Gas Centrifuge Enrichment Plants Research Articles

Assessing high fidelity multi-component models to facilitate safeguards at Gas Centrifuge Enrichment Plants

The International Atomic Energy Agency (IAEA) inspectors routinely carry out environmental sampling (ES) as a verification method. Collection of environmental swipe samples at various locations in Gas Centrifuge Enrichment Plants (GCEPs) is an important process in detecting misuse of a declared facility and possibly the existence of undeclared nuclear material. These samples are measured for isotopic composition in uranium containing particles by Thermal Ionization Mass Spectrometry (TIMS) or Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Even though ES is highly effective in detecting the absolute value of enrichments and their deviations from the declared values, it cannot explain the cause of those changes. Several potential explanations can serve as possibilities for particles detected above or other than the declared enrichment. These include normal and non-malicious events such as the design of the enrichment cascades, unintentional failures of the machines, or overshoot during startup of a cascade. It can also be the result of deliberate misuse by the facility operators. The primary objective of this work is to understand how these factors affect the enrichments produced by a cascade and quantify anticipated multi-isotopic concentrations for each case. The following methodology is employed to determine signatures at a particular facility.1)Utilize a new two-dimensional multi-component diffusion code to obtain centrifuge performance data and use that information to design and perform cascade analysis. Compare and contrast the results with previous 1-D radially averaged solutions from the Pancake code.2)Design a GCEP cascade with the production goal of 19.75% 235U for each set of machine data above. Investigate two cascade scenarios that include enrichment of natural uranium (NU) feed to 19.75% 235U in a single cascade compared to a two-step process of NU to 5% and then 5% to 19.75%.3)Simulate the intentional vs unintentional off-normal scenarios in the cascades to assess the differences in isotopic concentrations.A non-ideal squared-off cascade model developed at the University of Virginia is used to calculate flow rates and isotopic concentrations of the process gas. The analysis is performed using the Rome machine model operated at 600 m/s rotor speed. The upper and lower bounds of normal and abnormal enrichments in a typical facility are used in conjunction with ES results to understand the root causes of such observations.

Minor isotope safeguards techniques (MIST): Analysis and visualization of gas centrifuge enrichment plant process data using the MSTAR model

This paper presents a development related to the use of minor isotope safeguards techniques (MIST) and the MSTAR cascade model as it relates to the application of international nuclear safeguards at gas centrifuge enrichment plants (GCEPs). The product of this paper is a derivation of the universal and dimensionless MSTAR cascade model. The new model can be used to calculate the minor uranium isotope concentrations in GCEP product and tails streams or to analyze, visualize, and interpret GCEP process data as part of MIST. Applications of the new model include the detection of undeclared feed and withdrawal streams at GCEPs when used in conjunction with UF6 sampling and/or other isotopic measurement techniques.

Multi-detector system approach for unattended uranium enrichment monitoring at gas centrifuge enrichment plants

Improving the quality of safeguards measurements at Gas Centrifuge Enrichment Plants while reducing the inspection effort is an important objective given the number of existing and new plants that need to be safeguarded. A useful tool in many safeguards approaches is the on-line monitoring of enrichment in process pipes. One requirement of such a monitor is a simple, reliable and precise passive measurement of the 186-keV line from 235U. The other information required is the amount of gas in the pipe, which can be obtained by a transmission or pressure measurement. We describe our research to develop such a passive measurement system. Unfortunately, a complication arises in the interpretation of the gamma measurements, from the contribution of uranium deposits on the wall of the pipe to the 186-keV peak. A multi-detector approach to address this complication is presented where two measurements, one with signal primarily from gas and one with signal primarily from deposits, are performed simultaneously with different detectors and geometries. This allows a correction to be made to the 186-keV peak for the contribution from the deposit. We present the design of the multi-detector system and the results of the experimental calibration of the proof-of-principle prototype built at LANL.

Timely Verification at Large-Scale Gas Centrifuge Enrichment Plants

ABSTRACTThis article examines challenges in international nuclear safeguards pertaining to the timely detection of highly enriched uranium production at large-scale gas centrifuge enrichment plants. To establish where present gas centrifuge enrichment plant safeguards measures and approaches could be strengthened, we have created a discrete time model for simulating hypothetical misuse scenarios, both through transient phases and at steady-state. We find that timely detection of misuse at modern large-scale facilities presents a challenge for international safeguards. A toolbox of unattended measurement systems, along with remote monitoring, however, could be used to improve detection timeliness, enabling the initiation of follow-up activities, potentially on a rapid time scale. These measures, which would need very low false alarm rates, should be implemented in a graded approach, depending on the characteristics of each enrichment plant and an analysis of plausible acquisition paths for the State in which it is situated. Some of these technologies could provide significant benefit to plant operators.

A Game Theoretic Approach to Nuclear Safeguards Selection and Optimization

ABSTRACTThis article presents a novel application of an inspection game to find optimally efficient nuclear safeguard strategies. It describes a methodology that allocates resources at and across nuclear fuel cycle facilities for a cost-constrained inspectorate seeking to detect a state-facilitated diversion or misuse. The methodology couples a simultaneous-play game theoretic solver with a probabilistic model for simulating state violation scenarios at a gas centrifuge enrichment plant. The simulation model features a suite of defender options based on current International Atomic Energy Agency practices and an analogous menu of attacker proliferation pathway options. The simulation informs the game theoretic solver by calculating the detection probability for a given inspector-proliferator strategy pair. To generate a scenario payoff, it weights the detection probability by the quantity and quality of material obtained. Using a modified fictitious play algorithm, the game iteratively calls the simulation model until Nash equilibrium is reached and outputs the optimal inspection and proliferation strategies. The value the attacker places on material quantity and quality is varied to generate results representative of states with different capabilities and goals. Sample model results are shown to illustrate the sensitivity of defender and attacker strategy to attacker characteristics.

Advanced Enrichment Monitoring Technology Based on Transmission Measurements with an X-ray Source and NaI(Tl) Spectrometer

In this paper, we report our progress toward the development of an advanced enrichment monitoring technology for safeguarding gas centrifuge enrichment plants. We compare the ${\rm UF}_{6}$ gas pipe attenuation and sensitivity to X-ray tube HV variations for two transmission energies: 22 keV and 25.5 keV. The first experimental enrichment results taken with a static ${\rm UF}_{6}$ gaseous source and X-ray tube based transmission source over a wide gas pressure range are presented.

Monte carlo feasibility study of an active neutron assay technique for full-volume UF6 cylinder assay using a correlated interrogation source

Uranium cylinder assay plays an important role in the nuclear material accounting at gas centrifuge enrichment plants. The Passive Neutron Enrichment Meter (PNEM) was designed to determine uranium mass and enrichment in 30B and 48Y cylinders using total neutron and coincidence counting in the passive mode. 30B and 48Y cylinders are used to hold bulk UF6 feed, product, and tails at enrichment plants. In this paper, we report the results of a Monte-Carlo-based feasibility study for an active uranium cylinder assay system based on the PNEM design. There are many advantages of the active technique such as a shortened count time and a more direct measure of 235U content. The active system is based on a modified PNEM design and uses a 252Cf source as the correlated, active interrogation source. We show through comparison with a random AmLi source of equal strength how the use of a correlated driver significantly boosts the active signal and reduces the statistical uncertainty. We also discuss ways in which an active uranium cylinder assay system can be optimized to minimize background from 238U fast-neutron induced fission and direct counts from the interrogation source.

Experimental determination of the thickness of aluminum cascade pipes in the presence of UF6 gas during enrichment measurements

We present a method of determining the wall thickness of a pipe in a Gas Centrifuge Enrichment Plant (GCEP) when an empty pipe measurement is not feasible. Our method uses an X-ray tube for transmission measurements and a lanthanum bromide (LaBr3) scintillation detector on the opposite side of the pipe. Two filters, molybdenum (K-edge 20.0keV) and palladium (K-edge 24.35keV) are used to transform the bremsstrahlung spectra produced by the X-ray tube into more useful, sharply peaked, spectra. The maximum energies of the peaks are determined by the K-edges of the filters. The attenuation properties of the uranium hexafluoride (UF6) gas allow us to determine wall thickness by looking at the ratio of selected regions of interest (ROIs) of the Mo and Pd transmitted spectra. While the attenuation factor at these two transmission energies in the UF6 gas is nearly equal, attenuation in the aluminum pipe wall at these two energies differs by a factor of about 60. This difference allows measurement of attenuation in the pipe independent of attenuation in the UF6 gas. Feasibility studies were performed using analytical calculations, and filter thicknesses were optimized. In order to experimentally validate our attenuation measurement method, a UF6 source with variable enrichment and pipe thickness was built. We describe the experimental procedure used to verify our previous calculations and present recent results.

Load cell monitoring in Gas Centrifuge Enrichment Plants: Potentialities for improved safeguard verifications

This paper describes the principle of load cell monitoring in Gas Centrifuge Enrichment Plants (GCEPs) and how this technique can be implemented in order to improve nuclear safeguards in these kinds of installations. We present a few different possibilities of exploitation of the data that can be obtained by acquiring in continuous mode the weights of the cylinders in the feed and withdrawal (F/W) stations and how to derive conclusions concerning the operation of the plant (conformity or not with respect to “normal” operation). Furthermore the different diversion scenarios for GCEP are discussed and we show how mass monitoring techniques can contribute to detect each of them. Finally we resume the advantages and limitations of the technique and outline some important practical issues concerning the implementation of process monitoring in GCEP, in particular for what concerns the inspectorate/operator relationships. Load cell monitoring could play an important role in the safeguard implementation of future GCEPs.

Advanced technology for enrichment monitoring for gas centrifuge enrichment plants

We report our developments of the next generation of uranium enrichment monitoring technology for gas centrifuge enrichment plants (GCEPs). The main challenge presented by current technology is the need for periodic replacement of the short half-life (1.27 year) 109Cd transmission source. We report on a transmission source at the 22.1 keV K-edge of ruthenium based on an X-ray tube with a “notch” filter. As part of the design we have modeled the NaI detector passive shielding with the MCNP code. Some preliminary results from experiments and modeling will be presented.

Pakistan's bomb-making capacity

The gas centrifuge enrichment plant at Kahuta, Pakistan could be producing barely enough material to make one nuclear weapon per year, or as many as 12, depending on the material used and the number of working centrifuges.

Interest in Private Uranium Enrichment Resurfaces

Private enterprise once again has its eyes on uranium enrichment. Since its inception, enriching uranium in the U.S. into fuel-grade material has been—and still is—a government monopoly. Past attempts to bring private industry into the uranium enrichment business failed. But now, John W. LaFond, executive vice president of American Enrichment Co. (AEC), thinks the time and circumstances are right. AEC, a joint venture that includes Boeing, E. F. Hutton, and Ebasco, an engineering-construction company, was formed last year specifically to make a pitch for private uranium enrichment. Speaking at the recent annual conference of the Atomic Industrial Forum in Washington, D.C., LaFond said that AEC has arrived at an almost perfect juxtaposition of astrological privatization signs. He believes that, since the Department of Energy has abandoned and written off its proposed gas centrifuge enrichment plant at Portsmouth, Ohio, barriers to private entry into the business have been significantly lowered. In additi...

Air mass spectrometer leak detection using the special air leak test (SALT) cart

Air mass spectrometer leak detection is being utilized in the Gas Centrifuge Enrichment Plant as a method of rapidly localizing leaks in this extremely large and complicated maze of process piping. A SALT cart has been developed to minimize the time and problems such as long time constants, helium permeation, low pumping speeds, and large helium hoods associated with helium mass spectrometer leak detection. By using the SALT cart to positively indicate the presence of air, in conjunction with process valve manipulations, leaks can be quickly localized to specific sections of piping. This process saves time and effort which would otherwise be spent helium probing nonleaky sections. Once a leak has been localized, the SALT cart can aid in pinpointing the leak using various tracer gases. A helium mass spectrometer leak detector may also be placed in series with the SALT cart taking full advantage of the SALT’s high speed and the leak detector’s high sensitivity. Cart design will be discussed in addition to testing methods and sample results.

Concrete Bearing Capacity around Large Inserts

Concrete bearing stress test results on large embedded inserts subjected to shear failure loads are presented. Tests were performed on eight individual inserts that were cast into a prototype concrete slab reinforced similarly to the concrete floor slab in the Gas Centrifuge Enrichment Plant (GCEP) at Piketon, Ohio. Analyses were made to examine the rigidity of the insert as a beam on an elastic foundation. These analyses, which agreed with field measurements, indicate that an insert rotates as a rigid body. With this knowledge and assuming that the ACI rectangular stress block exists in front of the insert, the maximum bearing stress is computed and compared to fc′. The results indicate that the average bearing stress on the concrete at the failure load is 3.78fc′.