Reactor operating rules

2 Pressure and temperature margins for plant operation derived from comparison between reactor operating ruie (ABC) and caicuiated iimit iine. (Reproduced with the permission of the institute of Materiais, Minerais and Mining and W. S. Maney and Son Ltd.) 

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For optimum utilization of a given set of ideal reactors operating as ah isothermal reactor network, an examination of the 1 /( — rA) versus CA curve is a good way to find the best arrangement of units. The following general rules have been enunciated by Levenspiel (24). 

For the parallel reactions in equation 10.7.1 one may use this general rule to select the follpw-ing operating conditions as optimum from a selectivity viewpoint when the reactor operates isothermally. 

The rules for intrinsically safe batch and semi-batch reactor operations are extensively discussed by Steensma [175] and Steinbach [177,178]. 

Concerning the hydrodynamics and the dimensioning of the test reactor, some rules of thumb are a valuable aid for the experimentalist. It is important that the reactor is operated under plug-flow conditions in order to avoid axial dispersion and diffusion limitation phenomena. Again, it has to be made clear that in many cases testing of monolithic bodies such as metal gauzes, foam ceramics, or monoliths used for environmental catalysis, often needs to be performed in the laminar flow regime. 

Network A is huilt of n basic systems, and all the reactions take place in a fed-batch reactor. As such, the analytical model developed for network A is an extension of the model developed for the basic system (see Section 4.1.3.1). Based on the principles detailed in Section 4.1.3.1, the operational rules of network A are described by... 

Various schemes of reactor operation under forced unsteady-state conditions are shown in Figs 1-4. An unsteady-state process in a fixed bed reactor can be created by oscillations in the inlet composition or temperature (Fig. 1). As a rule, a simple stepwise periodic control (Fig. 1 (a)) is preferable to other types of inlet... 

We can construct the matrix of stoichiometric coefficients and reduce it to a diagonal form to determine the number of independent reactions. However, in this case, we have three reversible reactions, and, since each of the three forward reactions has a species that does not appear in the other two, we have three independent reactions and three dependent reactions. We select the three forward reactions as the set of independent reactions. Hence, the indices of the independent reactions are m = 1, 3, 5, and we describe the reactor operation in terms of their dimensionless extents, Zi, Z3, and Z5. The indices of the dependent reactions are = 2, 4, 6. Since this set of independent reactions consists of chemical reactions whose rate expressions are known, the heuristic rule on selecting independent reactions is satisfied. The stoichiometric coefficients of the selected three independent reactions are... 

Maintaining required purity of the coolant and cover gas is a necessary condition for successful operation of any reactor facility. In case of sodium cooled reactor these requirements are determined by Specifications on sodium coolant for nuclear reactors (TV - 6 - 01 - 788 - 73) and Rules of the BN-600 reactor operation. They are most rigid for the primary circuit, since nuclear safety of the reactor is immediately concerned. 

To identify the probable cause of the transients, 20 postulates were studied and 14 of them were tested during reactor operation. Based on recorded observations, calculations, tests and analysis, inadvertent raising of CR by operator just before the incident was ruled out. The postulates studied can be broadly classified into the following five categories viz. process parameter changes, absorber movement, voids collapse and sodium filling, fuel movement and moderator ingress ... 

It is clear from what happened that the operators at Chernobyl did not realise the significance of violating the operating rules and taking the reactor to an extremely unstable condition. They seem to have been determined to carry out the planned test to the exclusion of all other considerations. In the UK considerable emphasis is placed on operators being trained to appreciate the factors bearing on safe operation of the plant and to adhere strictly to them. 

The Site Licence is a simple document containing a brief identification of the site, the type and size of the reactors, and a plan from an Ordnance Survey map delineating the site boundary. The Licence refers to schedules which require operating rule and maintenance schedules to be written and formally submitted to the Nil for approval. These are legally binding upon all station personnel and such documents are unique to a particular power station site. 

Hydrodynamics, mass, and heat transfer in the commonly used three-phase fixed-bed reactors were briefly outlined. Also, scale-up rules and alternative ways to scale down trickle-bed reactors are discussed. In spite of the extensive studies on the hydrodynamics, mass, and heat transfer in three-phase fixed-bed reactors, clearly, a lot of work remains to be done in providing a fundamentally based description of the effect of pressure on the parameters of importance in three-phase fixed-bed reactors operation, design, and scale-up or scale-down. It is evident that atmospheric data and models/correlations cannot, in general, be extrapolated to operation at elevated pressures. The physics conveyed by the standard two-phase flow models is minimalistic because it insufficiently describes the role and presence of interfaces and their thermodynamic properties. The explicit inclusion of interfaces and interfacial properties is essential because they are known to have a significant role in determining the thermodynamic state of the whole system. 

UsuaUy, such double oxides are highly temperature-resistent and it can be expected that these fission products will show virtually no thermal-induced migration in the fuel matrix. This assumption has been confirmed by numerous measurements that show a distribution dependent on the bumup profile of the fuel. Most of the information in this area has been gained by examining fast breeder reactor fuels (Kley-kamp, 1985), i. e. materials which had been irradiated at distinctly higher fuel temperatures than LWR fuels. For this reason, thermal-induced migration of the polyvalent fission products in LWR fuels, with their distinctly lower temperatures during reactor operation, can be ruled out. 

The operators noticed that the control rod reactivity margin was too low -the control rods had been raised so far that they would be unable to have any significant and immediate effect to reduce reactor power when required. Indeed, the reactivity margin was at a level where operating rules stipulated that the reactor should have been shutdown. No such action was taken. 

Because of the flexibility required in operating a research reactor, it may be necessary to rely for safety in certain activities on administrative controls and procedures. Special consideration shall be given in design to ensuring that, if reliance on administrative controls and procedures is necessary, such controls are feasible. Administrative procedures may include operating rules in the form of OLCs, which are derived from the design of the reactor and the safety analysis. 

Samant and Ng [28] compared various scale-up rules for agitated reactors. They suggested that a scale-up rule of power per unit volume and constant average residence time (where the power per unit volume and average residence time cannot be increased) is the most suited in many operations. However, this still may not improve or preserve the performance of the systems. Therefore, adequate consideration must be given to a tradeoff between performance and operating constraints. 

All RBMK reactors have positive void coefficients which means that increasing the boiling rate increases the steam fraction in the core which increases reactivity causing more steam void which causes more reactivity and so on. Competing factors provide stability, but startup, shutdown and maneuvering below about 600 MWt are unstable, hence, there is a rule prohibiting extended operation below 700 Mwt. 

With regard to mistakes, two separate mechanisms operate. In the rule-based mode, an error of intention can arise if an incorrect diagnostic rule is used. For example, a worker who has considerable experience in operating a batch reactor may have learned diagnostic rules that are inappropriate for continuous process operations. If he or she attempts to apply these rules to evaluate the cause of a continuous process disturbance, a misdiagnosis could result, which could then lead to an inappropriate action. In other situations, there is a tendency to overuse diagnostic rules that have been successful in the past. 

If the consequences of not waiting until the pressure had dropped were serious and/or omitting to check the pressure was likely, then it would be necessary to break down the operation "charge reactor" to its component steps. This approach to deciding on the level of decomposition is called the PxC rule (where P is the probability of failing to carry out an operation and C the cost of the consequences). The size of the product PxC determines whether or not to describe the operation in more detail (Shepherd, 1985). 

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