Hoppe_M4.4_Midterm
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Describe the defense in depth physical protection barriers separating the public from fission products.
Defense in depth is a method of protection that uses a series of separate and redundant means of preventing the release of radiation or contamination to the public. Using this method, the failure or violation of any single barrier will not cause a hazard or release of radioactive materials. In the case of physical barriers, there are generally four major layers set in place.
The first is the fuel matrix, constructed and operated in such a manner as to preclude the release of fission products. The cladding around the fuel provides the second layer, creating a strong “armor” that is resistant to damage, as well as acting as a containment for the fuel if damage were to still occur. Next is the reactor
coolant system that surrounds the fuel. Any release from the cladding would only be
able to go into the reactor coolant, which is captured in a strong and robustly designed system of pipes, valves, and other components, designed to have no leakage under strenuous conditions, as well as to provide some amount of shielding effect. Finally, in the case of a rupture in the coolant, there is the containment system. Not only does it provide physical protection, it includes a series of emergency systems developed to mitigate the pressures, temperatures, and radiation that would be present in such a catastrophic event. This is usually the final
line of protection for the public, and is intended to be able to fully contain a design risk accident. Explain the new safety barrier that was included in the design for the reactor facility in Shippingport, Pennsylvania. Examine why this new safety barrier was included.
The power plant in Shippingport, PA was the first major nuclear facility intended for the sole purpose of electrical power production, making it a significant step forward in the nuclear industry. As part of this design purpose, it was the first reactor to have a fully dedicated containment system which housed the entirety of the primary systems of the plant. This was necessary due to the “flagship” purpose of the reactor, in order to reassure the public of its safety and promote the use of nuclear power in civilian development. New to the field of nuclear power, it was not originally encompassed in many existent nuclear regulations. This stringent design made safety an important focus, which helped to authorize and further pursue the use of nuclear power. Describe four industry changes that occurred as a result of the Three Mile Island accident. What aspect of the event were each of these changes intended to address?
One of the large changes that came about was the rise in operator training and qualification. Although plant design played a factor, there were actions the operators potentially could have taken to prevent or mitigate the disaster. In response to this, more stringent regulations were passed regarding the requirements and recurring training and testing given to nuclear operators, to promote a more specialized and effective line of reactor operators. Plant designs were also affected by the event. Many weak areas of the Three Mile Island design were noted that could be improved upon, and this became a widespread trend of fortifying and improving reactor plants nationwide. The mindset
continues to this day, with a constant focus on seeking out and correcting weak areas.
The level of oversight also became much more strict, in part as an effort to enforce new regulations. The NRC inspection program became significantly more involved and robust, as well as the creation of the Institute of Nuclear Power Operations to provide additional backup. The inspection revamp included scheduling, focus areas, and reporting aspects to fully promote a more effective process.
Information sharing became noted as a valuable region to expand upon as well. This falls into two major arenas; the international coordination, and the public. Uniting the nuclear industry worldwide to promote improvement and seek help has shown to be invaluable, as displayed by the international effort that took place in the wake of the Fukushima Daiichi accident. Promoting public knowledge of nuclear power and clearly distributing information helps significantly with public trust, as well as emergency response. Describe the key differences in the physical design of the Chernobyl nuclear power plant compared to US nuclear power plants with regard to defense in depth. Describe the United States Nuclear Regulatory Commission’s (USNRC) assessment of the Chernobyl nuclear accident in terms of applicability to U.S. commercial reactors and their operating staff.
There are a large number of notable differences between Chernobyl and traditional American nuclear plants. As a factor of defense in depth, plant design is a significant portion of this. The Chernobyl design was inherently dangerous due to the thermal coefficients and construction of the moderator, whereas American plants would have an opposite reaction to the events that occurred. The level of safety systems in American plants is robust, which is many layers of defense in depth, whereas Chernobyl suffered catastrophically due to a lack of safety systems in place to mitigate the disaster. Another facet is emergency planning; there are strictly delineated roles and procedures in place for potential accidents in U.S. plants, whereas the Chernobyl
incident was initially covered up, leading to a significantly delayed evacuation and response to the disaster, affecting a great number of people in preventable ways. A large part of the NRC response to Chernobyl was to verify that such incidents could not take place in our designs, as well as to carefully review and improve the principles we operate under. Although the specific reactor design is not relatable, there are still valuable lessons to be learned in how the sequence of events was allowed to happen, and especially in the way the response was handled.
It was also an opportunity to study the effects of a large scale nuclear disaster, and improve planning if another should occur. Describe the origins and intent of the Maintenance Rule (10CFR50.65). Describe what the licensee (nuclear facility) must do before performing maintenance on plant equipment with regard to the maintenance rule.
The Maintenance Rule came into existence due to the NRC noting a trend of poorly performed, or completely ignored, maintenance in nuclear facilities, leading to degraded systems and lower margins to safety. In order to correct and improve upon this issue, which had the potential to spiral into a nuclear accident, the NRC began the process of strictly regulating and monitoring maintenance efforts in nuclear plants.
The licensee is required to submit to the regulatory requirements of the Maintenance Rule, which not only outlines the responsibilities of maintenance, but also provides guidelines on what maintenance is considered governed. The licensee uses these guidelines to develop a comprehensive maintenance plan for all safety related systems and adhere to it, performing, tracking, and routinely evaluating their maintenance programs. As a result of the 9/11 terrorist attacks, the United States Nuclear Regulatory Commission (USNRC) made certain enhancements with regard to security personnel at nuclear facilities a requirement. Describe these enhancements.
As with many high-risk facilities across the nation and world, nuclear plants were looked at closely in regards to security after the attacks on 9/11. With the idea of such attacks potentially being used to target a facility that could unleash radioactive fallout, there was great cause for concern to seek out any need for improvement. The NRC ordered nuclear facilities to improve their security profiles in a number of ways. This included physical security, such as barriers, guards, patrols, and location, as well as improved security measures involving personnel, access control, and planning. Defueling, nuclear material transport, and coordinating with airport security measures to reduce the risks of an aerial threat.
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Continued efforts include a focus on design basis threat analysis, incorporating the continuity of security into those plans, as well as improving safety on defueling, nuclear material transport, and coordinating with airport security measures to reduce the risks of an aerial threat. How does the contents of a licensee’s FSAR relate to the concept of defense in depth?
A Final Safety Analysis Report, or FSAR, is an important document submitted to the NRC in order to authorize the licensing of a nuclear facility. The report contains a large volume of information on the design, testing, and analysis of reactor plant systems and construction, including operational planning and location,
population effects, and numerous other categories. This document falls into defense in depth as it provides a layer of critical review for the NRC, allowing for another step of complete analysis of the design criteria for a reactor plant. The requirements of the report are rigorous, ensuring that the licensee has fully researched and implemented the safety requirements for design and planning of a nuclear plant. This layer of defense may not be physical in nature, but provides an excellent step for reactor safety. Describe the requirements and structure of a licensee’s cyber security program. Cybersecurity is an important and growing role in nuclear power, as the field continues to evolve into more integrated and complex operations. The NRC has gone so far as to create a dedicated department, the Cyber Security Branch (CSB), to further their ability to appropriately regulate this factor in nuclear power.
Licensees must follow the “Cybersecurity Roadmap,” which lays out a seven-
step process for implementing and maintaining a robust cybersecurity program. In more final steps, digital assets must be controlled and monitored. There is also an ongoing process to monitor and access the security program itself, for failures and opportunities to improve and strengthen. Immediately following the Chernobyl accident, a massive accident management operation began. In this operation, helicopters were used to dump materials on the exposed reactor core. Describe the three materials that were used and what the purpose of each was.
Helicopters were used to dump thousands of tons of material onto the exposed reactor in an attempt to smother the dangers present. One material was used literally in that sense, sand. The sand was hoped to cover up the ongoing fires and flammable materials, removing the source of oxygen and extinguishing the fire to mitigate further damage.
Similarly, the helicopters also added dolomite to the inferno, in an attempt to absorb residual heat and create carbon dioxide as a byproduct, both of which would serve to limit the spread of flames. Boron was poured on for a different reason, to attack the radioactive problem.
Boron is an excellent neutron absorber, and by spreading it onto the exposed nuclear fuel, responders hoped to contain the ongoing nuclear reaction that was causing the damage to occur. Describe the release of radiation that occurred following the Three Mile Island Accident. What was the source of the radiation released and how significant was this release?
When the TMI-2 reactor overheated and a portion of the fuel was uncovered by water, a nuclear meltdown occurred. Effective plant design and operator actions contributed to what could have been a significantly more egregious disaster, and thankfully only a small amount of radioactive gas was released from the plant, which suffered to major damage or breach to the containment. Although the release is still significant in the context of a nuclear accident, there have been no noted effects on the environment or health of the public. Numerous in-depth studies over the years have confirmed that the average dose to anyone in the vicinity was less than that obtained during a routine medical x-ray. § 52.157 Contents of applications; technical information in final safety analysis report.
(n.d.). NRC Web.
https://www.nrc.gov/reading-rm/doc-collections/cfr/part052/part052-
0157.html
Chernobyl | Chernobyl Accident | Chernobyl Disaster - World Nuclear Association
.
(2022, April). World-Nuclear.org. https://world-nuclear.org/information-
library/safety-and-security/safety-of-plants/chernobyl-
accident.aspx#:~:text=From%20the%20second%20to%20tenth
Chernobyl Accident and Its Consequences
. (2019, May 1). Nuclear Energy Institute.
https://www.nei.org/resources/fact-sheets/chernobyl-accident-and-its-
consequences#:~:text=A%20Safety%20Comparison%20with%20the
%20U.S.&text=The%20first%20key%20difference%20is
Cybersecurity
. (n.d.). NRC Web.
https://www.nrc.gov/security/cybersecurity.html
Historic American Engineering Record PA-81. (n.d.) Department Of The Interior.
https://memory.loc.gov/master/pnp/habshaer/pa/pa1600/pa1658/data/pa1658dat
a.pdf
Defence In Depth In Nuclear Safety
. (n.d.) International Nuclear Safety Advisory
Group.
https://www-pub.iaea.org/MTCD/publications/PDF/Pub1013e_web.pdf
NRC: Frequently Asked Questions About NRC’s Response to the 9/11/01 Events
. (n.d.).
Www.nrc.gov. https://www.nrc.gov/security/faq-911.html
NRC’s Nuclear Maintenance Rule
. (2016, September 20). The Equation.
https://blog.ucsusa.org/dlochbaum/nrcs-nuclear-maintenance-rule/
Three Mile Island Accident Fact Sheet
. (n.d.) U.S.NRC.
https://www.nrc.gov/docs/ML0825/ML082560250.pdf
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