Nuclear Plant Risk Assessment


The use of nuclear energy is increasingly emerging as the energy source of the future due to its high degree of sustainability and its clean nature. It especially has an upper hand against carbonized fossil fuels that emit global warming gases that have adverse effects on human lives. The use of nuclear energy is however not without challenges. Apart from its demand for high levels of expertise and finance, nuclear energy poses potentially fatal risks to the environment, workers, and the human population around nuclear plants (Bateman, 2006). An example of the fatal nature of nuclear accidents is the Chernobyl Disaster in Ukraine. The reactor vessels ruptured in a series of explosions that resulted in radiation exposure over a wide geographical region forcing the evacuation of people and resettlement of over 336,000 people (Slovic, 2000). The radiation exposure from the disaster is estimated to have caused over 4000 deaths through cancer over time. It is due to such risks that nuclear plants need to employ rigorous measures to eliminate all possible safety threats and enhance the acceptability of nuclear energy use. This paper puts forward risk assessment matrices suitable for use in a nuclear power plant for various applications.


For a risk management program to be effective, there is a need to understand the following major aspects of the risk; the degree of control, familiarity with the hazard, impact on people, environmental impacts, economic effect, and the extent of consequences. This paper will design two risk assessment matrices, one for application in job safety analysis and the other for environmental impact risk management. It will then compare the two matrices focusing on their strengths and limitations. It will include a briefing note on how the matrices should be applied in s step by step basis. In the end, the matrices will be used to design a sample hazard register with the necessary hazard assessment record. This will enable a clear and straightforward illustration of how risk assessment matrices can be applied in a nuclear plant.

Environmental impact risk assessment matrix

The risk assessment matrix below is meant to effectively manage risk by doing the following: identifying the critical applications prone to risk, quantifying the potential impact, detailing the escalation process, identifying solutions, and implementing them in time to avert disasters in the nuclear plant (International Atomic Energy Agency- IAEA, 2008). The table below shows the general aspects of risks that need to be accurately identified at an early stage to guide the risk mitigation strategy. The table gives categorizations that are explained in detail in the section that follows.

Risk. (Identification of the problem ) Probability Impact Risk exposure Impact time frame Mitigation strategy
Possible risks include malfunction in the plant, toxicity of spent fuel, uranium mining, etc. Probability ranges are:
The impact categories are:
It is the product of probability and impact.
<1 –Low risk
1.0-3.0-Moderate risk
3.01-4.99 high risks.
Contains two dates:
Earliest and latest dates that impact could materialize.
the appropriate mitigation strategy is identified according to the nature of the problem

Features in the matrix

Each of the sections in the matrix is elaborated as follows:

  • Risks

This section involves a careful analysis of the problem at hand. It clearly defines what the risk is. A nuclear plant may pose risk to the environment in many stages. From the beginning, the nuclear energy production process converts uranium into its elemental form which decomposes to give radioactive compounds (Allbaugh, 1997). High levels of enriched uranium in the environment may expose people to cancer. The sourcing of uranium should therefore be assessed to ensure that it does not leave hazardous waste in the mining sites. Another potential risk is a malfunctioning nuclear power plant. This can create a seriously catastrophic problem with widespread effects. Checks for malfunction are required high levels of expertise from a wide range of engineering knowledge that would ensure total containment of radioactive material (Slovic, 2000).

They continue to produce and radiation that may hurt the environment a natural water body is involved.

  • Probability

This refers to the probability of a certain risk occurring. The ranges in the matrix are interpreted as follows:

Probability Interpretation
0.01-1.0 very unlikely to occur
0.11-0.40 unlikely to occur
0.41-0.60 may occur about half of the time
0.61-0.90 likely to occur
0.91-0.99 very likely to occur
1 Will certainly occur

The probability rating is determined by considering a wide variety of factors using scientific methods.

Risk Impact

The definitions for the risk impact categories in the matrix are given below:

Impact definition
5-critical This is an event that if it occurred, would cause widespread environmental problems that would result in immediate fatalities and long-term dangers. It would necessitate decommissioning of the plant (Shulz & Marwah, 2001)
4- serious An event that if it occurred, would result in fewer fatalities but major cost schedules in mitigation levels over the long term period. The plant would continue functioning but in a strained manner.
3-moderate An event that if occurred would cause not result in long-term effects but may cause immediate fatalities in a localized scene. The costs involved in its mitigation would be in the short term.
2-minor An event that if it occurred, would not result in fatalities but would only cause damage to plant infrastructure that would require only small costs to remedy (Shulz & Marwah, 2001)
1-negligible An event that if occurred would not have any effect on the environment.

Risk exposure

In this matrix, the risk exposure is calculated by getting the product of probability and occurrence impact. The definitions of the categories are as follows:

Low risk: this category of risk exposure has little or no potential to increase environmental protection measures. Normal management is enough to control environmental risk

Moderate risk: special action and management attention is required to control risk on the environment.

High risk: requires significant additional action, high management attention, and financial cost to remedy environmental effects.

(Knief & GPU Nuclear Corporation, 2002).

Impact time frame

Two dates should be specified: one is the date that the risk effects could be experienced while the second one is the latest date that the risk effects could be experienced. The two dates are important in determining when the mitigation efforts should be put in place and after how long they should be withdrawn i.e. when the risk is passed by events.

Mitigation strategy

The appropriate mitigation strategy is identified according to the nature of the risk at hand, its probability, impact, risk exposure, and timeframe. It is therefore unique to the problem at hand and can take many forms.

Job safety analysis matrix

Job Hazard Analysis Matrix
Severity of Injury Probability of an Accident Occurring
Level Description A
Several Times
Extremely Improbable
  1. I
Fatal or Permanent Disability 1 1 1 2 3
  1. II
Severe Illness or Injury 1 1 2 2 3
  1. III
Minor Injury or Illness 2 2 2 3 3
  1. IV
No Injury or Illness 3 3 3 3 3
Risk Priority
Code Risk Level Action Required
1 High Work activities must be suspended immediately until hazards can be eliminated or controlled or reduced to a lower level.
2 Medium Job hazards are unacceptable and must be controlled as soon as possible by different ways such as personal protective equipment methods or maintenance.
3 Low No real or major hazard exists.
Controls are not required but may increase the safety and comfort level of employees.

This job safety matrix is designed to ensure that workers can identify potentially hazardous work situations and the steps that they can be taken in efforts to control the dangerous situations they might be exposed to. The first line of action involves measures to reverse technical hitches in the plant that might result in hazardous situations. For unexpected situations, there are guidelines on how effects could be mitigated (Wilborn, 2001).

Features in the matrix

The severity of injury: the severity of the injury is the extent to which the risk can cause injury, disability, or death to the workers. It is determined either through experience where it had happened before or through analysis of the risk at hand. The severity of the injury is determined by factors such as whether the patient goes to the hospital, whether they leave the hospital on the same day, the period that a person stays in hospital, the number of people affected, whether it causes mutation, chronic illness or possibly leading to death (Jones, 1996).

Probability of accident occurring: the probability ranges from; frequent several times, rare, probable, and extremely improbable. These levels are determined by considering factors like; whether the accident is unknown in the plant but possible in the industry or whether it is known because it has happened in the industry and the number of times it has happened in the industry.

Color coding: There are three colors in the matrix – green, yellow, and red. They are used to signal the degree of hazard. Since both the consequence and frequency have been color-coded the matrix user will see at a glance how severe the potential risk is to the company after making hazard registration. Each color describes risk as follows:

  • Red: Intolerable risk.
  • Yellow: the high risk that requires the incorporation of risk reduction measures.
  • Green: the low risk that can be managed through normal plant procedure. It does not require special risk management measures (Ewing, 2004).

Comparison of the matrices

Structure: The major similarity between the two matrices is the fact that they are both structured to identify the risk at hand, quantify the risk level, determine its probability of occurrence, identify the potential impact and come up with control measures that are based on the findings. Generally, this is the basic structure that risk assessment matrices take for most companies. As Heaberlin notes, risk analysis procedures are centered on identifying, evaluating, controlling, and communicating potential hazards and in the workplace associated with the performance of certain tasks (Heaberlin, 2000). The two risk assessment matrices in this paper are structured in a manner that is common to the mainstream.

Procedure: In the environmental impact assessment, hazard analysis is performed by General Hazards Analysis and workers training and qualifications provide that are provided by company policy (National Research Council, 2003) It assigns workers with the proper skills and abilities to perform the risk assessment scientifically. For instance, the General Hazards Analysis gives guidelines on how to determine the probability ranges and risk exposure. The job safety analysis matrix on the other hand does not follow prescribed procedures in making the risk assessments. It is less scientific than the environmental impact matrix and does not use much mathematics (Mike, 2002).

Despite them being structured similarly, the two matrices have a difference in the methodology they apply to make a risk assessment. The environmental impact risk assessment matrix uses statistical data to quantify the risks involved. This makes it especially useful in a screening stage involving scientific and technical evaluation. On the other hand, the job safety analysis matrix does not employ statistics to quantify the risk. As such, this matrix will be useless and another tool will be required for purposes of; scientific and technical evaluation, auditing, and use of statistics (Heaberlin, 2000).

Briefing note

The following flow diagram would guide a person on how to use the environmental impact assessment matrix. It is further explained in the section that follows it.

How to use the environmental impact assessment matrix
Figure 1. How to use the environmental impact assessment matrix

Risk identification: this step is important as it identifies the risks that pose threat to the plant’s security/protection plan. For example, personal risks are those that are caused by workers in the plant due to negligence or any other personal fault. The understanding of the type of risk is important since it will guide the mitigation measures (Brain, 2001).

Risk evaluation: it is divided into three categories; predictability, probability ad severity. The likelihood of an event happening is referred to as probability. Mechanical malfunctions and radiation exposure highly are examples of highly probable events in a nuclear power plant while vandalism and hostage situations are low probability factors due to high-security levels (Allbaugh, 1997). The aspect of predictability enables risks to be foreseen and resolved in time putting into consideration the severity factor.

Selecting risk reduction measures: risk avoidance can be achieved by eliminating risk-causing factors, for instance by having properly maintained alarms, equipment, and access control (IAEA, 2008). In risk acceptance, the risk cannot be effectively eliminated or it would not be cost-effective to do so e.g. small amounts of radiation can be allowed to leak if the effects would not be very adverse to warrant the implementation of highly costly measures.

Developing risk reduction methods: this is done by considering the timeline, costs, personnel, materials, and materials necessary to implement the risk elimination plans. The last three steps involve the implementation, evaluation, and reassessment of risk mitigation measures (Allbaugh, 1997).

The above are areas that a user would be required to focus on, to effectively put the matrix into practice. They will greatly help the user in understanding the problem at hand and determine relevant and effective solutions. As Slovic notes, “Risks must be well understood, and risk management approaches developed before decision authorities can authorize a program to proceed into the next phase of the risk management process (Slovic, 2000).”

Sample hazard register

This section gives an example of an appropriate hazard register that can be generated from the use of the risk analysis matrix. The register is designed for two possible risks; radiation from spent fuel and the case of a malfunctioning nuclear plant. It identifies the probability of these events, the impact, and the risk exposure of these events. From these aspects, the register develops mitigation strategies that might apply to each.

Risk. Probability Impact Risk exposure Impact time frame Mitigation strategy
Radiation from spent fuel. 0.62.
This probability level means the event is “likely to occur”. Though it has never happened in this plant, it happens in nuclear plants ad hence cannot be ruled out.
Thus impact level is defined as “serious”. It can have widespread effects in the biosphere if it leaks out.
The risk exposure figure is obtained by getting the product of impact and probability i.e. 0.62 multiplied by 4. Special action and management attention are required to control risk on the environment.
Risk is long term; over 20 year period. Partitioning: involves separating short-life radionuclides from long-life radionuclides to reduce the radiotoxicity both in activity and in time (Jones, 1996).
Transmutation: making a change in long-lived radio nuclear to shorter-lived radio ones using radioactive bombardment. (Mike, 2002).
Conditioning: Operates the rendered nuclear waste that handles transportation, storage, or disposal (Jones, 1996).
A Malfunctioning nuclear plant and attacks. 0.85
This probability level means the event is “likely to occur”. Though it has never happened in this plant, it happens in nuclear plants ad hence cannot be ruled out.
Thus impact level is defined as “serious”. This is an event that if it occurred, would cause widespread environmental problems that would result in immediate fatalities and long-term dangers. It would necessitate decommissioning of the plant
This is High risk: it requires significantadditional action, high management attention, and financial cost to remedy environmental effects.
The period for this risk can vary depending on the nature of the malfunction. Process Inherent Ultimate Safety (PIUS): adopting a PIUS canoffer complete protection against core overheating in case of any significant equipment failure, or natural disasters such as earthquakes and tornadoes, and operator mistakes (Lewins & Becker, 1997).
Design: to offer protection caused from inside sabotage by plant personnel knowledgeable on reactor design, terrorist attacks, military attacks. (Wilborn, 2001).

This register demonstrates how the risk assessment matrix is put into practice to identify the risk at hand, quantify the risk level, determine its probability of occurrence, identify the potential impact and come up with control measures that are based on the finding.


The risk assessment matrices presented in this paper provide an appropriate illustration of how risk can effectively be managed in a nuclear power plant. The matrices have been designed in a simplified manner which is easily applicable. They are meant to offer a systematic method of problem tackling that starts by clearly identifying the problem and all the factors associated with it. The matrices then proceed to identify workable solutions that are pegged to factors like the probability, impact, exposure level, and timeline of the risk. This ensures that the risk management plan is effective in managing risk in a nuclear plant.


  1. Allbaugh, J.M. (1997). Fact Sheet: Nuclear Power Plant Emergency.
  2. Bateman, M. (206). Tolley’s practical risk assessment handbook. Butterworth-Heinemann.
  3. Brain, M. (2001). How nuclear stuff works.
  4. Ewing R.C. (2004). Energy, Waste and the Environment: A Geochemical Perspective, Gieré, R. and Stille, P. Eds. London, Geological Society.
  5. Flavin, C. & Nicholas L. (1999). Nuclear power nears Peak. 
  6. Heaberlin, S. (August 2000). Nuclear Safety and Technology Applications Projects and Research.
  7. International Atomic Energy Agency- IAEA. (2008). Best Estimate Safety Analysis for Nuclear Plants: Uncertainty Evaluation. Safety Report Series, No. 52.
  8. Jones, E. (1996). Risk Assessments: From Reactor Safety To Health Care.
  9. Knief, R.A. and GPU Nuclear Corporation (2002). Risk management: expanding horizons in nuclear power and other industries. 5th Ed. CRC Press.
  10. Lewins, J. & Becker, M. (1997). Advances in Nuclear Science And Technology. Vol.24. N.Y.: Plenum Press.
  11. National Research Council. (2003). End Points for Spent Nuclear Fuel and High-Level Radioactive Waste in Russia and the United States. Washington, DC. The National Academies Press.
  12. Shulz, A. and Marwah, O.S. (2001). Nuclear proliferation and the near-nuclear countries. Ballinger Publishing Company.
  13. Slovic, P. (2000). Perception of risk: reflections on the psychometric paradigm. Social theories of risk, 95-108.
  14. Wilborn H. (2001). Meltdown: A Race against Nuclear Disaster at Three Mile Island. Cambridge: Candlewick Press.