Page 434 - Fundamentals of Magnetic Thermonuclear Reactor Design

412 Fundamentals of Magnetic Thermonuclear Reactor Design

of a neutron activation analysis. The dose rate of ionising radiation from tri-
tium, DR , is assumed to be proportional to the concentration of tritium in air.
T
Occupational exposure is calculated with consideration for the radiation effect
weakening by local or temporary protective equipment, such as shields and her-
metically sealed accoutrement.

14.3.4 Radioactive Waste, Reactor Decommissioning

Critical to the future of fusion energy and technology is the solution for the
radioactive waste disposal problem. One of the advantages of the fusion reactor
is that it produces a relatively small quantity of radioactive waste containing
long-lived radioisotopes, while fission reactors mostly produce fission products.
According to the PPCS-AB fusion reactor design estimates, the specific activity
of long-lived radioisotopes is 45 TBq/(GW · year), as compared to 4800 TBq/
el
(GW · year) for a PWR-type fission reactor. At the same time, the design
el
experience with demonstration and commercial fusion reactors suggests that
the mass of radioactive materials (RMs) removed from fusion reactors while
in operation and after decommissioning per generated electric power will be
much greater than for fission reactors. This makes the fusion radioactive waste
disposal a serious challenge.
Liquid and solid RMs are subdivided into very low-, low-, medium-, and
high-activated materials (see Table A.14.1.4) [11]. They are collected and sorted
with consideration for their radioactive, physical and chemical properties and
subsequent handling methods. As part of the initial sorting procedure, they are
divided into radioactive and non-radioactive waste and categorised according
to their properties. Decontaminated low-activity dust-gaseous and liquid waste
are dissolved to acceptable levels and discharged to air or water reservoirs. To
reduce radioactivity, waste packages are kept prior to processing in temporary
storage facilities for periods from a few days to a few tens of years. Condition-
ing is undertaken as a safety measure to decrease waste volume and change it
into a form that is suitable for transportation, storage and disposal [12].
Liquid waste conditioning methods include sedimentation, extraction, ion
exchange, distillation and solidification. Solid waste management techniques
include compacting, burning and calcination (roasting at 500–700 K), while
gaseous waste is treated by chemical absorption, adsorption and filtration. The
conditioning end-products are immobilised solid RMs in the form of compact
packages. When stored, they are separated by category and group. Long-term (a
few tens of years) storage facilities include burial trenches, and above-ground
and below-ground systems equipped with storage condition and radionuclide
migration monitoring instruments. Deep underground repositories, salt forma-
tions and caverns in stable geological formations are used where it is necessary
to keep RM waste away for hundreds of years. Fusion reactors of the PPCS and
ARIES type do not generate any RMs that would be classified as high-activated
waste after 100 years disposal.