Posiva testing copper canister inspection technology at Olkiluoto

The copper cast iron canister is the most significant technical release barrier of the final disposal concept. It is required to remain intact for tens of thousands of years, which is why the quality of the canister must be fully verified prior to final disposal.

NDT methods enable quality assurance without changing the characteristics of the actual final disposal product. In addition to ultrasound and X-ray inspection, the high quality of the final disposal canister is ensured by utilising eddy current and visual inspection methods. In the eddy current method, a magnetic field is induced in copper, which conducts electricity. With eddy current sensors, it is possible to identify changes in the magnetic field. The changes are caused by material faults, i.e. changes in the material characteristics. Because the material characteristic changes in components are minor, the signals (changes) identified with sensors are usually caused by faults in the material. The ultrasound method is an acoustic method requiring an acoustic contact between the sensor and the item being tested. Water is the usual contact substance in mechanised inspections. Should the tested canister component have defects, they are reflected back to the ultrasound sensor in the same way as in using sonar to find shoals of fish.

Kuparikapselin tarkastuslaitteen testaus web
Copper canister inspection technology testing in Olkiluoto.

Posiva has been testing different NDT methods in disposal canister inspection at the SKB canister laboratory in Oskarshamn for a long time already. The same methods have also been used in defect identification in the quality assurance of welds created in sealing the canister cover.

This year, the copper overpack NDT inspection method has been tested in Olkiluoto. The main focus has been on the joint operation of the Posiva-obtained canister component rotation equipment and eddy current and ultrasound equipment. The equipment has been tested in the inspection of the final disposal canister's full-sized copper overpack (T84).

jorma pitkänen web
Development engineer Jorma Pitkänen.

Why are copper overpack NDT inspections being performed in Olkiluoto right now?

"The rotation device (manipulator) was completed in the autumn of last year and the first copper cast mould inspection was performed with it in the autumn of 2013", says development engineer Jorma Pitkänen. We are now continuing with more detailed testing that provides information about the joint operation of the manipulator and the inspection equipment."

How does the equipment functionality seem? Have there been any surprises?

"The manipulator has been robust and efficient enough. However, there have been some deficiencies in the speed control of the rotation device in relation to the eddy current device. The deficiencies will be taken care of in future. We have also noticed that the copper pipe moves, as expected, to some extent in the longitudinal direction when it is rotated. This will be prevented in future inspections by taking relatively small structural steps.

What experiences have been obtained from the ultrasound inspection?

"Changes are needed in the speed control of the rotation device engine. In addition, the water through which the ultrasound signal travels from the sensor to the copper pipe does not spread evenly enough on the active contact surface of the sensor, which means that the sound barrier does not properly penetrate the component being tested. This can be fixed by making minor changes to the structure of the ultrasound sensor clamp."

How small a defect is eddy current technology capable of identifying?

"Regarding surface defects, eddy current inspection is used, and its impact extends to a depth of about 10 mm. At this depth range, eddy current technology is capable of reliably identifying defects of an approximate depth of 2 mm. The requirement is that at least 35 mm of the copper overpack thickness is intact, flawless material."

What is the case for using ultrasound technology?

"With ultrasound technology, the copper overpack can be inspected at a depth of 5–50 mm, that is, throughout the overpack thickness. This results in a fault size of up to 1 mm, but in the powerfully dampening copper, the fault size identified increases to about 2–2.5 mm according to initial estimates."

How long does the copper overpack inspection take?

"Now that the equipment is being introduced, the inspection will take about one and a half weeks. From now on, testing can be done within a week, and during the final disposal plant's operation stage, it should be possible to inspect one copper canister in one day."

How will the inspection equipment package be developed further?

"The sensor and clamp geometry needs further improvement, and the sensor technology IT and application software need to be developed so that the entire copper overpack is covered in a single inspection in regard to ultrasound. Different kinds of technology can also be combined in the same measuring process so that the inspection time is shorter."

Return to headlines

Share article:
This website stores cookies on your computer. These cookies are used to improve our website and provide more personalised services to you.


To make this site work properly, we sometimes place small data files called cookies on your device. Most big websites do this too.

1. What are cookies?

A cookie is a small text file that a website saves on your computer or mobile device when you visit the site. It enables the website to remember your actions and preferences (such as login, language, font size and other display preferences) over a period of time, so you don’t have to keep re-entering them whenever you come back to the site or browse from one page to another.

2. How do we use cookies?

A number of our pages use cookies to remember your actions and preferences (such as login, language, font size and other display preferences.)

Also, some videos embedded in our pages use a cookie to anonymously gather statistics on how you got there and what videos you visited.

Enabling these cookies is not strictly necessary for the website to work but it will provide you with a better browsing experience. You can delete or block these cookies, but if you do that some features of this site may not work as intended.

The cookie-related information is not used to identify you personally and the pattern data is fully under our control. These cookies are not used for any purpose other than those described here.

3. How to control cookies

You can control and/or delete cookies as you wish – for details, see You can delete all cookies that are already on your computer and you can set most browsers to prevent them from being placed. If you do this, however, you may have to manually adjust some preferences every time you visit a site and some services and functionalities may not work.