95 research outputs found
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Overview of NWIS software
The Nuclear Weapons Identification System (NWIS) is a system that performs radiation signature measurements on objects such as nuclear weapons components. NWIS consists of a {sup 252} Cf fission source, radiation detectors and associated analog electronics, data acquisition boards, and computer running Windows NT and the application software. NWIS uses signal processing techniques to produced a radiation signature from the radiation emitted from the object. The signature can be stored and later compared to another signature to determine whether two objects are similar. A library of such signatures can be used to identify objects in closed containers as well as determine such attributes as fissile mass and it some cases enrichment. There are three executables built from the software: (1) Windows NT kernel-mode device driver; (2) data acquisition application; and (3) data analysis application. The device driver is the interface between the NWIS data acquisition boards and the remainder o f the software. The data acquisition executable is the user's tool for making an NWIS measurement; it has limited data display abilities. The data analysis executable is a user's tool for displaying an NWIS measurement, including matching it to other NWIS measurements. A users manual for the software is included
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Extrapolations to critical for systems with large inherent sources
An approach to delayed critical experiment was performed in 1981 at Pacific Northwest Laboratory with a cylindrical tank of plutonium-uranium nitrate solution. During this experiment, various methods to determine the critical height were used, including (1) extrapolation of the usual plot of inverse count rate vs. height, which estimates the delayed critical height (DCH); (2) the inverse count rate vs. height divided by count rate, which corrects somewhat for the change in inherent source size as the height changes; (3) ratio of spectral densities vs. height, which extrapolates to DCH; (4) extrapolations of prompt neutron decay constant vs. height, which extrapolates to the prompt critical height (PCH); and (5) inverse kinetics rod drop (IKRD) methods, which measure {Delta}k/k{Beta} very accurately for a particular solution height. The problem with some of the extrapolation methods is that the measured data are not linear with height, but, for lack of anything better, linear extrapolations are made. In addition to the measurements to determine the delayed critical height subcriticality measurements by the {sup 252}Cf source driven frequency analysis method were performed for a variety of subcriticality heights. This paper describes how all these methods were applied to obtain the critical height of a cylindrical tank of plutonium nitrate solution and how the subcritical neutron multiplication factor was obtained
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Calibration measurements using the ORNL fissile mass flow monitor
This paper presents a demonstration of fissile-mass-flow measurements using the Oak Ridge National Laboratory (ORNL) Fissile Mass Flow Monitor in the Paducah Gaseous Diffusion Plant (PGDP). This Flow Monitor is part of a Blend Down Monitoring System (BDMS) that will be installed in at least two Russian Federation (R.F.) blending facilities. The key objectives of the demonstration of the ORNL Flow Monitor are two: (a) demonstrate that the ORNL Flow Monitor equipment is capable of reliably monitoring the mass flow rate of {sup 235}UF{sub 6} gas, and (b) provide a demonstration of ORNL Flow Monitor system in operation with UF{sub 6} flow for a visiting R.F. delegation. These two objectives have been met by the PGDP demonstration, as presented in this paper
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Theoretical evaluation of ex-vessel monitoring for initial fuel loading of a liquid metal fast breeder reactor
Transport theory calculations were used to determine the feasibility of monitoring the fuel loading to initial criticality of the Clinch River Breeder Reactor (CRBR) with a detector in a cavity outside the reactor vessel. Such monitoring of the CRBR with an ex-vessel detector will be different from monitoring of previous LMFBRs, where in-vessel detectors were used. The feasibility of ex-vessel monitoring will depend mainly on two criteria: (1) sensitivity - will there be enough counts to obtain adequate counting statistics; and (2) interpretability - will the count rate obtained during the initial fuel loading sequence be sufficient to determine the neutron multiplication or reactivity. Satisfying these criteria will assure that the reactor can be loaded safely to initial criticality. The sensitivity criterion can be satisfied by inserting an additional neutron source (one much more intense than the inherent neutron source of the fuel subassemblies) into the core center and using ex-vessel detectors with high sensitivity, such as multiple BF/sub 3/ counters mounted in a graphite moderator block. These calculations were used to determine the intensity of the additional source required to produce adequate counting rates at the ex-vessel detectors
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Verification of Uranium Mass and Enrichments of Highly Enriched Uranium (HEU) Using the Nuclear Materials Identification System (NMIS)
This paper describes how the Nuclear Materials Identification System (NMIS), developed by the Oak Ridge National Laboratory (ORNL) and the Oak Ridge Y-12 Plant, was used to verify the mass and enrichment of hundreds of Highly Enriched Uranium (HEU) metal items in storage at the Y-12 Plant. The verifications had a relative spread of {+-}5% (3 sigma) with relative mean deviations from their declared values of +0.2% for mass and {minus}0.2% for enrichment. NMIS's capability to perform quantification of HEU enabled the Y-12 Plant to meet their nuclear material control and accountability (NMC and A) requirements. These verifications were performed in the storage vault in a very time and cost effective manner with as many as 55 verifications in one shift of operation
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Active neutron interrogation for verification of storage of weapons components at the Oak Ridge Y-12 Plant
A nuclear weapons identification system (NWIS), under development since 1984 at the Oak Ridge Y-12 Plant and presently in use there, uses active neutron interrogation with low-intensity {sup 252}Cf sources in ionization chambers to provide a timed source of fission neutrons from the spontaneous fission of {sup 252}Cf. To date, measurements have been performed on {approximately}15 different weapons systems in a variety of configurations both in and out of containers. Those systems included pits and fully assembled systems ready for deployment at the Pantex Plant in Amarillo, Texas, and weapons components at the Oak Ridge Y-12 Plant. These measurements have shown that NWIS can identify nuclear weapons and/or components; nuclear weapons/components can be distinguished from mockups where fissile material has been replaced by nonfissile material; omissions of small amounts (4%) of fissile material can be detected; changes in internal configurations can be determined; trainer parts can be identified as was demonstrated by verification of 512 containers with B33 components at the Y-12 Plant (as many as 32 in one 8-hour shift); and nonfissile components can be identified. The current NWIS activities at the Oak Ridge Y-12 Plant include: (1) further development of the system for more portability and lower power consumption, (2) collection of reference signatures for all weapons components in containers, and (3) confirmation of a particular weapons component in storage and confirmation of receipts. This paper describes the recent measurements with NWIS for a particular weapons component in storage that have resolved an Inspector General (IG`s) audit finding with regard to performance of confirmation of inventory
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Estimating Attributes of Nuclear Weapon and Other Fissile Material Configuration Using Features Of Nuclear Materials Identification Signatures
This brief describes a strategy that, when implemented, will allow the attributes, i.e., the physical properties, of nuclear weapon and other configurations of fissile material to be estimated from Nuclear Material Identification System (NMIS) signatures for arms control, treaty verification, and transparency purposes. Attributes are estimated by condensing measured NMIS signatures into ''features'' that approximately represent physical characteristics of the measurement such as gamma-ray transmission, induced fission, etc. The features are obtained from NMIS signatures to estimate quantities related to gamma and neutron transmission through the inspected item and gamma and neutron scattering and production via induced fission within the inspected item. Multivariate, i.e., multiple-feature, linear models have been successfully employed to estimate attributes, and multivariate nonlinear models are currently under investigation. Attributes estimated employing this strategy can then be examined to test the supposition that the inspected item is in fact a nuclear weapon
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Passive Nmis Measurements to Estimate Shape of Plutonium Assemblies (Slide Presentation)
The purpose of this work is to estimate shape of plutonium assemblies using new signatures acquired by passive NMIS measurements (no external source). Applications include identification of containerized regular shapes of plutonium, identification by shape without template, verification of shape for template initialization, and potential utility for estimating shape of holdup in plutonium processing facilities. To illustrate the technique and test its feasibility, laboratory measurements have been performed with californium spontaneous fission sources as a surrogate for plutonium. Advantages of the technique include the following: passive (requires no external source for plutonium measurements), stationary (no scanning of the assembly is required), penetrative (shape is estimated from neutron emissions), obscurable (spatial resolution can be deliberately degraded by changing detector size and/or timing resolution), inexpensive (majority of NMIS components are commercial products), portable (detection system is transported to the item, not vice versa). It is concluded that passive NMIS measurements can infer the mass of plutonium assemblies: NMIS correlations scale directly with spontaneous fission rate (Pu-240); NMIS correlations scale with fissile mass (Pu-239) and multiplication. New third-order correlations can estimate the shape of fission sources (Pu-240 & Pu-239) from passive measurements. Surrogate measurements of californium spontaneous fission sources have demonstrated the feasibility of this concept. Measurements of various shapes of plutonium are necessary to continue the development of this technique
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Nuclear engineering laboratory self regulated power oscillation experiments at the Health Physics Research Reactor
Self regulated power oscillation experiments with a variety of initial conditions have been performed with the ORNL Health Physics Research Reactor (HPRR) by undergraduate nuclear engineering students from The University of Tennessee for several years. These experiments demonstrate the coupling between reactor kinetics and heat transfer and show how the temperature coefficient of reactivity affects reactor behavior. A model that consists of several coupled first order nonlinear differential equations is used to calculate the temperature of the core center and surface and power as a function of time which are compared with the experimental data; also, the model is also used to study the effects of various model parameters and initial conditions on the amplitude, frequency and damping of the power and temperature oscillations. A previous paper presented some limited experimental results and demonstrated the correspondence between a simple point model and the experimental data. This paper presents the results of experiments for: (1) the initial power fixed at 9 kW with central core temperatures of 300/sup 0/F and 500/sup 0/F, annd (2) the initial central core temperature fixed at 500/sup 0/F with initial powers of 6 and 8 kW
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