Page 447 - Fundamentals of Magnetic Thermonuclear Reactor Design

424 Fundamentals of Magnetic Thermonuclear Reactor Design

of construction materials, although the rate of those processes would be at least
a factor of 10 lower than for the DT fuel. This is particularly important with
respect to tritium, considering its high radiotoxicity, mobilisation ability and
permeability. In addition, energy released in the nuclear fusion reactions in this
case is mostly carried by charged particles and electromagnetic quanta, mean-
ing that the fusion-to-electricity conversion efficiency would be above 50%, that
is, much higher than with conventional fuel cycles [22,23].
3
Plasma in a D- He-based tokamak must be very hot. For example, ARIES-
III plasma operating temperature by the ignition moment is designed to be close
to 60 keV (cf. below 20 keV in DEMO-S). Therefore, approximately 50% of
fusion power is converted to electromagnetic radiation, of which up to 80% can
be converted to electric power.
ARIES-III design activities included the analysis of four potential accidents:
l The plasma quench followed by the divertor partial evaporation.
l Coolant ingress from the divertor into the vacuum chamber, and its combustion.
l Loss of blanket system coolant.
l Loss of blanket system coolant and its ex-vessel combustion.
Passive mechanisms for limitation of effluents, regardless of accident type,
are designed into ARIES-III for safety-related reasons. Fatal releases outside
the protective area are ruled out whatever the reactor operational state is.
3
ARIES-III supports the attractiveness of the D- He fuel concept for mag-
netic fusion reactors, at least from the safety and environmental points of view.

APPENDIX A.14.1 DEFINITIONS, LIMITS AND CRITERIA
Definitions, limits and criteria as specified in Russian regulatory documents [9,11]:
Absorbed dose: energy imparted by ionising radiation to the mass unit of a
matter. Measurement unit: grey (Gy), 1 Gy = 1 J/kg.
Collective effective dose: measure of collective risk of stochastic effects of
ionising radiation, equal to the total of individual effective doses. Measurement
unit: man-sieverts (man-Sv).
Dose limit (DL): annual effective or equivalent dose of human-induced ra-
diation that must not be exceeded in normal operation conditions. DL compli-
ance helps prevent deterministic effects and keep potential stochastic effects at
an acceptable level.
Effective dose: measure of the risk of long-term effects of ionising radiation
on the human body, organs and tissues, accounting for their sensitivity to radia-
tion. Measurement unit: sieverts (Sv).
Equivalent dose: absorbed dose in an organ or tissue multiplied by a proper
coefficient depending on the radiation type. Measurement unit: sieverts (Sv)
(Table A.14.1.2).
Group B staff: personnel that does not work with technogenic radiation
sources, but works in the area of their impact.