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All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Site-Directed Research and Development Fiscal Year 2013 Annual Report

A hallmark of high-performance research and development is sustained achievement that endures. R&D organizations and laboratories have changed the course of technology and the world, and their innovations impact us for generations. At the center of the Nevada National Security Site’s (NNSS) science, technology, and engineering (ST&E) mission is the Site-Directed Research and Development Program (SDRD), which, through sustained achievement, has had an indelible impact on our mission and altered some of our most important work for the foreseeable future. The innovations created in the SDRD program have a remarkably high return on investment, and the SDRD program has helped raise the overall emphasis on the ST&E mission. In recent years the technology mission and its importance to the long-term vitality of the NNSS has been a prominent focus of National Security Technologies, LLC (NSTec). For example, NSTec created the Chief Technology Officer (CTO) position and filled it in August 2013 (see Foreword). SDRD was functionally realigned to report to the CTO concurrent with this change in leadership structure. A new corporate systems–based approach to strategic applied science and technology is starting to materialize, and expectations are that this shift of attention to technology innovation will bring about powerful outcomes for our mission and customers.

information sciences↗
DOE OSTI2019

Scale-Up of Coal-Based Supercritical CO 2 cycle technology

The Allam Cycle is a transformational technology that enables a step change in the performance, efficiency, and cost of electricity for electrical generating units by using supercritical CO 2 (sCO 2 ) as the working fluid in the turbine for power generation. The objectives of this Phase I effort were to select a host site for a large pilot system through a process of down selection, develop a conceptual design, and conduct a pre-front-end engineering design (pre-FEED) study for a sCO 2 cycle pilot plant that uses domestic coal reserves as the primary feedstock, thereby furthering technology development of the coal-based Allam Cycle. The project was divided into four main tasks: 1) Project Management and Planning; 2) Conceptual Pilot Plant Definition and Host Site Selection; 3) Preliminary Design, Cost, and Schedule Development; and 4) Commitments and Environmental Information Volume (EIV). All project management activities occurred in Task 1. Host site selection was conducted in Task 2, while conceptual design and pre-FEED activities took place under Task 3. Task 4 enhanced the project by securing commitments for the next phase of the program and completing an initial EIV. The Great Plains Synfuels Plant (GPSP) has been selected as the host site for the large-scale pilot, and its owner, Dakota Gasification Company (DGC), is a committed partner. GPSP was compared to two other host site candidates during Phase I: the existing natural gas Allam Cycle facility in La Porte, Texas, and the Energy & Environmental Research Center’s (EERC) high-bay demonstration facility in Grand Forks, North Dakota. Costs for hosting the pilot plant were estimated for each facility, and those costs are shown in Table ES-1. Based on these estimates, the DGC site was clearly shown to be the lowest cost option and was selected as the host site for the project.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2021

Laser Wavelength Shift from Splitters and Switches

The Detonation Science and Technology Group (Q-6) operates several photon Doppler velocimetry (PDV) systems as a diagnostic tool for measuring velocities in the 1–10 km/s range during high explosive (HE) detonation experiments. Q-6 uses “heterodyne” PDV systems that are produced by Traverse Solutions and Instrumentation, LLC (TS&I). These heterodyne systems combine wavelength (WL) tunable source and “reference” lasers with a WL offset of 10–100 pm from each other. Properly setting the source and reference WLs for an experiment can be critical for collecting the desired experimental data. The tunable lasers report WL readings in their control software, but these readings are based on a lookup table from a temperature reading and are not able to be calibrated. Therefore, recent test fire programs that require PDV as a diagnostic have also implemented requirements for monitoring the WL of the tunable lasers using a precision WL meter. To monitor the WL of several PDV lasers without disconnecting any patch fibers form the experimental setup, Q-6 developed a system splitters with a coupling ratio (%) of 99:1 and an optical switch with the switch output going to a single WL meter. A brief experiment was developed to determine if the splitters and/or switch introduced any WL bias into the readings. The purpose of this report is to document the system, the experiment, and its results.

42 ENGINEERING↗
DOE OSTI2023

Lessons Learned From Ventilation and Glovebox Flooding Via Overfilling of the Wet Vacuum System in a Plutonium Facility

In the summer of 2021, operations personnel requested maintenance personnel to fill a wet vacuum (Wetvac) seal water tank in a plutonium facility at Los Alamos National Laboratory (LANL). After the filling was finished, the fill valve of the Wetvac seal water tank was left open and a ‘dead-man’ valve on an isolation line failed to close properly. After a series of other failures, the water exited the glovebox and contaminated three rooms of the first floor of the facility and an underlying area in the basement. A retrospective analysis of this event determined that there was no risk of a criticality due to the inherent design features of the ventilation system. This paper will explain the driving factors behind how this event was able to happen, as well as some of the major lessons learned that can be universally applied to other nuclear facilities. One of the main causes of the event was the delegation of work to maintenance personnel that were not qualified for the work being asked of them. Additionally, there was a lack of coordination between criticality safety engineers and facility operations equipment owners regarding equipment and connections present on the seal water tanks for the Wetvac, specifically the presence of overflow drain lines. The respective criticality safety evaluation credited an overflow drain line being present on the seal water tanks that was later found to have not been present. Lastly, there are lessons to be learned regarding equipment configuration and designing systems with safety in mind.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

DistOPF: Advanced Solutions for Distribution Optimal Power Flow Analysis - DistOPF v0.2 Documentation

To achieve an affordable and reliable energy system, research on power distribution system is often focused on integration of distributed generators, energy storage solution, EV charging, smart meters, and other advanced assets that may benefit from or require more advanced control and optimization techniques. Despite this focus on advanced distribution system topics, early researchers and grid scientists often start from scratch when developing optimization programs for power distribution systems. This report introduces DistOPF, a Python package that consolidates years of research into a versatile and modular tool. DistOPF provides researchers with essential capabilities to solve distribution system Optimal Power Flow (OPF) problems using standard network models. Additionally, it offers a platform to benchmark both new and existing algorithms against established test systems.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2025

Progress Towards the Validation of a new RELAP5-3D model of the High Temperature Test Facility

Validation is a key step in the development of any type of systems model. As the next generation of reactors approaches, the need for codes that have been validated for these new types of systems continues to grow. An example of a prominent option is the Reactor Excursion Leak Analysis Program (RELAP5-3D), developed by Idaho National Laboratory. This code was developed for the purpose of systems level thermal-hydraulic modeling of light water reactors (LWRS) and postulated transients that can occur in LWRS.RELAP5-3D has been substantially validated against LWR data. Due to its long history as a reactor safety analysis tool, there has been an effort to adapt RELAP5-3D for the purposes of advanced reactor concepts such as prismatic high-temperature gas-cooled reactors (HTGRs). However, RELAP5-3D has not nearly been validated and verified for HTGRs to the degree of LWRs, warranting verification and validation opportunities with computational benchmarks and existing experimental facilities. Examples of such facilities include the modular high-temperature gas-cooled reactor (MHTGR) 350 and the high temperature engineering test reactor (HTTR) from Japan. The MHTGR 350 is a benchmark design concept for code-to-code verification purposes; therefore, it does not provide any experimental data for validation opportunities The HTTR provides useful multiphysics validation data but does not have the in-core instruments to generate thermal-hydraulic experimental data to help with RELAP5-3D validation. Consequently, a facility that could provide key in-core temperatures for thermal-hydraulic validation was still needed. The High Temperature Test Facility (HTTF) is an integral effects facility for HTGR thermal hydraulics developed and operated by Oregon State University. HTTF represents ¼ length scale of the General Atomics MHTGR and is rated for a total power of 2.2 MW. Axially, the core consists of an upper and lower reflector and 10 blocks, numbered from bottom to top (Block 1 is right above lower reflector). The core is heated via graphite resistive heater rods, with respective channels distributed throughout the core. The primary coolant is helium and heat can radiate out of the core to the reactor cavity cooling system (RCCS), which is cooled by water. The primary purpose of the facility is to investigate pressurized conduction cooldown (PCC) and depressurized conduction cooldown (DCC) transients, which are also referred to as the pressurized and depressurized loss of forced cooling respectively. Two experiments were chosen to perform the validation study with a RELAP5-3D model of HTTF. These experiments are PG-27 (PCC) and PG-29 (DCC). These were chosen based off of the quality of available experimental data before and during the experiment which led to their inclusion in the HTGR Thermal Hydraulics Benchmark.

22 - GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2019

Characterizing Regional Methane Emissions from Natural Gas Liquids Unloading

A “bottom-up” probabilistic model was developed using engineering first-principles to quantify annualized throughput normalized methane emissions (TNME) from natural gas liquid unloading activities for 18 basins in the United States in 2016. For each basin, six discrete liquid-unloading scenarios are considered, consisting of combinations of well types (conventional and unconventional) and liquid-unloading systems (nonplunger, manual plunger lift, and automatic plunger lift). While previous work has advocated that operational malfunctions and abnormal process conditions explain the existence of super-emitters in the natural gas supply chain, this work finds that super-emitters can arise naturally due to variability in underlying component processes. Additionally, average cumulative methane emissions from liquids unloading, attributed to the natural gas supply chain, across all basins are ~4.8 times higher than those inferred from the 2016 Greenhouse Gas Reporting Program (GHGRP).

Zaimes, George G.↗
DOE OSTI2015

Rigid Biopolymer Nanocrystal Systems for Controlling Multicomponent Nanoparticle Assembly and Orientation in Thin Film Solar Cells. Final Report

The focus of the proposed research is to direct the assembly of single or binary nanoparticles into meso- or macroscale three-dimensional crystals of any desired configuration and crystallographic orientation without using prohibitively expensive lithographic processes. The epitaxial nucleation of defect-free, surface-bound bulk single crystals will revolutionize technologies for energy to generate new types of solar cells that yield maximum conversion efficiencies. It has been proposed that having a nanostructured bulk hetero-interface will enable efficient charge-carrier separations, similar to organic based heterojunction cells but with potential improvements, including thermal and long-term stability, tunability of energy levels, large adsorption coefficients and carrier multiplication. However, engineering such devices requires nanoscale control and ordering in both 2- and 3-dimensions over macroscopic areas and this has yet to be achieved. In Nature, bulk organic and inorganic materials are arranged into precise and ordered programmed assemblies through the sequestration of raw materials into confined spaces and association through highly specific non-covalent interactions between biomolecules. Using similar strategies, the proposed research will focus on confining metal and semiconductor nanocrystals to pre-determined surface patterns and controlling their arrangement through tunable, orthogonal biomolecular binding. Once a perfect two-dimensional seed layer has been constructed, successive layers of single nanocrystals will be nucleated epitaxially with long-range order and tunable crystallographic orientations. The proposed research exploits the ability of biomolecules to bind specific targets in a tunable, orthogonal, multivalent, and reversible manner to the arrangements of DNA-nanoparticle conjugates on chemically defined surfaces. Through careful balance of the attractive and repulsive forces between the particles, the array, and the outside surface, it is envisioned that single or mixed nanoparticles can be packed to adopt uniform crystal orientation in two and three dimensions from simple mixing and annealing of biomolecule-nanoparticle conjugates with biomolecule-stamped surfaces. To control the crystallographic alignment of each particle with its neighbors, the nanoparticles will be assembled using a mixture of non-covalent biomolecular interactions. To create solar cells in which layers of donor and acceptor nanocrystals that are not only oriented normal to the top and bottom electrodes but are also arranged in a checkerboard pattern, multicomponent nanocrystals (e.g. CdSe, CdTe) will be conjugated with biochemical linkers such that only interactions between the CdTe and CdSe promote particle packing within the array. The proposed research will: (1) elucidate the role of single and binary cooperative particle-DNA interactions in influencing nanoparticle crystallographic orientation in two and three dimensions; (2) understand how confinement of nanoparticles on patterned arrays of biomolecules and modification of the surrounding substrate can nucleate long-range order over macroscopic areas via predefined grain boundaries; and (3) synthesize and characterize DNA conjugated semiconductor nanocrystals and assemble them into 2- and 3-D binary superlattice arrays for photovoltaics.

14 SOLAR ENERGY↗
DOE OSTI2014

Los Alamos Explosives Performance Key to Stockpile Stewardship

As the U.S. Nuclear Deterrent ages, one essential factor in making sure that the weapons will continue to perform as designed is understanding the fundamental properties of the high explosives that are part of a nuclear weapons system. As nuclear weapons go through life extension programs, some changes may be advantageous, particularly through the addition of what are known as "insensitive" high explosives that are much less likely to accidentally detonate than the already very safe "conventional" high explosives that are used in most weapons. At Los Alamos National Laboratory explosives research includes a wide variety of both large- and small-scale experiments that include small contained detonations, gas and powder gun firings, larger outdoor detonations, large-scale hydrodynamic tests, and at the Nevada Nuclear Security Site, underground sub-critical experiments.

42 ENGINEERING↗
DOE OSTI2015

Accelerating functional verification of an integrated circuit

Illustrative embodiments include a method, system, and computer program product for accelerating functional verification in simulation testing of an integrated circuit (IC). Using a processor and a memory, a serial operation is replaced with a direct register access operation, wherein the serial operation is configured to perform bit shifting operation using a register in a simulation of the IC. The serial operation is blocked from manipulating the register in the simulation of the IC. Using the register in the simulation of the IC, the direct register access operation is performed in place of the serial operation.

42 ENGINEERING↗
DOE OSTI2015

The february 2014 accidents at WIPP - 15024 (What Happened and What We Know About Why)

With almost 15 years of successful and safe operations, the WIPP facility was suddenly shutdown in February 2014 due to two unrelated accidents underground. A fire burned the front tires and engine of a salt haul truck, creating significant soot and forced evacuation of the mine. A second unrelated incident occurred 9 days later when at least one drum of non-compliant waste from Los Alamos National Laboratory burst, introducing airborne radioactivity into the underground ventilation air. Some radioactivity was released to the atmosphere at the surface. Bioassay showed that 22 workers received low internal doses, with no long-term adverse health effects expected for these employees. Independent environmental monitoring indicated very low levels off-site and dose reconstruction modeling indicated no members of the public were exposed. Comprehensive accident investigations resulted in significant planned changes to enhance safety management programs at WIPP, and a recovery plan was developed. In addition to safety management program augmentation, recovery involves new and enhanced underground ventilation systems and decontamination of affected areas underground. Resumption of initial waste disposal operations is scheduled for early in FY16, with a return to normal operations (17 shipments per week) within about three years. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Grizzly: A Multi-scale and Multi-Physics Tool to Model Aging of Nuclear Power Plant Components

Grizzly is a multi-scale multi-physics tool being developed at Idaho National Laboratory (INL) as part of the US Department of Energy's Light Water Reactor Sustainability program to provide improved safety assessments of systems, components, and structures in nuclear power plants subjected to age-related degradation. Its goal is to provide an improved scientific basis for decisions surrounding license renewal, which would permit operation of commercial nuclear power plants beyond 60 years. Grizzly is based on INL's MOOSE framework, which enables multi-physics simulations in a massively parallel computing environment. The reactor pressure vessel (RPV) has been chosen as the initial application for Grizzly. The primary concern for the RPV is that it becomes increasingly susceptible to fracture initiation at the sites of pre-existing flaws over time. This is because exposure to irradiation and high temperatures embrittles the steel. Assessing the safety of an RPV under transient conditions involves simulations at multiple scales. At the engineering scale, strongly coupled equations of heat conduction and solid mechanics are solved to simulate the global response of the RPV to accident conditions. Sub-models are used to represent regions with pre-existing flaws and the stress intensity factors are evaluated from the domain integrals. Crack propagation is then determined using a model that provides the temperature and neutron fluence dependent fracture toughness of the RPV steel. The ability of Grizzly to provide accurate engineering scale estimates of RPV safety beyond 60 years of operation strongly relies on the predictability of the embrittlement model. Multiple models for embrittlement have been proposed, and the physically based empirical model is implemented in Grizzly. However, the formation of late blooming phases greatly reduces the confidence on the extrapolated values obtained from embrittlement model, which is further exacerbated by the absence of real field data for validation. Experimentally validated lower length scale models can significantly improve the predictability of the embrittlement model beyond the calibrated range and the development of such models is another ongoing effort in Grizzly. The modeling activity in Grizzly spans across different length scales, and can be divided into: (i) Irradiation induced microstructure evolution at the atomistic and single crystal length scale using molecular dynamics, atomistic kinetic Monte-Carlo, phase-field and rate theory; (ii) Effect of the irradiation induced defects on the flow stress and fracture processes at the polycrystalline scale using crystal plasticity. Subsequently, the prediction from these models can be used to obtain irradiation induced ductile-to-brittle transition temperature (DBTT) shifts from specimen-scale simulations; (iii) Global thermo-mechanical response of the RPV under normal and accident scenarios, and probabilistic risk analyses at the engineering scale using the DBTT shifts obtained from the lower length scale models. The item (i) has been discussed in a previous report. In this extended abstract an overview of items (ii) and (iii) is provided. The extended abstract summarizes the current status of the modeling effort under Grizzly. At the engineering scale, reduced order model development is underway using the statistical tool RAVEN. This will allow probabilistic analysis considering a wide range of flaw topologies in a computationally efficient manner. Coupling the irradiation induced defect growth predictions to crystal plasticity is also in progress. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2021

The Planetary Ephemeris Program: Capability, Comparison, and Open Source Availability

We describe for the first time in scientific literature the Planetary Ephemeris Program (PEP), an open-source general-purpose astrometric data-analysis program. We discuss, in particular, the implementation of pulsar timing analysis, which was recently upgraded in PEP to handle more options. This implementation was done independently of other pulsar programs, with minor exceptions that we discuss. We illustrate the implementation of this capability by comparing the postfit residuals from the analyses of time-of-arrival observations by both PEP and Tempo2. The comparison shows substantial agreement: 22 ns rms differences for 1065 pulse time-of-arrival measurements for the millisecond pulsar in a binary system, PSR J1909-3744 (pulse period 2.947108 ms; full width half maximum of pulse 43 μs), for epochs in the interval from 2002 December to 2011 February.

42 ENGINEERING↗
DOE OSTI2020

Evaluation of Engineered Barrier Systems (FY19 Report)

This report describes research and development (R&D) activities conducted during fiscal year 2019 (FY19) specifically related to the Engineered Barrier System (EBS) R&D Work Package in the Spent Fuel and Waste Science and Technology (SFWST) Campaign supported by the United States (U.S.) Department of Eneregy (DOE). The R&D activities focus on understanding EBS component evolution and interactions within the EBS, as well as interactions between the host media and the EBS. A primary goal is to advance the development of process models that can be implemented directly within the Genreric Disposal System Analysis (GDSA) platform or that can contribute to the safety case in some manner such as building confidence, providing further insight into the processes being modeled, establishing better constraints on barrier performance, etc.The FY19 EBS activities involved not only modeling and analysis work, but experimental work as well. The report documents the FY19 progress made in seven different research areas as follows: (1) thermal analysis for the disposal of dual purpose canisters (DPCs) in sedimentary host rock using the semianalytical method, (2) tetravalent uranium solubility and speciation, (3) modeling of high temperature, thermal-hydrologic-mechanical-chemical (THMC) coupled processes, (4) integration of coupled thermalhydrologic- chemical (THC) model with GDSA using a Reduced-Order Model, (5) studying chemical controls on montmorillonite structure and swelling pressure, (6) transmission x-ray microscope for in-situ nanotomography of bentonite and shale, and (7) in-situ electrochemical testing of uranium dioxide under anoxic conditions. The R&D team consisted of subject matter experts from Sandia National Laboratories, Lawrence Berkeley National Laboratory (LBNL), Los Alamos National Laboratory (LANL), Pacific Northwest National Laboratory (PNNL), the Bureau de Recherches Géologiques et Minières (BRGM), the University of California Berkeley, and Mississippi State University. In addition, the EBS R&D work leverages international collaborations to ensure that the DOE program is active and abreast of the latest advances in nuclear waste disposal. For example, the FY19 work on modeling coupled THMC processes at high temperatures relied on the bentonite properties from the Full-scale Engineered Barrier EXperiment (FEBEX) Field Test conducted at the Grimsel Test Site in Switzerland. Overall, significant progress has been made in FY19 towards developing the modeling tools and experimental capabilities needed to investigate the performance of EBS materials and the associated interactions in the drift and the surrounding near-field environment under a variety of conditions including high temperature regimes.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2014

Methodological Aspects of Shielding and Activation Analyses for ITER Diagnostics Systems - Paper 125

It is expected that the diagnostics systems of the ITER tokamak will provide valuable measurement data about the first in its kind D-T fusion plasma with emission of 14 MeV neutrons. These systems must withstand the neutron and secondary photon radiation along the ITER operation. Under the neutron irradiation the ITER materials are getting radioactive and therefore an adequate shielding must be provided along all the time of ITER operation and shut-down for the reliable machine operation and for the safe personnel access to its components, such as the diagnostics ports. These are the prerequisites for the shielding and activation analysis of the ITER diagnostics systems discussed in this paper. This paper provides insight into the current tasks of neutronics support for the development of ITER diagnostics systems. The tasks themselves range from relatively straightforward ones such as Monte Carlo radiation transport calculations for shielding analyses of the diagnostics systems, to more advanced tasks of Shut-Down Dose Rate (SDDR) analyses for which the dedicated Rigorous 2-Step mesh-based (R2Smesh) and Direct 1-Step (D1S) methodologies were applied. The accuracy and precision of the ITER neutronics analysis is dependent on the methodological approaches and the implying modeling assumptions. In addition to the SDDR challenges, another distinguishing feature of fusion neutronics is a wide use of CAD-based neutronics modeling to design components of fusion devices such as ITER and DEMO. Basically, there are two possibilities of CAD geometry settings in Monte Carlo (MC) radiation transport models, either by the geometry format conversion of CAD models into the format of MC models by means of the interface programs such as McCad and MCAM or by the direct use of CAD geometry engine in MC calculations such as it was realized in the DAGMC code approach. Several conversion interfaces and the DAGMC software library have been tested on the 3D ITER model developed for the CAD-MCNP benchmark. It was concluded that the considered approaches have reached the maturity level to allow their application to real ITER design analyses.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

A Strategy to Conduct an Analysis of the Long-Term Performance of Low-Activity Waste Glass in a Shallow Subsurface Disposal System at Hanford

The federal facilities located on the Hanford Site in southeastern Washington State have been used extensively by the U.S. government to produce nuclear materials for the U.S. strategic defense arsenal. Currently, the Hanford Site is under the stewardship of the U.S. Department of Energy (DOE) Office of Environmental Management (EM). A large inventory of radioactive and mixed waste resulting from the production of nuclear materials has accumulated, mainly in 177 underground single- and double-shell tanks located in the central plateau of the Hanford Site (Mann et al., 2001). The DOE-EM Office of River Protection (ORP) is proceeding with plans to immobilize and permanently dispose of the low-activity waste (LAW) fraction onsite in a shallow subsurface disposal facility (the Integrated Disposal Facility [IDF]). Pacific Northwest National Laboratory (PNNL) was contracted to provide the technical basis for estimating radionuclide release from the engineered portion of the IDF (the source term) as part of an immobilized low-activity waste (ILAW) glass testing program to support future IDF performance assessments (PAs).

eSTOMP↗
DOE OSTI2023

Zirconium Scattering Sensitivity in Neutron Transport Calculations of Multiplying Systems [Slides]

This presentation touches on motivation and applications of Zirconium. Performance of evaluated libraries on double and quasi differential experiments is considered. Additionally, the performance of evaluated libraries in select ICSBEP benchmarks is considered. Provided is a detailed look in the performance of evaluated libraries in preliminary benchmark configurations for IER-516: Zirconium Test Assembly (ZTA). Conclusions and recommended experiments to satisfy Zirconium scattering nuclear data needs are presented.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Preparing MPICH for exascale

The advent of exascale supercomputers heralds a new era of scientific discovery, yet it introduces significant architectural challenges that must be overcome for MPI applications to fully exploit its potential. Among these challenges is the adoption of heterogeneous architectures, particularly the integration of GPUs to accelerate computation. Additionally, the complexity of multithreaded programming models has also become a critical factor in achieving performance at scale. The efficient utilization of hardware acceleration for communication, provided by modern NICs, is also essential for achieving low latency and high throughput communication in such complex systems. In response to these challenges, the MPICH library, a high-performance and widely used Message Passing Interface (MPI) implementation, has undergone significant enhancements. Here, this paper presents four major contributions that prepare MPICH for the exascale transition. First, we describe a lightweight communication stack that leverages the advanced features of modern NICs to maximize hardware acceleration. Second, our work showcases a highly scalable multithreaded communication model that addresses the complexities of concurrent environments. Third, we introduce GPU-aware communication capabilities that optimize data movement in GPU-integrated systems. Finally, we present a new datatype engine aimed at accelerating the use of MPI derived datatypes on GPUs. These improvements in the MPICH library not only address the immediate needs of exascale computing architectures but also set a foundation for exploiting future innovations in high-performance computing. By embracing these new designs and approaches, MPICH-derived libraries from HPE Cray and Intel were able to achieve real exascale performance on OLCF Frontier and ALCF Aurora respectively.

Guo, Yanfei [Argonne National Laboratory (ANL), Ar↗