Page 442 - Fundamentals of Magnetic Thermonuclear Reactor Design

Safety of Fusion Reactors Chapter | 14 419

The radiotoxicity of ITER is dominated by the in-vessel components. It de-
creases by several orders of magnitude within 50–100 years followed by a much
slower decrease due to longer-lived radioisotopes. Total radioactive mass imme-
diately after the reactor shutdown is estimated at 31,000 t. Material remaining as
radioactive waste after a decay time of 100 years is estimated at 6100 t.

14.4.3 ITER Safety Analysis for Normal
and Off-Normal Situations
To avoid underestimation, potential effluents and releases of RSs are assessed
for end of reactor operation lifetime conditions using conservative assumptions.
Table 14.3 shows that no radioactive hazardous substances have a release rate
exceeding the design release limits.
Under a reactor’s normal operation for workers allowed access to radiation
sources, individual effective annual dose is within 25 mSv/year, while the col-
lective annual dose averaged over the ITER service life is 0.5 man-Sv.
By the time a comprehensive safety analysis began, the reactor design and
engineering process had been still underway. For this reason, gamma radiation
doses were determined using expert estimates or based on the maximum accept-
able level for a given access zone, that is, <10 µSv/h. Whenever this limit is ex-
ceeded, optimisation procedures are initiated. To determine the dose produced
3
by tritium in air, the coefficient 3 × 10 −11 Sv m /(h Bq) (10 µSv/h at a tritium-
3
in-air concentration of 0.3 MBq/m ) was used. For the purposes of estimation, it
had been assumed that the main operations would be done behind the bioshield
using the remote handling equipment and that the presence of workers would
only be necessary during preparatory operations.
A conservatively estimated collective annual dose during maintenance of the
diagnostic systems is ∼17% of the maximum acceptable dose (500 man-mSv).
This gives a dose headroom of around 25% when extrapolated to the reactor as
a whole. This is considered insufficient by the international fusion community,

TABLE 14.3 Estimate of Effluents from the Reactor
Release outside the reactor per year
Harmful and hazardous substances Absolute Guideline limit (%)
Tritium in air
As HTO and DTO 0.05 g (18 TBq) 50
As HT and DT 0.18 g (67 TBq) 18
−4
Tritium in water 10 (0.14 TBq)
Activated dust 0.25 g metal 25
Activated corrosion products 0.85 g metal 17