Determining the risk levels

This is the final of a three-part series on the Fukushima Daiichi nuclear disaster.

Gerald Lalor and Charles Grant, Guest Editors

Unlike the previous two nuclear accidents, Three Mile Island and Chernobyl, the primary cause of the accident was external - the unforeseen severity of the external hazard. The reactors handled the enormous earthquake well but the magnitude of the tsunami was beyond the cooling-system design value. It is now easier to picture the possibility of nearly overwhelming natural events and it will be the task of seismologists and earth scientists to better determine the risk levels involved. It is still too early to determine the consequences of the accident, the eventual outcome of which is mainly dependent on the water cooling achieved on the reactor cores and spent fuel pools and the damages caused. This will be better understood after the usual enquiry is completed.

There have been no radiation deaths, and the risk seems to be low compared with the general devastation caused by the massive earthquake and tsunami.

Effects on other countries

Nuclear power plants have proven their value to society, but the recent events have again raised the spectre of nuclear safety. This will certainly re-arm the opponents of nuclear energy in the public debate that will certainly take place about the use of nuclear energy. This debate should bear in mind the remarkable overall safety record of the established reactors and the differences between these and the new ones. Indeed, those who seek to write nuclear off completely are missing what could be breakthrough developments with hybrid technologies and small reactor, that will in the near future reshape the way we think about nuclear energy. One important aspect is passive nuclear safety, a feature that does not require operator actions or electronic feedback to shut down safely in the event of system failures.

The debate will no doubt continue for a long time and countries will reach their own conclusions. Some indications of country opinions are shown in Table 2.

There may be a slowing of reactor construction, but with China and India, driving the expansion of nuclear power and so many countries from elsewhere in Asia, Eastern Europe and the Middle East, pursuing nuclear power in response to high fossil fuel prices and concerns about global warming, the world's stock of 443 nuclear reactors could more than double in the next 15 years, according to the World Nuclear Association.

Each country will make its own decision. However, there are lessons to be learned from Japan. The main one perhaps is not to underestimate the powers of nature, and this, no doubt, will strengthen the appeal of the next generation of reactors which include passive failsafe systems making use of intrinsic properties and natural forces such as gravity and convection to cool down a reactor when pumps or external power fail.

Jamaica and Nuclear Energy

It is probably worth reminding readers that the International Centre for Environmental and Nuclear Science has been operating a small nuclear reactor called SLOWPOKE (Safe Low Power (K)ritical Experiment), which was provided by the European Union. The reactor was designed for training and a technique known as neutron activation analysis, which is used in Jamaica for investigations on water, soils, rocks, and sediments, food composition and trace elements in human tissues.

SLOWPOKE is a forerunner of safe reactor design. It has performed flawlessly over two decades and, as the manufacturer states, there is no plausible set of circumstances under which it can be a hazard. Experience with SLOWPOKE has intensified interest in the advent of the small modular reactors and their application to electricity generation in Jamaica since (as shown in Figure 3) it is now the cheapest energy source.

Nuclear power has previously not been considered feasible for Jamaica, but the new player in the game, the small modular, factory-built reactor, sized, say, 10-150MW, seems likely to have a profound possibilities for countries with smaller grids. They offer substantial benefits in safety, security, siting, proliferation resistance, economics and operational flexibility, including load following. In some models, the nuclear island is so small that the reactor is placed underground and be provided with seismic protection to reduce the probability of earthquake damage.

These small reactors (and as shown they are small) offer substantial benefits in safety, security, siting, proliferation resistance, economics, and operational flexibility, including load following. In some models, the building size for the nuclear island is so reduced that it is actually placed underground which improves safety and security. The smaller size would also allow the use of seismic isolators, if that is thought necessary, to reduce the probability of earthquake damage. It seems feasible also that they would reduce the need to develop a very complex regulatory framework and infrastructure.

Other interesting features include: factory manufacture, modularity, and self-regulating safety systems that are fail-safe and so allow a reduced site boundary and emergency planning zone (EPZ), allowing installation virtually anywhere. The small reactors have shorter installation times, and they are designed to be simple to operate. Moreover, buying a series of small modular reactors, instead of one larger one, allows units to be added as needed with each paying down the infrastructure and construction debt, thus providing a smaller upfront financial commitment and helping to maintain unit power levels at the recommended size for each grid.

Conclusions

The tsunami of March 11 has probably destroyed some of the cores at the Fukushima plant and generated consternation there and throughout Japan units and, indeed, much of the world. It is a much worse accident than was Three Mile Island but pales in comparison with Chernobyl. It has already riveted attention on better nuclear safety and the need to design for extraordinary events. A significant amount of this is included in the new reactor designs. It includes that of small reactors. The promise of nuclear energy is large indeed, but each country will determine its own way and one expects that in this due attention will be given to the new designs that show so much promise.