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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on KP(OF)2 by Materials Project

KP(OF)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. K1+ is bonded in a 8-coordinate geometry to six equivalent O2- and two F1- atoms. There are a spread of K–O bond distances ranging from 2.78–3.13 Å. There are one shorter (2.87 Å) and one longer (3.18 Å) K–F bond lengths. P5+ is bonded in a tetrahedral geometry to two equivalent O2- and two F1- atoms. Both P–O bond lengths are 1.49 Å. Both P–F bond lengths are 1.60 Å. O2- is bonded in a distorted single-bond geometry to three equivalent K1+ and one P5+ atom. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a distorted single-bond geometry to one K1+ and one P5+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one K1+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KP(HO2)2 by Materials Project

KH2PO4 crystallizes in the monoclinic P2/c space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 2-coordinate geometry to two equivalent H1+ and six O2- atoms. Both K–H bond lengths are 2.97 Å. There are a spread of K–O bond distances ranging from 2.65–3.05 Å. In the second K1+ site, K1+ is bonded to six O2- atoms to form distorted KO6 pentagonal pyramids that share corners with four equivalent PO4 tetrahedra and an edgeedge with one PO4 tetrahedra. There are a spread of K–O bond distances ranging from 2.83–2.91 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with four equivalent KO6 pentagonal pyramids. There is two shorter (1.51 Å) and two longer (1.61 Å) P–O bond length. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share an edgeedge with one KO6 pentagonal pyramid. There is two shorter (1.50 Å) and two longer (1.65 Å) P–O bond length. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a distorted single-bond geometry to one K1+ and one O2- atom. The H–O bond length is 1.01 Å. In the second H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.03 Å) and one longer (1.54 Å) H–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to two K1+, one P5+, and one H1+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one P5+, and one H1+ atom. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one P5+, and one H1+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to two K1+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KP(HO2)2 by Materials Project

KH2PO4 crystallizes in the orthorhombic P2_12_12_1 space group. The structure is three-dimensional. K1+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of K–O bond distances ranging from 2.75–2.91 Å. P5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of P–O bond distances ranging from 1.51–1.65 Å. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one K1+, one P5+, and one H1+ atom. In the second O2- site, O2- is bonded in a distorted water-like geometry to one P5+ and one H1+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent K1+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent K1+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KP(HO2)2 by Materials Project

KH2PO4 crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. K1+ is bonded in a 8-coordinate geometry to eight equivalent O2- atoms. There are four shorter (2.91 Å) and four longer (2.92 Å) K–O bond lengths. P5+ is bonded in a tetrahedral geometry to four equivalent O2- atoms. All P–O bond lengths are 1.56 Å. H1+ is bonded in a linear geometry to two equivalent O2- atoms. Both H–O bond lengths are 1.21 Å. O2- is bonded in a distorted bent 120 degrees geometry to two equivalent K1+, one P5+, and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KP(HO)2 by Materials Project

KH2PO2 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. K1+ is bonded in a 6-coordinate geometry to six equivalent O2- atoms. There are a spread of K–O bond distances ranging from 2.78–2.96 Å. P5+ is bonded in a distorted tetrahedral geometry to two equivalent H1- and two equivalent O2- atoms. Both P–H bond lengths are 1.43 Å. Both P–O bond lengths are 1.52 Å. H1- is bonded in a single-bond geometry to one P5+ atom. O2- is bonded in a distorted single-bond geometry to three equivalent K1+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KP(HO2)2 by Materials Project

KH2PO4 crystallizes in the orthorhombic Fdd2 space group. The structure is three-dimensional. K1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of K–O bond distances ranging from 2.88–3.03 Å. P5+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.53 Å) and two longer (1.60 Å) P–O bond length. H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.05 Å) and one longer (1.48 Å) H–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted water-like geometry to two equivalent K1+, one P5+, and one H1+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent K1+, one P5+, and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KP(HO2)2 by Materials Project

KH2PO4 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 2-coordinate geometry to one H1+ and nine O2- atoms. The K–H bond length is 2.93 Å. There are a spread of K–O bond distances ranging from 2.70–3.34 Å. In the second K1+ site, K1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of K–O bond distances ranging from 2.76–3.06 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of P–O bond distances ranging from 1.51–1.59 Å. In the second P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of P–O bond distances ranging from 1.51–1.61 Å. There are five inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.55 Å) H–O bond length. In the second H1+ site, H1+ is bonded in a linear geometry to one K1+ and two O2- atoms. There is one shorter (1.05 Å) and one longer (1.46 Å) H–O bond length. In the third H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.05 Å) and one longer (1.47 Å) H–O bond length. In the fourth H1+ site, H1+ is bonded in a linear geometry to two equivalent O2- atoms. Both H–O bond lengths are 1.21 Å. In the fifth H1+ site, H1+ is bonded in a linear geometry to two equivalent O2- atoms. Both H–O bond lengths are 1.21 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to two K1+, one P5+, and one H1+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to three K1+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the sixth O2- site, O2- is bonded in a trigonal planar geometry to one K1+, one P5+, and two H1+ atoms. In the seventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the eighth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KP(HO2)2 by Materials Project

KH2PO4 crystallizes in the orthorhombic C222_1 space group. The structure is three-dimensional. K1+ is bonded in a 12-coordinate geometry to two equivalent H1+ and ten O2- atoms. Both K–H bond lengths are 2.85 Å. There are a spread of K–O bond distances ranging from 2.78–3.33 Å. P5+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.55 Å) and two longer (1.56 Å) P–O bond length. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a linear geometry to two equivalent K1+ and two equivalent O2- atoms. Both H–O bond lengths are 1.21 Å. In the second H1+ site, H1+ is bonded in a linear geometry to two equivalent O2- atoms. Both H–O bond lengths are 1.20 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to three equivalent K1+, one P5+, and one H1+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent K1+, one P5+, and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KP(HO2)2 by Materials Project

KH2PO4 crystallizes in the tetragonal I-4 space group. The structure is three-dimensional. K1+ is bonded in a 8-coordinate geometry to two equivalent H1+ and six O2- atoms. There are one shorter (2.84 Å) and one longer (2.86 Å) K–H bond lengths. There are a spread of K–O bond distances ranging from 2.71–2.91 Å. P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.63 Å. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to two equivalent K1+ and one O2- atom. The H–O bond length is 0.99 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to one K1+ and one P5+ atom. In the second O2- site, O2- is bonded in a distorted single-bond geometry to three equivalent K1+ and one P5+ atom. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to two equivalent P5+ atoms. In the fourth O2- site, O2- is bonded in a water-like geometry to two equivalent K1+ and two H1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KP(HO2)2 by Materials Project

KH2PO4 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. K1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of K–O bond distances ranging from 2.75–3.36 Å. P5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of P–O bond distances ranging from 1.53–1.58 Å. There are three inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a linear geometry to two equivalent O2- atoms. Both H–O bond lengths are 1.21 Å. In the second H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.06 Å) and one longer (1.45 Å) H–O bond length. In the third H1+ site, H1+ is bonded in a linear geometry to two equivalent O2- atoms. Both H–O bond lengths are 1.20 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent K1+, one P5+, and one H1+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent K1+, one P5+, and one H1+ atom. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent K1+, one P5+, and one H1+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent K1+, one P5+, and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KP(HO2)2 by Materials Project

KH2PO4 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 1-coordinate geometry to five O2- atoms. There are a spread of K–O bond distances ranging from 2.79–3.00 Å. In the second K1+ site, K1+ is bonded in a 1-coordinate geometry to three H1+ and seven O2- atoms. There are a spread of K–H bond distances ranging from 2.83–2.96 Å. There are a spread of K–O bond distances ranging from 2.82–3.11 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of P–O bond distances ranging from 1.52–1.60 Å. In the second P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of P–O bond distances ranging from 1.52–1.59 Å. There are four inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a distorted linear geometry to one K1+ and two O2- atoms. There is one shorter (1.06 Å) and one longer (1.43 Å) H–O bond length. In the second H1+ site, H1+ is bonded in a linear geometry to one K1+ and two O2- atoms. There is one shorter (1.08 Å) and one longer (1.39 Å) H–O bond length. In the third H1+ site, H1+ is bonded in a distorted linear geometry to one K1+ and two O2- atoms. There is one shorter (1.04 Å) and one longer (1.49 Å) H–O bond length. In the fourth H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.03 Å) and one longer (1.56 Å) H–O bond length. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one K1+, one P5+, and one H1+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one K1+, one P5+, and one H1+ atom. In the third O2- site, O2- is bonded in a distorted water-like geometry to two equivalent K1+, one P5+, and one H1+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent K1+, one P5+, and one H1+ atom. In the fifth O2- site, O2- is bonded in a bent 120 degrees geometry to one P5+ and one H1+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one K1+, one P5+, and one H1+ atom. In the seventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to three K1+, one P5+, and one H1+ atom. In the eighth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KP(HO2)2 by Materials Project

KH2PO4 crystallizes in the monoclinic Cc space group. The structure is three-dimensional. there are four inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of K–O bond distances ranging from 2.77–3.07 Å. In the second K1+ site, K1+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of K–O bond distances ranging from 2.75–3.25 Å. In the third K1+ site, K1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of K–O bond distances ranging from 2.79–3.29 Å. In the fourth K1+ site, K1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of K–O bond distances ranging from 2.77–3.20 Å. There are four inequivalent P5+ sites. In the first P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.53 Å) and two longer (1.59 Å) P–O bond length. In the second P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of P–O bond distances ranging from 1.53–1.60 Å. In the third P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.53 Å) and two longer (1.59 Å) P–O bond length. In the fourth P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of P–O bond distances ranging from 1.53–1.60 Å. There are eight inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.04 Å) and one longer (1.51 Å) H–O bond length. In the second H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.05 Å) and one longer (1.48 Å) H–O bond length. In the third H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.06 Å) and one longer (1.45 Å) H–O bond length. In the fourth H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.04 Å) and one longer (1.51 Å) H–O bond length. In the fifth H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.07 Å) and one longer (1.40 Å) H–O bond length. In the sixth H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.08 Å) and one longer (1.37 Å) H–O bond length. In the seventh H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.06 Å) and one longer (1.44 Å) H–O bond length. In the eighth H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.05 Å) and one longer (1.47 Å) H–O bond length. There are sixteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the seventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the eighth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the ninth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the tenth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one K1+, one P5+, and one H1+ atom. In the eleventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the twelfth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the thirteenth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one K1+, one P5+, and one H1+ atom. In the fourteenth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the fifteenth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom. In the sixteenth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two K1+, one P5+, and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Thermochemical Modeling in Molten Fluoride Salts for Radionuclide Speciation

An important aspect of the licensing process for nuclear reactors is providing a reasonable assurance of safety to the general public. This includes modeling potential radionuclide releases from the reactor during normal operations and accident scenarios, which is known as the reactor’s source term. A new class of advanced (non-LWR) reactors are being developed which use molten salts as the coolant fluid. Because the molten salt coolant represents a credited barrier for radionuclide transport between the fuel and the environment, a necessary aspect of mechanistic source term (MST) analysis for the KP-FHR is modeling the thermochemistry of molten salts. Provided here is a review of the theory of the thermodynamic principles governing multicomponent phase equilibria, the background of molten salt thermochemistry research, and a summary of the thermochemical data relevant to the KP-FHR coolant salt, Li 2 BeF 4 , commonly referred to as “FLiBe”. A review of literature is followed by a brief introduction to methods that can be used to model the thermochemical behavior of molten salt mixtures. The methodology outlined is based on the use of a commercial thermodynamic modeling software called FactSage, which is one of only a few available softwares based on the modified quasichemical model(MQM), which is the recommended solution model for molten salts.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Predicting Volume of Distribution in Humans: Performance of In Silico Methods for a Large Set of Structurally Diverse Clinical Compounds

Volume of distribution at steady state (V D,ss ) is one of the key pharmacokinetic parameters estimated during the drug discovery process. Despite considerable efforts to predict V D,ss , accuracy and choice of prediction methods remain a challenge, with evaluations constrained to a small set (<150) of compounds. To address these issues, a series of in silico methods for predicting human V D,ss directly from structure were evaluated using a large set of clinical compounds. Machine learning (ML) models were built to predict V D,ss directly and to predict input parameters required for mechanistic and empirical V D,ss predictions. In addition, log D, fraction unbound in plasma (fup), and blood-to-plasma partition ratio (BPR) were measured on 254 compounds to estimate the impact of measured data on predictive performance of mechanistic models. Furthermore, the impact of novel methodologies such as measuring partition (Kp) in adipocytes and myocytes (n = 189) on V D,ss predictions was also investigated. In predicting V D,ss directly from chemical structures, both mechanistic and empirical scaling using a combination of predicted rat and dog V D,ss demonstrated comparable performance (62%–71% within 3-fold). The direct ML model outperformed other in silico methods (75% within 3-fold, r 2 = 0.5, AAFE = 2.2) when built from a larger data set. Scaling to human from predicted V D,ss of either rat or dog yielded poor results (<47% within 3-fold). Measured fup and BPR improved performance of mechanistic V D,ss predictions significantly (81% within 3-fold, r 2 = 0.6, AAFE = 2.0). Adipocyte intracellular Kp showed good correlation to the V D,ss but was limited in estimating the compounds with low V D,ss .

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Setup and verification of a SCALE/KENO platform for generic FHR benchmark calculations

The work presented in this article is preliminary to downstream analysis of a generic fluoride salt-cooled high-temperature reactor (gFHR) core performed by the University of Tennessee in collaboration with Kairos Power (KP). A Monte Carlo transport model of the publicly available gFHR equilibrium core is developed in SCALE/KENO with multigroup energy treatment. Several output quantities of interest are used to verify the simulations against a benchmark model developed by KP using the continuous energy Monte Carlo code Serpent 2. Good agreement is seen in flux and fission rate profiles with a maximum relative difference of 1.4% and 2.8% respectively. Furthermore, an effective multiplication factor bias of 44 pcm was observed between the two simulations. The fuel temperature reactivity coefficient calculated with SCALE is within uncertainty to the reference model. This verification acts as a publicly reproducible benchmark for the gFHR in SCALE/KENO. A simplified depletion model is also presented where a single fuel pebble is depleted to discharge burnup through the equilibrium core while the equilibrium core is assumed to be invariant. This method produces results that intercept the equilibrium core concentrations in every case, however, an interesting artifact of this particular depletion model is uncovered. The phenomenon is shown to be a fundamental feature of the differential rate equations and inspires questions about how this system behaves when the time evolution of the equilibrium core is considered. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2025

Post-Irradiation Examination on MiniFuel UCO and UO 2 TRISO Particles Irradiated in HFIR at High Power

Post-irradiation examination (PIE) of MiniFuel compacts was conducted at Oak Ridge National Laboratory (ORNL) under the Nuclear Science User Facilities project in collaboration with Kairos Power (KP) to evaluate the performance of tristructural-isotropic (TRISO) particles under high particle power and fluoride-salt-cooled high-temperature reactor (FHR)-relevant conditions. MiniFuel compacts containing low-enriched uranium oxide-uranium carbide (LEUCO), low-enriched uranium dioxide (LEUO 2 ), and natural UCO (NUCO) kernels were irradiated for four cycles at ORNL’s High Flux Isotope Reactor (HFIR) at target temperatures between 500°C and 900°C. Post irradiation, the experiment was disassembled at ORNL to recover the MiniFuel subcapsules, which were subsequently punctured to measure fission gas release. Subcapsule disassembly allowed the recovery of components of interest, such as silicon carbide (SiC) thermometry, fuel specimens, fission product sinks, and SiC spacers. The experimental irradiation temperature was confirmed by analyzing the SiC thermometry via dilatometry. PIE on the fuel specimens included gamma spectrometry and deconsolidation leach burn leach, which were complemented by imaging techniques such as x-ray computed tomography, optical microscopy, and electron microscopy. The PIE results provide insight into TRISO particle integrity, fission product retention, coating performance, and kernel migration, informing fuel qualification for application in KP’s FHR concept.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Post-Irradiation Examination on MiniFuel UCO and UO 2 TRISO Particles Irradiated in HFIR at High Power

Post-irradiation examination (PIE) of MiniFuel compacts was conducted at Oak Ridge National Laboratory (ORNL) under the Nuclear Science User Facilities project in collaboration with Kairos Power (KP) to evaluate the performance of tristructural-isotropic (TRISO) particles under high particle power and fluoride-salt-cooled high-temperature reactor (FHR)-relevant conditions. MiniFuel compacts containing low-enriched uranium oxide-uranium carbide (LEUCO), low-enriched uranium dioxide (LEUO2), and natural UCO (NUCO) kernels were irradiated for four cycles at ORNL’s High Flux Isotope Reactor (HFIR) at target temperatures between 500°C and 900°C. Post irradiation, the experiment was disassembled at ORNL to recover the MiniFuel subcapsules, which were subsequently punctured to measure fission gas release. Subcapsule disassembly allowed the recovery of components of interest, such as silicon carbide (SiC) thermometry, fuel specimens, fission product sinks, and SiC spacers. The experimental irradiation temperature was confirmed by analyzing the SiC thermometry via dilatometry. PIE on the fuel specimens included gamma spectrometry and deconsolidation leach burn leach, which were complemented by imaging techniques such as x-ray computed tomography, optical microscopy, and electron microscopy. The PIE results provide insight into TRISO particle integrity, fission product retention, coating performance, and kernel migration, informing fuel qualification for application in KP’s FHR concept.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

A two-dimensional numerical study of ion-acoustic turbulence

We investigate the linear and nonlinear evolution of the current-driven ion-acoustic instability in a collisionless plasma via two-dimensional (2-D) Vlasov–Poisson numerical simulations. We initialise the system in a stable state and gradually drive it towards instability with an imposed, weak external electric field, thus avoiding physically unrealisable super-critical initial conditions. A comprehensive analysis of the nonlinear evolution of ion-acoustic turbulence (IAT) is presented, including the detailed characteristics of the evolution of the particles’ distribution functions, (2-D) wave spectrum and the resulting anomalous resistivity. Our findings reveal the dominance of 2-D quasi-linear effects around saturation, with nonlinear effects, such as particle trapping and nonlinear frequency shifts, becoming pronounced during the later stages of the system's nonlinear evolution. Remarkably, the Kadomtsev–Petviashvili (KP) spectrum is observed immediately after the saturation of the instability. Another crucial and noteworthy result is that no steady saturated nonlinear state is ever reached: strong ion heating suppresses the instability, which implies that the anomalous resistivity associated with IAT is transient and short-lived, challenging earlier theoretical results. Towards the conclusion of the simulation, electron-acoustic waves are triggered by the formation of a double layer and strong modifications to the particle distribution induced by IAT.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗