Bellefonte_Nuclear_Power_Plant

How a Nuclear Plant Protects You!

High Level Introduction

Most of the nuclear industry falls under scrutiny from the public as a passed technology and a risk to the community. You may have heard of the famous Nuclear events that spawned general apprehension, Fukushima, 3-Mile Island, Chernobyl, etc. You may have also heard that the price to create electricity at a nuclear plant is one of the cheapest, but its almost as close as hydro. There are certainly deficiencies and room for improvement for the energy generation industry. But, it is going to be the norm to have Nuclear Power Plants running for another 20 or so years. This according to recent Licensing extensions given to U.S. Nuclear Plants, as well as, a new Watts Bar Nuclear Unit coming online as the first in the 21st Century.

To explain to you why the Hollywood style of Nuclear Plants isn’t exactly true, first you should learn the basic components and operation of a reactor. If you are already familiar, then hop to the -What risk is there?- section.

Components of the Reactor

The basic components of a Nuclear Plant can be summarized as: the reactor, systems that support and protect the reactor, and systems that support conversion to electricity. I will only focus on the reactor. There are several types of reactors used in modern day. For simplicity this article will mostly apply to the (PWR) Pressurized Water Reactor. If you would like to learn more about the different types go –here-.

PWR reactor fuel rods

The Containment Building is a building which houses the reactor vessel, steam generator, pressurizer, and supporting systems.
The Reactor contains:

  • The fuel rods contain fuel pellets which are bombarded with neutrons
  • The fuel rods are grouped into an assembly
  • A group of assemblies make up the reactor vessel

Now that a basic level of reactor understanding has been obtained, we can start to understand the risks.

How it Makes Power

Reactor Components

A high level overview of how a reactor turns the lights on in your house starts with atoms. Atoms that are considered marginally stable are hit with neutrons, which splits the atom into daughter atoms, more neutrons, and radiation products. The new neutrons hit other atoms to start the process over again resulting in a cascaded cycle.

The radiation products that are created by splitting the atoms are radiation alpha, beta, and gamma. These each help to produce heat. The heat is transferred through the fuel rod walls by convection into the containment area filled with a water mixture. The water heats up and is pumped into a steam generator, which is basically a heat exchanger. The coolant side of the steam generator transfers heat to the secondary side, which results in steam. The steam is dried and flows to the turbine, where through various levels of expansion turns the train rotor. The rotor is also connected to the generator, which rotates to induce current into the armature. We have created power to share with the electrical distribution system.

What Risk is there?

The risk associated to a reactor plant starts with the health and safety of the pubic. What types of danger is there to the local residents? There are 3 main ways a person can be exposed to harmful radiation: Inhalation, ingestion, and absorption. So to put it plainly, if a reactor explosion occurred like seen with Fukushima, to first 10 mile radius is predicted to have direct contact with radiation, by inhalation, absorption, and ingestion via the food chain. The next 40 miles are only susceptible to exposure through ingestion from the food chain. Now all of these predictions can change based on weather.

The risk associated to a reactor plant starts with the health and safety of the pubic. What types of danger is there to the local residents? There are 3 main ways a person can be exposed to harmful radiation: Inhalation, ingestion, and absorption. So to put it plainly, if a reactor explosion occurred like seen with Fukushima, to first 10 mile radius is predicted to have direct contact with radiation, by inhalation, absorption, and ingestion via the food chain. The next 40 miles are only susceptible to exposure through ingestion from the food chain. Now all of these predictions can change based on weather.

What Mitigation is there?

Essentially, there are so many barriers set in place, and so many levels of regulation that the possibility of a Large Release risk probability is limited to a worst case scenario of 1 in 100000 years. Meaning that if plant or external conditions caused a release of radioactive products into the atmosphere, worst case scenario shows that there is only a percent of probability of .001% for that to occur.

The barriers that are typically implemented are Prevention, Termination, and Mitigation.

Prevention = High quality design, inspection, operation such as:

  • Operation supports prevention of accidents by operating within limits of normal operating procedures
  • Limits are prescribed by plant design, FSAR, and plant procedures
  • Prevention can be to sustain normal operation.
  • The operator acts as backup to plant control system

Termination = Redundancy and diversity in safety equipment in conjunction with approved procedures and strategies
Mitigation = Multiple barriers to fission production release and emergency preparedness

Termination and Mitigation utilize:

  • A Requirement for the use of procedures
  • Automatic protection systems that terminate operations by tripping the reactor
  • Automatic actions that require station personnel to respond by using normal and emergency procedures to restore normal operation.

What if Protection Barriers Fail?

Fallout Zone prediction

If all the safety barriers failed and a General Emergency (Actual substantial core degradation or melting with loss of containment) is announced, a recovery process with begin. Major repairs will be made to contain the source of radiation. Clean-up efforts will be made to cleanse the environment as best as possible, but note we are dealing with radiation. Efforts will be made to clean up the plant exposure amounts. Procedures will be developed and errors recognized and sent to the entire nuclear industry. If the radiation can be contained and cleanup efforts successful, then the plant will aim for restart. Restart would depend heavily on the amount of radiation, cost of repair/cleanup, and public response.

What are the Areas for Improvement?

server auto

Automatic system troubleshooting – newer nuclear plants may have this capability, but older plants are dumb. If a condition exists in a plant build more than 15 years ago, it is mostly discovered by human interaction. Plant staff are physically required to monitor all plant systems and trends. I find it scary that a trend in performance is not automatically generated and analyzed. If a problem occurs that doesn’t have an annunciator, then a troubleshooting team must be created to narrow down on a cause. Typically, these systems are analog making it a time consuming, specialized level of effort.

I imagine a solution that uses measurements taken from ADCs on all plant equipment. The data is feed to a central server. The server utilizes all technical specifications and equipment relationships to accurately predict data behaviors and relationship responses. If the predicted values are trending in the wrong direction new predictions and projections can be determined and risk assessment achieved. If an issue presents in a system, then the central server would have immediate component identification and an automated or recommended response. Moreover, the system could identify changes in plant risk levels.

Scientific Research – Research into reversing the instability of radionuclides. We know how to create an unstable atom which produces by-products, but we do not know how to undo the by-products; making this method of energy generation inherently risky.

Conclusion

Even with a dated nuclear plant the levels of protection are extensive. It takes approvals on many, many levels to even make a change to plant equipment related to anything that could impact safety. Sometimes these changes even require license requirement changes.

In summary, there are 3 main barriers to a reactor that prevent fission products from release. There are many components needed to convert fission energy into electrical energy. There is a lot of risk associated with contact to radiation. But, there are also plenty of levels of protection via prevention, termination, and mitigation. Government regulation is beyond strict. Policies and procedures govern all actions. If an environmental disaster occurs, a certain level of protection is in the plant design. There is a defined plan if protective barriers fail. There are a couple known areas for improvement.

The risk of radiation release is so small, but if all else fails put your family in your car and drive north.

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About the Author
Devin Bates

Devin Bates

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Electrical Engineer, enjoys cookies, invents things in his mind, and thinks the Iguanas are to blame for the weekday.

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