Antineutrino Monitoring for Heavy Water Reactors

In this Letter we discuss the potential application of antineutrino monitoring to the Iranian heavy water reactor at Arak, the IR-40, as a nonproliferation measure. An above ground detector positioned right outside the IR-40 reactor building could meet IAEA verification goals for reactor plutonium inventories. While detectors with the needed spectral sensitivity have been demonstrated below ground, additional research and development is needed to demonstrate an above-ground detector with this same level of sensitivity. In addition to monitoring the reactor during operation, observing antineutrino emissions from long-lived fission products could also allow monitoring the reactor when it is shut down, provided very low detector backgrounds can be achieved. Antineutrino monitoring could also be used to distinguish different levels of fuel enrichment. Most importantly, these capabilities would not require a complete reactor operational history and could provide a means to reestablish continuity of knowledge in safeguards conclusions should this become necessary.

Figure 1

In the upper panel, data points show the event rate spectrum obtained in a 90 d data taking period for a core of average age of 45 d. The error bars indicate the statistical error in each bin. The blue line indicates the corresponding expected event rate spectrum for a core of average age of 315 d. The lower panel shows the difference in event rates between the 45 d core and the 315 d core and the corresponding statistical error bars.

Figure 2

Shown is the $1\sigma$ accuracy for the determination of the plutonium content of the reactor as a function of time in the reactor cycle. The data taking period is 90 d each. Dashed error bars indicate the accuracy from a fit to the plutonium fission rate $f_{\mathrm{Pu}}$, whereas the solid error bars show the result of a fit constrained by a burnup model. The blue/dark line indicates operation without refueling and the orange/light line indicates operation with a refueling after 270 d.

Figure 3

Shown are the fission fractions in uranium-235, upper panel, and plutonium-239, lower panel, for a natural uranium fueled core (NU) in green and for a 3% enriched uranium fueled core (LEU) in blue as a function of time elapsed in the reactor cycle. The fission fractions in both isotopes at time $t_1$ for the NU core match those at a later time $t_2$ for the LEU core as indicated by the horizontal dashed lines. The change of fission fractions after a fixed time interval $\mathrm{\Delta }t$, the so-called differential burnup, is indicated by the thick vertical black lines. There is a distinct difference in differential burnup between the LEU and NU cores for both isotopes as indicated by the thick red lines.