Safety analyses of the ARIES tokamak reactor designs

The ARIES design effort has sought to maximize the environmental and safety advantages of fusion through careful selection of materials and careful design. Three goals are that the reactor achieve inherent or passive safety, that no public evacuation plan be necessary, and that the waste be disposable as 10CFR61 class C waste. The ARIES-1 tokamak reactor design consists of an SiC composite structure for the first wall and blanket, cooled by 10 MPa helium. The breeder is Li 2ZrO 3, although Li 2O and Li 4SiO 4 were also considered. The divertor consists of SiC composite tubes coated with 2 mm tungsten. Owing to the minimal afterheat of this blanket design, loss-of-cooling accident (LOCA) calculations indicate maximum temperatures will not cause damage if the plasma is promptly extinguished. The ARIES-II design includes liquid lithium and vanadium, both of which have low activation, multiple barriers between the lithium and air and an inert cover gas to prevent lithium-air reactions. The ARIES-II reactor is passively safe with a total 1 km early dose of about 88 rem (0.88 Sv). This dose is the result of a full-scale lithium fire resulting from a LOCA with air ingress. ARIES-III was an extensive examination of the viability of a D– 3He fueled tokamak power reactor. Because neutrons are produced only through side reactions (D + D → 3He + n, and D + D → T + p followed by D + T → 4He + n), the reactor has the significant advantages of reduced activation of the first wall and shield, low afterheat and class A or C low level waste disposal. Since no tritium is required for operation, no lithium-containing breeding blanket is necessary. We modeled a LOCA in which the organic coolant was burning in order to estimate the amount of radionuclides released from the first wall. Because the maximum temperature is low, below 600°C, release fractions are small. We analyzed the disposition of the 20 g per day of tritium that is produced by D-D reactions and removed by the vacuum pumps. The ARIES-IV reactor has been designed for low activation and low stored energy. The coolant is helium and the breeder is lithium oxide. The structure is silicon carbide. Since the neutron multiplier, beryllium metal, is combustible, releasing about 60 MJ kg −1, beryllium is the chief source of chemical energy. Less than 10% of the 24Na inventory is likely to diffuse out of the SiC during a fire in which the beryllium is consumed. Therefore, the offsite dose would be less than 200 rem.