Missile Range Fast Burst Reactor Research Articles

Neutron calorimeter development at fission and fusion pulsed neutron sources

A neutron calorimeter fielded in pulsed neutron irradiation experiments at the National Ignition Facility (NIF) and White Sands Missile Range Fast Burst Reactor (WSMR FBR) is described, and results are provided and discussed. The calorimeter is modular in design to allow fielding of various neutron absorber materials and thicknesses, as well as use at both fission and fusion sources, all of which has been done. Neutron calorimeters designed for fission sources have been fielded at fusion sources as well, but these instances are not documented in available literature—making this work novel. The functional calorimeter consists of a neutron absorber and two sheathed, grounded thermocouples secured within a subassembly made of thermally insulating materials. This subassembly is placed into a sealed vessel for material and facility safety considerations. The device was fielded at NIF in four polar-direct-drive exploding pusher shots and eleven WSMR FBR pulses. Calorimeter data from NIF experiments show a discernable thermal response accredited to neutron heating within the first 10 s, but the data are dominated by noise from ambient X-ray heating after time = 10 s post-pulse. This response is highly consistent between shots and linearly related to incident neutron fluence and neutron absorber thickness. A temperature rise of 1.1E−2 K/(1013 neutrons/cm2) per millimeter of absorber thickness was determined for both 0.4 mm and 1 mm thick depleted uranium absorbers with linear best fit R2 of 0.97 and 0.98 for each thickness and y-axis offsets of 8.8E−3 and 1.3E−2, respectively. WSMR FBR experiment data show a temperature rise of 6.2E−2 K/(1013 neutrons/cm2) with linear best fit R2 of 0.14 and y-axis offset of 7.6E−3 for a calorimeter with a 1 mm thick enriched boron carbide (10B4C) absorber, though it must be noted that device-to-device variability is significant at both facilities. These data are also affected by noise on a similar timescale as at NIF, though the noise is significantly lesser in magnitude but oscillatory.

Test simulation of neutron damage to electronic components using accelerator facilities

The purpose of this work is to demonstrate equivalent bipolar transistor damage response to neutrons and silicon ions. We report on irradiation tests performed at the White Sands Missile Range Fast Burst Reactor, the Sandia National Laboratories (SNL) Annular Core Research Reactor, the SNL SPHINX accelerator, and the SNL Ion Beam Laboratory using commercial silicon npn bipolar junction transistors (BJTs) and III–V Npn heterojunction bipolar transistors (HBTs). Late time and early time gain metrics as well as defect spectra measurements are reported.

Monte Carlo Calculations of the Neutron Environment Produced by the White Sands Missile Range Fast Burst Reactor

The Monte Carlo method is used to calculate the leakage neutron spectrum of the White Sands Missile Range Fast Burst Reactor. The leakage spectrum is then used as the source spectrum for further calculations, which are directly compared to experimental data. The calculated spectrum differs somewhat from the experimentally measured shape, particularly in the 3- to 6-MeV region. The calculated spectra have a higher spectral index (fluence > 10 keV/fluence > 3 MeV) than the experimentally determined spectra. Generally, the two methods of determining the spectra appear to be in reasonable agreement.

Measurement of the Neutron Spectrum from a Fast Pulse Reactor in the Presence of the Experimenter's Table

The measurement of the neutron spectrum from the White Sands Missile Range Fast Burst Reactor (FBR) in the presence of the experimenter's table is reported herein. A reinvestigation of this neutron spectrum was performed as a result of a recently published work, which indicates that the experimenter's table has a considerable softening effect on the neutron spectrum from the FBR. Based on such spectral parameters as average energy, integral fluence, and spectral index, we find the neutron spectrum associated with the experimenter's table to be essentially identical to the free-field leakage spectrum.

Thermal Shock Effects in Fast Burst Reactors

The thermal shock effects that occur in a fast burst reactor (FBR) during its operation are analyzed. The thermoelastic displacement equation for radial motion is solved for a reactor initially at rest and having stress-free boundaries. Numerical results are presented for the dynamic displacements and stresses that occur in the White Sands Missile Range FBR for a burst of 1.2 x 10/sup 17/ fissions, a pulse width of 39 ..mu..s with the peak power reached in 119 ..mu..s.

Fast Burst Reactor Burst Rod Adaptor Failure Analysis

Failure of a 440C stainless steel burst rod adaptor from the White Sands Missile Range Fast Burst Reactor is analyzed. The operational history of the adaptor, including nature of loading, radiation accumulation, and thermal environment, was examined. Problems associated with handling radioactive materials were overcome through careful monitoring and disposal. The chemical composition of the adaptor material was checked by x-ray and electron probe spectroscopy. The failure surface was examined and photographed at various magnifications, using optical and scanning electron microscopes. Areas of crack origin, rapid fracture, final breakoff, and abrasion from rebound are identified. Metallographic specimens were prepared, the grain structure examined, and hardness profiles obtained. The grain structure indicated the presence of microvoids and carbide segregation, and slight hardening was noted. Failure occurred at the base of a male thread in a region showing significant tool markings. Examination of the failure surface indicated crack initiation due to Stage I fatigue followed by rupture from shock overload. Recommendations to avoid similar occurrences are given.

Correlation of Radiation Damage in Solid State Devices to Neutron Spectral Characteristics

Neutron spectral characteristics from the White Sands Missile Range Fast Burst Reactor (the FBR-II) has been studied with great detail the past several years. Results from these investigations have been directed primarily toward the measurement of neutron spectra under free-field and selected perturbed environments along with their respective spectral parameters such as spectral index and average neutron energy greater than 10 KeV. The present investigation consists of the exposure of groups of 2N2222A transistors to the neutron environments previously studied and the correlation of the device damage data with the neutron spectral parameters. Three of the test configurations were essentially free-field neutron environments. The neutron spectra and spectral parameters were identical for each of the three tests leading to the speculation that identical damages from the 2N2222A's should be observed. The measured damage from these devices corroborated such a prediction. Conversely, the neutron spectra and spectral parameters for the remaining two tests indicated highly perturbed neutron environments compared to the free-field measurements and, as such, would lead one to expect device damage different from free-field. However, damage of the devices revealed an amount of radiation damage essentially equivalent to that of the free-field environment.

Neutron Spectrum Perturbations Due to Scattering Materials and Their Effect on the Average Neutron Energy, The Spectral Index, and the Hardness Parameter

Measurements have been performed on the perturbing effect of a number of scattering materials by the 'free-field' neutron leakage spectrum from a Godiva Type Critical Assembly (White Sands Missile Range Fast Burst Reactor). The results of these measurements are interpreted in relation to some of the general parameters characterizing a neutron environment, namely, the average neutron energy >10 KeV, the spectral index and the hardness parameter. Three neutron spectrum measurements have been performed, each under different experimental configurations of scattering materials. Results from these measurements show the following with relation to the spectral index: (1) The neutron environment on the core surface and at 12-inches from the core surface (free-field) yield a spectral index of 6.8, (2) The neutron environment behind a 4.75-inch Plexiglas plate yield 4.6 for the spectral index and (3) The neutron environment behind a 2-inch aluminum plate yield 6.7 for the spectral index. With relation to the hardness parameter of a neutron environment, the respective values are 1.11, 1.22 and 1.12. Other spectral parameters are 1.54 MeV, 1.89 MeV and 1.55 MeV respectively, for the average neutron energy >10 KeV. These measurements are compared to the 'free-field' neutron leakage spectrum (measured at 20-inches from the core surface) in which the average neutron energy is 1.53 MeV, the spectral index is 6.7 and the hardness parameter is 1.12.

Improved Long Pulse Ionization Simulation Using Pulsed Reactors

Recently developed methods to improve the usefulness of pulsed nuclear reactors as sources for simulation of wide pulse ionization environments, generated by weapon produced neutrons, are described. These methods include the use of a special shield material which performs the dual role of attenuating neutrons and enhancing gamma dose rate, tailoring of pulse shapes by modifying the reactor burst characteristics through selective coupling between the reactor core and special reflector configurations, and use of special shield configurations to improve dose uniformity. Data obtained at the White Sands Missile Range Fast Burst Reactor and the Sandia Corporation SPR II for several shield configurations and reactor operating conditions are presented. Gamma radiation dose rates and 1 MeV damage equivalent neutron fluences obtained with and without use of the special shield material are compared. Dose rate enhancements of 5.2 and 3.3 times free fields were achieved behind shield thicknesses of 5 and 12 in., respectively. The respective neutron fluences were reduced by factors of 5.5 and 62. A peak dose rate enhancement of 12.4 times free field was achieved between slabs of shield material. Peak dose rates of 5 × 107, 1 × 107, and 1.2 × 106 rads(Si)/sec were achieved behind the shield material for pulse widths of 52 ?sec, 100 ?sec, and 1 msec, respectively, while limiting the neutron fluence to approximately 1 × 1011 n/cm2.

Short-Term Annealing in Transistors Irradiated in the Biased-Off Mode

A set of experiments was performed at the White Sands Missile Range Fast-Burst Reactor Facility in which measurements were made of the annealing of three types of transistors (two NPN and one PNP) which were irradiated while biased off. Anneal factors as high as 5 or 6 were observed in the NPN devices when turned on tens of milliseconds after the neutron burst. The PNP device (2N2875) showed an anneal factor of nearly 4 when turned on 29 msec after the radiation pulse. The injection dependence of the annealing is clearly evident.

Technique for Obtaining Radiation Hardened Semiconductor Devices by Irradiating Wafers

Many military electronic systems are required to function during or after exposure to a nuclear radiation environment. Bipolar transistors and related integrated circuits are very sensitive to the effects of neutron damage that decrease transistor current gain and increase transistor saturation resistance. These effects may result in post-irradiation circuit failure at neutron fluences below radiation specification, particularly when ordinary neutron effect screening techniques are used. This paper describes a screening technique that assures postirradiation electrical performance of semiconductor piece parts, eliminates the problem associated with the so-called maverick or unpredictable transistor, and monitors the effects of manufacturing process changes. This technique is economically attractive when applied on a lot-to-lot basis. Nuclear radiation is an additional environment to be considered in production lot-to-lot semiconductor quality assurance. For any environment, acceptable products are determined by 100 percent screening tests to the specification level (Group A) followed by sample environmental tests (Group B) that measure the level of success of the initial screening procedure. If silicon wafers have been subjected to reactor radiation, Group A and Group B screening techniques can be used to screen semiconductor devices for radiation effects on electrical parameters. This is accomplished by irradiating and thermal annealing the in-process silicon wafers, subjecting them to Group A tests and then subjecting samples to Group B tests. The screening technique has been demonstrated practical and repeatable through use of the White Sands Missile Range Fast Burst Reactor (FBR) and the University of Arizona TRIGA Reactor.