Scope & Objectives of DEMO Design

Scope and Objectives

DDA will address the following activities below. The first five items have high priority, and are directly relevant for ITER and JT-60SA exploitation so joint work is foreseen in these areas.  In addition, on the last three items information will be exchanged to share the whole view of DEMO. For each of these activities, possible collaborations and exchanges with ITER and JT-60SA will be considered.

For each activity the scope and objectives are described.

(1) Plasma scenario development

Scope:
Although JA and EU DEMOs consider different plasma operation scenarios, common physics issues have been identified. These include
(a) the assessment of the ramp-up scenario for highly elongated plasma by means of plasma equilibrium simulators,
(b) the assessment of plasma heat loads on the first wall. EU and JA developed analysis codes based on magnetic field line tracing.
(c) the study of plasma scenarios (to be developed) with no/small ELM.

Objectives:
One of the first activities to be carried out includes the identification of heating and current drive (H&CD) requirements for all the relevant discharge phases, namely flat-top, ramp-up and ramp-down, by considering all the functions such auxiliaries have to be employed for (i.e. current drive, radiative instability control, burn control, MHD instabilities control, access to H-mode). In particular, it is important to assess whether two or more functions (e.g. current drive and MHD instabilities control) can be performed by the same actuator at the same time, or not. Also, an indication on the most adequate technology (EC, NB) for each of the indicated functions shall be provided.

Regarding the plasma facing components (PFC), the objectives are to determine the heat load, the load specification; to characterize the foreseeable (e.g. plasma limiter phase during ramp-up/ramp-down) and unforeseeable plasma transients (e.g. disruptions, mitigated and unmitigated, including TQ/CQ, VDE, H-L transitions) leading to plasma – PFC interaction; and to analyse the loads due to charged particles, radiation, and runaway electrons (RE).

(2) Divertor and power exhaust

Scope:
In BA DDA Phase I, both JA and EU have been developed their power exhaust scenarios and divertor designs based on the ITER divertor concept. The JA and EU approaches will provide important case studies for their decision of the DEMO divertor design. In the BA DDA Phase II, JA and EU continue to improve the power handling scenario and the divertor design. The plasma performances of the plasma detachment and particle exhaust are evaluated by simulation codes such as SOLPS (EU) and SONIC (JA), thus it is necessary to confirm that physics models and results are consistent under the DEMO conditions

• Objectives:
• Perform the benchmarks between SOLPS and SONIC;
• Improve the detachment modelling to compare with each other simulations or experimental results.
• Identify common design criteria and strategies for the divertor target units and cassette from the viewpoints of the physics and engineering requirements.

(3) Breeding blanket design, and tritium extraction and removal:

• Scope and Objectives:
• The conceptual design of Breeding Blanket (BB), Tritium Extraction and Removal (TER) and Coolant Purification Systems (CPS) as integrated components of the BB systems will be developed to ensure the self-sufficiency of fuel in the entire fuel system.
• The Tokamak Exhaust Processing (TEP) system will be designed to complete the fuel system design.
• Dynamic tritium cycle simulator(s) will be developed to support the fuel system design.

(4)  Remote maintenance:

Scope and Objectives:
The purpose of this task is to produce a review document that highlights and selects emerging technology that have the potential to solve maintenance strategy challenges for the ex-vessel and active maintenance facilities of EU DEMO and JA DEMO.  This will require a review of current ex-vessel and active maintenance facility strategies of both future devices, a capturing of risks and technology gaps followed by an investigation into current industrial or emerging technologies that should be the focus of future concept design research programs to bridge the technology gaps. Engineering tools should also be identified.

(5) Safety:

Scope and Objectives:
The purpose is to develop DEMO safety concepts relevant to the current DEMO designs for reinforcing substantial environmental and safety advantages of fusion. In order to develop DEMO-relevant prevention and impact mitigation systems, safety study will cover i) definition of initial events and accident sequences, ii) assessment of mitigation systems for reference accident sequences, iii) development of waste characterization and management strategy, and iv) assessment of licensing constraints.

(6) Systems code:

Scope and Objectives:
The systems code is a key tool to understand overall DEMO concept such as core plasma size, tokamak configuration, radial build, plasma and divertor performance, engineering parameters of magnet/in-vessel components/BoP, power flow, cost information etc. The work items below will contribute to the principle/strategy of the DEMO design.

• The primary objectives of BA Phase II on systems code are as follows.
• Improvement of physical model and cross-check with more detail codes
• Extension and revision of costing model in systems code
• Assessment of magnet modelling in systems code
• Wide-range benchmarking about robustness of plasma design, uncertainty, cost estimation etc.

(7) Superconducting magnets:

Scope and Objectives:
The toroidal field (TF) coil Winding Pack (WP) including the conductor is challenging technology to withstand enormous electromagnetic forces and to allow the fabrication of large-scale TF coils anticipated in DEMO. The purpose of the magnet design is to develop the most feasible WP concepts based on the shared comparisons and benchmarking of designs on both EU and JA.

(8)Balance of plant (BoP) and plant system:

Scope and Objectives:
The identification of the reference operational scheme and of the reference technologies for the BoP is a key element for the design of the plant layout and the space allocation to the other major DEMO systems: these include the RM that requires large spaces and specific activation limits to be able to operate, the H&CD systems, the safety systems, the auxiliary systems, the large Tritium Extraction and Removal systems and the tritium plant.

• The objective of the balance of plant (BoP) and Plant system activities is to develop the overall plant concept of DEMO considering the following work items:
• Development of power conversion system
• Development of plant electrical system
• Development of cryo-plant system
• Delineation of layout of plant site and tokamak complex
• Assessment of Tritium permeation in the primary cooling system (Tritium handling in the primary coolant is treated in the Breeding Blanket design and Tritium Extraction and Removal of DEMO)