RSICC CODE PACKAGE CCC-704

RSICC CODE PACKAGE CCC-704

1. NAME AND TITLE

SlideRule 1.0: Nuclear Criticality Slide Rule.

2. CONTRIBUTOR

Oak Ridge National Laboratory, Oak Ridge, Tennessee.

3. CODING LANGUAGE AND COMPUTER

Visual C++; PC (Pentium or later), Windows 95/NT or later (C00704PC58601).

4. NATURE OF PROBLEM SOLVED

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,

and

· 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, and

· 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; and

· damp, high‑enriched (93 wt % 235U).

July 27, 2004

This notice was added at the request of the developers regarding dose terminology and the “Solve” capability of the electronic version of the “Nuclear Criticality Slide Rule”.

All reported radiation absorbed doses (rads) are “tissue-dose” estimates, not “free-air-dose” estimates.

The “Solve” capability for each of the five types of incidents can provide erroneous results for the determination of specific (i.e., Neutron, Gamma, Neutron Skyshine, Gamma Skyshine, Total Skyshine) “Estimated Prompt Doses Based on Total Fission Yield and Distance from Incident” (i.e., the lower left figure). The “Total Radiation” and Total Skyshine” are calculated correctly. When using the “Solve” feature for the lower left figure to determine the prompt dose of a specific radiation source (i.e., Neutron, Gamma, Neutron Skyshine, Gamma and Skyshine) one must approach the solution in a reverse mode. That is, iteratively solve for a known parameter (e.g., “Total Fissions” or “Distance”) by changing a specific dose value until the desired “Total Fissions” and “Distance” is returned by the “Solver.”

5. METHOD OF SOLUTION

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.ornl.gov/sci/sliderule/.

6. RESTRICTIONS OR LIMITATIONS

The SlideRule is currently limited to the five types of systems listed above. Modeling assumptions that limit or restrict the usefulness or accuracy are discussed in the documentation. See notice appended to Section 4 of this abstract regarding dose terminology.

7. TYPICAL RUNNING TIME

The code runs interactively and response time is nearly instantaneous.

8. COMPUTER HARDWARE REQUIREMENTS

SlideRule runs on Windows 95/NT or later personal computers with a minimum of 32 MB RAM. Nominal hard disk requirements are less than 10 MB.

9. COMPUTER SOFTWARE

The included SlideRule executable was created using Microsoft Visual C++ and runs under Windows 95/NT or later. Source files are not distributed.

10. REFERENCES

included in hard electronic (PDF) form:

C. M. Hopper, “Notice regarding dose terminology.” (July 27, 2004).

“Nuclear Criticality Slide Rule 1.0 ReadMe File” (ReadMe.txt, December 2001).

B. L. Broadhead, C. M. Hopper, R. L. Childs, and J. S. Tang, “An Updated Nuclear Criticality Slide Rule. Volume 1: Technical Basis,” NUREG/CR‑6504, Vol. 1 (ORNL/TM‑13322/V1) (April 1997).

C. M. Hopper and B. L. Broadhead, “An Updated Nuclear Criticality Slide Rule: Functional Slide Rule,” NUREG/CR‑6504, Vol. 2 (ORNL/TM‑13322/V2) (April 1998).