(1987). Introductory Nuclear Reactor Dynamics. Nuclear Technology: Vol. 76, No. 2, pp. 311-312.

Introductory Nuclear Reactor Dynamics

On the Theory of the Bubble Chamber

On the definition of cavitation intensity

We developed a fast-neutron multiplicity counter (FNMC) based on stilbene and EJ-309 organic scintillators . The system can detect and discriminate correlated photon and neutron multiplets emitted by fission reactions. We used the system to estimate the fissile mass of uranium oxide samples in active interrogation mode at the Zero Power Physics Reactor of Idaho National Laboratory (INL). Two sets of certified reference material (CRM) samples were characterized. The U-235 enrichment of the first set is constant at 93.2 wt%, and the UO 2 mass ranges between 0.5 and 4 kg. The second set includes samples of increasing enrichment (from 20 wt% to 97 wt%) and constant UO 2 mass of 230 g. We used two AmLi sources to induce fission reactions in the samples. Despite the intense gamma-ray background of the UO 2 and interrogating sources, the system could measure induced fission neutrons emerging from the interrogated samples without additional shielding surrounding the sample and only relying on pulse shape discrimination to classify neutron and gamma-ray pulses. The overall neutron count rate and time-correlated counts are well correlated with the sample fissile mass. We also proved that CRM samples can be used to build a calibration curve to assay the U-235 mass of unknown samples of different mass, geometry and enrichment, with an average bias error of 8%, for U-235 mass higher than 390 g.

Fast-neutron multiplicity counter for active measurements of uranium oxide certified material

Spent nuclear fuel chemical reprocessing plants process several 103 kg of spent nuclear fuel, especially Pu isotopes, which present significant potential for terrorism (Note: ∼8 kg Pu constitutes a threat level quantity). This requires detecting actinides in transit, but also, to ensure they are not diverted. Present-day sensors disallow real-time monitoring leading to significantly non-optimal operations. The tensioned metastable fluid detector (TMFD) sensor technology has been developed by researchers at Purdue University in partnership with Texas A&M University, and various national laboratories (sponsored in part by several United States federal agencies and private enterprise). It is based on nano-to-macro scale interactions of radiation with molecules of fluids that are in a state of tensioned metastability. Developed are lab-scale prototypes for adapting to chemical reprocessing plants providing real-time directionality to within ∼10°–20°, with ∼90% efficiency to detect neutrons (from eV to MeV) and alpha emitting nuclides energies to within 1–5 keV recoil resolution, and sensitivities to ultra-trace levels (e.g., to 10−15 g/cc Pu). TMFD systems are robust, portable and offer 100× lower cost potential compared with present-day systems (e.g., NE-213 based neutron–gamma liquid scintillator based systems). A multi-physics design framework has been developed, and validated. This paper highlights state-of-art developments and adaptations of TMFDs for in situ, real-time monitoring of U, Pu, Am and Cm actinides from the sensitive (in the past virtually impossible to monitor) front-end wherein radioactively hot spent nuclear fuel is chopped and dissolved, to throughout the subsequent stages in a chemical nuclear fuel chemical process.

Real-time monitoring of actinides in chemical nuclear fuel reprocessing plants

Neutron-induced cavitation tension metastable pressure thresholds of liquid mixtures

Tension metastable fluid detection systems for special nuclear material detection and monitoring

Transformational nuclear particle sensor systems have been developed for detecting a variety of radiation types via interactions with ordinary fluids such as water and acetone placed under metastable states of tensioned (yes, sub-zero or below-vacuum) liquid pressures at room temperature. Advancements have resulted in the development of lab-scale prototypes which provide real-time directionality information to within 10 degrees of a neutron emitting weapons of mass destruction (WMD) source, with over 90% intrinsic efficiency, with ability to decipher multiplicity and to detect WMD-shielded neutrons in the 0.01 eV range, to unshielded neutrons in the 1–10 MeV range, and with the ability to detect alpha emitting special nuclear material (SNM) signatures to within 1–5 keV in energy resolution, and detection sensitivities to ultratrace levels (i.e., to femto-grams per cc of SNMs such as Pu, and Am). The tension metastable fluid detector (TMFD) systems are robust, and are built in the laboratory with costs in the ∼$100+ range — with inherent gamma blindness capability. A multi-physics design framework (including nuclear particle transport, acoustics, structural dynamics, fluid-heat transfer, and electro-magnetics), has also been developed, and validated.

Transformational nuclear sensors — Real-time monitoring of WMDs, risk assessment & response

A directional-position sensing fast neutron sensor utilizing the acoustic tensioned metastable fluid detector (ATMFD) is described. This ATMFD system enables the determination of directionality of incoming neutron radiation with a single detector, and is developed based on a combination of experimentation and theoretical assessments. Benchmarking and qualifications studies conducted with a 1 Ci Pu–Be neutron source produced encouraging results. These results indicated that the ATMFD is not only comparable in technical performance with competing directional fast neutron detector-bank technologies under development worldwide, but it promised to do so with a single detector and at a significant reduction in both cost and size while remaining completely blind to nonneutron background radiation. Applications to neutron source spatial imaging and standoff detection with the ATMFD system are also presented. The ATMFD was found to successfully locate a hidden neutron source in a blind test. Assessments for practically relevant situations were conducted and it was revealed that an ATMFD system (with a 6 cm×10 cm cross-sectional area) could offer directionality on incoming neutron radiation from a 8 kg Pu source at 25 m standoff, with a resolution of 11.2°, with 68% confidence within 60 s. Position and neutron source image sensing capability were also demonstrated using two ATMFDs.

Jeffrey A. Webster

Papers

Real-time monitoring of actinides in chemical nuclear fuel reprocessing plants

Neutron-induced cavitation tension metastable pressure thresholds of liquid mixtures

Tension metastable fluid detection systems for special nuclear material detection and monitoring

Transformational nuclear sensors — Real-time monitoring of WMDs, risk assessment & response

Development of a novel direction-position sensing fast neutron detector using tensioned metastable fluids