Cerium Ruthenium Low-Energy Antineutrino Measurements for Safeguarding Military Naval Reactors

The recent agreement to transfer nuclear submarine reactors and technology from two nuclear-weapon states to a non-nuclear-weapon state (AUKUS deal) highlights an unsolved problem in international safeguards: how to safeguard naval reactor fuel while it is on board an operational nuclear submarine. Proposals to extend existing safeguards technologies and practices are complicated by the need for civilian international inspectors to gain access to the interior of the submarine and the reactor compartment, which raises national security concerns. In this Letter we show that implementing safeguards on submarine propulsion reactors using a low-energy antineutrino reactor-off method, between submarine patrols, can by-pass the need for onboard access all together. We find that, using inverse beta decay, detectors can achieve a timely and high level of assurance that a submarine’s nuclear core has not been diverted (detector mass of around 100 kg) nor its enrichment level changed (detector mass of around 10 tons).

Figure 1

Cross section (left panel) and side view (right panel) of two submarines at their berthing site. $R_1$ denotes reactor of vessel 1 and $N_1$ denotes the neutrino detector for that vessel. $d$ is the draft, $b$ is the beam of the vessel, and $r$ denotes how far the center of the reactor core is below the water line. $g$ describes the gap between vessels. $y_1$ is the vertical distance between the center of the reactor core $R_1$ and the neutrino detector $N_1$. $x_1$ is the horizontal, adjustable distance between $R_1$ and $N_1$. Water is depicted as light gray and the harbor floor as dark grey. Drawing is to scale, reactor size and position are notional.

Figure 2

Detector mass required to obtain a 90% detection probability with a 5% false positive rate as a function of the parameter $\xi =(d_{\max }/d_0{)}^2$, the average reactor power masking factor. We take $d_0=5\mathrm{m}$. The blue circles are the result for a single vessel detector, whereas the orange squares show two vessels berthed side by side.