Spontaneous chain

In fact, free radicals synthesized in the initiation process may induce spontaneous chain transformation of the acceptor only, which proceeds in the case of quite long chains. Otherwise, the process will not be developed at any noticeable rate. 

Drozd, R. X, Hohenberg, C. M., Morgan, C. X (1974) Heavy rare gases from Rabbit Lake (Canada) and the Oklo Mine (Gabon) Natural spontaneous chain reactions in old uranium deposits. Earth Planet. Sci. Lett., 23, 28-33. 

In conformity with the problems formulated, we used as objects systems which were known to be incapable of producing spontaneously chains of conversion at radiolysis temperatures of 77 and 4.2 K. In the course of y irradiation of... 

Sensitivity to moistiwe 1 kg of water could increase die system reactivity up to -. 5 peff- 20 kg could lead to accidents widi initiation of spontaneous chain reaction (K,ff>l)... 

The risk of water ingress into eventual pores and cavities in frozen coolant inside SRUs and thus an increase in reactivity up to initiation of spontaneous chain reaction must not be ruled out ... 

Under the used technology of SRU temporary storage the probability of water ingress into the container storing SRU must not be ruled out the risk of initiating spontaneous chain reaction will exist until every SRU is dismantled ... 

The three new initiation centers formed in reactions Eq. (9.18)—(9.20) have different chemical structures. Thus for the polymerization of propylene using either AlEts or AlEt2Cl as cocatalyst, K = n-propyl, R = ethyl, and R = H. However, for most catalyst systems and under normal conditions of monomer and alkylaluminum concentrations, spontaneous chain transfer reactions [Eq. (9.20)] can be neglected. 

Chain Transfer In the absence of any externally added transfer agent, three transfer reactions [Eq. (9.9)-(9.12)] may be considered, viz., chain transfer with monomer, chain transfer with aUcylaluminum, and spontaneous chain transfer. 

There are some differences between a narrow subject matter approach, which will be the subject of discussion during our Workshop, and approaches to safety analysis developed in Russia. We do not separate nuclear material management from technologies and facilities. Therefore, we develop safety analyses based on the assessment of technological safety, and nuclear materials are a component of this assessment. To go ahead, we should always analyze the statistics of equipment failures, the causes of troubles or accidents, including those with spontaneous chain reactions in the work with nuclear materials, and storage of nuclear materials. 

In 1997, we had two spontaneous chain reactions at the All-Russian Research Institute of Experimental Physics in Sarov and at the Novosibirsk Plant of Chemical Concentrates. There were the situations when we could not expect that chain reactions might take place at such facilities. 

Therefore, summing up the activities of Minatom in 1997, we had an ambivalent feeling. On one hand, the unbiased results which would suit us at any other time. However, two spontaneous chain reactions prompted us to draw the most important conclusion the problems of nuclear safety, the observance of regulations and standards should be the focus of attention, since the origin of all incidents was the infringement of general safety rules. 

Assessment of reliability of nuclear safety measures, spontaneous chain reaction (SCR) risk and consequences in the nuclear dangerous areas, plants, and during transportation of nuclear hazardous fissile materials ... 

Spontaneous chain termination through -elimination reactions ... 

Quite recently an interesting mathematical treatment has been reported for (quasiliving) polymerization involving reversible spontaneous chain transfer... 

The rate expression for spontaneous chain transfer is given by ... 

The livingness of a polymerization with regard to spontaneous chain transfer is characterized by the ratio tr,sp/ p- The smaller this number (or the greater its reciprocal), the greater is the degree of absolute livingness. Since the transferred reactive species is assumed to rapidly re-initiate monomer, polymerization... 

Eqn (2.20) can also be used to calculate the fraction of original chains that have terminated via spontaneous chain transfer, by substituting [Ptr.sp] in place of [Pt,sp] and ktr,sp in place of t,sp-... 

Thus, in the particular system chosen, chain breaking is by spontaneous chain transfer, and there is no dormant-active equilibrium (all centers are active all of the time). The rate constant for propagation represents the composite for paired and free ions. Eqn (2.10) (with K=oo and kapp = kp) shows that for this system, 99% conversion is reached within about 9ms. Moreover, eqn (2.20) shows that 99% of the original chains have decomposed via spontaneous chain transfer within about 46 s. Clearly, such a system would not be considered living and it would offer no control from the point of view of end group fidelity or block copolymer synthesis. 

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