a sequence of physical events - Three Mile Island

a representative sample of carbon removed every720 hours of filter system operation and tested in alaboratory to verify that the radioiodine removal capabilityhas not been seriously degraded. Theoperating license also exempted this section. Thecarbon did not meet the applicable requirements atinstallation in February 1978, and was not periodicallytested to verify its condition. Thus, we findthat the degraded carbon contributed to greater radioiodinereleases than would have occurred hadthe carbon filters met all NRC requirements.The fuel handling building exhaust system is theonly engineered safety feature air filtration systemat TMI-2 designed to prevent releases of radioiodineto the environment after an accident and, therefore,was the only air filtration exhaust system coveredby the TMI-2 technical specifications. Met Ed did,however, install the same grade of carbon qualifiedto the same specification in all of the TMI-2 air filtrationsystems.The filters and cleanup components for the fuelhandling and auxiliary buildings were installed andtested in place in February 1978 and were not testedor inspected thereafter. Final painting and cleanupof these buildings between February and December1978 generated significant amounts offumes and aerosols that degraded the cleanup components.The components would most likely havebeen replaced had inplace testing occurred andshown degradation of the filters. We find that thedesign and testing of these filter systems did notpermit the condition of the filters and leakagearound the filters to be identified at any time frominitial functional testing.The lack of periodic inplace testing was due to (1)the technical specification exemptions on the fuelhandling building filtration system, and (2) the lack ofrequirements for periodic inplace testing of the auxiliarybuilding filtration system, because the filtrationsystem is not considered to be an engineered safetyfeature system in the NRC licensing review process.Based upon postaccident determinations offilter carbon efficiencies, we find that radioiodinereleases were higher than those releases mighthave been with NRC requirements for periodic inplacetesting and carbon in the filter system. Wefind, also, that these radioiodine releases werehigher by approximately a factor of 5, which is estimatedfrom an analysis of expected removal efficiencieswith inplace testing (95%) versus measuredefficiencies (approximately 75% as shown in Table11-4).The reactor building air purge has a capacity of50000 cubic feet per minute. Cleanup componentsin the system are a prefilter, a HEPA filter, a 2-inch-deep carbon adsorber, and a second HEPAfilter. This filter system was not used in response tothe March 28 accident, but may be of importanceduring recovery operations when, and if, the containmentstructure is purged (see Section II.B.2.h).Liquid Radwaste System - The liquid radwastetreatment system for TMI-2 consists of equipmentand instrumentation necessary to collect, process,monitor, and recycle or dispose of radioactive liquidwastes. The system is composed of three basicsubsystems: the makeup and purification system,the miscellaneous waste system, and the industrialwaste treatment system. Prior to treatment in thesubsystems, wastes are segregated based on theirorigin, activity, and chemical composition. Treatmentis on a batch basis, after which samples areanalyzed to determine whether the waste is to beretained for further processing or discharged undercontrolled conditions to the Susquehanna River viathe blowdown system of the mechanical draft coolingtower. There were no releases of liquidradwaste by this normal discharge path during orsubsequent to the March 28 accident.The makeup and purification system, as shown inFigure 11-10, is used to maintain the quality andboron concentration of the primary coolant. Astream of the primary coolant, termed the letdown,is taken continuously from the reactor, treated, fedto the makeup tank, and ultimately returned to thereactor. The letdown can be held up in any of threereactor coolant bleed holdup tanks.The liquid radwaste treatment system treats theliquid radwaste prior to discharge to the environment.The letdown stream is a designed pathwayfor primary coolant to enter the cleanup componentsin the auxiliary building.The makeup tank, located downstream of thecleanup components, is designed to temporarily retainthe treated letdown. The makeup tank containsa manually operated vent (MU-V-13) to allow anyhydrogen overpressure to be vented. The standardoperating procedures specify an operating pressureof between 10 and 20 pounds per square inchgauge (psig). The operator vents hydrogen if thepressure is high, or adds nitrogen if the pressure islow. Since radioactive gases may be present in thevent stream, the vent is connected to the ventheader and the waste gas decay tanks. The makeupand purification system for TMI-2 is separatedfrom the TMI-1 system. Liquid radwaste generatedby operation of the makeup and purification systeminclude the letdown (when the boron concentrationis being lowered) and demineralizer regenerationwastes.The miscellaneous waste treatment system treatsthe liquid radwaste collected in the containment and347