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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2 Radiolysis and Nuclear Reactions
2 Radiolysis and Nuclear Reactions
Pages 23-36
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From page 23... ...
and uranium hexafluoride gases, radiation `decomposition of solid uranium hexaBuoride, the effects of an excess of reducing species in the salt, and the difficulties associated with a simple remelting operation. RADIOACTIVE SOURCE TERMS When reactor operation was terminated in late 1969, the molten fuel salt was transferred from the reactor to two drain tanks and ~1000 kg (one metric ton)
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From page 24... ...
of the total uranium content in the fuel salt and 75 ppm of the total uranium content in the flush salt (the 233U isotopic fraction in the flush salt is approximately half that in the fuel salt due to the higher concentrations of 235U and 238U in the flush salt)
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From page 25... ...
. 25 24,400 23,985 415 approximately 99 percent of which is contributed by the isobaric pairs 9 Sr/Y and ~37Cs/Ba.3 Uranium, plutonium, americium, and their decay products contribute substantially less radioactivity (1496 Ci, primarily alpha activity from the 232U and 233U decay daughters)
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From page 26... ...
a 232 U and its daughter chain 232U 70 y 228Th 1.9 y 224Ra 3.66 d 220R~ 55.6 s 2~6po 150 ms 2~2pb 3.25 h 2~2Bi 1.01 h 2~2po 45 s 208Tl 3.05 m 233 U and its primary daughter chain 233u 1.59 x 105 y 229Th 7300 y 225Ra 14.8 d 22sAc 10 d 221Fr 217At 213Bi 213po 2o9pb Activity in Fuel Salt tci~b 27 4 kg 233 U 113 116 116 116 116 116 116 74.3 41.7 Activity in Flush Salt (Ci) b 0 2 kg 233 U 0.81 0.83 0.83 0.83 0.83 0.83 0.83 0.53 0.30 4.9 m 32ms 45.6 m 4ms 3.25 h 129 132 132 132 132 132 132 84.8 302 265 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.70 0.70 0.70 0.70 0.70 0.70 0.70 0.70 1.90 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Other signifcant uranium and transuranicisotopes 2.5kg U 0.02 kg U 234u 2.45 x lOsy 17.4 15.2 0.11 98.2% Pu 1.8% Pu 23spu 87.7 y 0.89 0.87 0.02 239pu 24,110 y 41.7 40.9 0.75 24opu 6540 y 15.3 15.0 0.28 24~pu 14.4 y 212 208 3.82 241~ 433 y 23.2 22.8 0.42 Summary of actinide inventories Totalactinideactivity,Z<92 931 815 5.9 Total uranium activity 448 393 2.8 Total transuranic 293 288 5.3 activity Total activity 1672 1496 14.0 NOTE: d = day; h = hour; m = minute; ms = millisecond; s = second; y = year.
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From page 27... ...
The existence of a high radiation field from the gamma radiation external to the fuel salt storage vessels makes it difficult for personnel to work on nearby equipment within the shielding except by remotehandling techniques or by brief operations designed to limit the episodic exposure to acceptable levels. Equipment can deteriorate over an extended period of time in the presence of radiation-induced chemically reactive gases such as fluorine and uranium hexafluoride.
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From page 28... ...
The release of F2 apparently is due to recombination of fluorine atoms liberated by radiation effects on the fluoride salts, with each radiation source (alpha, beta, and gamma) potentially responsible for this effect.6 6Radiolysis (i.e., energy deposition in the salt due to energetic alpha, beta, or gamma radiation)
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From page 29... ...
Compared to gamma radiation, alpha particles have a shorter range and a denser ionization track, considerations that are important because individual fluorine atoms must be produced in close proximity to combine to form F2. Another argument in favor of alpha (over gamma)
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From page 30... ...
Further radiation and thermal measurements established that 2.6 kg of uranium had been transported from the fuel salts and was deposited in the upper 1-foot section of the ACE located outside the main reactor building. Both fluorine and uranium hexafluoride react with charcoal, forming CFX and nonvolatile uranium fluorides.
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From page 31... ...
Radiation Decomposition of Solid Uranium Hexafluoride The reverse of radiation-induced formation of UFO from the fuel salts also can be a problem. In deposits of solid UFO, decomposition by its alpha radiation from the uranium must be considered.
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From page 32... ...
32 U232 OR ~' U232 99% - a 1% - SF Th228 1 00% - a Ra224 1 00% - a Rn220 1 00% - a Po216 100% - a Pb212 1 00% - p Bi212 OR ~' Bi212 64.07% - p~ 35.93% Po212 100% -a AN EVALUATION OF DOE ALTERNATIVES FOR MSRE U233 OR ~' U233 99.99% - a 1 e-003% - SF Th229 100% - a Ra225 1 00% - pAc225 100% - a Fr221 100% -a At217 OR 99% - a Bi213 OR ~' Bi213 97.84% - ,B- 2.16% - a Ti208 100% - p~ Pb208 Pb209 1 00% - p Bi209 At217 1 % - pRn217 100% - a Po213 Ti209 Po213 100% - a 100% - ,8~ 100% - a Pb209 1 00% - pBi209 Pb209 1 00°~ pBi209 FIGURE 2.1 Decay chains for 232U and 233U. NOTE: SF = spontaneous fission.
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From page 33... ...
. Long-Term Effects of Leaving Plutonium in the Salt After Uranium Removal Plutonium migration in the MSRE system has not received significant attention because the formation and migration of quantities of UFO dominate nuclear criticality safety implications.
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From page 34... ...
In reacting with 135 moles of total uranium in the two fuel drain tanks, all of the uranium initially present as UF4 would be reduced to the less soluble UF3, precipitation of which is unlikely at a uranium concentration of approximately 0.12 mole percent.9 Further reaction of the 155 remaining unsatisfied equivalents of chemical reducing agents could yield 12 kg of uranium metal. Melting of the salts without eliminating this excess of reducing equivalents could result in formation of some uranium metal, although it is not clear that uranium metal would be formed in preference to zirconium metal or possibly the zirconium fluoride ZrF3.
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From page 35... ...
The melt composition is almost certainly different than at reactor discharge and may contain metallic zirconium, but even if single atoms of uranium metal were formed locally in the solid phase, there does not appear to be any mechanism that could cause this material to agglomerate into a dense metal phase. Surrogate samples of fuel salt were irradiated (in 1963)
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From page 36... ...
Cautious approaches to attaining this condition were suggested (Peretz, 1996c) and are discussed in greater detail in Chapters 4 through 6, after further elaboration of salt chemistry in Chapter 3.
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