The emergency services will be tested today during an exercise at Wylfa nuclear power station on Anglesey.
The test will check the response of all the emergency services in the event of an incident involving the transport of radioactive material.
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Local authorities said the move is necessary to "avert the growing number of deaths and increasing harm linked to psychoactive substances".
Sunny and bright spells for most of us this afternoon, feeling pleasantly warm.
North Wales Fire and Rescue Service say incidents of deliberate fires are more common during the school holidays.