Integral Inherently Safe Light Water Reactor (I2S-LWR)

This research project will evaluate the concept of an advanced (beyond Gen-III+), large light water reactor (LWR) (GWe-class), with advanced fuel design, several specific novel design features, and safety enhanced beyond the passive safety in state-of-the-art LWRs. It is not competing with the current large Gen-III+ reactors (such as the Westinghouse AP1000 or the Areva EPR) with respect to markets or timeline, but addressing the next step in nuclear power generation.

State-of-the-art LWR designs include:
1. Large LWRs with power levels by definition >700MWe, and in practice of the order of 1 GWe (typically in the 900-1,600 MWe range for modern large LWRs).
2. Passive safety in some of the large Gen-III+ LWRs (e.g., AP1000) notably enhances safety characteristics when compared to the older generation reactors currently operating.
3. Enhanced safety is achieved in some conceived small modular reactor designs by features (including an integral primary circuit) which deterministically eliminate some accident initiators and probabilistically promote the safety level beyond passive safety ("inherent safety").
However, it is perceived that inherent safety limits the power level to small/medium size. The new concept to be investigated in this project aims to achieve both large power and inherent safety simultaneously.

This project will evaluate a novel concept of a high-power ("GWe-class", i.e., at least 900 MWe, and preferably 1 GWe or more) inherently safe LWR. Inherent safety is used to denote:
- a safety level beyond that of passive Gen-III+ LWRs (achieved by elimination of accident initiators and enhanced probabilistic indicators);
- a long-term self-sustained decay heat removal capability with no need for intervention in case of an accident and loss of external power;
- improved resilience to seismic events.
Additional desirable safety characteristics are incorporated as well.

Key design elements enabling the design objectives to be achieved are:
- fuel with increased accident tolerance;
- compact core design;
- compact heat exchanger design;
- ambient/air as the ultimate heat sink for decay heat removal;
- integral primary circuit layout;
- seismic isolators.

This project will investigate and evaluate a range of design details and choices in respect of the reactor core, fuel design, fuel cladding, coolant flow conditions, heat exchangers, instrumentation and plant configuration in order to identify and assess both technically and economically options that meet the design objectives.

A critical novel aspect of the concept is high power (and high power density) in an integral primary system layout. Conventional wisdom is that a higher power density will challenge safety performance. However, in this new assessment, it is realised that high power density may have both positive and negative impacts on safety indicators, and thus the overall effect is not necessarily negative. The major positive impact, as compared to large power loop reactors, is that it enables an integral configuration, which is significantly more conducive to inherent safety.

From an economic perspective, the compact design leads to a reduced footprint which reduces the cost. High specific power reduces fuel carryover charges. Compact design facilitates (and reduces cost) of a design resilient to seismic events and security treats. A portion of that saving is used for a long-term self-sustained decay heat removal system, overall providing increased safety and competitive design.

This research project will evaluate the concept of an advanced (beyond Gen-III+), large light water reactor (LWR) (GWe-class), with advanced fuel design, several specific novel design features, and safety enhanced beyond the passive safety in state-of-the-art LWRs. If this evaluation confirms the expectations of the concept's proponents, it will bring a safer, more cost-effective and more environmentally friendly form of nuclear power closer to realisation.

This will benefit:
- electricity consumers, through provision of electricity in a cost-effective and environmentally friendly way;
- the nuclear power industry and the electricity supply industry, through the development of a new, more cost-effective and inherently safer reactor design;
- the general public, through the provision of electricity with low carbon emissions and less environmental impact than current nuclear reactor designs;
- UK science and engineering, through the increased interest generated in these disciplines by groundbreaking projects such as this, and in particular in young people, attracting more of them to study these strategically important subjects at university.

The research to be conducted at the University of Cambridge will focus in particular on evaluating the potential to use thorium-bearing fuels in the inherently safe high-power LWR concept. In addition to establishing basic feasibility, we will assess the extent to which the use of thorium-bearing fuels facilitates better use of uranium resources in comparison to conventional Gen-III+ reactors and fuel cycles. If thorium-bearing fuels are indeed an attractive option, then there is considerable potential for Springfields Fuels Limited in Preston to benefit as Westinghouse (the parent company) are substantially involved in this proposal.