Water boronate assemblies

Rieck [Rl] has used the computer codes LEOPARD IBl] and SIMULATE [FI] to predict the power distribution in the fuel and poison arrangement shown in Fig. 3.19 for the first fuel cycle for this reactor, and the amount of thermal energy produced by each assembly up to the time when the reactor ceases to be critical with all soluble boron removed from the cooling water. Figure 3.20 is a horizontal cross section of one-quarter of the core of this reactor. Each square represents one fuel assembly. The core arrangement has 90° rotational symmetry, about the central assembly 1AA at the upper left of the figure. 

The reactor core is an open PWR type core made up of 213 fuel assemblies with standard PWR fuel rod diameter and a reduced height. The 2000 MWt core is located near the bottom of the reactor pool, which is a high-boron content water mass enclosed by a prestressed concrete vessel. The PIUS reactor does not use control rods, neither for reactor shutdown nor for power shaping. Reactivity control is accomplished by means of reactor coolant boron concentration control (chemical shim) and by coolant (moderator) temperature control. 

Eiiqierimental comparisons of the various assemblies include critical mass as a functicn of boron content or metal-to-water ratio and buckling as a function of boron content. 

If no credit for soluble boron in the SFP water is taken, the effective neutron multiplication factor (fceff) of the spent fuel storage racks loaded with fuel of the maximum fuel assembly reactivity must not exceed 0.95, at a 95% probability, 95% confidence level, if flooded with unborated water. If credit is taken for soluble boron in the SFP water, then the of the spent fuel storage racks loaded with fuel of the maximum fuel assembly reactivity must not exceed 0.95, at a 95% probability, 95% confidence level, if flooded with borated water. The /teff must also remain below 1.0 (i.e., subcritical) at a 95% probability, 95% confidence level under the assumed loss of soluble boron in the pool water, that is, assuming unborated water in the SFP (CFR, Title 10, Part 50). Finally, reactivity effects of abnormal and accident conditions are also evaluated to assure that under these conditions the reactivity will be maintained less than 0.95. 

Additionally, accident and abnormal conditions are considered such as misplacement ot a tuel assembly outside the rack, misleading ot a tresh, unburned assembly into the center ot the non-flux trap racks, variation ot water temperature, drop ot an assembly onto the top ot the rack, and lateral rack movement during a seismic event. For accident conditions, soluble boron in the SFP may be credited to ensure that the reactivity does not exceed 0.95. 

An essential part of the crihcality safety analysis is to ensme that the computer code accurately predicts the effective multiplication factor. Therefore, the computer code is benchmarked against experimental data, using critical experiments that encompass the pertinent design parameters of the canister basket. The most important parameters are (1) the enrichment, (2) the geometrical spacing between fuel assemblies, (3) the boron loading of the fixed neutron absorbing panels, and (4) the soluble boron concentration in the water. 

Pellet type uranium dioxide fuel is used with the average enrichment of 15.2% the neutron moderator and coolant is water specially treated according to specified water chemistry. Cylindrical fuel elements with stainless steel cladding are installed in 109 fuel assemblies of 55 fuel elements each 216 absorber rods with boron carbide based neutron absorber are divided into 6 groups. Fuel assemblies also include burnable absorbers made of Gd-Nb-Zr alloy. The load is 147 kg. 

Shinkai and Kanekiyo discuss the development of boronic acid-based supra-molecular systems. Supramolecular systems discussed include sugar-responsive gels, porphyrin-boronic acid, systems that exhibit guest-induced spectroscopic changes, two-dimensional self-assembly at the air-water interface, boronic acid-functionalized metal nanoparticles and boronic acid-appended polymers. 

The reactor has two independent mechanically driven control and protection systems (CPSs), each consisting of 135 absorber assemblies, three in a control member of the reactor CPS. The reactor also has a liquid boron shutdown system, based on injection of the sodium pentaborate water solution (NaBsOg, 3 g/kg). Each of the systems can scram the reactor and maintain it in a sub-critical state, as illustrated by the data of Table VIII-3. 

In a boihng water reactor (BWR), the CEA are crosses inserted from the bottom of the core between fuel assemblies. Different absorber materials are used, either B4C boron carbide (compacted powder about 70% density) or hafniiun, in parallel tubes or in plates in the wings of the crosses. 

A beautiful tubular structure has been reported by Durka and coworkers [80] very recently from simple 1,2-phenylenediboronic acid 40 (Fig. 3.21). The dibo-ronic moieties form an alternating hexameric ring, and the rings are further connected laterally to a tube. The tubes may host interesting water clusters, but the incorporated water molecules are interacting weakly with the boronic framework, thus are not responsible for templating the self-assembly. 

---