Hang previously fallen from grace so rapidly, the use of nuclear power plants appears to have found favour again in certain corners and with select governments.
The UK government for example, is keen to renovate its nuclear programme and stipulated in its recent White Paper, the need to build enough reactors to replace the ageing fleet that provided 20% of its electricity in past decades. If anything, it is thought that expansions are hoped for that would see 40% of future electricity generated by such reactors.
This would apparently lead to long-term economic health for the country and scope for technology links between the UK and neighbouring France, relatively skilled and pioneering in the field of nuclear power at present.
It is also thought that the world is awake again to the merits of nuclear power. Technology has advanced so far that previous concerns of abundant waste, critical safety measures and spiralling costs have all but evaporated. With the fuel considered relatively bountiful and as a low-carbon energy source, it also finds support in today’s climate of environmental anxiety.
Debate still surrounds the use of nuclear power, however. Where it is to be used, there seems almost as much debate concerning the safe control, storage and production of the radioactive materials that drive this method of energy provision.
Dry cask storage and helium
As is the case among many industry processes, waste products and by-products are a common occurrence, with this termed as ’spent nuclear fuel’ in the nuclear power process.
Spent fuel is nuclear fuel that has been irradiated in a reactor to the point where it is no longer useful in sustaining a nuclear reaction. This is still high level radioactive waste however, and is naturally potentially hazardous. In the US, where coal and nuclear plants generate most of the electricity in the country, spent fuel is a hot topic and the storage of which is highly contentious. A number of methods of storage are available, perhaps the most practical and widely preferred of these is dry cask storage (DCS).
Until a permanent waste repository is developed and completed, it seems the helium-utilising technique of DCS is one of the best solutions. According to the US Nuclear Regulatory Commission (NRC), periodically around one third of the nuclear fuel in an operating reactor needs to be unloaded and replaced with fresh fuel.
For many years nuclear power plants have temporarily stored spent fuel in special water pools at the reactor site, but with commercial reprocessing never fully developed in the US and a permanent waste repository not yet developed either, these pools are nearing capacity and cask storage takes on greater importance - as does helium as a result.
So what is dry cask storage?
Providing above ground and long term storage spent nuclear fuel, DCS is quite a simple and yet extremely safe and reliable system of sealing used fuel in large airtight steel and concrete canisters. Offering both structural strength and radiation shielding , the cylindrical canisters or casks allow spent fuel to be surrounded by inert gas, typically helium, inside the welded or bolted closed cask.
The steel cylinder provides a leak-tight containment of the spent fuel, with the vertical system referred to as ’dry’ because the used product is surrounded by the inert helium gas, rather than water. With each cylinder or cask immersed in an additional layer of concrete and generally located on a concrete pad, DCS provides hardened structures capable of withstanding natural disasters and terrorist attacks. A stipulation is that the spent fuel must have already been cooled in the spent fuel pool for at least one year and preferably five, though the DCS method is considered to be safe and environmentally sound as well as space-saving. In fact over the last twenty years, the US’ NRC claims, there have been no radiation releases which have affected the public and no radioactive contamination.
Also useful as a method of safe transportation, DCS is an efficient and effective means of increasing fuel storage capacity.
Efficient & space saving
DCS is already widely used across the US and at the Indian Point Energy Centre in Buchanan, New York, workers have been transferring spent nuclear fuel rods to this storage in recent months.
A three-unit nuclear power plant located 24 miles north of New York City, the Indian Point plant operates two pressurised water reactors and is owned by Entergy Nuclear Northeast, a subsidiary of the Entergy Corporation. Nearing its spent fuel storage capacity, efforts are needed at Indian Point to make room for new fuel to produce electricity and this has been underway since the turn of the year.
The spent fuel rods at Indian Point are being placed inside helium filled casks, then drained and dried using helium. Describing the importance of using DCS and the efforts being made at the site, Entergy Vice President Joe Pollock commented, “This is a tremendous achievement and a historic day for Indian Point. The entire team has been working toward this goal since Entergy purchased the plants in 2000 and 2001. The move to dry cask storage is an important step toward preparing Indian Point for continued safe operation.”
Driving gases demand?
France is believed to derive around 79% of its energy from nuclear power and with the UK set jump back on the nuclear bandwagon once again, it’s not inconceivable to suggest an increased requirement for helium or inert gas in this market.
In the US, where reliance on nuclear power is heavy, attention is increasingly turning to helium-consuming DCS. Robyn Bentley, Entergy Spokeswoman, said back in January 2008, “We’ve been safely storing fuel on-site since 1976 in the spent fuel pools. It was the expectation that there would be a national repository for the used fuel, but there still is no location.”
Neil Sheehan, Spokesman for the NRC, had affirmed this and noted the switch to DCS as he said, “These places are running out of room, and they need to come up with another storage option.”
Another application of gases in the nuclear power sector is that of modular helium reactors (MHR), seen by some as the best nuclear energy source for the next century.
Conceptualised many years ago, the MHR is an advanced nuclear power system that dispenses with many of the previous public concerns over nuclear power and with the growing worldwide demand for electricity, could soon be driving industrial gas/helium demand.
Worldwide demand for electricity is expected to burgeon considerably over the coing decades, as the industrialisation and infrastructure development of developing countries continues and a rising world population takes its toll.
Catering for this could be the advent of MHR. As a second-generation nuclear power plant design under development, MHR traces its origins as far back as the 1960’s when five helium-cooled reactors demonstrated the benefits of helium-cooled nuclear technology. MHR designs had been developed in Germany and the US in the 1980’s but were not deemed economically viable.
Rapid advances from the 1990’s onwards, including high efficiency gas turbine energy conversion systems, have led to vastly increased efficiency and competitive economics and ensure the MHR method is an ideal system for meeting a surging electricity demand.
The MHR method of nuclear power could soon be capable of generating electricity capacity at a net efficiency of 47% (according to a 1997 report by the Uranium Institute) - a level that can apparently be obtained by no other nuclear reactor technology. The natural benefits of helium coolant, which is inert and has no reactivity effects, mean that the MHR is meltdown-proof and passively safe and would therefore minimise the need for a developing country to have an elaborate nuclear regulatory infrastructure.
While nuclear power is increasingly finding favour then and the UK government could be about to put its faith in nuclear power to prevent over-reliance on foreign energy/gas supplies, it seems somewhat ironic that it could be the application of inert industrial gases that helps to make this possible.