mechanical forces that might be generated by core melting, and to contain the bulk of fission products in a class-9 accident. This would be a stricter criterion than those applied to light water reactors.
A number of commentators point out that reducing the probability of core melting 10–50 times below the probability of core melting in LWR’s can be set as an objective for LMFBR designs, but that it is unrealistic to expect conclusive demonstration that the objective has been met.77
The unanswered questions for LMFBR safety, then, are: whether inherent or engineered safety features eliminate or greatly reduce the probability of core melting; whether, if this probability cannot be reduced to desirable unlikelihood, engineered features can contain the consequences; and by what mechanisms reasonable consensus can be reached that these objectives have or have not been met.
A preliminary analysis of HTGR safety has been conducted by the vendor, and there has been some assessment of its features in design reviews of the Fort Saint Vrain reactor and other proposed HTGR installations. Salient features of this analysis are discussed in the report of the Risk and Impact Panel. The Working Group on HTGR Safety of that panel concluded tentatively that the HTGR may be less susceptible to large radioactive releases than the LWR. The HTGR has demonstrably better tolerance for storing decay heat without releasing fission products and may be less subject to a large LOCA, but it has the extra mechanism of graphite oxidation for potential release of fission products and heat. In case of loss of the helium coolant, for example, air could not be used for emergency cooling because it would burn up the graphite.78
Sabotage of Nuclear Facilities As already noted, deliberate sabotage has not been included in the discussion of nuclear accidents, as it is not usually included in accident analysis of other systems. Nevertheless, the question has been raised whether the existence of nuclear facilities presents an “attractive nuisance” to would-be terrorists, who might use the threat of sabotage to extract concessions from society, or to people bent on destruction.
This discussion is limited to a general review. Details can be found in the recently issued report of the National Academy of Sciences on the safety of nuclear power.79 That report (like this discussion) is necessarily limited to information in unclassified literature.
Three points must be considered: the degree of vulnerability of nuclear installations, consequences that might credibly ensue, and comparison of vulnerability and consequences with those of other energy sources.
Nuclear systems are probably less accessible, and harder to sabotage, than many competing energy systems. Access is more carefully controlled than to other thermal power plants, and all thermal plants are inherently