The only thing that is certain ...
The only thing that is certain in project management is that the project will not keep to the plan! Some tasks will be completed before their due date but others will overrun, sometimes putting the overall project schedule at risk. Similarly, things happen that can cause the project to exceed its budget or to fail to meet its performance targets.
Project management is the art of keeping a grip on all these things so that the project meets all its objectives - time, cost, performance - despite everything that can go wrong. Project risk management is the science of determining the major risks to the project and prioritising contingency plans and management actions to minimise the effect on the project.
At the heart of project risk management is the development and maintenance of a project risk register which details the risks to the project with an assessment of their likelihood, an assessment of the magnitude of the risk and management actions to be implemented if necessary.
Over the years I have worked with several comapanies in both nuclear and non-nuclear fields to manage the risk on large projects including DTI funded projects in NW Russia. Of course, I have applied these techniques to my own projects too.