Lecture Notes for Section X, Processing of DSRS for BDC Disposal including
Conditioning and Storage
1. Introduction
The purpose of this lesson is to introduce the student to DSRS Conditioning and Storage.
The objectives of the lecture is for the student to understand the terms “Conditioning”
and “Storage” as they apply to disused sealed radioactive sources and the relationship
between conditioning and storage.
2. Scope/Structure
The scope of this lesson is to define DSRS conditioning and how storage interfaces with
the conditioning of sources. The South African BOSS (Borehole Disposal of Disused
Sealed Sources) example serves as the backbone of the presentation on conditioning in
preparation of eventual borehole disposal. Since many member states have processed
DSRS into safer forms, but have not yet sited a borehole disposal facility, storage is an
important aspect of the safety scheme for DSRS’.
The structure of this lesson is:
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Presentation Resources
Regulatory Framework
Definitions
Processing of DSRS: Conditioning
• What is conditioning?
• Why condition sources?
• BOSS example and requirements,
• Hot cell uses and requirements
Processing of DSRS: Storage
• Why store?
• Member state experience.
• Generic requirements for storage,
Summary
3. Concepts
The primary concepts in the lesson is the conditioning of DSRS in preparation for
disposal at a borehole disposal facility (BDF) and the related DSRS storage in lieu of
disposal. Additionally, the regulatory framework for DSRS conditioning and storage was
presented at the start. The framework is the avenue used by the regulatory body to
dictate and guide the licensee in acceptable methods to condition and store DSRS.
Conditioning, in the BOSS context, is the placement of SRS into a 316 L stainless steel
capsule. The capsule walls are 3 mm thick. The capsule comes in one length and two
different diameters to accommodate the various sizes of SRS. After placement of the
SRS into the capsule, the capsule is TIG welded closed and leak checked. The sealed
capsule is then placed into the center of another stainless steel container.
Conditioning provides:
• Conversion to a Special Form radioactive material for transportation,
• Proper documentation,
• Physical protection from damage/leakage, and
• Package standardization for handling.
Sources come in a wide variety of strengths. For Cat 3 sources and lower, conditioning
can take place in a lightly shielded conditioning unit (see picture in Section 5). For Cat 1
or 2 sources, a shielded hot cell is needed.
For efficient operations, the conditioning unit should consist of five zones. These zones
are:
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Receiving zone – source receipt point & characterization records review area;
Transfer zone – SRS placed into capsule behind shielding (e.g., lead brick wall),
this is the point where the source is physically removed from its device and placed
into the 316 L SS capsule;
Welding zone – TIG welded behind special welding shield and subsequent
capsule cooling area;
Leak testing zone – necessary leak testing equipment & lead brick personnel
shield;
Container filling/storage zone – transfer to temporary shielded container for
storage or transport.
The Transfer zone has a calibrated radiation monitor to check the source’s level of
radioactivity (e.g., strength). Additional shielding must be carefully placed to prevent
interference from other nearby sources.
The DSRS Acceptance Criteria is typically limited by the worker dose limit in the
Conditioning Unit. Additionally, contamination control is important when handling
sources as the operator can be surprised when working with a leaking source. Generic
requirements for conditioning include:
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Contamination control per the regulations, license, or regulatory body directive,
Receiving area surveys are required for the incoming transport packages prior to
handling;
Transfer zones – Pb shielding bricks covered with double poly to prevent
contamination and the generation of mixed waste;
Operations area size is minimized so the potential for contamination spread is
limited;
Operations are optimized to limit exposure from DSRS; and
Ventilation system – exhaust fan over highest contamination potential to control
air flow and contamination spread; HEPA filters are used in the effluent controls.
At the heart of these operations is good health physics practices. The conditioning unit
areas should be subject to the following standard health physics protocols:
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All containers within the supervised area should be checked for contamination
before the campaign and at regular intervals during it.
Radiation levels within the supervised area should be established prior to the
intended work (e.g. encapsulation operation). The radiation level in the transfer
zone should be checked before and after the transfer of the contents of a transport
or storage container to a capsule.
When source strength exceeds the capability of the lightly shielded conditioning unit, the
BOSS hot cell can be used. In essence this hot cell is one steel box inside another steel
box. The void space between the boxes is 1.55m, filled with sand to act as shielding.
There is a window to allow the operator to use manipulators to work on the source inside
the shielded portion of the hot cell. The window is simply a tank of water with clear
unbreakable polycarbonate sides. The hot cell can accommodate a 37 TBq (1,000 Ci)
Co-60 sealed radioactive source. At this level the worker’s dose rate is 0.045 mSv/hr.
The hot cell is equipped with closed circuit TV so no area inside the shielded space is not
viewable by the trained operator.
While ideally the conditioned SRS would be immediately disposed down the borehole,
this rarely happens. From reported member state experience, many SRS have been
conditioned in some manner, but few have actually been borehole disposed. Thus the
alternative is storage of some length: short term/interim to long term (up to 100 years).
Central storage is preferred in that controls can prevent human intrusion into the facility
with the unwanted public exposure.
Per GSR-5, waste needs to be stored such that it can be inspected, monitored, retrieved,
and preserved in a manner for its subsequent management. For long term storage, care
must be taken to prevent degradation of the waste packages (and any markings). Design
of central storage facilities will depend on the DSRS inventory, DSRS strength, and
estimated time in storage. Experienced qualified personnel will be needed to lay out the
facility to minimize worker doses during the periodic inspections and routine monitoring.
For unconditioned SRS, a recommended national policy is that waste not be put back into
the public domain (e.g., on the road again) if processing/remediation can be performed
where the radioactive material is located. In this vein, the conditioning unit/BOSS hot
cell should be moved to the licensee’s location rather than incur the transportation risk of
moving the SRS to the processing equipment.
Packaging designed for storing high activity sources at the central storage facility are
similar to the reusable transportation cask, but not as robust in their shielding and overall
construction. The controlled storage conditions available at a fixed facility lend to a
lighter design. Whereas transportation packages need to withstand vehicle accidents and
other events, the storage facility packages are primarily needed, in a passive role, for
shielding and ensuring source integrity is maintained.
Packaged sources in a central storage facility must comply with member state regulations.
The critical compliance items include:
 Packages stored in proper radiation zones based upon surface dose rate,
 Contamination surveys of the packages and storage areas,
 Package markings/symbols (in freezing or above 35 C environments, markings
may become brittle or become unglued to the package surface), and
 Package ID tag traceable back to the records.
For inventory control, packages need to be stored in an orderly manner for easy visual
identification. Well organized storerooms allow technicians to quickly verify the DSRS
packaging is not degrading. From experience, DSRS packages should be stored:
 Away from commonly occupied areas,
 In an engineered space (e.g., floor loading, contour)
 Away from non-radioactive material,
 Away from store-for-decay, and
 Long term storage away from “soon to ship” inventory.
Other important storage concerns are:
 Source – packaging compatibility (Avoid storage Sr-90 sources in a lead
container to prevent bremsstrahlung radiation.)
 Ensure physical barriers are in-place to prevent unauthorized intrusion (and
possible theft). Barriers may also include video cameras that sense motion and
alert a responsible manager at the facility.
 Where possible, shield higher dose rate packages with similar type low-dose
packages to help with storage organization,
 Ventilation provided when gaseous radionuclides are present. The two primary
isotopes are Iodine or Radium/Radon.
In the borehole disposal concept, conditioning is a key component of the protection of the
public safety case/assessment. Conditioning involves placing at least one SRS into a 316
L stainless steel capsule. After the capsule is sealed, the package will be stored, most
likely for several years/decades. While the packaged SRS in controlled storage is safer
than an unconditioned source in the public domain, the ultimate resolution (i.e., disposal)
has not been obtained. While in storage, the package needs compliance inspections to
ensure environmental conditions (e.g., pitting of the stainless steel or localized corrosion)
do not degrade the container potentially leading to a leaking source.
4. Definitions
Conditioning
Conditioning – the sealing of an SRS into a capsule. Usually followed by interim
storage.
SRS – sealed radioactive source
Storage – as the placement of the source in a facility where isolation, environmental
protection and human control (e.g., monitoring) are provided with the intent that the
source will be retrieved.
Transfer/transport flask – a Type A transport container designed for the public domain
transport of conditioned SRS and for transferring disposal packages to the disposal
borehole. Exists only as a design at present.
5. Additional information
Conditioning and Containerization Schematic
(adjacent to disposal borehole)
Capsule weld in progress.
Note: lead shield to limit dose to worker.
Conditioning Unit in South Africa.
Note borehole to the right of the unit.
6. References
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International Atomic Energy Agency, BOSS: Borehole Disposal of Disused
Sealed Sources – A Technical Manual, IAEA-TECDOC-1644, IAEA Vienna
(2011)
International Atomic Energy Agency, Handling, Conditioning and Storage of
Spent Sealed Radioactive Sources, IAEA-TECDOC-1145, IAEA Vienna
(2000).
International Atomic Energy Agency, Management of Disused Long lived
Sealed Radioactive Sources (LLSRS), IAEA-TECDOC-1357, IAEA Vienna
(2003).
International Atomic Energy Agency, Predisposal Management of Radioactive
Waste, General Safety Requirements, Part 5, IAEA, Vienna (2009).
7. Summary of the Lesson
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•
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•
•
•
Presentation Resources
Regulatory Framework
Definitions of terms
Processing of DSRS: Conditioning
• What is conditioning?
• Why condition sources?
• BOSS example and requirements,
• Hot cell uses and requirements
Processing of DSRS: Storage
• Why store?
• Member state experience.
• Generic requirements for storage,
• Package in storage compliance.
Summary
8. Questions and Answers
A list of 5-10 questions, which will be used to assess the effectiveness of the lecture in
relaying the intended information/concepts to the participants. Questions should not focus
on direct regurgitation of the presented material, but should force the participants to apply
the concepts learned and think critically. The questions may take any form: fill in the
blank, matching, multiple choice, problem solving, narrative, etc. The answers to the
questions should also be provided.
Question #1: What is conditioning? Why is it important?
Answer: Conditioning is the placement of DSRS into a stainless steel capsule and
welding the capsule shut. By isolating the DSRS, public safety during storage,
burial operations and post-closure of the disposal facility is enhanced.
Question #2: Define “storage”? How long can it last?
Answer: the placement of the source in a facility where isolation, environmental
protection and human control (e.g., monitoring) are provided with the intent that
the source will be retrieved. Storage can last up to 100 years.
Question #3: Conditioning of DSRS provides what four benefits?
Answer: Conditioning provides:
• Conversion to a Special Form radioactive material for transportation,
• Proper documentation,
• Physical protection from damage/leakage, and
• Package standardization for handling.
Question #4: What five zones make up the Conditioning Area? In a few words, briefly
describe each.
Answer: The manned area for the conditioning operation should consist of the
following five zones:
• Receiving zone – receipt point & review characterization data
• Transfer zone – SRS placed into capsule behind shielding (e.g., lead brick
wall);
• Welding zone – TIG welded behind special shield and capsule cooling area;
• Leak testing zone – contains leak test equipment & personnel shield
• Container filling/storage zone – transfer to temporary shielded container for
storage or transport.
Question $5: Describe the BOSS Hot Cell design.
Answer: BOSS Hot Cell Design
• One steel box inside another steel box
• Annulus (1.55 m) is the bio shield; full of sand
• BOSS hot cell includes a tank of water to act as a window;
• Areas not viewable through the window can be seen with closed circuit TV
(CCTV);
Hot Cell Operations
• With sand density of 1.6 kg/L, radiation levels for 1,000 Ci Co-60 SRS will be
0.045 mSv/hr on the outer wall.
Question #6: It is preferred to bring the processing equipment to the DSRS. Briefly
describe why?
Answer: By bringing the conditioning equipment to the DSRS location, the public is
not put at risk if the reverse were practiced, where the DSRS was transported in the
public domain to the conditioning facility.