Slide Rule Workshop
Oak Ridge National Laboratory
Slide Rule for Nuclear Criticality Accident Response
Oak Ridge National Laboratory has developed rapid "in-hand"
and electronic methods 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 hand-held version provides rapid assessments for direct radiation approximations.
The electronic version 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 slide rule 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, and
- dose-reduction factors for variable thicknesses of steel, concrete, and water.
The slide rule 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, and
fission yield estimates.
The slide rule 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 personnal as an uncontrolled
system approaches criticality.
The Slide Rule for Nuclear Criticality Accident Response is intended for
criticality safety and radiation protection engineers, health physicists, and emergency
response personnel. The Slide Rule is available in working hand-held hard copy or as a
Windows PC program. The workshop includes hands-on training with both versions. If you are interested in coming to one of our future Slide Rule Workshops, please contact Bryan Broadhead (865) 574-4476.
To purchase the hand-held version of the Slide Rule, register online at www.ornl.gov/sliderule/sliderule_order_form.html.
Oak Ridge National Laboratory (ORNL) is operated by UT-Battelle, LLC, for the U.S. Department of Energy.