HAZARDS SUMMARY REPORT FOR THE VMR CRITICAL-ASSEMBLY EXPERIMENTS

Moderator Reactor (VMR), a reactor concept under investigation by American-Standard for the AEC. The VMR is light-water moderated and cooled and is fueled with slightly enriched uranium dioxide pellets loaded into aluminum tubes. The core consists of 37 hexagonal fuel cans each loaded with 61 fuel pins. The cooling water, which flows upward around the pins inside the fuel can, boils in passing through the core. Reactor control in the prototype will be achieved by varying the moderator height. The site, laboratory, and the critical assembly, including control and safety mechanisms, are described in detuil. Special characteristics of the assembly pentinent to safety were calculated. The nuclesr energy released and the average and maximum fuel temperatures resulting from step reactivity increases up to 2% DELTA k/k are presented graphically for two cases. In the first case, fuel-temperature effects are considered to be the oniy shutdown mechanism; in the second radiolytic gas is considered to contribute to shutdown, in addition to fuel-temperature effects. The accident considered to be the maximum credible accident causes a step addition in reactivity of 1.5% DELTA k/k. The nuclear-energy release is between 160 and 310 megawatt-sec depending on the assumed shutdown mechanisms. This accident does not cause any fuel to be vapcrized (and probably none to be melted) and, hence, there does not appear to be a hazard from fission-product activity. It appears that this criticalassembly program can be conducted with reasonable assurance of safe operation and that no public persons will be jeopardized by its operation. (auth)