Safety Assessment of Borehole Disposal of Unwanted Radioactive Sealed Sources

in Egypt Using Goldsim®

October 12, 2004

Patrick D. Mattie, M.S., P.G. and John R. Cochran, PhD.

Albuquerque, NM 87185-0735

Phone (505)284-4796

Email: pdmatti@sandia.gov

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,for the United States Department of Energy’s National Nuclear Security Administration

under contract DE-AC04-94AL85000.

• Radioactive Sealed Sources– What is a radioactive sealed source?

• A radioactive sealed source is any radioactive material that is encased in a capsule designed to prevent leakage or escape of the radioactive material

Background

• Radioactive Sealed Sources– What are radioactive sealed sources used for?

• RSS are used for a wide variety of applications at hospitals, in manufacturing and research.

• Typical uses are in portable gauges to measure soil compaction and moisture or to determine physical properties of rocks units in boreholes (well logging).

• Hospitals and clinics us RSS for teletherapy and brachytherapy.

• Oil exploration and medicine are the largest users of RSSs.

Background

Radioactive Sealed Sources

Typical 60Co and 137Cs RSS from medical applications. The largest SRS shown here is ~ 2 cm (~ 1 inch) in diameter and the volume is less than 15 cc (less than 1cubic inch) (photo from photo gallery at www.iaea.org).

• The RSS Problem:– Accidental mismanagement of RSS each year results

in a large number of people receiving very high or even fatal doses of ionizing radiation.

– Deliberate mismanagement of RSS is a growing international concern. Because of their small size, potency, availability, and “nuclear” nature, there is a concern that a terrorist could use RSS to create a radiological weapon or dirty bomb.

Background

• The RSS Problem:– In the spring of 2000, three people died in Egypt

because of a sealed source that came into the possession of a farmer.

– Mismanaged sealed sources can have a devastating effect on health and environment

– Sealed sources must be managed and disposed effectively in order to protect human health and the environment.

– Effective national safety and management infrastructures are prerequisites for efficient and safe sealed sources transportation, treatment, storage, and disposal.

Background

• IMPRSS Project:– Integrated Management Program for Radioactive

Sealed Sources in Egypt (IMPRSS)

– A cooperative development agreement between the Egyptian Atomic Energy Authority (EAEA), Egyptian Ministry of Health (MOH), Sandia National Laboratories (SNL), the University of New Mexico (UNM), and Agriculture Cooperative Development International (ACDI/VOCA).

Background

• IMPRSS Project:– Scope: To greatly improve the cradle-to-grave

management of RSSs in Egypt

– SNL coordinates the work scope between the participant organizations.

– Included in this project are activities to conduct a Preliminary Safety Assessment (PSA) of an intermediate-depth borehole disposal in thick arid alluvium in Egypt based on Sandia’s experience with Greater Confinement Disposal.

Background

• Egypt’s RSS Inventory:– 60Co (t1/2 = 30 yr), typically used for medical treatments

and research. Found in both fixed and portable units.

– 137Cs (t1/2 = 30 yr), medical treatments, well logging, industrial gauges, and research. Found in both fixed and portable units.

– 241Am/Be (t1/2 = 433 yr), in portable devices used for well logging and moisture detection equipment.

– 226Ra (t1/2 = 30 yr), medical treatments and industrial gauges. Found in both fixed and portable units.

Background

• Safety Assessment for Permanent Disposal:– SNL conducted the Safety Assessment that provided

the technical analysis used by the U.S. EPA to license the world’s only geologic disposal facility - the Waste Isolation Pilot Plant.

– SNL also conducted the Safety Assessment of the only U.S. intermediate-depth disposal facility – the TRU wastes in the Greater Confinement Disposalboreholes

– SNL is the lead laboratory for the performance assessment for the Yucca Mountain Project for high-level waste and spent nuclear fuel disposal.

Background

• Greater Confinement Disposal (GCD):– The EAEA, teaming with Sandia is conducting a

Preliminary Safety Assessment (PSA) of an intermediate-depth borehole disposal in thick arid alluvium in Egypt based on experience with the U.S. Greater Confinement Disposal.

– Sandia has recently demonstrated that intermediate-depth disposal in thick arid alluvium provides geologic isolation similar to that provide by a mined geologic Laboratories repository, but at a faction of the cost.

– Sandia’s GCD borehole assessment will be used as the basis for EAEA’s RSS assessment and disposal methodology.

Disposal Plan

BACKFILL 21mGRAVELLY SAND

DISPOSAL ZONE 15m

TOTAL DEPTH 36mDIAMETER 3m

UNSATURATED ZONE 235mGRAVELLY SANDNO FAST FLOW PATHSNO GROUNDWATER

RECHARGE

SATURATED ZONE

GCD Disposal Plan

Typical GCD Disposal Concept:

– No Fast Flow Paths

– No Groundwater Recharge

Simple geological settings and homogeneous materials are preferable to complex geologic settings and materials, as simple settings and materials are easier and less expensive to characterize and easier and less expensive to model, providing greater confidence in the Safety Assessment.

GCD Disposal Advantage

Safety Assessment

• A radiological safety assessment is a systematic analysis of a proposed disposal facility and its immediate surroundings that estimates radiation dose to humans for comparison of the estimates with a set of performance criteria.

• A safety assessment provides simulations of a range of plausible future outcomes, which are developed in a manner to provide confidence that the results of the analysis do not overestimate the ability of the disposal system to protect human health.

• Inherent uncertainties in assessing performance for the next 10,000 years requires a probabilistic model

For this project, the site search criteria are based on the characteristics of the GCD site and the preliminary site selection criteria are:

– Arid climate, < 130 mm per year precipitation

– Thick deposits of sand and gravel (alluvium), > 150 m thick

– Deep water table, > 150 m below land surface

– No potential for surface flooding.

Site Selection Criteria

GCD Disposal Plan

Photographs from Western Desert of Egypt

Disposal System Model

• Goldsim has been selected for the preliminary disposal system assessment for the Egyptian GCD Study

• The goal of this project is to conduct a Preliminary Safety Assessment (PSA) of an intermediate-depth borehole disposal in thick arid alluvium in Egypt based on Sandia’s experience with Greater Confinement Disposal.

• The results of the Preliminary Safety Assessment will then be used to decide of Egypt desires to implement such a disposal system.

RSS_Source_Term Waste_Zone

UZ_20m_to_10m

UZ_10m_to_2m

Bioturbation_Zone

UZ_30m_to_40m

UZ_40m_to_50m

UZ_50m_to_100m

Perimeter

Perimeter_20_to_10

Perimeter_10_to_2

Perimeter_2_to_0

Perimeter_30_to_40

Perimeter_40_to_50

Perimeter_50_to_100

Prototype Model

GCD Disposal System Goldsim Model Characteristics

• Radial Network of cells are needed to represent UZ transport of radionuclides to the biosphere

• GCD Model will be a Probabilistic Model– Uncertain parameters will be defined as a distribution

• GCD Model will utilize Goldsim’s Monte Carlo/Latin Hypercube Simulation options

• GCD Model will utilize Goldsim’s Contaminant Transport Module– Transport and Source Term Elements will be used

Summary

• The GCD design will take advantage of Egypt’s abundant regions of thick arid alluvium

• The GCD design can isolate wastes at relatively low cost

• Using Sandia National Laboratories GCD model will decrease the cost and time necessary to design license a disposal facility

• The approach is sensible and can permanently remove dangerous and unwanted RSS from the biosphere