On March 28, 1979 the most serious United States commercial nuclear power plant accident happened outside of Middletown , Pennsylvania . Although no deaths occurred, the accident at Three Mile Island Unit 2 was the worst in operating history. It highlighted the need for changes in emergency response planning, reactor operator training, human factors engineering, and radiation protection. The accident was a result of equipment malfunctions, worker errors, and design related problems that ultimately led to a partial core meltdown and a small release of radioactivity.
Early morning on March 28, 1979 the Three Mile Island plant, which used pressurized water reactors, “experienced a failure in the secondary, non-nuclear section of the plant” (NRC). Due to a mechanical or electrical failure, the central feedwater pumps terminated and “prevented the steam generators from removing heat” (NRC). As a consequence the turbine and reactor shut down, this caused an increase in pressure within the system. When pressure increases in the primary system a monitored pilot-operated relief valve opens until pressure reaches an acceptable level then shuts. In the case of the Three Mile Island accident the pilot-operated relief valve never closed and no signal was given to the operator. Consequently, the open valve poured out cooling water to assist in the lowering of pressure “and caused the core of the reactor to overheat” (NRC). The indicators which were designed to let the operator know when malfunctions were occurring provided conflicting information. There was no indicator displaying the level of coolant in the core nor was there a signal that the relief valve was open; therefore, the operators assumed the core was properly covered. Alarms went off in the plant due to the loss of coolant but the operators were confused on what was wrong thereby making the situation worse. The overheating caused a rupture in the zirconium cladding and melting of the fuel pellets. Thankfully, the worst case consequences of a dangerous meltdown such as a breach of the walls f the containment building or releases of large amounts of radiation did not happen.
Impact of the Accident
The Three Mile Island accident prompted several upgrades in the maintenance and building of nuclear power plants. As described by the United States Nuclear Regulatory Commission Three Mile Island Fact Sheet, some of the changes which occurred post accident are the following: upgrading and strengthening of plant design and equipment requirements, identifying human performance as a critical part of plant safety, revamping operator training and staffing requirements, improved instruction to avoid the confusing signals that plagued operations during the accident, enhancement of emergency preparedness, regular analysis of plant performance, and expansion of performance-oriented as well as safety-oriented inspections.
In addition, the accident permanently changed the nuclear industry and the Nuclear Regulatory Commission’s approach to regulation. The Nuclear Regulatory Commission (NRC) developed broader and more vigorous regulations and inspections in order to circumvent the public’s worry and distrust. Since the Three Mile Island accident, the NRC has expanded its method of regulation. As shown in Figure 2.5, the NRC’s “primary mission to protect the public health and safety, and the environment from the effects of radiation from nuclear reactors, materials, and waste facilities” is carried out in five different manners: regulations and guidance, licensing and certification, oversight, operational experience, and support for decisions (NRC website). By promoting each facet of its regulation method, the NRC strives to protect plant workers, the environment, and society as a whole.
Figure 2.5: Nuclear Regulatory Commission’s Regulation Process
Although no injuries occurred due to the accident, the idea of an extremely dangerous nuclear meltdown happening near one’s household is disturbing. Yes, nuclear power provides 15% of the United States ’ electricity but the risks of disposal and possible radiation exposure outweighs the desperateness of electrical power. What if X number of people were injured or killed due to the accident? Would taking that risk and sacrificing those people be worth nuclear power?