ML12340A344
| ML12340A344 | |
| Person / Time | |
|---|---|
| Site: | Three Mile Island  |
| Issue date: | 12/31/2012 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| Beltz, G | |
| References | |
| NUREG/KM-0001 | |
| Download: ML12340A344 (24) | |
Text
Three Mile Island Accident of 1979 Knowledge Management Digest NUREG/KM-0001 December 2012
Three Mile Island on April 10, 1979, 13 days after the accident.
1 NUREG/KM-0001Table of Contents Introduction
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3 The Accident
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4 Investigations and Lessons Learned
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5 Regulatory Actions
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6 Research .................................................................................................................
8Timelines ...............................................................................................................
11 Retrospectives
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14DVD Topics
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16President Jimmy Carter observes the radiation monitors in the Three Mile Island, Unit 2 control room on April 1, 1979, accompanied by Pennsylvania Governor Richard Thornburgh and the NRC's Harold Denton (front to back).
2Three Mile Island Unit 2 Timeline 3 NUREG/KM-0001 IntroductionAlthough it caused no deaths or injuries, the accident at the Three Mile Island, Unit 2 (TMI-2) nuclear power plant was the most serious incident in U.S. commercial nuclear power history. The accident began in the early morning hours of March 28, 1979, at the power plant near Middletown, PA, and its effects on nuclear safety and regulation continue to this day. Three Mile Island spurred the U.S. Nuclear Regulatory Commission (NRC) to tighten and heighten its regulatory oversight of the nuclear power industry to ensure safety for the public and the environment. Investigations and the implementation of lessons learned brought about sweeping changes in the U.S. nuclear industry. These included improvements in emergency response planning, reactor operator training, human factors engineering, radiation protection, and many other areas of nuclear power plant operations. The NRC has intensively studied and documented the TMI-2 accident. This knowledge management digest and the supporting DVD contain the reports that the NRC and other government organizations issued following extensive investigations in the accident. Although a few key documents have become digitized these historically important reports. On the DVD, the table of contents on the main welcome screen lists these reports and provides access to them.In addition to the large collection of reports, the DVD also provides a multimedia presentation of the special NRC event, "The Accident at Three Mile Island-A Look Back: Preserving the Institutional Memory after 30 Years."
4 The Accident The sequence of certain events-equipment malfunctions, design related problems, and operator errors-led to a partial meltdown of the TMI-2 reactor core, resulting in a very small offsite release of radioactivity. In an atmosphere of growing uncertainty about the condition of the plant, on the morning of March 5-mile radius of the plant to stay indoors. He also advised pregnant women and preschool-age children to leave the area.nontechnical discussion of the accident, including onsite actions and offsite responses. Another good resource on the accident is the main report by the volumes of both these reports provide technical details.provides a technical summary of the accident. The training manual also provides an overview of the regulatory implications of the accident (Section 2.3).
5 NUREG/KM-0001The chronology of events can be found in all of the above documents. The summaries of the accident. These and other reports on the accident are provided on the accompanying DVD (see the section Accident Overview).
Investigations and Lessons LearnedTwo weeks after the accident, the President of the United States, Jimmy Carter, appointed a 12-member Presidential Commission to investigate the accident at a comprehensive investigation of the accident and made recommendations Island-A Ten-Year Review," updated that initial response to include each of the To help gain a comprehensive insight into the accident, the NRC sponsored both internal and external investigations. The NRC asked the "Rogovin Committee" to perform an investigation.
analysis and assessment of the causes and implications of the accident. As already noted, the NRC published A Report to the Commissioners and to the Public." Working internally, the NRC created a Lessons-and evaluated safety concerns originating from the TMI-2 accident that required licensing actions at other nuclear power plants. The NRC published the task Learned Task Force Status Report and Short-Term Lessons Learned Task Force Final Report."
6 Many other groups, both internal and external to the NRC, also performed Development.The DVD provides many of the key investigation reports on TMI (see sections Government Investigations and NRC Investigations and Lessons Learned
).Regulatory ActionsThe NRC implemented a number of regulatory actions resulting from investigations and lessons learned reviews, and completed many more "spin-off" the NRC approved, included NRC orders to individual licensees and generic communications, such as bulletins and generic letters issued to nuclear power plant licensees. The NRC used these regulatory tools in the days to months following the accident.Commissioners considered the recommendations. The agency consolidated "TMI Action Plan," published in 1980. The plan included approximately 371 individual requirements. The NRC found that of these, 13,863 action plan items Some of these requirements involved changes to the internal NRC organization, processes, and practices. A few requirements caused the Commission to issue rulemaking process. Both of these long-term regulatory tools required extensive internal and external stakeholder involvement, and were completed during the prioritization and closeout of the TMI Action Plan requirements.
7 NUREG/KM-0001 Generic Communications operating power plant licensees to take a number of immediate actions to avoid repeating several of the events that occurred during the accident, and which 06A, 06B, 06C, and 08). The bulletins and related evaluations also substantially informed other staff activities, such as those associated with the generic study communications including generic letters that transmitted information and usually required action or a response, and information notices related to issues in which the licensees considered action appropriate. The DVD provides most of the generic communications relevant to TMI-2 (see the section titled Generic Communications and Policy Statements
).TMI Action Planrecommendations in a different way. These recommendations were collected and that the Commission approved for implementation at nuclear power plants. In about schedules, applicability, method of implementation review, submittal dates, action items.associated with the implementation and closeout of TMI Action Items (see the section titled Industry Wide Regulatory Actions
).Rulemaking and Regulatory Guides-In most cases, the NRC implemented the TMI Action Plan issues through the review of new licensee applications These regulations, and a few others that could be considered relevant to the TMI accident, included the following: upgrading emergency planning regulations in 1980, requirements related to hydrogen control in Mark I and Mark II containments for boiling water reactors (BWRs) in 1981, upgrading operations 8licensee event report rule in 1983, requirements related to hydrogen control in Mark III containments for BWRs and ice condenser containments for pressurized reactors in 1985, improving personnel dosimetry processing in 1987, updating the operator licensing requirements in 1987, and mandating participation in the implementing agency regulations. Regulatory guides are not substitutes for regulations, and the NRC does not require that licensees comply with them. Notable regulatory guides that the NRC revised or created during the Power Plant Simulation Facilities for Use in Operator Training and License rulemakings and regulatory guides (see the section titled NRC Annual Reports
).NRC Commission Policy Statements
-Several policy statements that the Commission issued were directly or indirectly related to the TMI Accident. A for future regulatory positions. Two notable policy statements that continue to have far-reaching regulatory applications include "Severe Reactor Accidents provided the basis for redirecting NRC research programs and other regulatory analyses, and for the use of probabilistic risk assessment in risk-informed NRC Commission policy statements relevant to TMI-2 (see the section titled Generic Communications and Policy Statements
).Researchdesign basis approach to relying on a multifaceted approach, which emphasized improved operations, human factors considerations in control rooms and 9 NUREG/KM-0001emergency procedures, realistic performance of systems and containments under severe accident conditions, and probabilistic risk assessments (PRAs) to identify accidents increased substantially. Some examples included allocating additional resources to R&D activities, such as the construction of new experimental facilities, the development of analytical tools, and, in general, the development of the information needed to gain greater insights into severe accident behavior. Since the accident, the NRC, and to some extent the industry, have developed a large body of information on severe accidents, including the probability of severe accidents, core-melt phenomenology, associated accident sequences, and the effects of severe accidents on plant systems, components, and structures, especially those that provide barriers to such as the reactor containment structure.also supported an extensive research program, known as the "TMI-2 Accident consistent understanding of the accident.
The primary objective of the program was to develop an understanding of core damage progression in the upper core region, the heat up and the formation and growth of the molten central region of the core, the relocation of approximately 19 metric tons of debris to the lower head, reactor vessel and the containment.and nuclear industry organizations also contributed important post accident research. In 1980, four organizations-the N RC, and the Dprogram executed R&D activities relating to the cleanup of TMI-2 and the study of the accident for the enhancement of nuclear power safety and reliability. The Closed-circuit television inspections of the reactor core revealed a rubble bed approximately 5 feet below the normal location of the top of the fuel assemblies.
10 The DVD provides many of the NRC reports, which document R&D activities relating to the TMI-2 accident and its unique recovery and cleanup (see the section titled Recovery and Research Activities provided on the DVD (see the section titled GEND Research Reports
). NRC annual reports provide summaries of NRC research activities (see section titled NRC Annual Reports
).At left is a status page recorded at the NRC Operations Center on the second day of the accident showing temperature readings that were measured by plant technicians with a handheld voltage meter on the wires from reactor core exit thermocouples.
These thermocouples were temporary installed to measure coolant temperatures above the reactor fuel in support of startup testing of the new reactor. We now know that many of these temperature readings were measured at newly formed false junctions fuel" regions of the core. Today, all pressurized water reactors are required to Class 1E instrumentation for core exit thermocouples, sub-cooling margin monitors, and reactor coolant inventory monitors.
11 NUREG/KM-0001Timelines Plant Recovery and Cleanup Milestones
-By the close of the weekend of condition. On Sunday, April 1, 1979, President Jimmy Carter, Rosalynn children to vacate the area within a 5-mile radius of TMI was lifted. Within 1 to the condenser and out of the cooling towers. The purging of radioactive of the accident. Shortly before the second anniversary, the reactor was placed in loss-to-ambient cooling mode, where heat losses are transferred into the reactor building ambient and out through the reactor building fan coolers.
The reactor vessel head was removed in 1985, while the removal of loose fuel debris from the reactor vessel began later that year, and was completed in 5 years. Workers used numerous manual and hydraulically powered long-handled tools to perform a variety of functions, such as pulling, grappling, cutting, scooping, and breaking up the core debris. In 1986, 7 years after the accident, a special Workers perform defueling operations from a shielded defueling work platform (DWP), surface with 6-inch steel shield plates, and is designed to provide access for defueling tools and equipment into the reactor vessel.
12 core sampling drilling rig was used to reveal the extent of the hard crust layer and placed the debris in wet pool storage for study and safekeeping. The evaporation of 2 million gallons of slightly contaminated accident-generated water at TMI was completed in 1993 over a 2- to 3-year period.In late 1993, TMI-2 was placed in NRC-approved post-defueling monitored storage, a passive monitored state in which the plant will remain until the licensee decommissions both units simultaneously. From 2000 to 2001, the NRC Actions at TMIresponding to the accident, then by approving and overseeing recovery activities by the licensee and its contractors. A team began to form with the arrival of the to expand throughout the weekend with the arrival of engineers, scientists, and Important NRC actions during TMI-2 recovery included:level contaminated accident water in the auxiliary building in October 1979.Issuance of the Commission order to implement the TMI-2 recovery order to purge radioactive krypton gas from the reactor building atmosphere in June 1980.Issuance of the NRC action plan for cleanup operations in July 1980 February 1981.
13 NUREG/KM-0001Creation of the public Advisory Panel for the Decontamination of Three Mile Issuance of the Commission Policy Statement endorsing the Programmatic Issuance of the safety evaluation report on the use of the Submerged Demineralizer System to process the highly contaminated accident-generated water in the reactor building sump and reactor coolant system in June 1981 Issuance of an amendment to the memorandum of understanding with the and highly radioactive solid waste for research and long-term storage (see the reactor building polar crane in November 1983.
October 1984.
slightly contaminated accident generated water in June 1987, and on dealing with post-defueling monitored storage and subsequent cleanup in August 1989.million gallons of accident-generated water.The NRC wrapped up onsite NRC involvement at TMI 2 by the time that the headquarters project directorate assumed responsibility for the technical review and project management functions. In September 1993, the NRC approved the "post-defueling monitored storage" at TMI-2 and associated license conditions public Advisory Panel for the Decontamination of Three Mile Island Unit 2 was 14 The timeline feature on the DVD provides a summarized chronology of key recovery milestones and NRC actions. Users may read a short description of many of the actions by clicking on the text on the timeline from the interactive window on the DVD (see the section titled Timeline).RetrospectivesFor the 30th anniversary of the TMI-2 accident, the NRC hosted a special all-day event titled, "The Accident at Three Mile Island-30th Anniversary, A Look Back: Preserving the Institutional Memory." The event featured several presentations, Historian Sam Walker.two shipping casks used to ship fuel debris by rail to the Department of Energy's Idaho National Laboratory.
15 NUREG/KM-0001 Following the individual presentations, the NRC hosted a panel discussion titled "Remembering the Accident." The panel included a distinguished group, all of whom made key decisions during the accident: Richard Thornburgh, former Mathews, former assistant to President Jimmy Carter.
The DVD provides a multimedia presentation of this event (see section titled Multimedia
).A press conference during the early days of the accident with Pennsylvania Governor Regulation, Harold Denton (left).
16DVD TopicsTo help navigate the DVD, the outline below provides topics and headings that the user can access directly from the interactive window. The user may also click on the text on the Timeline for a short description and related documents.
Important Note:
Many of the documents on the DVD are historical in nature, for current information on regulations, Commission policy statements, regulatory guidelines, regulatory processes, and research results.Main Welcome Screen
- Regulatory Research, NRC
-List of Documents Found on this DVD
-Accident OverviewTimelineHistorical Documents
NRC Investigations and Lessons Learned
Industrywide Regulatory Actions
Recovery and Research Activities NRC Annual ReportsMultimedia
17 NUREG/KM-0001Three Mile Island Accident of 1979 Knowledge Management DigestPrepared by:
Don Marksberry
Carolyn Siu Amy Bonaccorso Mark Henry Salley Contributions by:Publications Branch in the Division of Administrative Services of the Dickinson College Community Studies Center National Archives and Records AdministrationIndependent spent fuel storage installation for the dry storage of the fuel debris from TMI-2 located at the Department of Energy's Idaho National Laboratory.
18of the core. This action did not immediately stop further core melting, but it did prevent the core from melting through the reactor vessel.Notes: (1) cold leg Loop 2B inlet, (2) cold leg Loop 1A inlet, (3) cavity, (4) loose core previously molten material on bypass region interior surfaces, (12) upper grid damage (NUREG/CR-6042).
19 NUREG/KM-0001Numerous manual and hydraulically powered long-handled tools were used to perform a variety of functions, such as pulling, grappling, cutting, scooping, and breaking up the core debris. These tools were used to load debris into defueling canisters positioned underwater in the reactor vessel. Later, a core boring machine (lower right)
This DVD was developed using Visual Basic Professional 2008. Make sure you have Windows XP and Visual Basic framework 3.5 or above for the DVD to work correctly.
NUREG/KM-0001 December 2012