The Health and Safety Executive (HSE) reported on one incident in the last quarter of 2001. This incident was reported by BNFL when it detected Tc-99 in groundwater taken from a borehole on its Sellafield site. This was the result for the first analysis of groundwater from this borehole for this isotope. The incident report noted that the sample may have been a false analysis. Subsequent analyses have confirmed Tc-99 in this borehole and, at lesser concentration, in others in the same area. Activity has also been detected beyond the site boundary, but at much lower concentrations.

HSE asked BNFL to determine the source of activity and report the work that the company is undertaking to prevent further leakage from the plant and to prevent activity leaving the site.

BNFL confirmed that the probable source of activity in the ground is the sludge storage tanks in Building B241. These tanks have been suspected to be leaking for some years, and recent modifications have been made to address this. The recent detection appears to confirm that leaked material reached groundwater on the site. The fall off of activity concentration in boreholes away from the plant is consistent with B241 being the source of the activity.

To remove the potential for leakage, BNFL is proposing to commence emptying the storage tanks in 2002. The safety case for this is currently being considered.

The Environment Agency said it is satisfied the reported concentration of Tc-99 is radiologically insignificant. However, until the source of the activity is known, there is regulatory concern. It requested BNFL to confirm the point of leakage.