Particle blockage and flow degradation in Savannah River Site reactor fuel/target assemblies

G. T. Geiger, I. K. Paik, D. C. Patterson, D. C. Smith, D. J. Foti

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

Abstract

Cooling of fuel-target assemblies in Savannah River Site reactors is provided by the downflow of process cooling water through the concentric, annular channels formed by fuel and target rings. Process cooling water is supplied to the assembly channels via a plenum through narrow slots and small holes. During a Loss of Fuel Accident (LOFA), melted material may be transported to the plenum and partially block the flow to an assembly. This flow blockage may lead to a Flow Instability (FI) within the assembly and with the cascading effect of additional melting. A two-part investigation was conducted to study the impact of melted fuel-target material on the flow in another assembly. A statistically-based, analytical approach was used to determine the probability of sufficient flow blockage of the slots and holes. Briefly, the amount of melted mass reaching the plenum was determined via filtering considerations within the process water piping while the concentration of entrained particles was determined via sediment transport theory. Geometrical considerations describe conditions required for pluggage of a single hole while statistical arguments were made for the probability for pluggage with the given flow conditions. This analysis was extended to the multi-holed geometry of the assemblies in the plenum by use of a binomial distribution of probabilities calculated for one hole. Finally, an estimate was made of the minimum number of holes that must remain open to avoid FI. To confirm the validity of the analytical predictions, an experiment was conducted at the Savannah River Laboratory. The apparatus consisted of a full-scale fuel-target assembly (about 20 ft. long, 4-inch diameter), a plenum model with prototypic holes and slots and geometrically prototypic neighbors, and a particle injection system. Aluminum spheres, disks, and fines, ranging in size from 1/12-inch to 1/4-inch, comprised the particle debris and were injected using an air-actuated valve. Instrumentation was centered around pressure and particle mass measurements and video recordings. Pressure measurements were used to determine 1) the water flow rate through the system (nominally 370 gpm) and 2) the extent of pluggage at various parts within the apparatus. A particle collection system was established to determine the locations within the apparatus in which particles were lodged. Visual observations in the otherwise closed system were made via a fiberscope and recorded on video tape. The test procedure consisted of establishing the desired water flow in the system, activating the automatic data acquisition system, and injecting the particles. Following the collection of pressure data, the fiberscope was inserted into the system to visually evaluate the extent of particle pluggage. Finally, if most of the particles were not captured by the particle collection system, the assembly was disassembled to find the remaining particles. The results demonstrated that flow degradation sufficient for FI was not probable with the conservative parameters used in the study. The statistical formulation resulted in a probability distribution for the number of blocked holes to be expected and showed that the probability of blockage sufficient for FI is vanishingly small. Experimentally, even with twice the mass of particulates injected than would be expected during a LOFA, no significant flow blockage was observed.

Original languageEnglish
Title of host publicationThermal Hydraulics of Advanced and Special Purpose Reactors
PublisherPubl by ASME
Pages71-77
Number of pages7
ISBN (Print)0791807991
StatePublished - 1992
Externally publishedYes
EventWinter Annual Meeting of the American Society of Mechanical Engineers - Anaheim, CA, USA
Duration: Nov 8 1992Nov 13 1992

Publication series

NameAmerican Society of Mechanical Engineers, Heat Transfer Division, (Publication) HTD
Volume209
ISSN (Print)0272-5673

Conference

ConferenceWinter Annual Meeting of the American Society of Mechanical Engineers
CityAnaheim, CA, USA
Period11/8/9211/13/92

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