ML15238B627
| ML15238B627 | |
| Person / Time | |
|---|---|
| Site: | Three Mile Island  |
| Issue date: | 08/26/2015 |
| From: | John Clements Reactor Decommissioning Branch |
| To: | |
| John P. Clements | |
| References | |
| Download: ML15238B627 (37) | |
Text
Three Mile Island Unit 2Case Study OverviewIAEA International Project on Managing the Decommissioning and Remediation of Damaged Nuclear Facilities (DAROD)31 August
-4 September, 2015John P. ClementsHealth Physicist, Division of Decommissioning, Uranium Recovery, and Waste Programs Accident OverviewA combination of equipment malfunctions, design
-related problems and worker errors led to TMI
-2's partial meltdown and very small off
-site releases of radioactivity Accident ProgressionAt about 4 a.m. on Wednesday, March 28, 1979, TMI
-2 experienced a failure in the secondary, non
-nuclear section of the plant A mechanical or electrical failure prevented the main feedwater pumps from sending water to steam generators that remove heat from the reactor coreThe plant's turbine
-generator and then the reactor itself automatically shut downImmediately, pressure in the primary system (the nuclear portion of the plant) began to increase Accident ProgressionTo control pressure, a pilot
-operated relief valve (a valve located at the top of the pressurizer) opened
-The valve should have closed when the pressure fell to proper levels, but it became stuck open.Control room instruments incorrectly indicated that the valve was closed leaving staff unaware that cooling water was pouring out of the stuck
-open valveAs coolant flowed from the primary system through the valve, other instruments available to reactor operators provided inadequate information, and no instrument showed how much water covered the core Plant staff assumed if the pressurizer water level was high, the core was properly covered with water and did not realize the plant was experiencing a loss
-of-coolant accidentWater escaping through the stuck valve reduced the primary system pressure so much that reactor coolant pumps had to be turned off to prevent dangerous vibrationsTo prevent the pressurizer from filling completely, staff reduced emergency cooling water amounts into the primary system -starving reactor core of coolant, causing it to overheatFuel overheated to the point at which the zirconium cladding ruptured and the fuel pellets began to meltLater found that about half of the core melted during the early stages of the accidentAccident Progression Accident Animation TMI-2 reactor is permanently shut down and all its fuel has been removedReactor coolant system is fully drained and the radioactive water was decontaminated and evaporated Radioactive waste from the accident was shipped off
-site to an appropriate disposal area, and the reactor fuel and core debris was shipped to the Department of Energy's Idaho National LaboratoryCurrent plan is to keep the TMI
-2 facility in long
-term, monitored storage until the operating license for the TMI
-1 plant expires, at which time both plants will be decommissionedCurrent Conditions at TMI-2 Regulatory Issues A specialized U.S. NRC team was established shortly after the accident
-including representatives of the NRC's Office of Inspection and Enforcement (IE), the 5 NRC Regions, and the Office of Nuclear Reactor Regulation (NRR)A Public Affairs Office was established in Middletown, PA, and staffed on a 24
-hour basisRegulatory Approaches/Issues The NRC site team initially supported emergency response functionsWithin days of the accident, the site team performed on
-site recovery activities, which can be broken down into four major areas:
1)Reviewed system modifications and system additions 2)Reviewed all procedures (emergency and normal operation and maintenance) which were necessary to post-accident activities 3)Provided close and continuous monitoring for the operations 4)Provided consultation, review, and analysis of the ongoing rad
-waste, cleanup, and health physics activitiesRegulatory Approaches/Issues The NRC's licensing process was generally utilized to allow for remediation/decommissioning of TMI-2For example, NRC Orders were issued to:Suspend operating license and require maintenance in a shutdown condition per NRC approved proceduresPermit the usage of the Epicor
-II filtration and ion exchange system to decontaminate intermediate level waste waterIncorporate revised technical specifications to reflect the damaged conditionPermit the licensee to purge the reactor building of krypton-85Public comments were sought and several Environmental Assessments were preparedRegulatory Approaches/Issues The overall NRC regulatory approach was impacted as a result of the TMI accident, both in the short term and the long termShort Term (days to months)
-The NRC issued several orders to individual licensees and issued generic communications, such as bulletins and generic letters, to all nuclear power plant licenseesLong Term (months to years)
-Investigations and the implementation of lessons learned brought about sweeping changes in the U.S. nuclear industry
-including improvements in emergency response planning, reactor operator training, human factors engineering, radiation protection, and many other areas of nuclear power plant operationsRegulatory Approaches/Issues Technical Issues Fuel melting and reactor core damage had occurredContaminated coolant water remained in the basement of the containment buildingThe containment building was contaminated but remained in
-tact and functionalFirst entry into the reactor building containment was conducted by two utility staff on July 23, 1980 (image to the right)Technical Issues
-Post Emergency State of the Facility Technical Issues
-Post Emergency State of the Core 1.Cold leg Loop 2B inlet 2.Cold leg Loop 1A inlet 3.Cavity4.Loose core debris 5.Crust6.Previously molten material 7.Lower plenum debris 8.Hard layer debris 9.Damaged in
-core instrument guide 10.Hole in baffle plate 11.Coating of previously molten material on bypass region interior surfaces12.Upper grid damage Decontamination of intermediate
-level contaminated water(defined as less than 3.7 MBq/mL [100 µCi/mL]) in the auxiliary buildingEnvironmental Assessment issued and approval granted to use the Epicor
-II filtration systemPurging of the reactor building atmosphere Environmental Assessment and evaluation completedControlled and filtered purge accomplished over a 14 day period, per NRC approved proceduresThe maximum cumulative radiation dose and the maximum dose rate measured at off
-site locations were a fraction of the limits allowed under NRC regulationsTechnical Issues/Challenges Technical Issues/ChallengesEPICOR-II System Decontamination of highly contaminated wastewaterThe NRC Approved the use of the Submerged Demineralizer System (SDS)The SDS operated underwater, in one of the spent fuel pools of TMI Unit 2It consisted of a liquid waste treatment subsystem, a gaseous waste treatment subsystem, and a solid waste handling subsystemThe approval to operate the SDS did not include water disposalTechnical Issues/Challenges Removal of fuel debris from the reactorOperators removed damaged fuel and structural debris from the reactor vessel by "pick and place" defueling of loose core debrisWorkers performed defueling operations from a shielded defueling work platform (DWP) located nine feet above the reactor vessel flangeThe DWP had a rotating 17
-foot diameter surface with six-inch steel shield plates, and was designed to provide access for defueling tools and equipment into the reactor vesselTechnical Issues/Challenges Technical Issues/ChallengesShielded defueling work platform (DWP)
Technical Issues/ChallengesNumerous 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.
Microorganisms inside the reactor vesselA large population of microorganisms developed in the reactor coolant system (RCS), clogging cleanup system filters and hindering the view of defueling activitiesLicensee conducted a multi
-phase program to restore water clarity consisting of high
-pressure hydrolancing
, the addition of hydrogen peroxide, and the use of a high-pressure positive displacement pump A diatomaceous earth (swimming pool
-type) filter was operated in conjunction with the letdown and makeup of batches of reactor coolant, to remove the organic material and improve the clarity of the RCS waterTechnical Issues/Challenges NRC and DOE signed Memorandum of Understanding (MOU) on waste disposalTheMOU formalized the working relationship between the two agencies with respect to the removal and disposal of solid nuclear waste generated during the cleanup of TMI-2Significant step toward ensuring the TMI site would not become a long
-term waste disposal facilityThe MOU covered only solid nuclear waste, and did not cover liquid waste resulting from cleanup activitiesDOE also agreed to accept fuel and highly radioactive resins from the water purification systemTechnical Issues/Challenges NRC and DOE signed Memorandum of UnderstandingMOU addressed three basic categories of TMI
-2 waste:1)waste determined by DOE to be of generic value in terms of beneficial information to be obtained from further research and development activities 2)waste determined to be unsuitable for commercial land disposal because of high levels of contamination, but which DOE may also undertake to remove, store, and dispose of on a reimbursable basis from the licensee 3)waste considered suitable for shallow land burial, to be disposed of by the licensee in licensed, commercial low
-level waste burial facilitiesTechnical Issues/Challenges Epicor resin waste disposalThe NRC approved the licensee's request to dispose of Epicor resin liners via shallow land disposal, as they were similar to typical reactor resin wastes Several shipments were also made to various laboratories for testing purposesSubmerged Demineralizer System resin waste disposalSubmerged Demineralizer System liners were sent to DOEDOE conducted research on glass vitrification (solidification) of this type of solid waste at HanfordTechnical Issues/Challenges Disposal of slightly contaminated waterThe licensee was approved for a treatment/disposal method involving the forced evaporation of the water contaminated during the accident and used in subsequent cleanup operations at the TMI site
-to be completed over a 2.5 year periodResidue from this operation, containing small amounts of the radioactive isotopes cesium
-137 and strontium
-90, and large volumes of boric acid and sodium hydroxide, would require solidification and disposal as low
-level wasteTechnical Issues/Challenges Institutional Framework and Strategic Planning Organizational arrangements/structures shifted from operational NRC oversight prior to the accident, to an augmented on and off
-site emergency response structure during the emergency phase, and to a new structure enhanced by lessons learned after the emergencyChanges to the NRC's organizational framework occurred in the establishment of a TMI Program Office and a TMI
-2 Project Directorate, and an Office for Analysis and Evaluation of Operational Data (AEOD)The NRC formed a 12 member Public Advisory Panel including local citizens, local and state governmental officials, and scientists, meeting regularly with both the public and NRC CommissionersInstitutional Framework The pre-existing regulatory and political decision making processes were generally adequate in that the NRC's licensing process was utilized for many decisionsThe current post defueling monitored storage state of TMI-2 represents a unique approach as it placed the facility into monitored storage for an unspecified period of timeFunding provisions are provided by the licensee, who provides annual funding status and cost analysis reportsInstitutional Framework Several investigation committees were formed shortly after the accident, which influenced organizational/structure changesThe President of the United States, Jimmy Carter, appointed a 12
-member Presidential Commission to investigate the accident at Three Mile Island. This group, known as the "KemenyCommission," conducted a comprehensive investigation of the accident and made recommendations based upon their findingsThe NRC sponsored both internal and external investigations, and asked the independent Special Inquiry Group, known as the "RogovinCommittee" to perform an investigationStrategic Planning Many groups, both internal and external to the NRC, also performed separate investigations. These included:The U.S. Congress and its General Accounting Office (GAO)The Ad Hoc Dose Assessment Group, which comprised various Federal agenciesThe NRC's Advisory Committee on Reactor SafeguardsStrategic Planning The TMI accident permanently changed both the nuclear industry and the NRCPublic fear and distrust increasedNRC's regulations and oversight became broader and more robustManagement of the plants was scrutinized more carefullyCareful analysis of the accident's events identified problems and led to permanent and sweeping changes in how NRC regulates its licensees
-which, in turn, has reduced the risk to public health and safetyInstitutional Framework Changes Upgrading and strengthening of plant design and equipment requirementsIncludes fire protection, piping systems, auxiliary feedwater systems, containment building isolation, reliability of individual components (pressure relief valves and electrical circuit breakers), and the ability of plants to shut down automaticallyIdentifying the critical role of human performance in plant safety led to revamping operator training and staffing requirements, followed by improved instrumentation and controls for operating the plant, and establishment of fitness
-for-duty programs for plant workers to guard against alcohol or drug abuseInstitutional Framework Changes Enhancing emergency preparedness, including requirements for plants to immediately notify NRC of significant events and an NRC Operations Center staffed 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> a dayDrills and response plans are now tested by licensees several times a year, and state and local agencies participate in drills with the Federal Emergency Management Agency and NRCRequirement for plant specific simulators establishedIntegrating NRC observations, findings, and conclusions about licensee performance and management effectiveness into a periodic, public reportInstitutional Framework Changes Having senior NRC managers regularly analyze plant performance for those plants needing significant additional regulatory attentionExpanding NRC's resident inspector programExpanding performance
-oriented as well as safety
-oriented inspections, and the use of risk assessment to identify vulnerabilities of any plant to severe accidentsStrengthening and reorganizing enforcement staff in a separate office within the NRCEstablishing the Institute of Nuclear Power Operations, and formation of what is now the Nuclear Energy Institute to provide a unified industry approach to generic nuclear regulatory issues, and interaction with NRC and other government agenciesInstitutional Framework Changes Installing additional equipment by licensees to mitigate accident conditions, and monitor radiation levels and plant statusEnacting programs by licensees for early identification of important safety
-related problems, and for collecting and assessing relevant data so operating experience can be shared and quickly acted upon; andExpanding NRC's international activities to share enhanced knowledge of nuclear safety with other countries in a number of important technical areasInstitutional Framework Changes Three Mile Island Accident of 1979 Knowledge Management Digest, NUREG/KM-0001, December 2012, U.S. NRC Office of Nuclear Regulatory ResearchU.S. NRC Backgrounder on the Three Mile Island Accident, http://www.nrc.gov/reading
-rm/doc-collections/fact
-sheets/3mile
-isle.html
, Page Last Reviewed/Updated Friday, December 12, 2014U.S. NRC Regulatory Process for Decommissioning & Actions Related to Damaged Facilities after Accident, Larry W. Camper, Director Division of Waste Management and Environmental Protection, U.S. Nuclear Regulatory Commission, USA, IAEA International Expert s' Meeting on Decommissioning and Remediation after Nuclear Accident, January 28
-
February 1, 2013, Vienna, Austria, http://www
-pub.iaea.org/iaeameetings/IEM4/29Jan/Camper.pdfReferences