Physical Searches for Orphan Sources

Introduction By the end of this module students will be able to: Describe the types of physical searches Develop a prioritized plan for a physical search Describe the personnel that comprise the search team and their responsibilities List the equipment needed Define assessment and action levels Describe how the search is performed List some criteria for stopping a search

Overview Types of physical searches and when to perform them Planning and conducting searches in such a way that: maximizes the chances of finding sources uses resources and time efficiently maintains the safety of the search team Knowing when to stop a search

Physical Searches Involve one or more persons trying to locate radioactive sources visually and with radiation detection equipment Are generally performed: As a search for a specific missing source or when a source is suspected to be in an area After an administrative search indicates a need Routinely to provide assurance that no additional unknown sources exist or are not entering an area

Passive vs. Active Searches Passive Searches: Detectors and people stationary Placed at choke or nodal points to detect any sources passing by Active Searches Personnel with mobile detectors move to a likely location for an orphan source Systematically search the location This module focuses on active searches

Routine vs. Specific Searches Often involve passive, portal searches Can be active during regular inspections To provide assurance that all sources are known Wide area routine active searches without cause are not usually cost effective Specific: After an administrative search indicates the possibility of an orphan source When a source is known to be missing or injuries are discovered Similar processes except for resources and urgency involved

Search Planning

Elements of a Search Plan Objectives Boundaries of search (geography and time) Radionuclide(s) being sought Monitoring methods (hand, vehicle, aerial) Limits of detection for instruments available Procedures for dealing with found sources Responsibilities of parties involved Provision of staff, equipment and finances

Practical Planning Steps Develop a prioritized list of sites to search Determine search team membership Ensure all team members have the proper training Obtain all materials and equipment needed Determine recovery, storage or disposal options Obtain approval for search and source movements from the relevant authorities and facility owner

Search Locations Last known location of missing source First priority is within boundaries of facility Then retracing sequence of events leading to source becoming missing If not found, expand to include other areas Check transportation through likely areas Search sites can also be selected based on results of an administrative search

Search Limitations Geographic boundaries Weather constraints Search boundaries Weather constraints Practical constraints Equipment limitations Site access restrictions Time or funding limits

Search Team Members: Team leader Communications co-ordinator Radiation safety officer Search personnel trained to use radiation detection equipment Local guide (if needed)

Search Team Need or provide training in: Preparation Search procedures Source securing, storage and transfer procedures Health and safety precautions Preparation Equipment and material procurement Transfer sample plan onto search maps or GPS

Search Team Responsibilities: Conduct searches Record all readings on search maps Take digital photos of site, buildings, devices, sources Locate and temporarily secure found sources Assist in packaging and transporting these sources to storage or disposal facilities Document search efforts

Preparation for a Specific Search Conduct briefing Equipment Procedures, including: Radiation safety Search Contamination control Develop safety plan Dose limits Turn back dose rates Integrating dosimeters and limits

Preparation for a Specific Search Develop search information Search plan transferred to site search maps Site history Radionuclides expected Establish communication plan Cell or satellite phones Radios Call-in times Stop time

Preparation for a Specific Search Gather materials and supplies Radiation safety references Contamination control materials Consumables Food and water

Preparation for a Specific Search Check radiation detection instrumentation: Appropriate for radionuclides that may be encountered Calibrated Pre-operational checks completed Efficiencies for radionuclides that may be encountered Gather equipment/materials for source packaging/ transportation

Equipment Limitations Ability to detect the type of radiation emitted by the radioactive source being sought The dose or count rate that can be distinguished from background by a particular detection system Detector geometry and efficiency Counting time Background radiation variability User technique and ability

? Decision Rule When should further investigation of alarms or variations in dose/count rate be performed? Recommended at 2 or 3 times background radiation level Some search instruments do not provide indication of counts or dose rate and only give an alarm – alarms should to be investigated using other instrumentation

Use of Assessment and Action Levels Assessment level Two times background rate: Stop and let the meter stabilize Action level Three times background rate: “Hot spot” discovered Stop and evaluate further

Onsite Preparations Select background measurement area Determine background count rate Calculate assessment and action levels Two times background rate (assessment level) Three times background rate (action level)

Onsite Preparations Team leader verifies assignments for team members and establishes call-in times Walk around the site: Look for suspicious items Determine if the search plan needs modification Review boundaries Take detection equipment (audible response on) Establish contamination control area (if necessary)

Broad Area Building Searches Search buildings first Visit all floors Search rooms with the following items first Radiation-related signs Attic or basement areas Suspicious looking items Garbage containers Industrial shop areas Floor drains Sewer lines

Broad Area Field Searches Search after buildings Pay particular attention to: Radiation-related signs Ditches, sheds or trailers Suspicious looking items Garbage containers Above-ground tanks Septic or sewer areas Earthen mounds Underground tanks

Source Localization and Identification Localize the source Use the appropriate range radiation detection instrument to approach the source Move in slowly May need the use of tools such as a shovel to find the source (use care not to damage the source)

Source Localization and Identification Control access to the area and post trefoil sign as appropriate Assess the need for shielding Get accurate dose rate measurements at 1 meter if dose rates allow Identify the radionuclide Estimate the activity of the source Evaluate the best follow up actions

Possible Actions as a Result of the Search No sources found… If expected to find source: Revise search plan Expand search areas Perform further administrative searches If didn’t expect to find a source: Document the area searched Sources found… Prepare sources for transfer to authorized recipient or secure in place If search was to verify an inventory, document the source location

When do you stop searching? Factors to consider: Whether or not there are any further useful clues or leads to be investigated Category of the source, if known Likely consequences of the source being found by a member of the public Half-life, activity and time since the loss of source Likelihood of the source being in a location accessible to the public Need for resources to be used for other work Public and political pressure and level of concern

Document the Search Record the following data for found sources: The unique identification of the source (typically the manufacturer, model number and serial number of the source and the device) The location of the source (installed location or location of authorized use) The isotope and activity of each source. For all sources, record radiation measurement data (dose rate and spectrum/isotope identification) The status of the source, i.e., “in use,” “disused,” “waste,” “missing”

Document the Search Record: Copy all survey documentation Actions taken to secure the source Disposition of the source Copy all survey documentation Write a discussion of the problems encountered during the search Include digital photographs of the site, buildings, source or device, and important features that are correlated to the search maps

Summary Planning, preparation, and procedures are important components in all types of physical searches Key decisions involve: What type of search to make? Where to search? What resources are needed and available? What to do with any found sources? When to stop?