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Title: Pebble Fuel Handling and Reactivity Control for Salt-Cooled High Temperature Reactors

This report documents the work completed on the X-PREX facility under NEUP Project 11- 3172. This project seeks to demonstrate the viability of pebble fuel handling and reactivity control for fluoride salt-cooled high-temperature reactors (FHRs). The research results also improve the understanding of pebble motion in helium-cooled reactors, as well as the general, fundamental understanding of low-velocity granular flows. Successful use of pebble fuels in with salt coolants would bring major benefits for high-temperature reactor technology. Pebble fuels enable on-line refueling and operation with low excess reactivity, and thus simpler reactivity control and improved fuel utilization. If fixed fuel designs are used, the power density of salt- cooled reactors is limited to 10 MW/m3 to obtain adequate duration between refueling, but pebble fuels allow power densities in the range of 20 to 30 MW/m3. This can be compared to the typical modular helium reactor power density of 5 MW/m3. Pebble fuels also permit radial zoning in annular cores and use of thorium or graphite pebble blankets to reduce neutron fluences to outer radial reflectors and increase total power production. Combined with high power conversion efficiency, compact low-pressure primary and containment systems, and unique safety characteristics including very large thermal marginsmore » (>500°C) to fuel damage during transients and accidents, salt-cooled pebble fuel cores offer the potential to meet the major goals of the Advanced Reactor Concepts Development program to provide electricity at lower cost than light water reactors with improved safety and system performance.This report presents the facility description, experimental results, and supporting simulation methods of the new X-Ray Pebble Recirculation Experiment (X-PREX), which is now operational and being used to collect data on the behavior of slow dense granular flows relevant to pebble bed reactor core designs. The X-PREX facility uses novel digital x-ray tomography methods to track both the translational and rotational motion of spherical pebbles, which provides unique experimental results that can be used to validate discrete element method (DEM) simulations of pebble motion. The validation effort supported by the X-PREX facility provides a means to build confidence in analysis of pebble bed configuration and residence time distributions that impact the neutronics, thermal hydraulics, and safety analysis of pebble bed reactor cores. Experimental and DEM simulation results are reported for silo drainage, a classical problem in the granular flow literature, at several hopper angles. These studies include conventional converging and novel diverging geometries that provide additional flexibility in the design of pebble bed reactor cores. Excellent agreement is found between the X-PREX experimental and DEM simulation results. This report also includes results for additional studies relevant to the design and analysis of pebble bed reactor cores including the study of forces on shut down blades inserted directly into a packed bed and pebble flow in a cylindrical hopper that is representative of a small test reactor.« less
Authors:
 [1] ;  [1]
  1. Univ. of California, Berkeley, CA (United States). Dept. of Nuclear Engineering
Publication Date:
OSTI Identifier:
1179799
Report Number(s):
DOE/NEUP--11-3172
11-3172; TRN: US1500400
DOE Contract Number:
AC07-05ID14517
Resource Type:
Technical Report
Research Org:
Univ. of California, Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Nuclear Energy (NE). Nuclear Energy University Programs (NEUP)
Country of Publication:
United States
Language:
English
Subject:
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; PEBBLE BED REACTORS; TEMPERATURE RANGE 0400-1000 K; NUCLEAR FUELS; SAFETY ANALYSIS; X RADIATION; REACTIVITY; THERMAL HYDRAULICS; HELIUM COOLED REACTORS; SOLIDS FLOW; CONTROL; DESIGN; GRAPHITE; COMPUTERIZED SIMULATION; THORIUM; POWER DENSITY; TEST REACTORS; FLUORIDES; COMPARATIVE EVALUATIONS; TOMOGRAPHY; VALIDATION; NEUTRON FLUENCE; PACKED BEDS; POWER GENERATION; REACTOR TECHNOLOGY; RESIDENCE HALF-TIME; REACTOR ACCIDENTS; CONVERSION; DAMAGE; DRAINAGE; EFFICIENCY; OPERATION; PERFORMANCE; TRANSIENTS; MOLTEN SALT COOLED REACTORS; REACTOR CORES; MOTION