Roles for process monitoring in support of nuclear materials accounting

The Next Generation Safeguards Initiative includes a process monitoring (PM) project with near-term and long-term objectives. One role for PM is to support nuclear materials accounting (NMA), particularly in cases where NMA cannot meet loss detection goals, such as at large throughput facilities. At large facilities, interim inventory verifications are frequent, perhaps every 10 days, and there is limited ability to reduce in-process inventory, which is often measured with relatively high uncertainty. Therefore, inprocess inventory can have a relatively large impact on NMA performance as measured by the standard error of the material balance. In the context of safeguarding a large aqueous reprocessing facility to recover plutonium from spent nuclear fuel, this paper describes four roles for solution monitoring (SM) as a type of PM in support of NMA. First, SM helps understand facility status at the time of interim inventory. Second, SM can provide a by-difference estimate and associated uncertainty of material holdup in process equipment that is not directly measureable but is bracketed by measurement points. Third, SM can assess the adequacy of measurement error models such as those used to quantify the uncertainty in solution volume measurements. Fourth, SM together with models of unit operations can provide an inferred or estimated book value for waste or other low-Pu-mass streams that allows tighter control limits than are possible with NMA alone

A dissolver diversion scenario illustrating the value of process monitoring

In large throughput spent nuclear fuel reprocessing plants such as the Rokkasho Reprocessing Plant (RRP) there is a low detection probability for material losses of interest to the IAEA (8 kg of Pu) using even the most optimistic near-real-time accounting (NTRA) methods currently employed. A particularly low detection probability is seen in the head end where “input” shipper declarations (via reactor burnup calculations) having relatively large uncertainties (5-10%) are compared to “output” measurements consisting of waste (leached hulls) measurements plus accountability tank measurements. Currently, a dissolver monitoring system applied by the IAEA utilizes semi-quantitative neutron assay of hull batches to detect changes in the neutron count rate that could indicate excess Pu in the leached hulls. The goal of the exercise reported in this paper is to provide an alternative dissolver process monitoring concept. The approach is to infer the completeness of spent fuel dissolution from easily- monitored process parameters. To provide a framework, a scenario was developed and evaluated where fuel and its contained Pu is purposely left undissolved, resulting in excess Pu in the hulls. The magnitude of the scenario was calculated based on the loss of 8 kg of Pu over the course of 90 working days. Based on the chemical models and material balance calculations presented here, relatively large changes in temperature, acid concentration or reaction time are needed for the stated material loss. Further, these process changes would be easily observable using current process monitoring technologies, but further work is needed to evaluate authentication strategies and performance under plant and long term conditions. Total uncertainties will depend upon the errors associated with model calculations and measurement errors. Estimation of these uncertainties is the next logical step for understanding the value of process monitoring in this scenario

Gravel antidunes in the tropical Burdekin River, Queensland, Australia

The geological record is punctuated by the deposits of extreme event phenomena, the identification and interpretation of which are hindered by a lack of data on contemporary examples. It is impossible to directly observe sedimentary bedforms and grain fabrics forming under natural particle-transporting, high-velocity currents, and therefore, their characteristics are poorly documented. The deposits of such flows are exposed however, in the dry bed of the Burdekin River, Queensland, Australia following tropical cyclone-induced floods. Long wave-length (up to 19 m) gravel antidunes develop during short (days) high-discharge flows in the upper Burdekin River (maximum recorded discharge near the study reach over 25 600 m s in February 1927). Flood water levels fall quickly (metres in a day) and flow is diverted away from raised areas of the river bed into subchannels, exposing many of the high-stage bedforms with little reworking by falling-stage currents. Gravel bedforms were observed on the dry river bed after the moderate flows of February 1994 (max. 7700 m s) and January 1996 (max. 3200 m s). The bedforms had wave-lengths in the range 8-19 m, amplitudes of up to 1 m with steeper stoss than lee faces and crest lines generally transverse to local peak-discharge flow direction. The gravel fabric and size sorting change systematically up the stoss and down the lee faces. The antidune deposits form erosive based lenses of sandy gravel with low-angle downstream dipping lamination and generally steep upstream dipping a-b planes. The internal form and fabric of the antidune gravel lenses are distinctly different from those of dune lee gravel lenses. The erosive based lenses of low-angle cross-bedded gravel with steep upstream dipping a-b planes are relatively easy to recognize and may be diagnostic of downstream migrating antidunes. The antidune gravel lenses are associated with thick (to 1 m) high-angle cross bed sets. Ancient antidune gravel lenses may be diagnostic of episodic high-discharge conditions and particularly when they are associated with high-angle cross-bedded gravelly sand they may be useful for palaeoenvironmental interpretation

Galileo's first images of Jupiter and the Galilean satellites

The first images aof Jupiter,Io, Europa, and Ganymede from the Galileo spacecraft reveal new information about Jupiter's Great Red Spot (GRS) and the surfaces of the Galilean satellites. Features similar to clusters of thunderstorms were found in the GRS. Nearby wave structures suggest that the GRS may be a shallow atmospheric feature. Changes in surface color and plume distribution indicate differences in resurfacing processes near hot spots on Io. Patchy emissions were seen while Io was in eclipse by Jupiter. The outer margins of prominet linear markings (triple bands) on Europa are diffuse, suggesting that material has been vented from fractures. Numerous small circular craters indicate localzed areas of relatively old surface. Pervasive birttle deformation on an ice layer appears to have formed grooves on Ganymede. Dark terrain unexpectedly shows distinctive albedo variations to the limit of resolution