Page 406 - Fundamentals of Magnetic Thermonuclear Reactor Design

384 Fundamentals of Magnetic Thermonuclear Reactor Design

The ASME Code (Section VIII, Division 2) was chosen as a regulatory
framework for designing various vessels. Cryogenic piping is designed based
on ASME B31.3. Ducts for the transport of radioactive fluids, such as tritiated
water, and pipes making part of the first confinement barrier are developed ac-
cording to the same C&S (ASME B31.3 for category M liquids). The RCC-MR
2007 codes govern the design and manufacture of tokamak VVs and heating
neutral beam injectors, as well as the diagnostic and heating equipment for other
ITER components.
The European EN 13445-6 (Unfired Pressure Vessels), EN 13480 (Metallic
Industrial Piping), and EN 13458 (Cryogenic Vessels–Static Vacuum Insulated
Vessels) meet the main requirements of the European Pressure Equipment Di-
rective and the French laws on the development of pressure equipment contain-
ing radioactive fluids. One can find more information on the EU harmonised
standards at http://ec.europa.eu/enterprise/policies/european-standards/index_
en.htm.
ITER-specific C&S include the following:

l Magnet Structural Design Criteria
l Structural Design Criteria for In-vessel Components (SDC-IC)
l Technical specifications for the electrical insulation and dielectric windows
for plasma diagnostics purposes
The regulatory framework for the MS structural assessments is based on
heavily modified C&S governing the design of pressure vessels and nuclear
power plant components (ASME Sections III and VIII, ASME B31.3; API 579,
etc.). The modification was needed because of the specific behaviour of the MS
structural materials at cryogenic temperatures and the unique technical solu-
tions for its design.
For example, the ultimate and yield strength of structural steels used in the
superconducting coils increase considerably when the coils are cooled down
to operating temperatures, while their plastic flow becomes intermittent and
dependent on the loading rate. The stress ‘equalisation’ effect in constructional
elements weakens significantly as a result of local plastic deformations. The
materials become susceptible to a static brittleness and fatigue crack propaga-
tion.
The primary mechanical loads for an MS are the alternating ponderomotive
forces, while in the nuclear power plant the main stresses are due to the weight
and the coolant pressure.
Current in-service and even periodic inspection of ITER is impossible ex-
cept for a few limited regions. This calls for imposing more stringent require-
ments for potential initial defects and their propagation rates.
The superconducting coils are complex anisotropic structures, and their
electrical insulation may perform the load-bearing function. Its strength re-
quirements depend, among other things, on its electrical engineering role. The
magnetomechanical interactions of the MS components may lead to the loss of