Nuclear Energy Risk Assessment and Safety

Dina Al-Alami
July 16, 2015

Submitted as coursework for PH241, Stanford University, Winter 2015

Fig. 1: Trojan Nuclear Plant, shortly before its demolition in 2006. Source: Wikimedia Commons)

People demand zero risk, but that's impossible, said Rip Anderson, a scientist in Sandia National Laboratories in Gwyneth Craven's book Power to Save the World: The Truth about Nuclear Energy where he describes a scientist's interaction with him about Nuclear Energy. He continues stating: Just living has its risks. Every energy resource does too. But if you look at science, nuclear always comes out ahead. The nuclear world today has a culture of safety thats drilled into everybody. [1]

In the late 1960s, the Sierra Club in California didn't want the big hydroelectric project messing up their wilderness areas, and thus issued a campaign with the slogan, Atoms not Dams. Nevertheless, five years later, the Sierra Club changed its policy and stopped supporting nuclear. As we can tell, the controversy around nuclear energy is largely around its safety, and the way to minimizing this controversy is by assessing and reducing the risk of nuclear energy. [1]

The Department of Energy in the United States develops a Probabilistic Risk Assessment (PRA) with techniques that must be implemented in regards to (1) Facility structures, systems and components (SSCs) and operating states, (2) Internal events and Hazards, (3) External events and hazards and (4) Accident Phenomena and Progression. [2]

In 1975, the US Nuclear Regulatory Commission (NRC) did the first study regarding the probabilities and consequences of severe reactor accidents in commercial nuclear power plants. This study was called the Reactor Safety Study that could be implemented in nuclear power plants such as the one shown in Fig. 1. Initially, the PRAs estimated the probabilities of such accidents to be higher than reality and preditied the offsite consequences were lower than predicted. Hence, the NRC introduce research programs to continue improving the assessments of risks for severe accidents in light-water reactors. More data about the operational practices of the plants were gathered, and more methods were introduced and put into place to assess impacts of human errors. Once this PRA started being more and more developed, it started playing a role in the regulatory process of the NRC. However, after the 1979 Three Mile Island incident, the NRC had to adjust its use of the PRA and more resources were put into adjusting it. This entailed more experimental and analytical studies of the physical processes of accidents in nuclear power plants. By 1988, individual plant examination could be done by PRA to ensure the safety of the nuclear power plants. [2]

According to the US NRC there are three levels of risk in the PRA. The first level of PRA estimates the frequency of accidents that cause damage to the nuclear reactor core, commonly called core damage frequency. In Level 1 PRA, it models that different plant responses to different kinds of accidents and those different response paths are called "accident sequences." Once any event occurs that challenges the normal path of the plant operation, an initiating event is formed. The second level of PRA starts with the first level of PRA of core damage accidents and continues to estimating the frequency of accidents that "release radio activity from the nuclear power plant." These accidents are usually termed as "severe accidents." Examples of what can be assessed in the second level, taken from the NRC website are: do the tubes in the steam generator rupture? or Is the reactor core debris in a coolable configuration? The third level PRA, continues on the second level PRA, and also estimates the consequences in regards to human injury and public damage to the environment. [3]

The framework of risk can be divided also into financial, operations and safety risk. Starting with the financial, risk could be within risk of foreign exchange, cost of products and resources, price fluctuations, competition, insurance, derivative pricing, interest rates and capital market performance. Whereas, issues in operations include training, human resources, inventory, outage management and so on. Whereas, issues in safety include radioactive hazards, and environmental protection and industrial safety. These risks can be assessed through a structured approach within risk management. This lies within the framework below adopted from the International Atomic Energy Agency's report called Risk Management: A tool for improving nuclear power plant performance. The framework is that for a proposed action, the risks need to be identified, measured and ranked in order. Then, the techniques and strategies to manage risks are identified including how to reduce risks, retain risks and transfer risks. Then, the strategies are implemented, and finally, the implementation needs to be monitored to end up with operative solutions. [4]

In conclusion, the Nuclear Energy world has advanced in a way to apply different levels of safety requirements and risk management methods to minimize the risks associated with nuclear energy. The main challenge is to be able to measure the people's acceptance of risk, as it is hard to quantify what level of risk the public would accept.

© Dina Al-Alami. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] G. Cravens, Power to Save the World: The Truth About Nuclear Energy (Vintage, 2008).

[2] R. P. Carlisle, "Probabilistic Risk Assessment in Nuclear Reactors: Engineering Success, Public Relations Failure," Technol. Cult. 38, 920 (1997).

[3] "Next Generation Nuclear Plant Probabilistic Risk Assessment White Paper," Idaho National Laboratory, INL/EXT-11-21270, September 2011.

[4] "Risk Management: A Tool for Improving Nuclear Power Plant Performance," International Atomic Energy Agency, IAEA-TECDOC-1209, April 2001.