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Nuclear Energy Conference & Expo (NECX)
September 8–11, 2025
Atlanta, GA|Atlanta Marriott Marquis
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Deep Space: The new frontier of radiation controls
In commercial nuclear power, there has always been a deliberate tension between the regulator and the utility owner. The regulator fundamentally exists to protect the worker, and the utility, to make a profit. It is a win-win balance.
From the U.S. nuclear industry has emerged a brilliantly successful occupational nuclear safety record—largely the result of an ALARA (as low as reasonably achievable) process that has driven exposure rates down to what only a decade ago would have been considered unthinkable. In the U.S. nuclear industry, the system has accomplished an excellent, nearly seamless process that succeeds to the benefit of both employee and utility owner.
Ivars Neretnieks
Nuclear Technology | Volume 71 | Number 2 | November 1985 | Pages 458-470
Technical Paper | Radioactive Waste Management | doi.org/10.13182/NT85-A33698
Articles are hosted by Taylor and Francis Online.
The diffusivities measured by various investigators of several species in compacted bentonite clay have been compiled and analyzed. Small anions diffuse slower than an uncharged molecule such as methane. Large anions move orders of magnitude slower still. The actinides thorium, uranium, plutonium, neptunium, and americium are considerably retarded by sorption effects. Their movement can be explained by pore diffusion with retardation. Cesium, strontium, and protactinium move considerably faster than can be explained by these effects. The faster mobility is probably due to surface migration. A simplified model is presented by which the importance of the backfill barrier in retarding the radionuclides can be assessed. It is based on the computation of the evolution of the concentration profile of the diffusing nuclide in the backfill. Using this model, the flow rate out from the backfill to the flowing water can be compared to the inflow into the backfill due to leaching. A second model treats nuclides with solubility limitations in a similar way. A diagram is presented where the maximum outflow or concentration of a nuclide from the backfill can be determined as a function of barrier thickness and nuclide diffusivity and decay constant. Using the experimentally obtained diffusivities, it is found that a 0.375-m-thick backfill will eventually let through practically all 129I, 99Tc, 226Ra, 231Pa, 234U, 235U, 238U, and 237Np. The maximum release rate for 137Cs, 90Sr, 239Pu, 240Pu, and 243Am will decrease by one to three orders of magnitude compared to the leach rate. Americium-241 will decay to insignificance in the backfill.
