Evaluation of the U.S. Department of Energy's Alternatives for the Removal and Disposition of Molten Salt Reactor Experiment Fluoride Salts (1997) / Chapter Skim
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Appendix E: Hazard Scoping of Major Actions for Remediation
Appendix E: Hazard Scoping of Major Actions for Remediation
Pages 111-120
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From page 111... ...
, include the following: Action 1: Removal (principally from the piping and the freeboard of the tanks) and analysis of the reactive gases f uorine IFS and uranium hexafI~oride LUFF from the vent lines of the salt drain tanks, now under pressure.
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From page 112... ...
Collection of a salt sample Obtaining a solid sample of the fuel salt in the drain tank appears to be an operation with hazards that result from gaseous radon contamination, as discussed in Chapter 4 and Appendix C The sampling method considered here by the panel is a simple core drilling operation, with the drill and contained sample removed from the drain tank to a hot cell for sample handling and analysis, conducted after the reactive gases F2 and UFO have been rem overt from the Coining ~nr1 the drain tank freeboard.
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From page 113... ...
These effects can be monitored during melting and the heat inputs arranged so as to minimize differential effects by relieving most volumetric effects on the free surface of the salt bed. A third hazard is that tanks may leak due to progressive corrosion during fluorination operations.
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From page 114... ...
The relative corrosion rates for different timetemperature-reagent compositions for alternative fluorination processes should be tested and confirmed, and the process conditions optimized, by using small-scale laboratory tests. In risk terms, this hazard appears likely to remain seriously uncertain unless creative inspection methods are found or developed.
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From page 115... ...
The second hazard is the possibility of criticality due to possible segregation of fissionable material. The criticality hazard can be limited by using a low salt melting rate and by progressively fluoridating out the uranium content of the melt zone before further melting occurs.
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From page 116... ...
Remaining uncertainties in the conditions required for this process can be determined by a series of laboratory melting tests with simulated "reduced" uranium in salt so as to permit measurement of diffusion and reaction rates. A continuous monitor of the degree of subcriticality of the system, such as sensitive neutron monitoring, would provide a measurement to support calculations and provide additional assurance of safety.
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From page 117... ...
The combined chance of the occurrence of criticality can be estimated reasonably to be substantially below the target levels generally considered satisfactory by nuclear safety authorities worldwide. This preliminary estimate is assumed to be subject to documentation and verification by a Safety Analysis Report, or its equivalent, normally required for all operations involving the processing or transport of Missile materials.
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From page 118... ...
However, the flush tank may not be a good surrogate for the physical removal test because of the absence of thimbles. The mitigation measures already taken are recognized as useful, but the pane} believes that preventive measures are also needed because an unexplained event, even if well mitigated, can raise concerns of institutional credibility that could render it difficult for the Department of Energy to proceed with fuel and flush salt remediation on an orderly schedule and budget.
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From page 119... ...
Stabilization of the salt residues after fluorination by chemical Bettering is a less practiced operation but with less significant hazards.
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