Accident reactive

In general, it is possible to ensure that the additional reactivity due to a control rod expulsion is of the order of 0.15 per cent (but, in any case, well below 0.6 per cent, which would originate a prompt criticality ). The accident reactivity excursion is mitigated by the Doppler coefficient and is terminated by the reactor scram. Roughly 10 per cent of the fuel can be damaged (DNBR < 1) and the effective whole-body doses outside the plant may reach 10-20 mSv in two hours at the edge of the exclusion area. 

All chemicals should be stored with attention to incompatibilities so that if containers break in an accident, reactive materials do not mix and react violently. 

Chain reactions do not go on forever. The fog may clear and the improved visibility ends the succession of accidents. Neutron-scavenging control rods may be inserted to shut down a nuclear reactor. The chemical reactions which terminate polymer chain reactions are also an important part of the polymerization mechanism. Killing off the reactive intermediate that keeps the chain going is the essence of these termination reactions. Some unusual polymers can be formed without this termination these are called living polymers. 

Consequence Phase 3 Develop Detailed Quantitative Estimate of the impacts of the Accident Scenarios. Sometimes an accident scenario is not understood enough to make risk-based decisions without having a more quantitative estimation of the effects. Quantitative consequence analysis will vary according to the hazards of interest (e.g., toxic, flammable, or reactive materials), specific accident scenarios (e.g., releases, runaway reactions, fires, or explosions), and consequence type of interest (e.g., onsite impacts, offsite impacts, environmental releases). The general technique is to model release rates/quantities, dispersion of released materials, fires, and explosions, and then estimate the effects of these events on employees, the public, the facility, neighboring facilities, and the environment. 

Nitric acid is indicated as being particularly dangerous with carboxylic acids. It is interesting to note that an accident is reported with the nitric acid/lactic acid mixture combined with hydrogen fluoride in actual fact, lactic acid has a structure which is very close to that of this particular compound. The latter will certainly be less reactive due to the steric nature of the second methyl group. 

Lithium is extremely reactive with water and hydrogen peroxide. These are the only reactions which cause accidents. But one can find other dangerous reactions of this class of substances elsewhere in this Part (see p.146). 

Sodium is, like all other alkali metals, a very strong reducing agent (more reactive than lithium), which has extremely violent reactions with numerous compounds. It causes a large number of accidents. Sodium peroxide is a very reactive oxidant, which has violent interactions with reducing agents. Carbonates, and especially sodium hydroxide, are bases which react with acids (the reaction is aggravated by the formation of carbon dioxide). 

Chlorine is one of the strongest oxidants whether it is in the elementary form or as oxidised anions, with oxidation states of +l (hypochlorites) to +VII (perchlorates). The chloride ion with an oxidation state of -I is very stable (octet electronic structure) only hydrochloric acid is dangerously reactive, linked to its strongly acidic character. This explains the nature of the dangerous reactions which have already been described and have caused a large number of accidents. The accidental aspect is aggravated by the fact that the derivatives mentioned in this paragraph are much used. 

There have not been any accidents recorded that have mentioned metal halides (except with interhalogens , which are very reactive anyway). Nevertheless, it seems important that calcium should not be in contact with such halides without taking any precautions. It was noticed that calcium starts glowing when it is heated with boron trifluoride. 

Apart from chromium and chromium (II) salts, which are reducing, the table of accidents involving chromium derivatives is mainly one of very reactive oxidants. The effect of this dangerous property is worsened by the fact that the cited substances are commonly used, not only in industry (especially in sur ce treatment) but also in analysis, research and training laboratories. 

Rubidium is more reactive than potassium. Therefore there is greater risk of dangerous reactions of the seime nature. Since it belongs to the category of alkali metals which are less used, like caesium, this explains why there is only a small number of accidents. 

When analysing these different lists one realises that the different sources do not agree with each other. So far as the NFPA reactivity code is concerned, codes 2 and 3 have been attributed to epoxides and ethers that are unsaturated. Their purpose is to inform the reader about dangerous polymerisation and not peroxidation risks. The accidents described below also involve compounds such as dibutyl ether that are not considered as dangerous in the regulations or NFPA Extracting a fatty substance and a floor wax with diethyl ether gives rise to a detonation. 

The main danger factor is the polyhaiogenation on one carbon site only. The substitution (1) or elimination (2) reaction can then lead to an intermediate carbene (or to a transition state that has this character). Its reactivity and instability will create accidents. 

There are a few similarities between this accident and the previous one. When dinitroanilines (all isomers) are submitted to the effect of hydrogen chloride in the presence of chlorine, which seems to play a catalytic role, they give rise to a very violent reaction after a period of induction that can be very long if the temperature is low. Again a large volume of gas is also released. 2,3-Dinitroaniline is the most reactive, 3,5-the less reactive. 

When the lactone was introduced, the temperature reached 165 and then 180 C very quickly even though an attempt was made to cool the medium. The reactor detonated and a fire broke out. It seems obvious that the temperature rise is due to the high reactivity of lactone, but the main factor in this accident seems to be related to the behaviour of dichlorophenoi, which in such conditions gives rise to an aromatic nucleophilic substitution reaction that leads to the formation of a dichlorodioxin (see halogen derivative on p.283). 

Acid chlorides and anhydrides, especially the former, are the most reactive carbonyl compounds, hence the most dangerous. The dangerous reaction that is involved in accidents usually corresponds to the equation below, in which X is a chlorine atom or a O2C-R group and H-X a compound with a mobile hydrogen ... 

As far as reactivity is concerned, there is no link between the different classes of compounds this chapter is concerned with. Therefore, they will be analysed separately, excluding borates, since no accident involving them could be found in the sources (which does not mean that they are not dangerous, but that they are hardly used). 

Poor sleep architecture and fragmented sleep secondary to OSA can cause excessive daytime sleepiness (EDS) and neu-rocognitive deficits. These sequelae can affect quality of life and work performance and may be linked to occupational and motor vehicle accidents. OSA is also associated with systemic disease such as hypertension, heart failure, and stroke.21-23 OSA is likely an independent risk factor for the development of hypertension.24 Further, when hypertension is present, it is often resistant to antihypertensive therapy. Fatal and non-fatal cardiovascular events are two- to threefold higher in male patients with severe OSA.25 OSA is associated with or aggravates biomarkers for cardiovascular disease, including C-reactive protein and leptin.26,27 Patients with sleep apnea often are obese and maybe predisposed to weight gain. Hence, obesity may further contribute to cardiovascular disease in this patient population. 

The benefits of replacing chlorine with STABREX are in reducing environmental toxicity (because it is less toxic to aquatic wildlife), in reducing accident risk (because it is less hazardous and easier to handle), and in reducing chemical waste (because it works better, is more stable in transport/storage, is less volatile and less reactive). Environmental toxicity and accident risk have been substantially reduced in more than 2,500 industrial water systems worldwide. 

Review and analyze the EPA document on reactive chemicals (see footnote 29), and describe the steps required to prevent accidents of this type. 

Kohlbrand, H. T., "The Relationship between Theory and Testing in the Evaluation of Reactive Chemical Hazards," in Proceedings of the International Symposium on Prevention of Major Chemical Accidents, p. 4. 69, Center for Chemical Process Safety/AIChE, New York, NY (1987). 

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