Burnable poison rods

Chemical shim control is effected by adjusting the concentration of boric acid dissolved ia the coolant water to compensate for slowly changing reactivity caused by slow temperature changes and fuel depletion. Eixed burnable poison rods are placed ia the core to compensate for fuel depletion. 

Boron may also be used as a burnable poison to compensate for the change in reactivity with lifetime. In this scheme, a small amount of boron is incorporated into the fuel or special burnable poison rods to reduce the beginning-of-life reactivity. Bumup of the poison causes a reactivity increase that partially compensates for the decrease in reactivity due to fuel burnup and accumulation of fission products. Difficulties have generally been encountered when boron is incorporated directly with the fuel, and most applications have used separate burnable poison rods. 

The reactor core of an IPWR generally uses proven technology from loop-type PWRs or BWRs to minimize cost Typically, the fuel assemblies are square arrays of Zircaloy-4-clad, enriched UOj (< 5% U) fiiel rods with some burnable poison rod (GdjO,) positions. 

Core reactivity is controlled by means of chemical poison dissolved in the coolant, burnable poison rods and control rod assemblies. Soluble boron and burnable poison rods are utilized for shutdown and fuel bumup reactivity control. Control rod assemblies (37 clusters) are used for power regulation and hot shutdown. The core consists of 3 regions with enrichments of 2.4%, 2,67 % and 3. 0%, It has a negative temperature coefficient of reactivity. The core has a fuel cycle of 12 to 16 months with a discharge bumup of 30,000 MWd/tU. 

Burnable poison material and form. Fuel rod with GdjOj and burnable poison rod of borosilicate glass... 

Some confidence is established in the above calculational procedure for the configurations of interest noting the successful KENO run for the critical TMI-2 core (zero power, hot 530°F, clean, all rods out). This critical configuration had a boron level of 1500 ppm. The keff calculated for this configuration at temperature was 1.05Q 0.004. Since the fixed B4C burnable poison rods were estimated to have worth of 4.5% in keff and the.modeling assumed these rods to be lost, the agreement can be considered excellent. The 0.3%, core volume occupied by stainless steel, which is... 

The TMI core (see Fig, 1) is a Babcock Wilcox 177 fuel assembly plant containing three fuel enrichments 1.98, 2.64, and 2.96 wt%. Each assembly may contain one of three types of lump burnable poison rods, two types of control rods, or stainless-steel orifice rods. Preservation of the assembly loading pattern was considered to be essential in studying reactivity changes due to disruptive core mechanisms. 

LBP LUMPED BURNABLE POISON ROD ASSEMBLY cl TABLE 4.2-7 FOR DESIGN. 

The reactivity wortiis of the control rods and lumped burnable poison rods are significantly reduced by the hi soluble boron content in the reactor. 

Core physics benchmarks, on the other hand, must be representative of the reactor system of interest. They are designed to test reactor analysis methods in their intended areas of application. Thus, characteristic physical features such as geometric heterogeneities, water gaps, voids, burnable poison rods, etc., must be represented. 

Number indicates number of burnable poison rods S indicates source rod... 

Arrangement of burnable poison rods, initial core loading. 

Effect of burnable poison rods on soluble poison requirements. 

The reactor core contains 349 hexagonal fuel assemblies, each of them consisting of 129 fuel rods with a diameter of 9.1 mm and a length of 3.21 m the fuel rods are kept in position by 15 honeycomb-type spacer grids which are fixed on a central channel. Seventy-three of the fuel assemblies contain movable control assemblies with boron steel as an effective material in the V213 fuel assemblies, six of the fuel rods are replaced by fixed burnable poison rods. 

Burnable poison rods are based on the gadolinium like in icebreaker reactors, they provide a near-complete compensation of the burn-up reactivity swing. 

Burnable absorber Fuel Burnable poison rod 9 weight % Gd203 Pyrex including natural boron... 

---