Physical damage to sources, containers and

The containers in which radiation sources are transported, moved and stored are generally designed to provide adequate shielding and radiation safety under most climatic conditions. They demand a degree of maintenance that may need to be increased in more arduous working environments, for example, in salty or sandy environments where corrosion and increased wear may be of concern. Installed gauges often remain in position for long periods of time and it is important that they are kept clean so that identification markings, labels or other safety markings — which some might consider to be cosmetic features — do not become illegible. Otherwise, in the longer term, the obvious profile, discernible relevant markings and even the source’s identity may be lost. The care and maintenance of ancillary equipment for controlling the radiation source (tubes and cables used for radiography and handling rods used for well logging) are similarly very important.

Increased dose rates and unacceptable external exposures may result if the shielding of a radiation source container is damaged by mechanical, thermal or chemical means. Suitable precautions will normally include:

(a) Taking regular measurements of the shielding properties of radiation source containers.

(b) Monitoring measured surface dose rates using control charts (see example documentation, Fig. 19); the charts are likely to indicate even subtle deterioration in the standard of radiation safety.

Date of measurements . . . .

Instrument used: Gamma meter . . . Neutron meter . . . .

Radioactive sources storage container results µSv/h

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µSv/h µSv/h µSv/h

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µSv/h µSv/h

Controlled area results

ROTARY TABLE

DRILL FLOOR

µSv/h

µSv/h µSv/h µSv/h

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UP PIPE DECK

‘V’ DOOR

RPO Signature . . . .

FIG. 19. Example of a radiation survey form.

(c) Performing source leakage tests (smear tests) at intervals advised by the source or equipment manufacturer or as required by the regulatory body;

sources that are at greatest risk of rupture when placed downhole may demand the most frequent testing, for example, biannually.

Sealed sources used in the oil and gas industry may become damaged or ruptured to the extent that the radioactive material leaks or is released in loose form from the encapsulation. For instance, despite taking the necessary precautions there is always some risk of the integrity of the source encapsu-lation being compromised during attempts to retrieve a disconnected source from a well. Leakage may also result from mechanical, thermal or chemical conditions exceeding the specifications of the source or from the unlikely situation of poor quality control by the manufacturer or improper encapsu-lation of the sealed radioactive material. Sealed sources are leak tested after manufacture and before transport, and additional tests may be arranged as required by the end user or to meet the requirements of the regulatory body.

A ruptured industrial radiography source could create a severe, immediate health threat to individuals [20]. The most common radioactive materials used, ¹⁹²Ir and ⁶⁰Co, are incorporated into sources with activities generally of several hundreds or thousands of gigabecquerels. Therefore, if the encapsulation becomes compromised, extensive contamination can result, with the consequent potential for extremely large internal and external doses being received by those exposed to the contamination.

To deal with an event involving the rupture of an industrial radiography or well logging source (including the rupture, during recovery attempts, of a well logging source that has become lodged downhole), written emergency procedures that the licensee can implement in conjunction with the operator [23] need to be immediately available, including procedures for the:

(a) Immediate notification of the regulatory body by the licensee in conjunction with the operator.

(b) Securing of the affected area in order to limit the spread of contamination and to prevent anyone from incurring either an internal or external dose as a result of being exposed to the ruptured source.

(c) Restriction of access until a person is authorized, by reason of training and experience, to assess the problem, including the extent of the contam-ination, and decide on further actions such as decontamination procedures. In the case of damage occurring while attempting to retrieve a disconnected source from a well, the access restrictions apply to the area around the wellhead and to any equipment used in the recovery operations.

(d) Retrieval of all contaminated items and their storage in such a way as to prevent further exposures and the spread of contamination, pending their decontamination to authorized clearance levels [24] or their disposal as radioactive waste in accordance with the requirements of the regulatory body.

(e) Monitoring for internal contamination of those persons involved in the operations that gave rise to the incident or who were in the immediate area when the incident occurred, and assessment of the total, committed effective doses resulting from the internal and external exposures of those persons [25, 26].

(f) Retention in the company records of the results of these assessments and the copying of them to the companies that employ the workers involved.

General guidance is available on occupational radiation protection in intervention situations and emergencies [1].

If damage to a radiography source is identified in the early stages, widespread contamination can be avoided. A ruptured radiography source may be returned to the shielded position in the exposure container, or otherwise shielded to decrease the immediate health threat. Risks associated with a damaged radiography source can be further minimized by:

(a) Managing individuals who may be contaminated so that the contami-nation is contained within a controlled area;

(b) Decontaminating any person found to be contaminated, in accordance with established procedures [27];

(c) Handling with care any potentially contaminated items, such as ancillary radiographic equipment, and, if possible, placing them in bags to prevent any spread of contamination;

(d) Setting up cordons to prevent access to the area concerned in the event of there being any doubt whether contamination exists but where there are elevated radiation readings;

(e) Treating any potentially contaminated item or area as contaminated until an assessment can be completed, i.e. the exposure device, any material used to shield the radioactive source, the area, and any equipment in the immediate vicinity [23];

(f) Performing leak tests on the radiography sources as soon as possible after any incident or other occurrence that could cause stress to the source encapsulation.