Case ref: MLA/2017/00033
Licence ref: L/2017/00222/1

Case summary

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Project description

Project title

Project background

Sizewell B power station is located on the Suffolk coast, approximately 3 km east of the town of Leiston and 1 km north of Sizewell village. Sizewell B is a pressurised water reactor (PWR) facility containing one nuclear reactor.
During normal operation of the power station the Circulating Water System draws seawater in from a point on the seabed 600 metres off-shore at a flow rate of up to 58 cubic metres per second. The water flows through an intake tunnel below the seabed to an in-shore “forebay,” drawn by the four main circulating water (MCW) pumps located there. Subsequently, the water flows through the Turbine-Generator condensers for heat removal purposes and then through the in-shore “surge chamber,” before entering another tunnel that discharges the water back to the sea at a point on the seabed 200 metres off-shore. This process is covered by a Consent issued under the Water Resources Act 1991 (now covered under the Environmental Permitting Regulations, 2010), PRECS/3962C (see attached file).
During operation of the plant the following activities are required to maintain safe generation of electricity:
• Dewatering and desilting of the drumscreen chambers, culverts and forebay
• Cooling water intake and coarse screen inspection and cleaning
• Fitting and removal of stop gates
• Maintenance and refurbishment of cooling water intake including forebay, offshore intake structure, dosing line and instrumentation; drumscreen chambers and culverts; drumscreens; stop gates; cooling water outfall including surge chamber and offshore outfall structure.
It should be noted that the cooling water system is nuclear safety related plant and although the above works would normally be integrated within the station plan any significant defects would be required to be worked immediately.

Programme of works

The desilting activity is normally carried out during statutory outages at a 3-year interval frequency. One forebay and two drumscreens are de-silted in an outage and then repeated again two outages later. There are four drumscreens in total, so a rolling program of work is completed on two drumscreens at a time in this way. It takes approximately 12 days to complete the work, with de-silting occurring intermittently during this period. De-silting of the drumscreen/forebay areas is required at this frequency for the lifetime of the station.
Other activities that would normally be undertaken during outages include:
• Maintenance, inspection and cleaning of cooling water intake and coarse screen via diving operations.
• Fitting and removal of stop gates.
• Maintenance and refurbishment of hypochlorite dosing line.
• Other maintenance and refurbishment activities that can only be carried out during periods of CW system shutdown.
Drumscreen maintenance/refurbishment activities can also be undertaken during forced outages but may also be carried out during the winter months when all four pumps are not required to achieve optimal performance of the plant.
Whilst all other maintenance/refurbishment activities are planned in with other associated cooling water system programmes they can be associated with urgent maintenance and defect rectification which would need to be worked immediately.
Cooling water system activities are typically undertaken during outages at the end of every cycle. At present the cycle time is 18 months and the next scheduled outage is planned for November 2017. In future the cycle time maybe extended. It should also be noted that if the station had to shutdown within a month of a scheduled outage it is likely that the planned outage activities would be immediately commenced due to both operational and environmental impacts (increased discharges) associated with re-starting the reactor.

Other information

Applicant details

Mr Steve Friend / 01728653748 / steve.friend@edf-energy.com
EDF ENERGY NUCLEAR GENERATION LIMITED / Sizewell B Power Station EDF Energy Generation Nr. Leiston Suffolk, IP16 4UR / IP16 4UR

Date application submitted

Date application validated

Date initial decision made

Status