Nuclear

Nuclear by Stealth: New generation reactor development snuck in by stealth – What are you up to Mr Mantashe?

 Minister of Mineral Resources and Energy, Gwede Mantashe. (Photo: Flickr / GCIS)

South Africa’s debt burden is onerous, to say the least, and yet a new 2,500MW nuclear build programme has been snuck back onto the table while we were all distracted by the Covid-19 pandemic. What’s behind this, when the alternatives are far more attractive?

Dirk Knoesen and Leslie Petrik

Despite recent plans by the government to reignite the nuclear build programme, framed in their renewed request for information (RFI) by Mineral Resources and Energy Minister Gwede Mantashe for a 2,500MW new nuclear build programme, it is evident that much research is needed in many fields, from material sciences to safety demonstration, to attain the envisaged goals for safe and economic new or fourth-generation nuclear reactors.

Therefore, the feasibility of new generation nuclear reactors providing energy safely in the near future is slim, even by the minister’s own admission, and an inordinate amount of funding will be required to realise full-scale operation of new-build nuclear power stations in SA. Given the parlous state of SA finances and its growing debt burden, the RFI makes one wonder if some of the superpowers are brokering deals behind closed doors again.

Politics aside, and from a technical aspect, nuclear power’s contribution to the global energy mix has declined since 1996 as the rate of new nuclear build has been outpaced by the growth of sources such as solar and wind energy, which are now highly competitive. 

New generation nuclear systems are being developed in several countries, but the 13-member Generation IV International Forum (GIF) on new nuclear build predicted commercial deployment is unlikely before 2040. The most prevalent nuclear technology is the Light Water Reactor (LWR) that was developed in the US by Westinghouse (Cartlidge, 2016). 

It is well known that when using radioactive nuclear material, the risks (and costs) extend beyond the power station and relate also to the mining, enrichment, transport and storage of the radioactive material, and the final radioactive waste produced.

Frank von Hippel reminds us that any new generation nuclear generators are still nuclear processes, requiring all the standard, stringent precautions on safety and security around the whole power station. Any nuclear process using uranium as a source results in spent fuel and high-level radioactive waste (HLW) as a by-product, that needs long term storage (about 250,000 years for radio-toxicity to decay). 

Typically, an LWR of 1GWe capacity would discharge about 20-25 tonnes of spent fuel per year of operation. Von Hippel also notes that all fast reactors are highly problematic due to the “proliferation of weapons-grade plutonium”, which cannot adequately be regulated or controlled. To date, there is no plan in place in South Africa for long-term, deep geological storage, which would leave a hazardous waste legacy for future generations, or legitimate reprocessing of this waste.

It is well known that when using radioactive nuclear material, the risks (and costs) extend beyond the power station and relate also to the mining, enrichment, transport and storage of the radioactive material, and the final radioactive waste produced. These costs are always there, irrespective of the type of nuclear reactor in use, even after the reactor is closed down. With increasing international pressure to prevent pollution and protect the environment and humans, these costs will only escalate in future.

Drawbacks of the new generation-IV designs are well documented. For instance, the sodium-cooled fast reactor (Cartlidge 2016), which was designed in the 1950s, suffers from the serious drawback that enhanced fission reactions occur when losing the sodium coolant, and sodium reacts violently with water causing the steam generators used to drive turbines to catch alight. Sodium also becomes radioactive when exposed to neutrons, thus coolants other than sodium such as helium or lead are being considered, but helium as a coolant is far less efficient than sodium, and a lead is extremely corrosive. So far, fast-reactor development has cost more than $100-billion worldwide, without near-future prospects.

South Africa also indulged in this expensive nuclear fantasy in the early part of this century with the pebble bed modular reactor (PBMR). The PBMR was one of the fourth-generation nuclear reactors in development in South Africa before 2010. The original idea of the pebble bed reactor, using helium as coolant, was conceptualised to produce a safer nuclear system where it was envisaged that these lower power output nuclear reactors could be left alone if a serious mishap or accident occurred, by using what is referred to as a passive cooling system. Because helium cannot become radioactive, at least not at these energy levels, using it as the energy carrier gas would allow the gas to exit the core and drive the generator turbine as with the SA-designed reactor.

The pebble bed programme in SA had two main drivers, to improve on the engineering aspects, and to study the pebbles containing the nuclear source, for the prevention of leaked radiation. The idea was to manufacture the pebbles locally.

The original PBMR reactor concept purchased by SA from Germany was designed to deliver about 15MW. The amount of nuclear material necessary at this size was considered not enough to develop a core meltdown in serious breakdowns, as the internal temperature of the reactor could increase to an order of 1,000oC, which could still be contained by the reactor vat.

However, further research proved that the pebbles themselves could not fully contain the radioactive material, some of which leaked out and was carried away from the reactor core into the rest of the system outside the core by the helium gas. This was one of the reasons why Germany originally stopped its research on the PBMR.  

The pebble bed programme in SA had two main drivers, to improve on the engineering aspects, and to study the pebbles containing the nuclear source, for the prevention of leaked radiation. The idea was to manufacture the pebbles locally.

The scientists in SA investigated the problem with the pebbles and determined that radioactive silver, one of the many possible byproducts of nuclear fission, could migrate or diffuse through the protective multi-layers surrounding the nuclear material core at the centre of the pebble. The scientists studying this process eventually determined how the radioactive silver moved through the layers and then developed a different type of outer layer that prevented the silver migration to the outside of the pebble. 

The engineering side did what engineers are very good at, improving the technical aspect related to output and gas flow, etc. to the point of pushing the expected energy output to around 180MW, operating at temperatures close to 1,000oC. Aside from the astronomical cost to SA of this wasteful nuclear development programme, which was halted in 2010, this higher operational temperature, of course, creates new problems. 

Firstly, it required the development of new types of metal alloys to be used in the core and tubing that can withstand these high operational temperatures and pressures. Secondly, if an accident occurs in the system, the internal temperature can rise to above the melting range of the materials used in the reactor vat, causing a meltdown.

The reactor thus requires an active cooling system to keep the temperature in control, especially in case of a mishap occurring. But now it becomes a normal nuclear reactor with very much the same cost structure, but only delivering a fraction of the power. 

The helium gas used in some reactors such as the PBMR as the energy-carrying medium has several advantages, but also several big disadvantages. Helium cannot become radioactive so can pass safely through the reactor core and not affect the rest of the gas flow system. This does, however, present a serious problem if a leak occurs in the piping due to overheating or other causes, and normal air enters the system.

Besides the other gases in air (nitrogen, oxygen, carbon dioxide, etc), that will become radioactive in the core, a more serious problem is that the pebbles containing the nuclear fuel are covered in carbon layers and the reactor vat itself has a pure carbon protective layer on the inside of the vat that contains any radiation inside the reactor vat.

If air enters the vat at around the 1,000oC operating temperature, an explosive reaction between carbon and oxygen will occur that will blow the vat open. To prevent this, a sufficient amount of additional helium must be available to be pumped into the vat until the leaks are repaired and the temperature drops substantially. That may take hours to days and the volume of helium required will be enormous. Helium is extremely expensive and would need to be stored onsite in sufficient volumes, which only increases the total costs of the PBMR.

Cartlidge (2016) reported that China is building a reactor using spherical “pebble bed” fuel technology similar to the system investigated and discarded by South Africa. However, the designers have clearly not taken to heart the explosive nature of the system and, with estimated operational temperatures of 750˚C, this reactor will not achieve a high enough temperature to make it efficient.

This is because the biggest issue that applies to all thermal power generators (coal and nuclear), is elementary physics, namely the laws of thermodynamics. For any thermal process, the amount of useful energy that can be produced by a system depends upon the difference between the lowest and highest temperatures in the system. Only a fraction of that difference can be converted to useful energy, the rest is lost as waste energy. That is the reason why the maximum energy conversion from normal thermal sources such as coal (or gas or nuclear) is only about 30 – 40%.  Using water (steam), or air to provide the lower temperature in the process limits the practical lower temperature.

The standard, rhetorical argument against renewable energy of not providing a continuous power supply is already being deflated by the development of battery systems that can store multi-MWh of energy, also by having several different types of renewable sources online. There are also, of course, other renewable resources that can be developed.

The only sensible way to improve on this low efficiency is to increase the upper operational temperature but, as mentioned, that creates further problems in the materials either being used to contain nuclear emissions, or to convert the energy to electricity. The presently available metals used for the transfer of the hot steam or gas, and the metal used in turbines driving the generator, have an upper temperature limit above which they start losing their mechanical and material properties. Thus, at such elevated temperatures, they cannot contain the gas or steam any longer. Developing new heat-proof materials to the required standards adds greatly to the total cost of high-temperature fourth-generation reactors.

But overall, the reality is that in South Africa the energy demand from Eskom is declining as more houses, companies and even mines are investing in generating their own power, especially as the very real issue of load shedding is forcing the government to approve of self-generation, particularly based upon renewable energy.

Moreover, the present delivery costs of renewable electricity from solar and wind are already below the cost of fossil fuels such as coal (even in SA where coal is supposed to be the cheapest), and much lower than electricity provided by nuclear power (Eberhard and Lovins, Daily Maverick, 30 January 2018). In future, the cost of renewable electricity will decrease further, while the cost for fossil or nuclear will only continue to escalate, both in supplying the energy sources (coal, gas, nuclear material), and by needing to comply with the increasingly stringent international regulations for minimising pollution and environment protection.

The standard, rhetorical argument against renewable energy of not providing a continuous power supply is already being deflated by the development of battery systems that can store multi-MWh of energy, also by having several different types of renewable sources online. There are also, of course, other renewable resources that can be developed.

One serious contender for the future is using hydrogen as an energy carrier, where a renewable power plant can be used to extract hydrogen from any water source (Petrik et al 2013). New methods of storage and transport of large volumes of hydrogen are already coming online, even for possible use in air transport. 

SA has an actively funded Hydrogen Economy strategy, branded Hydrogen South Africa (HySA), which supports the HySA centres at several universities in order to develop and guide innovation along the value chain of hydrogen, and fuel-cell technologies in South Africa. Our current government has already invested many millions in this research and development programme.

The advantage of most of the technologies using renewable energy sources is that they do not require a thermal process, thus their efficiencies are substantially higher. Of course, the major advantage of renewable energy sources is their availability at no cost, and also that the energy (e.g solar or wind), can frequently be tapped where needed. These renewable energy technologies do not leave legacy wastes and are already fully commercialised. Creamer (2020) reports that renewables’ built capacity has increased from only 754GW in 2000, to around 2,537GW globally, showing its growing market share.

Finally, back to politics, one has to ask why the nuclear RFI was issued now, in the midst of the Covid-19 pandemic and despite our huge debt burden. Has someone been incentivised to bring nuclear onto the table again, hoping that we are all too distracted to notice? DM

Dirk Knoesen is Emeritus Professor in Physics, and Director of the Nanoscience Platform at the University of the Western Cape (UWC). He served on several panels and commissions at NRF, CSIR, DSI and the previous DST, universities and other related committees. He also served for several years on a scientific advisory board of PBMR in SA. His involvement with PBMR stopped after the project development was frozen in 2010, so for what has happened since then he is, like everyone else, dependent on news reports or some media publications.

Senior Professor Leslie Petrik, Department of Chemistry, UWC is leader of the Environmental and Nano Sciences (ENS) research group which explores a broad suite of material science topics including nano-materials and heterogeneous catalysts, high capacity adsorbents, zeolites, mesoporous materials, and other functional nanomaterials. She was involved in the development of the carbon-based materials for the PBMR but her involvement with PBMR also stopped after the project development was frozen in 2010. Since then, she has also studied high specification materials needed for hydrogen production and fuel cells as alternative energy sources, as well as on anticorrosion alloy coatings required in highly oxidative environments.

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