Easy-care coolants

Easy-care coolants. Boric acid (II, 8.2.1.) derivatives, e.g. boric acid ester, with different alkano-lamines are used in these formulations. In practice, the content of these derivatives is between 20 and 40%. The boron content of such a product then varies between 0.5 and 2%. 

Many users of such easy-care coolants are of the opinion that additional use of a chemical preservative is not necessary. We have investigated this question in extensive laboratory tests by subjecting such water-mixed coolants to a preservation challenge test (S M Boko test Figure 5). 

The conditions of this test can be made harder by incorporating the preservative into the coolant concentrate, storing it for ten days at +40 C, and only then diluting it with water to the use-concentration. In these challenge tests, boric acid esters, which are supplied as raw materials, and also numerous quite differently formulated easy-care coolants in practical use, were tested for their susceptibility to contamination and loadability on repeated contamination with microorganism. Among these easy-care coolants were also formulations that contained EP additives, for which a degree of antimicrobial effectiveness cannot be ruled out. 

However, the microbiological situation can be quite markedly improved by the use of preservatives. It is seen that in the case of easy-care coolants successful results can also be obtained with certain formaldehyde-free preservatives (here Grotan F 10). 

As a third product group, the results with easy-care coolants that contained such EP additives in their formulations are therefore presented, and a further formulation (coolant E), a preservative whose details are not known to us. 

Only with the use of a preservative and keeping to a 5% use concentration can better results be obtained. Should easy-care coolants therefore be preserved ... 

It is known that e.g. large car manufacturers use preservatives even with easy-care coolants, with the aim of keeping the microorganism counts to < 10 cfu/ml, one of the particular aspects being industrial hygiene. 

From the results of our tests, supported by the comments above, it can be concluded that the use of preservatives when using easy-care coolants is sensible not only for technical, but also for ecological and economic reasons. 

Even the easy-care coolants are not a general alternative. They display certain deficiencies in use they are problematical with hard water the concentrations must be adhered to very exactly, and in practice problems with yeasts and moulds repeatedly occur. 

Despite the large fission product and actinide inventory of the fuel, the leakage rate from the fuel pins may be kept to a very small value by adequate design and careful quality control in manufacture. The coolant circuits of reactors which are refueled on-load are particularly easy to maintain at a low level of activity, on account of the ease with which defective elements can be removed. In addition to any small escape of fission products from cracks or pinholes in the cladding, some activity will generally arise from slight contamination of the outsides of the fuel pins with fuel while they are being loaded. 

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