Bryan L. Fearey

Operator declaration verification technique for spent fuel at reprocessing facilities

Abstract A verification technique for use at reprocessing facilities, which integrates existing technologies to strengthen safeguards through the use of environmental monitoring, has been developed at Los Alamos National Laboratory. This technique involves the measurement of isotopic ratios of stable noble fission gases from on-stack emissions during reprocessing of spent fuel using high-precision mass spectrometry. These results are then compared to a database of calculated isotopic ratios using a data analysis method to determine specific fuel parameters (e.g., burnup, fuel type, reactor type, etc.). These inferred parameters can be used to verify operator declarations. The integrated system (mass spectrometry, reactor modeling, and data analysis) has been validated using on-stack measurements during reprocessing of fuel from a US production reactor. These measurements led to an inferred burnup that matched the declared burnup to within 3.9%, suggesting that the current system is sufficient for most safeguards applications. Partial system validation using gas samples from literature measurements of power reactor fuel has been reported elsewhere. This has shown that the technique developed here may have some difficulty distinguishing pressurized water reactor (PWR) from boiling water reactor (BWR) fuel; however, it consistently can distinguish light water reactor (either PWR or BWR) fuels from other reactor fuel types. Future validations will include advanced power reactor fuels (such as breeder reactor fuels) and research reactor fuels as samples become available.

Resonance ionization mass spectrometry of thorium: determination of the autoionization level structure and a re-determination of the ionization potential

Abstract We report on the use of resonance ionization mass spectrometry (RIMS) for the analysis of thorium isotopes. The 238U/230Th decay pair is useful for the dating of geologic samples in the ⩽ 350 000 year range, and details are needed on the resonance ionization spectrum of thorium in order to most efficiently effect ionization. This report describes the use of a two-color, two photon ionization process for thorium near the ionization threshold. A large number of autoionizing states are observed, a new value for the ionization potential, 50 890 ± 20cm−1 (6.310 ± 0.002 eV), is reported, and electric field effects are described.

Spectroscopic study of thorium using continuous-wave resonance ionization mass spectrometry with ultraviolet ionization

Abstract This paper presents recent results on an improved method of ionization for the cw-RIMS process for thorium (Th). This method involves the application of a high power ultraviolet (UV) argon ion laser for the second step in a two-step (1+1) (photon-to-resonance plus photon-to-ionization) ionization scheme. Over 90 thorium transitions are identified for use in a (1+1) continuous-wave resonance ionization mass spectrometry (cw-RIMS) ionization scheme. The excitation cross-section of several strong transitions was determined to be 10 −13 cm 2 . The optimum cw excitation scheme was with the resonant laser tuned to the 384.08 nm (26 036 cm −1 ) transition when using the multi-line UV argon ion laser for signal enhancement. For thorium, the increase in ionization efficiency was documented to be a minimum of one order-of-magnitude improvement over that achieved by conventional thermal ionization mass spectrometry (TIMS). The measured total ionization efficiency (detected ion signal/sample atoms loaded) was as high as 0.41%, which easily provided signal levels for efficiency measurements on sample sizes down to 25 ng, and should provide sufficient signal for isotopic analysis of volcanic-like samples as small as 1–5 ng of thorium. Based on geometric overlap considerations, the cw-RIMS ionization efficiency within the laser focal volume approaches ~100%. This cw-RIMS ionization efficiency promises to provide ample signal for the 230 Th/ 232 Th isotope ratio analysis of nanogram volcanic-like samples. The ability to determine accurately and precisely the 230 Th/ 232 Th isotopic ratios for nanogram samples represents an improvement over the TIMS technique, and is anticipated to have a significant effect on uranium-series disequilibrium measurements important in geochemistry and geochronology.

Comparisons of Calculated and Measured 237Np, 241Am, and 243Am Concentrations as a Function of the 240Pu/239Pu Isotopic Ratio in Spent Fuel

The Los Alamos National Laboratory (LANL) has developed a system for determining 237 Np, 241 Am, and 243 Am concentrations in spent fuel from measurements of the 240 Pu/ 239 Pu isotopic ratio using calculations performed with the HELIOS lattice-physics code. Benchmark calculations for several pressurized water reactors (PWRs) were performed and compared to measured values from the literature for fuels with burnups ranging from 0 to 50000 MWd/tonne U. A direct correlation can be found between the 240 Pu/ 239 Pu isotopic ratio and the higher-actinide concentrations for each fuel type. Comparisons of calculated with measured values suggests that the LANL technique would yield 237 Np and 241 Am concentrations within±5% and 243 Am concentrations within ±15% for PWRs. Expanding this system for all reprocessing applications will require more measured data (especially for boiling water reactors and VVER-type reactors), but the existing results show a marked improvement over the previous ORIGEN calculations. Also, a better determination of the 243 Am concentrations may support a greater confidence in the calculated results or suggest an alteration to the existing nuclear data. The present state ofthese neutronics calculations suggests that the technology exists to reduce the need for direct measurement of the 237 Np, 241 Am, and 243 Am concentrations in spent fuel.

Noble‐gas atmospheric monitoring for international safeguards at reprocessing facilities

Environmental monitoring of nuclear activities promises to play a large role in the improvements in international safeguards under the International Atomic Energy Agencys Programme 93+2. Monitoring of stable noble‐gas (Kr, Xe) isotopic abundances at reprocessing plant stacks appears to be able to yield information on the burnup and type of the fuel being processed. To estimate the size of these signals, model calculations of the production of stable Kr and Xe nuclides in reactor fuel and the subsequent dilution of these nuclides in the plant stack are carried out for two case studies: reprocessing of PWR fuel with a burnup of 35 GWd/tU, and reprocessing of CANDU fuel with a burnup of 1 GWd/tU. For each case, a maximum‐likelihood analysis is used to determine the fuel burnup and type from the isotopic data.

An Analysis of Reduced Collateral Damage Nuclear Weapons

In the new security environment with a new U.S. defense strategy, nuclear weapons remain critical to U.S. national security as well as to international security. However, legacy nuclear systems are not optimally configured for the new and emerging contingencies of this environment. A common thread likely to run through the desirable characteristics of most future systems is reduced collateral damage (RCD). Improved accuracy enables lower yield weapons to accomplish the missions once allocated to higher yield legacy warheads, with correspondingly reduced collateral effects. Lower yield, earth-penetrating weapons and other new or modified RCD weapons can play a critical role, in conjunction with the other capabilities of the New Triad, in achieving U.S. defense objectives of deterrence, dissuasion and assurance. As the United States implements the Nuclear Posture Review, it is important to assess such capabilities in the context of U.S. defense strategy and to be in a position to develop and deploy them—if required—within the much smaller nuclear force towards which the United States is moving.

Materials analysis by laser and ion beam sputtering with resonance ionization mass spectrometry

Abstract A comparison is made between sputter (ion beam)- and laser-sampling for resonance ionization mass spectrometry (RIMS). The temporal and spatial development of the generated plumes is discussed, as well as various aspects of the multistep ionization process. Lastly, several examples are given of the application of laser-ablation/RIMS to problems in optical damage.

Effect of Laser Characteristics On Thorium Isotopic Ratios Measured By Resonance Ionization Mass Spectrometry

ABSTRACT: We describe our development of resonance ionization mass spectrometry (RIMS) using continuous-wave lasers toward the measurement of isotopic ratios important in geochemistry and geochronology. Specifically, we compare the precision and accuracy of 230Th/232Th isotopic ratios measured by cw RIMS using both broad-band and narrow-band lasers. We also discuss the effectiveness of frequency-stabilizing techniques, i.e., external frequency locking of a broad-band dye laser and computer-controlled frequency centering of a narrow-band Ti:sapphire laser.

Calculated Actinide and Fission Product Concentration Ratios for Gaseous Effluent Monitoring Using Monteburns 3.01

Techniques have been developed at Los Alamos National Laboratory for accurately calculating certain spent-fuel isotope concentration ratios for pressurized water reactor assemblies using a linked MCNP/ORIGEN2 code named Monteburns 3.01, without resorting to an assembly or full-core calculation. The effects of various fuel parameters such as the number of radial fuel regions per pin, burnup step size, reactor power, reactivity control mechanisms, and axial profiles have been studied. The significance of each factor was determined. A method was also proposed for calculating spent-fuel inventories as a function of burnup for a wide range of reactors and fuel types. It was determined that accurate calculations can be obtained using a three-dimensional, modified pin cell with seven radial fuel regions and two (flat-flux) axial fuel regions calculated with 2000 MWd/tonne U burnup steps for burnups ranging from 0 to 50 000 MWd/tonne U. The calculational technique was benchmarked to measured values from the Calvert Cliffs Unit 1 reactor, and good agreement from the point of view of calibrating a monitoring instrument was found for most cases.

Photon burst mass spectrometry: ultrasensitive detection of rare isotopes

Progress is reported on the development of a new technique for measurement of trace levels of radioisotopes which is based on fluorescence detection of output from a mass spectrometer. Significant achievements include the observation of fluorescence and burst signals from Kr isotopes, including enriched samples of 85Kr with a 4- collector system. An isotopic abundance sensitivity of about 10-8 is demonstrates with 83Kr and 85Kr.