Water balance for new build nuclear18 May 2023
Arrangements around water supplies and discharges are critical for the UK’s next planned EPR at Sizewell which is being built in Suffolk, an area described as water stressed.
Above: Sizewell C has been granted a water discharge permit
At the end of March a water discharge permit was granted by the UK’s Environment Agency for the planned new EPR at Sizewell C (along with two others covering radiological discharges and the operation of power generators). The consent is required in addition to the development consent granted by the Secretary of State in July last year and approvals for the reactor design granted by the Office for Nuclear Regulation (ONR).
Planning for water supply and discharge at the site have proved to be a complex challenge for the project company, NNB Generation Company (Sizewell C) Limited (NNB), both for the huge volumes of cooling water required during the site operation, but also for the much smaller volumes of potable water required during operation and for the water required during construction. The Sizewell C (SZC) site is adjacent to that of the operating plant at Sizewell B on the Suffolk coast, which gives ready access to cooling water – albeit the eventual arrangements may have marked differences from both Sizewell B and from the EPR now under construction at Hinkley Point in Somerset. But the Suffolk region in the eastern UK is an area defined by the Environment Agency as under ‘water stress’, so there is little access to fresh water supplies on land to meet the site’s short- and long-term needs and questions remain over securing the water supply in the long-term.
The twin 1630 MWe reactors planned for Sizewell C will be direct-cooled. Each of the units will have its own dedicated cooling water intake tunnel 3-3.5km offshore. Seawater will then be abstracted from the Greater Sizewell Bay in the North Sea via the two dedicated intake heads and tunnels, one for each reactor, around 500m apart.
In its operational phase, the plant will require a continuous supply of cooling water at a rate of 132 m3 per second at the mid-tide level of seawater. Flow rates will vary between 125 and 140m3/s. The cooling water (waste stream A) represents approximately 99% by volume of the total overall daily discharges of non-radioactive effluent from SZC. The maximum daily discharge volume of cooling water would be approximately 11.4 million m3. During standard operation, cooling water would be returned to the Greater Sizewell Bay at a maximum temperature of 11.6°C above the ambient seawater temperature, having passed through the steam turbine condensers. The outfalls also include six much smaller waste streams.
The water discharge activity permit includes 19 pre- operational conditions which need Environment Agency approval before the proposed power station can be commissioned or begin to operate. Many of them arise because of the lengthy design process and construction period associated with Sizewell C, which means aspects of the detailed design are evolving.
Contaminants are of course of particular concern and the Environment Agency (EA) requires a priority hazardous substances management plan before hot functional testing begins. It must show how the operator intends phase out discharging priority hazardous substances, such as cadmium and mercury which is present as trace contaminants in bulk raw materials.
The EA also requires a report on the operational strategy for the control of biofouling of the cooling water system. That would include an appraisal of the operational conditions and chlorination strategy employed at Sizewell B, lessons from commissioning and operating any other EPR (eg Flamanville in France), details of how the operational strategy has been optimised to reduce the need for chemical dosing and validation of the impacts of the proposed dosing regime.
NNB also has to report on its plans for the use and discharge of hydrazine (N2H4), which is added to cooling water prevent oxidation of metals (rusting) in the steam generator. NNB said that that although other ‘oxygen scavengers’ are available, these either reduce the efficiency of the power station, or are more harmful to the environment than hydrazine. Hydrazine will be present within waste streams from the nuclear island waste monitoring and discharge system and tanks and within a waste stream from the conventional island liquid waste discharge system network and tanks. NNB has agreed to monitor hydrazine within these systems and use an appropriate treatment method – still to be determined and qualified - to reduce levels before any discharges occur if they may breach limits. In addition before commissioning at Sizewell C NNB will study the feasibility of further minimising hydrazine.
The need to protect fish in Greater Sizewell Bay has been highlighted by campaigners against the new plant at Sizewell C. As a result of the direct cooling of the Sizewell C power station with seawater, each unit will each incorporate a fish recovery and return (FRR) system to minimise the risk of injury to fish that are drawn into the cooling water system. The FRR systems will return the fish to the Greater Sizewell Bay. Each of the FRR systems is served by a dedicated discharge tunnel and outfall. These will discharge at locations where fish are not likely to be returned to the four cooling water intakes.
At Hinkley Point C, measures to ensure fish are not scooped up in the cooling water intakes include three so- called ‘acoustic fish barriers’ (AFBs). EDF has recently argued that the benefits of having three AFBs do not outweigh their costs. But in March this year the environment secretary ruled against EDF when it argued that only two fish barriers were required. Quoted in local media, Chris Fayers, Head of Environment at Hinkley Point C, said: “We are considering the detail of the planning inspector’s decision and the options available to us. Hinkley Point C is the first power station in the Bristol Channel to include any fish protection measures at all. Studies from the government’s own marine science experts have shown that the power station will have a negligible impact on local fish stocks with our proposed fish protection measures in place. This includes a fish return system, and water intakes designed to significantly reduce the number of fish coming into the pipes.”
At Sizewell C, it is not yet clear what measures will be required. NNB has to present EA with an updated site plan and a commissioning plan for the two FRR systems, details of the monitoring proposed to facilitate optimisation minimise fish kills and proposals for demonstrating the effectiveness of the optimisation. That will incorporate the lessons learnt through design evolution and from other EPRs at Hinkley Point or worldwide.
Other water supplies
Although cooling water is by far the largest water use for Sizewell C, general water requirements onsite are a complex challenge for NNB and the eventual operator of the reactors. In the decision letter granting development consent for Sizewell C the Secretary of State devoted 57 paragraphs to discussion of this issue. The supply will be provided by local water monopoly Essex and Suffolk Water (whose parent company is Northumbrian Water Ltd, NWL), and wastewater services will be provided by Anglian Water. But in its planning, NWL says the region is expected to be in deficit and “the water required deficit increases in 2032 due to a step increase in demand when we will start supplying Sizewell C with 2.2Ml/d as an annual average and 2.8Ml/d as a peak daily”.
When NNB applied for development consent it expected that it would be supplied with ‘mains water’ from the local Blyth Water Resource Zone, but the EA considers NWL abstractions in this zone to be ‘over licensed’, with NWL unable to meet additional water demand by abstracting more water.
NWL initially said it could supplement the supply, if necessary, in four ways: new water main supply pipes to bring water from other areas; trading abstraction licences with other local licence holders; storing water on-site; and water efficiency measures to reduce demand from mains supply.
During the development consent process, interested parties expressed ‘significant concerns’ about whether a sustainable supply for Sizewell C would adversely affect already stressed water resources. Natural England joined with other groups to ask for further information. NWL suggested that the plant would require a new water main pipeline from another catchment area and said the additional infrastructure required would take until September 2026 at the earliest.
But in addition, extra water supply and water and wastewater disposal would be required during the construction period of 10 years or more, both to meet the needs of thousands of temporary workers housed locally and for construction processes such as providing water cooling during tunnelling activities. NNB wanted to take over an existing water main to serve the accommodation campus and NWL was concerned it may be compelled to supply water, creating a critical risk to its existing customers in the absence of additional infrastructure.
In response, NNB submitted a revised strategy, which included a temporary desalination plant to supply potable water during the early construction phase until such a time as the NWL supply transfer main could be operational. Until the desalination plant started up (up to a year), water would supplied by tankers. The desalination plant comes with its own environmental concerns, including power consumption, sustainability, cost and wastewater (brine) discharge.
In its report to the Secretary of State, the ‘examining officer’ from National Infrastructure Planning said that the plan “does not address the need to fully consider the cumulative assessment of the environmental effects of the proposed water supply solution that is fundamental to the operation of the Proposed Development”. The examining officer makes a recommendation to the Secretary of State on whether to grant development consent for a project but the Secretary of State’s decision can go against the recommendation.
The Secretary of State sought further information from other sources including the nuclear regulator, the Office for Nuclear Regulation (ONR). The ONR said there is no specific Licence Condition covering the requirement for a reliable water supply but that it “would expect the licensee to put in place a reliable source of water before nuclear safety-related activities take place on the site that are dependent on such a supply. This may be during the later stages of commissioning, but such a supply will certainly be needed before the station begins to raise power from nuclear reactions in the core”. The examining officer noted that there was a possibility that a sustainable water supply would not be identified and therefore a possibility that the plant may not be able to operate.
NNB argued that the reason a long-term water supply is not known at this stage is that the long-term planning of water supply is subject to separate statutory provisions and processes that will result in Water Resource Management Plans (WRMP) for the region. This WRMP24 process is now under way and plans were published in draft for consultation in October 2022. It said that, with regards to the Development Consent, the Secretary of State was required not to duplicate other licensing processes and to assume that they would be properly carried out and “because on the evidence the source of the supply is unlikely to be a constraint to the construction and operation of the new power station, the source does not need to be known for the purposes of the Application.”
In his decision the Secretary of State noted that the Sizewell C development consent and the WRMP24 process for the sourcing of water are separate projects, and said, “This is evident from their separate ownership and because they are subject to distinct and asynchronous determination processes”. As a result the lack of a water strategy at this stage was not a bar to granting consent.
The decision means NNB can continue to work with NWL on its plans to source water while it progresses the project towards final investment decision. It may mean that the desalination plant first proposed to cover the construction phase will become permanent. Other options for securing long-term water supplies include import from neighbouring catchment areas; effluent reuse and desalination; and longer-term (post-2035) winter storage reservoirs. Whatever the final proposals, they must also be proof against climate change for a plant that could be in operation for up to a century.
Who’s who in water regulation
The UK’s Department for Environment, Food and Rural Affairs oversees water and environment policy and regulation, although some water policy is devolved to England, Scotland, Wales and Northern Ireland.
Monopoly water and sewerage companies provide water for both business and domestic users. Ofwat is the economic regulator holding the water companies to account on the delivery of five-year plans produced by the privatised water companies. The water companies are also required to produce long-term water resource plans.
Water is used by water companies and other users (such as agriculture and large industry) under abstraction licences granted by the Environment Agency (EA). The EA also leads on the development of the Water Industry National Environment Programme and is responsible for assessing the water resource planning for each water company.
Natural England is the government’s advisor on the natural environment. It is tasked with protecting and improving England’s natural environment and advise on the impacts on water dependent habitat sites. Similar bodies also exist in the separate devolved administrations.
Across the UK, water quality is currently maintained in accordance with the environmental objectives set out under the European Union’s Water Framework Directive. However, post-Brexit and the UK’s objectives may diverge from those in the EU Directive.
Author: Janet Wood, expert author on energy issues