANDU) Reactors and allows the nuclear fuel to be in its natural form; that is, it is not enriched. Heavy water coolant passes through the reactor core and removes the heat generated by the fission chain reactions. This heated reactor coolant heats light (ordinary) water and converts it to steam, which drives a turbine-generator to produce electricity.

The Enhanced CANDU 6 (EC6) Generation III reactor design is the evolution of the proven CANDU 6 design and offers superior safety performance and economics and suitability for small and medium electric grids. The EC6 is a 700 MWe class heavy-water moderated and heavy-water cooled pressure tube reactor. Heavy water is a natural form of water used as a moderator to slow down the fission chain reaction neutrons in the reactor. It is one of the most efficient moderators and enables the CANDU design to use natural uranium as fuel, which is unique to CANDU reactors. The use of natural uranium increases a country’s energy independence as fuel can be manufactured locally, and reprocessing and associated issues can be avoided.

Gas-cooled Reactors HTGR

Reactors that use gas as a coolant (and to drive a gas turbine) are called High Temperature Gas-Cooled Reactors (HTGRs) and include the Pebble Bed Modular Reactor (PBMR). Gas such as helium or carbon dioxide is passed through the reactor rapidly to cool it. Due to their low power density, these reactors are seen as promising for using nuclear energy outside of electricity production: in transportation, in industry, and in residential regimes.

HTGRs can operate at very high temperatures, leading to great thermal efficiency (near 50%!) and the ability to create process heat for things like oil refineries, water desalination plants, hydrogen fuel cell production, and much more. Each little pebble of fuel has its own containment structure, adding yet another barrier between radioactive material and the environment.

High temperature has a bad side too. Materials that can stay structurally sound in high temperatures and with many neutrons flying through them are hard to come by. Backup cooling systems are necessary. Because gas is a poor coolant, large amounts of coolant are required for relatively small amounts of power. Therefore, these reactors must be very large to produce power at the rate of other reactors.

Fast Reactors

This section is taken from an excellent Brave New Climate article. LWRs operate with water under pressure, hence the concern about pressure vessel leaks, coolant system leaks, etc, as well as the industrial bottleneck of only a single foundry in the world (though more are being built) capable of casting LWR pressure vessels. Fast reactors, on the other hand, usually use liquid sodium metal as the coolant, at or near atmospheric pressure, thereby obviating the need for pressure vessels.
Because the boiling point of sodium is quite high, fast reactors can operate at a considerably higher temperature than LWRs, with outlet temperatures of about 550ºC as opposed to the 320ºC of Gen III reactors. Here is a simplified rendering [x] of a sodium-cooled fast reactor to convey the design features:

As can be seen from the picture, the heat exchanger loop, immersed in the reactor pool, contains non-radioactive sodium, which is piped to a heat exchanger in a separate structure where it gives up its heat to a water/steam loop that drives a conventional (Rankine cycle) turbine. This system assures that in the unlikely event of a sodium/water interaction caused by undetected breaching of the double-walled heat exchanger, no radioactive material would be involved and the reactor vessel itself would be unaffected. Such an event, however unlikely, could result in the cessation of flow through the intermediate loop and thus an inability of the system to shed its heat. In a worst-case scenario where such an event happened with the reactor at full power and operators, for whatever reason, failed to insert the control rods to scram the reactor, the passively-safe system would nevertheless shut itself down safely due to inherent properties of the metal fuel (see below), with the large amount of sodium in the reactor vessel then allowing the fission product decay heat from the core to dissipate.

Thorium Reactors

The earliest reactor used for electricity generation used Sodium to cool the nuclear fuel. Sodium, a liquid metal, allows the neutrons from the nuclear reaction to move at greater speed and so these reactors are referred to as Fast Reactors. They can also make, or breed, nuclear fuel from materials that are initially non-radioactive, and so these are also called Breeder or Fast Breeder Reactors. The UK is reported to be considering an offer from GE Hitachi to build one of these Integral Fast Reactors, called “PRISM”, to use up the approximately 100 tons of Plutonium currently being stored at many nuclear sites in that country.

Another type of breeder reactor uses liquid Fluoride (a molten salt) to cool not Uranium but Thorium, which is more abundant globally. These are Liquid Fluoride Thorium Reactors (LFTRs) and are sometimes informally referred to as “Lifters”.

Get more details on each of these types by clicking on the name, or click here for details of more advanced reactors (Generation-IV).



Design Descriptions


Above diagram from the US Nuclear Regulatory Commission.

ABWR: The U.S. Advanced Boiling Water Reactor design uses a single-cycle, forced circulation, reactor with a rated power of 1,300 megawatts electric (MWe). The design incorporates features of the BWR designs in Europe, Japan, and the United States, and uses improved electronics, computer, turbine, and fuel technology.

The design is expected to increase plant availability, operating capacity, safety, and reliability. Improvements include the use of internal recirculation pumps, control rod drives that can be controlled by a screw mechanism rather than a step process, microprocessor-based digital control and logic systems, and digital safety systems. It also includes safety enhancements such as protection against over pressurizing the containment, passive core debris flooding capability, an independent water makeup system, three emergency diesels, and a combustion turbine as an alternate power source.

ACR700: The ACR-700 ® is an evolutionary, Generation III+, 750 MWe class pressurized tube reactor, designed to meet industry and public expectations for safe, reliable, environmentally friendly, low-cost nuclear generation. The ACR-700 is designed for a 2016 in-service date, and is currently undergoing a pre-licensing review in Canada.

ACR1000: The ACR-1000 ® is an evolutionary, Generation III+, 1200 MWe class pressurized tube reactor, designed to meet industry and public expectations for safe, reliable, environmentally friendly, low-cost nuclear generation. The ACR-1000 is designed for a 2016 in-service date, and is currently undergoing a pre-licensing review in Canada.

AP600: This is a 600 MWe advanced pressurized water reactor that incorporates passive safety systems and simplified system designs. The passive systems use natural driving forces without active pumps, diesels, and other support systems after actuation. Use of redundant, non-safety-related, active equipment and systems minimizes unnecessary use of safety-related systems.

AP1000: This is a larger version of the previously approved AP600 design. It is a 1,000 MWe advanced pressurized water reactor that incorporates passive safety systems and simplified system designs. It is similar to the AP600 design but uses a longer reactor vessel to accommodate longer fuel, and also includes larger steam generators and a larger pressurizer.