5.6.2.1 Blast Shielding

To allow the vessel to deform radially but not to such an extent that it damages the reactor cavity walls or thereby itself, blast shielding may be used effectively to strengthen the radial wall.

Figure 5.17 illustrates the radial cross section of shielding of a typical LMFBR. The shielding is provided for radiation reduction, and it may therefore be composed of serpentine concrete encased in steel. However,

the total radial thickness of mild steel (7.5 in. in this case) forms a very efficient and effective blast shield, even taking no credit for other materials in the shielding system.

The analysis of the blast shield is performed using the Cole charge weight correlation (24):

/ = 1.46 W°-33(W°-33IR)0-9 (5.29)

where / is the specific impulse (lb-sec/in.2), W is the charge weight (lb TNT), and R is the reactor shield radius (ft).

The kinetic energy is

KE = (IAfjlM (5.30)

and the energy of strain is

SE = In do&t (5.31)

where A is the inner surface of the unit annulus (in.2), M is the annulus mass (slugs), ё is the radial elongation (in.), t is the annulus thickness (in.), and <ra is the average stress during the strain (lb/in.2).

For the blast shield to perform as required the strain energy must be greater than or equal to the kinetic energy. Assuming an elongation before rupture of a given amount and summing the strain energies for each annulus of the blast shield, this sum can be compared to the calculated kinetic energy to determine whether the blast shielding is adequate.

To satisfy the model, the nitrogen-cooling annuli and the concrete annuli are assumed to have been collapsed without significant energy absorption. The shield of Fig. 5.17 can accommodate 30001b of TNT assuming an elongation SR/R of 0.3. Thus it can be seen that the inclusion of radial radiation shielding will usually provide more than adequate blast shielding at the same time.