UK nuclear facilities are required to be resilient to external hazards up to a severity that would only be exceeded once in 10,000 years. Solar weather has relatively recently become recognised as a potential hazard and research is ongoing to characterise the hazard in terms of magnitude and frequency and determine its effects.
Regarding safety precautions, a severe solar storm could result in instability of the power transmission grid and associated transformers, which may result in loss of off-site power supplies to the nuclear power plant. Loss of power is a relatively frequent event, which has many potential causes apart from solar storms and all UK nuclear power plants therefore have appropriate robust back-up electrical equipment sufficient to power essential cooling systems independently of the availability of grid supplies. Operating experience shows that these arrangements provide ample protection against loss of grid events.
A severe solar storm is also likely to produce an increase in energetic particles at ground level that could affect some electronic devices. UK nuclear power plant operators are undergoing detailed reviews to ensure that the abovementioned safety standard for external hazards is maintained. All nuclear power plants have fail-safe trip and shutdown systems, plus several layers of defence in depth via diverse systems to provide the post-trip cooling required to remove heat from the core. At least one of these, at every site, do not depend on complex electronic actuation or control systems and therefore have a high likelihood of surviving ground level particle damage. Operation of any one of the diverse systems is sufficient to ensure safety. So while the research into the potential detailed effects of solar weather remains in progress, there is no immediate concern about the safety of the power plants in the event of a severe solar storm.
Packages used to transport radioactive material do not rely on electrical or electronic devices and consequently will not be affected by disruptions to electricity supply or similar external hazards.