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Oak Ridge National Laboratory has developed a rapid PC-based tool for estimating pertinent information needed to guide response team actions and help characterize some types of nuclear criticality accidents. The concept uses a series of sliding graphs that function similarly to a slide rule. This tool was developed with the promise that visual demonstration of trends (e.g., dose versus time or distance) are helpful to response personnel. The SlideRule provides rapid assessments for direct radiation approximations and is useful for solving for parameters that are dependent upon independent specific parameters such as variable shielding, distances, and anticipated time related radiation doses to personnel. The SlideRule is designed to provide estimates of the following:
magnitude of the fission yield based on personnel or field radiation measurements,
neutron- and gamma-dose at variable unshielded distances from the accident,
the skyshine component of the dose,
time-integrated radiation dose estimates at variable times/distances from the accident,
1-minute gamma radiation dose integrals at variable times/distances from the accident,
dose-reduction factors for variable thicknesses of steel, concrete, and water.
The SlideRule estimates unknown data based on data available to emergency response personnel, including:
exposure information about "accident victims,"
estimates of potential exposures to emergency response re-entry personnel,
estimation of future radiation field magnitudes,
fission yield estimates.
The SlideRule provides estimates for five unreflected spherical systems that provide general characteristics of operations likely in facilities licensed by the NRC:
low-enriched (5 wt % 235U) uranyl fluoride;
damp, low-enriched (5 wt % 235U) UO2;
high-enriched (93 wt % 235U) uranyl nitrate solution;
high-enriched (93 wt % 235U) uranium metal;
damp, high-enriched (93 wt % 235U).
Analyses were performed to determine the characteristic radiation leakage spectra for each of the five types of critical systems. Two-dimensional air-over-ground radiation transport analyses were then performed at various times (up to 1000 minutes) after the criticality event to determine the neutron- and gamma-radiation dose per fission up to 4000 feet from the event. This information together with shielding attenuation data allows the fission yield to be estimated based on the measured dose and time/distance from the event. A complementary first-pulse fission yield estimator utilizes precursory system information and is based on relatively simple, but well-established formalisms. The resulting first-pulse fission yield estimates are presented as functions of vertical or horizontal cylindrical critical volume and solution addition rates. These estimates may then be used for determining appropriate mitigating measures for protection of personnel as an uncontrolled system approaches criticality. See the developers' website for a brief introduction http://www.cped.ornl.gov/sliderule/.
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Keywords: accidents, criticality, environmental impacts, fission products, neutron source, radiation doses.