New Nuclear

Ian Scott discusses the development of the waste-burning stable salt reactor (SSR)

NUCLEAR energy is in retreat globally. The International Energy Agency reports that on current trends, even with China’s ambitious programmes, nuclear energy will fall from 5.8% of world generating capacity to 3.7% by 2040.  Nuclear energy is becoming irrelevant, which is a tragedy as it seems very unlikely that climate change goals will be achieved without nuclear energy.

Ultimately, this decline in the relevance of nuclear energy is driven by its escalating costs which, without massive subsidy, simply make it uncompetitive.

Why has nuclear energy become so expensive? In the 1970s, nuclear power was highly competitive with fossil fuels, and several countries built profitable nuclear industries. The near disaster of Three Mile Island and actual disaster at Chernobyl, along with the meltdown at Fukushima highlighted that the technology was not safe enough. The industry has since doubled down on trying to make existing reactor designs safer by adding layer after layer of engineered safety systems and administrative controls around new reactor designs. Nuclear power plants are now amongst the safest facilities on Earth. However, in doing this, the industry ignored a fundamental principle of achieving safety, which is illustrated in the hazard pyramid shown in Figure 1.

When seeking to improve safety, one should first seek to eliminate or reduce the fundamental hazard. Only then should one seek to manage or contain the remaining hazards through engineered safety systems or administrative controls. The fundamental hazards of the current generation of pressurised water reactors (PWRs) are:

• making the reactor core out of a fuel in which the most hazardous radioactive fission products are trapped as gasses in the fuel pellets at pressures of about 1 t/cm²; and
• putting the reactor core inside a pressure vessel full of water at over 300°C which will flash into steam if the vessel fails, violently driving dispersion of the radioactive materials and allowing decay heat to melt the fuel pellets and release the highly pressurised fission gasses into an already-compromised vessel.

Given these hazards, it is perhaps not surprising that the current generation of reactors requires a plethora of
additional systems, containment and control in order to achieve the enviable levels of safety which are, in fact, achieved.

The stable salt reactor (SSR) is a new concept in nuclear reactors, albeit one based on ideas conceived, tested but not commercialised in the 1960s and 70s. It addresses both of those fundamental hazards:

• the fuel is a molten salt in which the most hazardous fission products are not gasses but non-volatile salts; and
• the coolant is a different molten salt which operates at atmospheric pressure and cannot be made to boil by decay heat if the reactor fails in any way.