Batch irradiation

Drawbacks of Batch Irradiation of Uniform Fuel and Poison... 

To point to the importance of using improved methods of fuel and poison management, we shall discuss qualitatively the multiple drawbacks of the simplest method, which is batch irradiation of fuel initially uniform in composition, with spatially uniform distribution of boron control poison and with complete replacement of fuel at the end of its operating life. An example of this would be a PWR charged with fuel of uniform enrichment containing 4 percent and 96 percent and controlled by adjusting the concentration of boric acid dissolved in the water coolant to keep the reactor just critical at the desired power level. When this reactor starts operation, the compositions of fuel and poison are uniform throughout the core, and the flux and power density distribution are very nonuniform. 

Figure 3.6 Bumup distribution in 1060-MWe PWR at end of period after batch irradiation of initially uniform fuel containing 3.2 w/o...

Partial batch replacement. Another method of fuel management, designed to deal with the nonuniform bumup of fuel, which is a second disadvantage of simple batch irradiation, is... 

The ratio of the burnup obtainable in n-zone scatter refueUng to that obtainable in simple batch irradiation is found by dividing Eq. (3.5) by (3.2) ... 

The ratio of the reactivity change per cycle in n-zone scatter refueling to the amount in simple batch irradiation is... 

The reactivity equals zero at a burnup of 20,833 MWd/MT. This is in excellent agreement with the reactivity-limited burnup of 21,085 MWd/MT for batch irradiation of 3.2 w/o fuel in this reactor obtained by Watt [W2] using the computer codes CELL [B2] and CORE [Kl]. 

Batch irradiators are far rarer conveyors are of the closed loop type wholly contained within the celt. Loading is done by personnel who enter the cell with the source in its safe storage location. The source is then brought to its operational position in the center of the cell and the conveyor is set in motion, moving the product around the source. When sufficient time has elapsed to ensure that the product has absorbed its appropriate dose, the source rack is returned to Us safe location, and personnel enter the cell to unload and reload the conveyor. 

The total absorbed dose will in addition depend on the path of containers through a continuous irradiator or the loading pattern in a batch irradiator, and on the number of exposure cycles. 

For a continuous irradiator with a fixed path or a batch irradiator with a fixed loading pattern, and with a given source strength and type of product, the key plant parameter controlled by the operator is conveyor speed or timer setting. 

The stones are batch irradiated in containers. At one facility a batch consists of about 2 kg of stones. Since only fast neutron irradiations are desired, the containers or the irradiation facility are often covered with Cd or boron. Because the temperature during irradiation must be controlled, some method of cooling the stones is necessary. 

Mizuno and coworkers [4] reported an enhancement in reaction efficiency, as well as regioselectivity, by conducting the photocycloaddition of a naphthalene derivative (1) (Scheme 6.1) in a microreactor. The authors found that in batch, irradiation of cyanonaphthalene derivative (1), using a filtered xenon lamp (A > 290 nm), afforded photocydoadducts (2) and (3) in 56% and 17% yield, respectively. In comparison, when conducting the reaction in a microreactor, employing an irradiation time of just 3.4 min, the desired compound (2) was obtained in an increased yield of 59%, while by-product (3) was reduced to 9%. 

---