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Research Papers

Thermo-Mechanical Safety Analyses of Preliminary Design Experiments for 238Pu Production

[+] Author and Article Information
Christopher J. Hurt

Oak Ridge National Laboratory,
Research Reactors Division,
P. O. Box 2008 MS6392,
Oak Ridge, TN 37831-6392
e-mail: hurtcj@ornl.gov

James D. Freels

Oak Ridge National Laboratory,
Research Reactors Division,
P. O. Box 2008 MS6392,
Oak Ridge, TN 37831-6392
e-mail: freelsjd@gmail.com

Prashant K. Jain

Oak Ridge National Laboratory,
Reactor and Nuclear Systems Division,
P. O. Box 2008 MS6167,
Oak Ridge, TN 37831-6167
e-mail: jainpk@ornl.gov

G. Ivan Maldonado

Department of Nuclear Engineering,
University of Tennessee,
429 Engineering and Sciences Annex,
1412 Circle Drive,
Knoxville, TN 37996-2300
e-mail: Ivan.Maldonado@utk.edu

1Corresponding author.

Manuscript received July 11, 2016; final manuscript received August 17, 2018; published online January 24, 2019. Assoc. Editor: Ralph Hill. This work is in part a work of the U.S. Government. ASME disclaims all interest in the U.S. Government's contributions.

ASME J of Nuclear Rad Sci 5(1), 011002 (Jan 24, 2019) (15 pages) Paper No: NERS-16-1069; doi: 10.1115/1.4041269 History: Received July 11, 2016; Revised August 17, 2018

Safety analyses at the high flux isotope reactor (HFIR) are required to qualify experiment targets for the production of plutonium-238 (238Pu) from neptunium dioxide/aluminum cermet (NpO2/Al) pellets. High heat generation rates (HGRs) due to fissile material and low melting temperatures require a sophisticated set of steady-state thermal simulations in order to ensure sufficient safety margins. These simulations are achieved in a fully coupled thermo-mechanical analysis using comsolmultiphysics for four different preliminary target designs using an evolving set of pre- and postirradiation data inputs, and subsequently evolving solution scopes, from the unique pellet and target designs. A new comprehensive presentation of these preliminary analyses is given and revisited analyses of the first prototypical target designs are presented to reveal the effectiveness of evolving methods and input data.

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References

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Figures

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Fig. 1

An NpO2/Al pellet (left) and target rods in target holder (right)

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Fig. 2

Simple diagram of the experiment safety review process at the HFIR

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Fig. 3

Pellet thermal expansion for varying heat-treatment temperatures as a function of temperature

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Fig. 4

General trend and contributions to pellet dimensional irradiation behavior

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Fig. 5

Partially loaded target PIE data and fitted curves for pellet shrinkage versus fission density

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Fig. 6

Example radial temperature profile taken from the fully loaded target model

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Fig. 7

Pellet heating rate versus axial position for the polynomial fits and input data at 0, 5, 10, 15, 20, and 26 days into the first cycle of the fully loaded target

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Fig. 8

Bare pellet meshes for capsule components (left) and the entire capsule (right) both for the coarse or case 3 mesh

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Fig. 9

Temperature contour (°C) of the ¼-pie splice entire bare pellet capsule (left) and the pellet domain with ×100 deformation due to thermal expansion (right) at EOC-1 for ∼28 μm cold gap SB conditions

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Fig. 10

Representation of partially loaded model target pin components

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Fig. 11

Representation of fully loaded model target pin components

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Fig. 12

Radial cut-view of prototypical target holder with seven prototypical target “pins”

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Fig. 13

Extremely coarse, extra-coarse, and fine mesh at the pellet and housing adjacent domains

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Fig. 14

The calculated limiting/allowable pellet diametrical shrinkages for a ∼5 μm fabrication gap against the measured PIE shrinkages for each pellet heat-treatment

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Fig. 15

Three-dimensional rotated temperature contour (°C) of the partially loaded target assembly (left) and temperature contour with deformation of the zoomed-in (and distorted) pellet stack/housing gas gap (right) for EOC-1 SB conditions

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Fig. 16

Three-dimensional rotated temperature contour (°C) for fully loaded target (left) and stress contour (Pa) of the hot pellet with 10,000× deformation (right) for the EOC-1 SB conditions

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Fig. 17

Calculated allowable pellet shrinkage with respect to fully loaded target temperatures along with partially loaded PIE data as a function of pellet heat generation

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Fig. 18

Pellet stack temperature profiles (°C) for day 0, 5, and 10 into the second cycle (not to scale, x-, y-axis dimensions in cm)

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Fig. 19

Pellet stack temperature profiles (°C) for day 15, 20 and 26 into the second cycle (not to scale, x-, y-axis dimensions in cm)

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Fig. 20

Mesh refinement for best estimate (primary) and cold case (no structural mechanics) models for the fully loaded target

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Fig. 21

Revised partially loaded target temperature profiles (°C) in the pellet region for EOC-1 (left) and EOC-2 (right)

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