Example: For the Tokamak reactor described in Example 2 above, lithium is fed to the breeder zone at a temperature ( T) of 2500C and leaves the zone at T = 600°C. Calculate the lithium flow rate required and the maximum wall temperature on the lithium side of the first wall if the heat output of the reactor is 2 GW and the heat transfer coefficient (a) between the lithium and the wall is 25,000 W/mK. Assume a specific heat ( ер) for lithium of 3.4 kj/kg K and a density (g) of 500 kg/rn4 Also assume that 70% of the energy from the reaction that is released to neutrons (80% of the total energy) is converted to heat in the lithium.

Solution: Of the total energy originally generated by the reactor, (20 + 0.7 x 80)% = 76% eventually finds its way into the lithium blanket. The heat released is given by

Q = VQcp(T0-T) = 0.76x2x109 =1.52 x 109 W where V is the flow rate of the lithium. Thus:

6cp (To — Г )

_ 1.52 xlO9

_ 500 X 3.4 X 10: X (600-250)

= 2.55 m-/s

As explained in Section 9.2, 80% of the energy arising from the fusion reaction is in the form of the kinetic energy of the neutrons, and the neutrons will pass into the lithium, reacting with it to form ‘He and T and also releasing heat into the lithium stream. It was assumed that 70% of the original neutron energy (56% of the total energy) is released as heat in the lithium (the remainder being used in the conversion of 7Li; see Section 9.2). Assuming that the remaining 20% of the fusion reaction energy is radiated from the plasma to the first wall, and finds its way into the lithium via that wall, the maximum wall temperature would be

Tmax = 600 + f1T°C

where AT is the temperature difference between the wall and the lithium and is given by

_ 2 x l09 x0.2

AT =———————-

first wall area x a

= 2x10x0.2 = 340c

470 X 25000

Thus, the maximum first wall temperature would be 634°C.

Problem. Repeat the calculations in the example for the reactor calculated on the more relaxed energy flux constraint given in Problem 2.

BfflUOGRAPHY

American Nuclear Society (ANS) 0983). Proceedings of the Fifth Topical Meeting on the Technology of Fusion Energy, Knoxville, Tenn., April 26-28.

Carmthers, R. (1977). “The Fusion Dilemma.” Interdisciplinary Sci. Rev. 6 (2): 127-41, 198l.(See also VIIIFusion Prague 1977, 8th European Conference on Controlled Fusion and Plasma Physics, vol. 2, 217-29.)

Gibson, A. 0977). ‘The JET Project.” Atom (254): 3-15.

International Atomic Energy Agency 0982). Plasma Physics and Controlled Nuclear Fusion 1982, Conference Proceedings, Baltimore, Md. September 1—8, vols. 2 and 3. IAEA, Vienna.

Lehnert 0977). “Thermonuclear Fusion Power.’’ Energy Res. 1, 5-25.

Lomer, W. M. 0983). “Remaining Steps towards Fusion Power.” Nucl. Energy, 153-57.

Pease, R. S. 0977). “Potential of Controlled Nuclear Fusion.” Contemp. Phys. 18,

113-35. (See also “Physics in Technology,” 144-51.)

—— (1978). “The Development of Controlled Nuclear Fusion.” Atomic Energy Rev. 16

(3): 519-46.

—— 0979). “Nuclear Fusion: The Development of Magnetic Confinement Research.”

Fusion Technol. United Kingdom Atomic Energy Authority.

Pease, R. S., and A. Schluter 0976). “The Potential of Magnetic Confinement as the Basis of a Fusion Reactor.” In Nuclear Energy Maturity, Proceedings of the European Nuclear Conference, Paris, 91-94, Pergamon, Elmsford, N. Y.

[1] The Atomic Energy Research Establishunent of the U. K. Atomic Energy Authorities, founded in 194(].

[2] Inlet pipe rupture in a Magnox reactor

Example: A severe accident in a Magnox reactor contained in a steel pressure vessel is rupture of an inlet cooling duct followed by 50 s of stagnation in the core. During this period the only means of cooling is heat lost by radiation to the graphite moderator, which remains at 350°C. The metal fuel pin has a diameter of 30 mm, and the initial can temperature is 450°C. The temperature drops across the Magnox cladding and fuel — to-clad gap may be neglected. The initial fuel rating (R) is 35 kW/m, and it takes 4 s for the control rods to enter the reactor to shut it down. What is the maximum Magnox cladding temperature at the end of the stagnation period?

Solution: We consider ihe four sources of energy that will make the clad temperature rise. (1) Delay in shutting down the reactor. The energy per meter length due to the

[3] High radiation levels and/or contamination on-site due to equipment failures or opera­tional incidents. Overexposure of workers (individual doses exceeding 50 millisieverts)."