The workers were decommissioning the Trawsfynydd station in Gwynedd last June.
They were using breathing apparatus to clean the cooling pond where irradiated fuel used to be stored at the plant.
According to BNFL, no long-term damage to their health occurred.
But two workers suffered a significant dose equivalent a quarter of the annual dosage permitted. Four others had much lower traces of radiation.
Station manager Alun Ellis said the level of radiation for all workers undertaking that kind of work was tested regularly and samples sent for examination to Sellafield.
![[ image: width=150]](/olmedia/480000/images/_481728_ellis150.jpg)
It was during one of those tests that the contamination was discovered.
The two workers involved were part of a group of eight employed by a firm of German subcontractors working at the site.
The firm, Hertel, is one of the world's leading decontamination companies.
It is thought that dust from the cleaning process was responsible for the contamination and possibly a faulty seal on the breathing apparatus of the two men led to the incident.
BNFL immediately closed the area and called in the nuclear installations inspectorate to supervise an internal investigation.
The investigation has recommended better ventilation be installed and has agreed that decommissioning in that area can recommence from the second week of December.
The cause of the initial contamination has still not been discovered.
Decommissioning began at the Trawsfynydd plant in 1993.
It is a Magnox reactor and decommissioning is likely to take several decades.
British Nucelar Fuels Limited
Gwynedd County Council
The BBC is not responsible for the content of external internet sites.
Labour explores Assembly election wounds
Delays hit coach crash compensation
Ex-headmaster guilty of more sex charges
Museum in pay-off probe
Euro row over "Welsh" money rebate
Germans challenge Cardiff for Tyson fight
Ticket chief resigns after World Cup fiasco
Quick-thinking driver foils 'carjacker'
Spring clean for river
Roman remains may halt rugby centre plan
Olympic rider Sir Harry is mourned
The Welsh Week at Westminster
Hanged farmer had been cautioned
Children take over the Assembly
Assembly security review follows pupil's 'threat'
Opposition parties criticise Health Secretary
Welsh airline is launched
Anglesey power plan may bring 1,500 jobs
Former paratroopers recruited drugs courier
Star's cyber-fans help Welsh charity
Labour election inquest blames party rifts
New factory creates 500 jobs
Bassey will go world wide on the web
French boycott gathers pace
Villagers fume at delay over sewage problem
Pensioner leaves fortune to birds
MP demands return of Glyndwr letter