BBC Scotland's Leslie Anderson reports

The Scottish Environment Protection Agency (Sepa) issued an enforcement notice after 700 gallons of waste were spilled at the Chapelcross Nuclear Power Station in Dumfriesshire on 3 September.

Three weeks ago, water from a sump below a fuel storage pond overflowed and the operators conceded the spillage may have contained low levels of radioactivity.

Sepa said a full investigation was carried out and tests of stream water nearby have shown no significant impact on the environment but the agency described the spillage as very serious.

Sepa wants procedures tighened up

It was the third radioactive waste handling problem at Chapelcross this year.

BNFL said it is conducting an internal inquiry and safety checks to ensure a similar spillage does not happen again.

Spokesperson Nigel Monckton said: "We regret that this latest event happened at Chapelcross.

"We are reviewing our procedures and will take actions to ensure that this type of thing does not occur in the future".

Sepa Environment Protection Officer, Dr Jim Gemmill, said: "This is the third incident involving problems with liquid radioactive waste handling on the site to come to our attention since December 1998.

"Sepa expect compliance with all conditions of the site's authorisation and although there appears to have been no contamination of the local watercourse in this instance, we must view this matter very seriously.

'Conditions and standards'

"This enforcement notice requires BNFL to meet certain conditions and standards laid down by Sepa with a set timescale.

"Failure to adhere to this may result in a report being sent to the Procurator Fiscal."

Sepa was notified a day after the latest incident and took a number of water samples from a local burn which showed normal levels of radiation.

Last December, inspectors with the safety regulator probed a leak of liquid radioactive tritium waste at Chapelcross and concluded that the spread of contamination had been caused by "inappropriate storage of liquid waste on site".

A month later, the regulator issued a "warning letter" to the plant's operators after it discovered that, in a separate incident, a radioactive discharge had not been properly monitored.