Section 18 of the Nuclear Substances and Radiation Devices (NSRD) Regulations requires licensees who use sealed radioactive sources, to have their sealed source leak tested at least once every twelve months. This requirement is also mentioned during the licence application when the applicant must explain their procedures to carry out leak testing. Most licensees rely on outside contractors to provide the leak testing service since the equipment and skills are beyond what the licensee realistically can maintain. Leak testing is a very simple procedure, but there are a few pitfalls of which a licensee should be aware. In this short article, some basic questions behind leak testing, from both a regulatory and operational point of view, are discussed.

Who can perform leak testing?

Under the NSRD regulations, licensees who posses sealed radioactive sources that have an activity greater than 50 MBq must carry out a leak test on these sources. This requirement is also applicable to licensees who use shielding material comprised of a nuclear substance (such as depleted uranium).

Licensees can do their own leak test sample analysis. However, they must first obtain CNSC approval for their leak test procedures and sample analysis equipment. The requirements for leak test approval can be found in the CNSC document "R-116: Requirements for Leak Testing Selected Sealed Radiation Sources". Any organization wanting to provide a leak testing service (whether in-house or to other users) must receive approval under R-116. In most cases obtaining approval is time-consuming and expensive, so most licensees contract their leak testing requirement to an outside service. Those who do must ensure that the contractor is a CNSC approved agency. Approved agencies will receive a letter from the CNSC acknowledging their approval and should produce it on request.

Many licensees use a contractor to analyze the collected leak test samples, but rely on their own employees to collect the samples. This is acceptable as long as the following conditions are met:

a) the person has access to and follows approved leak testing procedures,
b) has received radiation safety training to control any associated radiation hazard, and
c) has sufficient sampling materials and leak test sampling certificates

What needs to be leak tested?

There are some exemptions under the regulations when it comes to leak testing. Generally any sealed radioactive source with an activity greater than 50 MBq, and any shielding material manufactured from a nuclear material will need to be leak tested. However, a leak test does not have to be performed in either of the following cases:

a) when the source is gaseous, or
b) when the source is contained in a static eliminator that has been retained by the licensee for less than 15 months
Leak testing is not required for open sources of radioactive material.

Where do you leak test?

In most cases, a leak test consists of taking a swipe along any seams or visible opening on the sealed radioactive source holder. Before a person performs the leak test, they must have access to procedures explaining how to do the actual test. This information is often supplied by the manufacturer of the device in the support documentation that accompanied the device when it was purchased.

It is not necessary to swipe the actual sealed radioactive source. Attempting to swipe the source directly could result in damaging the source and could expose the person to an unnecessarily high radiation dose. If there is any doubt about where to take the swipe, refer to the leak testing procedures or contact a qualified agency for advice.

When does leak testing need to be done?

The frequency for leak testing is usually once every 12 months for sources in continuous operation. If the source is placed into continuous storage, the leak test is only required once every 24 months.

If the source is placed back into operation after being stored for 12 or more consecutive months, a leak test must be immediately performed. This leak test replaces any previous test that may have been done during the previous 12 months while in storage.

If the sealed source, or shielding, is not located in a radiation device (such as a spare ECD or stored logging tools) a leak test must be performed every 6 months.

Leak tests are required whenever an incident occurs that may damage the sealed source or shielding. The leak test must be performed as soon as possible after the incident.

Although most sealed sources will be leak tested once every 12 months as per the regulations, the CNSC does have the authority to change the frequency if they feel it is warranted. This change will be recorded as a condition on a licensee's licence.

Why are leak tests necessary?

The purpose of a leak test is to determine whether or not the sealed radioactive source has lost its integrity. The sampling process removes material from the device's surface and a qualified laboratory analyzes the sample for evidence of radioactive contamination. If more than 200 Bq is detected on a leak test sample, the source is considered to be leaking.

The chance of a source spontaneously leaking is extremely remote. Some major damage will have to be done to the device in order to cause the sealed source to leak, making it a very improbable incident. However with that said, radioactive material that enters a body is a far greater hazard and concern than radioactive material that is outside the body. Leak testing is a diligent and reasonable means by which we can prevent ingestion and inhalation of radioactive materials.

What do you do if a source is identified as leaking?

Once aware that a source is leaking (the measured activity on the sample being greater than 200 Bq), immediately discontinue use of the sealed source. Take immediate measures to control the spread of radioactive contamination from the sealed source. This may require specialized skills and equipment depending on the circumstances and an outside contractor may be needed. Once the sealed source has been secured, immediately notify the CNSC that a leaking source has been detected.

If the source is indeed leaking, the most likely resolution to the problem is to have the device sent for disposal. It is unlikely that the device will be repairable in this situation and disposal will be the only viable option.

Leak testing is a routine check on the integrity of the sealed source used in a variety of industrial, medical and research applications. The collection of leak test samples is a simple procedure. Analysis of the samples is somewhat more complex. Sealed radioactive source leak testing is a cost-effective way of protecting employees from internal radiation exposures. Ensuring there are procedures in place that describe the leak testing process and maintaining accurate records will make the entire process simple and hassle free.