Fuel fail and emission from research reactor

Print View Posted on: 02 March 2018

Event Date: 24 October 2016 Event Type: Research Reactor
Event Location: Norway, Institute for Energy Technology, Halden INES Rating: 2 (Final)

The previous rating, sent March 2, 2017 - was mistakenly given as a final rating.
This was only meant as the first rating of the event, and further inspections were being held to fully understand the incident at the Halden Research reactor.
The INES officer offers sincere appologies for the mistake.

The incident:
The Halden Boiling Water Reactor was in planned shutdown from October 9 2016. The planned outage tasks included to search for a fuel failure that had been discovered in July and the unloading of an experimental flask for analysis of material specimens with results to be delivered to customer by 30 November. The flask was equipped with booster fuel with higher enrichment. It was also possible that the booster fuel was the candidate for fuel failure.

Some of the material specimens had fallen down in the flask, and the fuel was therefore removed from the experimental flask.

17 October the booster fuel was placed in a basket in the fuel service compartment. The cooling in the basket was insufficient to maintain the cladding temperature at sufficiently low levels. The overheating of the fuel caused deformations of the cladding caused by high pressure inside the cladding. In some of the fuel rods a part of the cladding swelled into balloons. The cladding material was ductile and the balloons grew until the cladding ruptured.

Radiation Levels of I-131, I-132 and noble gasses in the reactor hall increased the following days. On October 21st The fuel in the fuel service compartment was inspected and several faults on fuel pins were detected.

The fuel cladding is a physical barrier protecting the surroundings from radioactive releases. The Barriers themselves are protected by defensive measures (defence in depth). The fuel which is cooled by water whilst in pile, was located in air and the protection from the fuel from overheating proved insufficient.

The fuel was then moved to an airtight storage container on October 24, however the container was discovered to not be leak tight.
The levels of I-131 and I-132 and noble gasses in the Reactor hall still increased.

The personell reacted to the alarm that warned about this on October 24th and evacuated (as per routine). The following day the radiation Levels had not decreased as expected, and the Norwegian Radiation Protection Authority (NRPA) was notified of the unintended release of I-131, I-132 and noble gasses.

The NRPA declared an emergency alert and IFE was put under enhanced oversight placing their own representatives at the site in Halden.
The NRPA judges that the Notification of the incident should have been made already on October 24th, and not on the 25th when they were notified.

Ventilation was closed on October 25.

The radiation levels were still high until October 31st when IFE mounted ekstra sealing to the container.

The total release to the air was approx. 150.6 MBq I-131, and 27.1 MBq I-132, as well as noble gasses.
Total release to water was 27.6 MBq I-131.

It has been discovered that there was only one safety layer remaining before a more significant release could have occured.

INES Rating: 2 - Incident (Final) as per 17 November 2017
Release beyond authorized limits? No
Overexposure of a member of the public? No
Overexposure of a worker? No

Contamination spread within the facility? Yes
Damage to radiological barriers (incl. fuel damage) within the facility? Yes

Degradation of Defence In-Depth Yes

Person injured physically or casualty? No
Is there a continuing problem? No

Monica Dobbertin
Norwegian Radiation Protection Authority

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