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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Automated Fissile Mass Estimation Python Script for the Advanced Experimental Fuel Counter (AEFC)

The Advanced Experimental Fuel Counter (AEFC) is a non-destructive assay (NDA) instrument developed to quantify the residual fissile mass in research reactor spent fuel assemblies. The system is installed in a spent fuel pool and measurements are acquired underwater. A calibration curve relates the totals and coincidence counting signal from active interrogation of the spent fuel assemblies to the fissile mass remaining in the fuel.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2011

Influence of the Density Law on Various Fissile Single Unit and Array Storage Methods

The advancement of computational technology has resulted in the wide-spread availability of powerful radiation transport Monte Carlo codes. Prevailing practices today rely heavily on Monte Carlo codes to provide the basis for assessing the reactivity of various fissile systems for nuclear criticality safety (NCS). In 1958, Weinberg and Wigner expressed their concerns on a 'deplorable trend in reactor design - the tendency to substitute a code for a theory'. Unfortunately, their concerns have largely become a reality in many modern NCS practices. lacking the time or information to understand the underlying neutron physics of the fissile system under consideration is indeed a deplorable trend. The purpose of this paper is to demonstrate that many features of criticality hand calculation methods are indeed based upon the fundamentals of the density law and that many correlations of important physics parameters can be more easily understood from such a perspective. Historically, the density law was recognized by many pioneers in the field, including during the Manhattan Project. However, it was by and large an 'oral tradition' in that bits and pieces of great physical insights of the pioneers were scattered in many earlier publications. This paper attempts to bring together some of the 'jewels' of the pioneers which might have been lost or forgotten.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2017

A Simplified Quantitative Model for Fissile Material Production from Fast Spallation Neutrons

The Accelerator Driven System (ADS) as a reactor to produce fissile material, or for partitioning & transmutation purposes, has potential as an inherently safe reactor since it can be shut down by simply turning off the accelerator. Multiple studies have focused on the intranuclear and internuclear physics involved in the spallation process for high-energy projectiles impacting high-Z targets relevant to ADS applications. To quantify spallation neutronics, and thereby fissile material production, generally requires numerical methods such as MCNP, and such calculations are specific to the geometry under consideration. This study uses published cross sections from the ENDF database and an assumed generic cylindrical geometry for the ADS target and fertile blanket to derive analytic expressions for the production of Pu-239 and U-233, without needing to run MCNP codes, yet matching published data.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Unmaking the Bomb: A Fissile Material Approach to Nuclear Disarmament and Nonproliferation

Achieving nuclear disarmament, stopping nuclear proliferation, and preventing nuclear terrorism are among the most critical challenges facing the world today. Unmaking the Bomb proposes a new approach to reaching these long-held goals. Rather than considering them as separate issues, the authors—physicists and experts on nuclear security—argue that all three of these goals can be understood and realized together if we focus on the production, stockpiling, and disposal of plutonium and highly enriched uranium—the fissile materials that are the key ingredients used to make nuclear weapons. The authors describe the history, production, national stockpiles, and current military and civilian uses of plutonium and highly enriched uranium, and propose policies aimed at reducing and eventually eliminating these fissile materials worldwide. These include an end to the production of highly enriched uranium and plutonium for weapons, an end to their use as reactor fuels, and the verified elimination of all national stockpiles.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2012

Impact of delayed neutron precursor mobility in fissile solution systems

A research version of the Monte Carlo software package MCNP6 is modified to incorporate advection and diffusion of delayed neutron precursors, resulting in the emission of delayed neutrons at locations different from the original fission sites. Results of two test problems, a pipe carrying flowing fissile solution and a sphere of fissile solution with precursor diffusion, show that the fission product mobility tends to perturb the fundamental mode, has a negative reactivity effect, and, perhaps most importantly, causes a decrease in the effective delayed neutron fraction. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2013

Repackaging of High Fissile TRU Waste at the Transuranic Waste Processing Center - 13240

Twenty-six drums of high fissile transuranic (TRU) waste from Oak Ridge National Laboratory (ORNL) operations were declared waste in the mid-1980's and placed in storage with the legacy TRU waste inventory for future treatment and disposal at the Waste Isolation Pilot Plant (WIPP). Repackaging and treatment of the waste at the TRU Waste Packaging Center (TWPC) will require the installation of additional equipment and capabilities to address the hazards for handling and repackaging the waste compared to typical Contact Handled (CH) TRU waste that is processed at the TWPC, including potential hydrogen accumulation in legacy 6M/2R packaging configurations, potential presence of reactive plutonium hydrides, and significant low energy gamma radiation dose rates. All of the waste is anticipated to be repackaged at the TWPC and certified for disposal at WIPP. The waste is currently packaged in multiple layers of containers which presents additional challenges for repackaging activities due to the potential for the accumulation of hydrogen gas in the container headspace in quantities than could exceed the Lower Flammability Limit (LFL). The outer container for each waste package is a stainless steel 0.21 m{sup 3} (55-gal) drum which contains either a 0.04 m{sup 3} or 0.06 m{sup 3} (10-gal or 15-gal) 6M drum. The inner 2R container in each 6M drum is ∼12 cm (5 in) outside diameter x 30-36 cm (12-14 in) long and is considered to be a > 4 liter sealed container relative to TRU waste packaging criteria. Inside the 2R containers are multiple configurations of food pack cans, pipe nipples, and welded capsules. The waste contains significant quantities of high burn-up plutonium oxides and metals with a heavy weight percentage of higher atomic mass isotopes and the subsequent in-growth of significant quantities of americium. Significant low energy gamma radiation is expected to be present due to the americium in-growth. Radiation dose rates on inner containers are estimated to be 1-3 mSv/hr (100-300 mrem/hr) with an unshielded dose rate on the waste itself of over 10 mSv/hr (1 rem/hr). Additional equipment to be installed at the TWPC will include a new perma-con enclosure and a shielded/inert glovebox in the process building to repackage and stabilize the waste. All of the waste will be repackaged into Standard Pipe Overpacks. Most of the waste (21 of the 26 drums) is expected to be repackaged at the food-pack can level (i.e. the food-pack cans will not be opened). Five of the incoming waste containers are expected to be repackaged at the primary waste level. Three of the containers exceed the 200 gram Pu-239 Fissile Gram Equivalent (FGE) limit for the Standard Pipe Overpack. These three containers will be repackaged down to the primary waste level and divided into eight Standard Pipe Overpacks for shipment to WIPP. Two containers must be stabilized to eliminate any reactive plutonium hydrides that may be present. These containers will be opened in the inert, shielded glovebox, and the remaining corroded plutonium metal converted to a stable oxide form by using a 600 deg. C tube furnace with controlled oxygen feed in a helium carrier gas. The stabilized waste will then be packaged into two Standard Pipe Overpacks. Design and build out activities for the additional repackaging capabilities at the TWPC are scheduled to begin in Fiscal Year 2013 with repackaging, stabilization, and certification activities scheduled to begin in Fiscal Year 2014. Following repackaging and stabilization activities, the Standard Pipe Overpacks will be certified for disposal at WIPP utilizing Non-Destructive Examination (NDE) to verify the absence of prohibited items and Non-Destructive Assay (NDA) to verify the isotopic content under the TWPC WIPP certification program implemented by the Central Characterization Project (CCP). (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

First Industrial Tests of a Drum Monitor Matrix Correction for the Fissile Mass Measurement in Large Volume Historic Metallic Residues with the Differential Die-away Technique

The fissile mass in radioactive waste drums filled with compacted metallic residues (spent fuel hulls and nozzles) produced at AREVA La Hague reprocessing plant is measured by neutron interrogation with the Differential Die-away measurement Technique (DDT. In the next years, old hulls and nozzles mixed with Ion-Exchange Resins will be measured. The ion-exchange resins increase neutron moderation in the matrix, compared to the waste measured in the current process. In this context, the Nuclear Measurement Laboratory (NML) of CEA Cadarache has studied a matrix effect correction method, based on a drum monitor ({sup 3}He proportional counter inside the measurement cavity). A previous study performed with the NML R and D measurement cell PROMETHEE 6 has shown the feasibility of method, and the capability of MCNP simulations to correctly reproduce experimental data and to assess the performances of the proposed correction. A next step of the study has focused on the performance assessment of the method on the industrial station using numerical simulation. A correlation between the prompt calibration coefficient of the {sup 239}Pu signal and the drum monitor signal was established using the MCNPX computer code and a fractional factorial experimental design composed of matrix parameters representative of the variation range of historical waste. Calculations have showed that the method allows the assay of the fissile mass with an uncertainty within a factor of 2, while the matrix effect without correction ranges on 2 decades. In this paper, we present and discuss the first experimental tests on the industrial ACC measurement system. A calculation vs. experiment benchmark has been achieved by performing dedicated calibration measurement with a representative drum and {sup 235}U samples. The preliminary comparison between calculation and experiment shows a satisfactory agreement for the drum monitor. The final objective of this work is to confirm the reliability of the modeling approach and the industrial feasibility of the method, which will be implemented on the industrial station for the measurement of historical wastes. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Point kinetics and coupled neutron transport - CFD modeling of criticality excursions in fissile solutions - 14584

The UK version of the CRITEX code is used to analyze criticality transients in Uranyl nitrate fissile solutions in the TRACY experimental facility. The CRITEX model consists of a point kinetics model of neutronic behavior coupled to a 1D thermal hydraulic model of a cylindrical system. The model is found to estimate the magnitude of the first power peak well. It is also found to be capable of representing subsequent oscillations if the bubble rise speed is suitably adjusted. The need to adjust the rise speed prevents the code from having a fully predictive capability, however with appropriate benchmarking the code is a useful tool for parametric studies. Imperial College's FETCH code consists of a coupling of the EVENT transient radiation transport code to the FLUIDITY CFD code. The EVENT code is an even parity Pn code for transient neutron and photon transport. The FLUIDITY code is a CFD code capable of handling multi-phase fluid flows in 2D and 3D. This includes modeling of the nucleation, growth and transport of radiolytic gas bubbles. The FETCH code is used to model axisymmetric transients in fissile solutions in the TRACY experimental facility. The use of a 2D CFD calculation allows inhomogeneous phenomena to be studied. The power is found to be deposited heterogeneously in the fluid, resulting in an inhomogeneous distribution of radiolytic gas bubbles, which is subsequently homogenized by natural convection. The mechanistic modeling in the FETCH code holds the promise of a fully predictive capability for criticality excursion analysis, based on the modeling of bubble nucleation, growth and advection by the liquid. Further development of the modeling is required and this is discussed in the paper. The multi-dimensional analysis provides important insights into the transient behavior. (authors)

42 ENGINEERING↗
DOE OSTI2015

Stability of fissile solution systems - 14614

A Dynamic System Simulation (DSS) has been developed for aqueous homogenous reactors (AHR) and subcritical accelerator-driven system employing fissile solution fuel. These models are comprised of coupled non-linear differential equations describing the neutronics, thermal hydraulic and radiolytic gas behavior in the time domain. Models of specific historic AHR, SUPO (Super Power), KEWB (Kinetics Experiment Water Boiler), and SILENE exhibit close agreement with experimental data in all operating modes including steady-state, ramp and step reactivity insertions. The set of non-linear equations have been utilized to generate a generic transfer function for this class of systems. Output from specific DSS models operating at steady-state is then utilized as input parameters into a transfer function specific to each. Traditional Bode amplitude and phase, Nyquist and Nichols plots, are then generated to examine stability. Results for SUPO and a generic accelerator-driven system suggest these systems are unconditionally stable in the linear approximation. This treatment offers a method to examine the physics and time-based evolution of a critical excursion in a fissile solution system and provides a means to examine the severity of the consequence. This approach provides insight into the characteristics of such and even and sensitivity to materials involved and configuration of the physical system. (authors)

42 ENGINEERING↗
DOE OSTI2013

Experimental spectrum of reactor antineutrinos and spectra of main fissile isotopes

Within the period between the years 1988 and 1990, the spectrum of positrons from the inverse-beta-decay reaction on a proton was measured at the Rovno atomic power plant in the course of experiments conducted there. The measured spectrum has the vastest statistics in relation to other neutrino experiments at nuclear reactors and the lowest threshold for positron detection. An experimental reactor-antineutrino spectrum was obtained on the basis of this positron spectrum and was recommended as a reference spectrum. The spectra of individual fissile isotopes were singled out from the measured antineutrino spectrum. These spectra can be used to analyze neutrino experiments performed at nuclear reactors for various compositions of the fuel in the reactor core.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2016

Effect of transverse vibrations of fissile nuclei on the angular and spin distributions of low-energy fission fragments

It is shown that A. Bohr’s classic theory of angular distributions of fragments originating from low-energy fission should be supplemented with quantum corrections based on the involvement of a superposition of a very large number of angular momenta L{sub m} in the description of the relative motion of fragments flying apart along the straight line coincidentwith the symmetry axis. It is revealed that quantum zero-point wriggling-type vibrations of the fissile system in the vicinity of its scission point are a source of these angular momenta and of high fragment spins observed experimentally.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Variants of Regenerated Fissile Materials Usage in Thermal Reactors as the First Stage of Fuel Cycle Closing

At present, 240 000 t of spent nuclear fuel (SF) has been accumulated in the world. Its long-term storage should meet safety conditions and requires noticeable finances, which grow every year. Obviously, this situation cannot exist for a long time; in the end, it will require a final decision. At present, several variants of solution of the problem of SF management are considered. Since most of the operating reactors and those under construction are thermal reactors, it is reasonable to assume that the structure of the nuclear power industry in the near and medium-term future will be unchanged, and it will be necessary to utilize plutonium in thermal reactors. In this study, different strategies of SF management are compared: open fuel cycle with long-term SF storage, closed fuel cycle with MOX fuel usage in thermal reactors and subsequent long-term storage of SF from MOX fuel, and closed fuel cycle in thermal reactors with heterogeneous fuel arrangement. The concept of heterogeneous fuel arrangement is considered in detail. While in the case of traditional fuel it is necessary to reprocess the whole amount of spent fuel, in the case of heterogeneous arrangement, it is possible to separate plutonium and {sup 238}U in different fuel rods. In this case, it is possible to achieve nearly complete burning of fissile isotopes of plutonium in fuel rods loaded with plutonium. These fuel rods with burned plutonium can be buried after cooling without reprocessing. They would contain just several percent of initially loaded plutonium, mainly even isotopes. Fuel rods with {sup 238}U alone should be reprocessed in the usual way.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2012

Fate of fissile material bound to monosodium titanate during cooper catalyzed peroxide oxidation of tank 48h waste

At the Savannah River Site (SRS), Tank 48H currently holds approximately 240,000 gallons of slurry which contains potassium and cesium tetraphenylborate (TPB). A copper catalyzed peroxide oxidation (CCPO) reaction is currently being examined as a method for destroying the TPB present in Tank 48H. Part of the development of that process includes an examination of the fate of the Tank 48H fissile material which is adsorbed onto monosodium titanate (MST) particles.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

LANL's Role in the U.S. Fissile Material Disposition Program

The process of Fissile Material Disposition is in part a result of the Advanced Recovery and Integrated Extraction System (ARIES), which is an agreement between the U.S. and Russia to dispose of excess plutonium used to make weapons. LANL is one sight that aides in the process of dismantling, storage and repurposing of the plutonium gathered from dismantled weapons. Some uses for the repurposed plutonium is fuel for commercial nuclear reactors which will provide energy for citizens.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2015

Simulator for an Accelerator-Driven Subcritical Fissile Solution System

LANL has developed a process to generate a progressive family of system models for a fissile solution system. This family includes a dynamic system simulation comprised of coupled nonlinear differential equations describing the time evolution of the system. Neutron kinetics, radiolytic gas generation and transport, and core thermal hydraulics are included in the DSS. Extensions to explicit operation of cooling loops and radiolytic gas handling are embedded in these systems as is a stability model. The DSS may then be converted to an implementation in Visual Studio to provide a design team the ability to rapidly estimate system performance impacts from a variety of design decisions. This provides a method to assist in optimization of the system design. Once design has been generated in some detail the C++ version of the system model may then be implemented in a LabVIEW user interface to evaluate operator controls and instrumentation and operator recognition and response to off-normal events. Taken as a set of system models the DSS, Visual Studio, and LabVIEW progression provides a comprehensive set of design support tools.

42 ENGINEERING↗
DOE OSTI2021

Increased Fissile Loading Flowsheet Review

A request was made by H-Canyon Process Engineering to assess the impact of blending dissolved, neutralized Spent Nuclear Fuel (SNF) with future sludge batches and their impact on downstream processing facilities including the Concentration, Storage and Transfer Facilities (CSTF), the Salt Waste Processing Facility (SWPF), the Defense Waste Processing Facility (DWPF), Saltstone, and the Effluent Treatment Facility (ETF). The purpose of this change is to accelerate the deinventory of SNF which is currently stored in the L-Area Disassembly Basin. The addition of SNF increases the mass of fissiles in each future sludge batch, due to their high enrichment. This high enrichment has the potential to complicate the programs to eliminate criticality events in the downstream processing facilities and will increase the number of canisters produced by DWPF because of the SNF mass increase. A separate report addressed the impacts to glass. The review and subsequent calculations were based on average predicted compositions of Accelerated Basin Deinventory (ABD) slurry, average compositions for predicted future sludge batches, average past salt batches and average past recycle batches to predict the feeds that will be processed in SWPF, DWPF, Saltstone, the 2H evaporator and ETF. Each of the processes was evaluated for potential issues.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2014

Characteristics of Fissile Solution Systems

This report describes some of the characteristics of fissile solutions systems, namely: the ability of fuel to flow rapidly during operation due to thermal forces and radiolytic gas dynamics drives the physics of these systems; exhibition of high negative reactivity feedback due to fuel temperature increase and radiolytic gas generated void (both decrease fuel density); evidence of well-damped systems and bounded reactivity excursions result in bounded (new) steady-state operating condition; they are very docile and slow to respond due to long neutron lifetime and high thermal inertia of the fuel (specific heat of fuel is an order of magnitude greater than solid fuels); operation requires large excess reactivity to be available ($5.00 or more); and finally they are sensitive to auxiliary systems such as cooling water, gas handling, and water makeup; small changes can have large effects due to the large feedbacks

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2014

Joint Distribution of the Neutron and Fission Numbers in a Fissile System

The equations for the PDF of the neutron number in a fissile system have been known for some time, but it is not clear what the relationship is between the number of neutrons in the system and the number of fissions that have occurred to make that neutron number come about. While the neutron number distribution can be written down independently of the fission number distribution, the converse is not true. The number of fissions that occur at a discrete point in time is a function of the number of neutrons in the system at that time, therefore if we want a probabilistic description of total fission number, we must extract it from the joint distribution of instantaneous neutron number, n, and total fission number, f. This memo describes our attempts to relate the probabilistic descriptions of these two quantities.

97 MATHEMATICS AND COMPUTING↗