Determining reactor flux from xenon-136 and cesium-135 in spent fuel

Abstract

The ability to infer the reactor flux from spent fuel or seized fissile material would enhance the tools of nuclear forensics and nuclear nonproliferation significantly. We show that reactor flux can be inferred from the ratios of xenon-136 to xenon-134 and cesium-135 to cesium-137. If the average flux of a reactor is known, the flux inferred from measurements of spent fuel could help determine whether that spent fuel was loaded as a blanket or close to the mid-plane of the reactor. The cesium ratio also provides information on reactor shutdowns during the irradiation of fuel, which could prove valuable for identifying the reactor in question through comparisons with satellite reactor heat monitoring data. We derive analytic expressions for these correlations and compare them to experimental data and to detailed reactor burn simulations. The enrichment of the original uranium fuel affects the correlations by up to 3 percent, but only at high flux. * Electronic address: anna˙hayes@lanl.gov

Development of a Reduced Order Model for Fuel Burnup Analysis

“…It is interested to note that, on one hand, 144 Nd is proportional to fuel consumption and is traditionally used as indicator of radial burnup [36]. On the other hand, 136 Xe and 135 Cs are sensitive indicators of the thermal neutron flux [37].…”

Spatial pattern of plutonium and radiocaesium contamination released during the Fukushima Daiichi nuclear power plant disaster

“…While variations in 134 Cs/ 137 Cs activity ratio are observed due to changes in fuel burnup, 135 Cs/ 137 Cs atom ratios vary as a function of neutron capture by the fission product 135 Xe, the parent nuclide of 135 Cs. Concentrations of 135 Xe change considerably according to reactor conditions 22 . Adding 135 Cs to the suite of isotopic analyses is necessary because all three reactors were boiling-water reactors with similar fuels (Reactor Units 1 & 2 - UO 2 ; Reactor Unit 3 - UO 2 /MOX) and operating conditions 23 .…”

Determination of initial fuel state and number of reactor shutdowns in archived low-burnup uranium targets

“…In samples that are greater than 5-10 years old, many of the short-lived fission products have decayed away necessitating the use of long-lived (t 1/2 [ *10 years) or stable isotopes to determine past reactor conditions. Select xenon (Xe) and daughter cesium (Cs) isotope ratios ( 136 Xe/ 134 Xe and 137 Cs/ 135 Cs) in spent reactor fuel can provide information on the reactor flux to which the fuel was exposed [1]. Ruthenium fission product isotope yields are dependent on the type of fission (e.g.…”

“…1). Hayes and Jungman [1] demonstrate that the 137/135 Cs ratio can be used to determine the reactor flux. This is because the unusually large capture cross section on 135 Xe (2.6 9 10 6 barns) results in a flux-dependent competition between the beta-decay of 135 Xe to 135 Cs and capture of 135 Xe to 136 Xe.…”

“…This is because the unusually large capture cross section on 135 Xe (2.6 9 10 6 barns) results in a flux-dependent competition between the beta-decay of 135 Xe to 135 Cs and capture of 135 Xe to 136 Xe. As the flux increases, 135 Xe is converted to 136 Xe at a faster rate than its beta-decay rate to 135 Cs [1]. Additionally, while a reactor is shut down 135 Xe forms only 135 Cs because capture reactions are not occurring.…”