David Reyna

Advances towards readily deployable antineutrino detectors for reactor monitoring and safeguards

The large flux of neutrinos that leaves a nuclear reactor carries information about two quantities of interest for safeguards: the reactor power and fissile inventory. Our SNL/LLNL collaboration has demonstrated that antineutrino-based nuclear reactor monitoring is feasible using a relatively small cubic scale detector made of Gadolinium loaded liquid scintillator at tens of meters standoff from a commercial Pressurized Water Reactor, deployed in an underground gallery that lies directly under the containment.

Advances toward a transportable antineutrino detector system for reactor monitoring and safeguards

Nuclear reactors have served as the neutrino source for many fundamental physics experiments. The techniques developed by these experiments make it possible to use these very weakly interacting particles for a practical purpose. The large flux of antineutrinos that leaves a reactor carries information about two quantities of interest for safeguards: the reactor power and fissile inventory. Our SNL/LLNL collaboration has demonstrated that such antineutrino based monitoring is feasible using a relatively small cubic meter scale liquid scintillator detector at tens of meters standoff from a commercial Pressurized Water Reactor (PWR). With little or no burden on the plant operator we have been able to remotely and automatically monitor the reactor operational status (on/off), power level, and fuel burnup. The initial detector was deployed in an underground gallery that lies directly under the containment dome of an operating PWR. The gallery is 25 meters from the reactor core center, is rarely accessed by plant personnel, and provides a muon-screening effect of some 20–30 meters of water equivalent earth and concrete overburden. Unfortunately, many reactor facilities do not contain an equivalent underground location. We have therefore attempted to construct a complete detector system which would be capable of operating in an aboveground location and could be transported to a reactor facility with relative ease. A standard 6-meter shipping container was used as our transportable laboratory — containing active and passive shielding components, the antineutrino detector and all electronics, as well as climate control systems. This aboveground system was deployed and tested at the San Onofre Nuclear Generating Station (SONGS) in southern California in 2010 and early 2011. We will first present an overview of the initial demonstrations of our belowground detector. Then we will describe the aboveground system and the technological developments of the two antineutrino detectors that were deployed. Finally, some preliminary results of our aboveground test will be shown.

Integrated readout of organic scintillator and ZnS:Ag/ 6 LiF for segmented antineutrino detectors

Antineutrino detection using inverse beta decay conversion has demonstrated the capability to measure nuclear reactor power and fissile material content for nuclear safeguards. Current efforts focus on aboveground deployment scenarios, for which highly efficient capture and identification of neutrons is needed to measure the anticipated antineutrino event rates in an elevated background environment. In this submission, we report on initial characterization of a new scintillation-based segmented design that uses layers of ZnS:Ag/6LiF and an integrated readout technique to capture and identify neutrons created in the inverse beta decay reaction. Laboratory studies with multiple organic scintillator and ZnS:Ag/6LiF configurations reliably identify 6Li neutron captures in 60 cm-long segments using pulse shape discrimination.

A High-Sensitivity Fast Neutron Imager

Several improvements were made to the NSC over the course of this project. The liquidscintillator-cell configuration was changed from nine cells in each plane to 16 cells in each plane (2” deep, 5” diameter cells in the front plane, 5” deep, 5” diameter cells in the rear plane). The cells were mounted in a new shock-proof frame that also provided motorized adjustment of the spacing between the two planes. To simplify transporting the system, the liquid scintillator material itself was changed from EJ-301 to the less-hazardous EJ-309 (higher flashpoint, more benign chemical content). Dual-mode imaging capabilities were implemented in software, enabling simultaneous Compton-camera gamma imaging in addition to the neutron imaging. Data acquisition was converted to an all-digital system using a newly available VME digitizer system, leading to both enhanced data analysis capabilities, and to a much more portable configuration (with a large separate electronics rack replaced by a single VME crate attached to the scatter-camera frame, as shown in Fig. 1). Maximum-Likelihood Expectation-Maximization (MLEM) methods were added to our image reconstruction toolkit.

Development of coherent germanium neutrino technology (CoGeNT) for reactor safeguards.

Antineutrinos are extremely penetrating elementary particles that have unique features of interest for safeguards at nuclear reactors. Current antineutrino detectors systems have large size and often use hazardous materials, presenting concerns to the safeguards agencies. We propose a new antineutrino detector, based on HPGe detector technology, which is much smaller and safer and therefore more likely to find widespread acceptance as a monitoring tool. The proposed system should be sensitive to a universally predicted but as-yet undetected antineutrino signature, the coherent neutrino-nucleus scattering, for which an unprecedentedly low noise threshold is required. Based on the noise analysis of an existing HPGe detector and the results of noise tests, a new system was designed and fabricated in collaboration with LBNL, though a full noise optimization has not been possible. Shielding design has been analyzed in the context of other deployment results, and an anticoincidence veto with high neutron efficiency has been tested.

Towards above-ground antineutrino detectors for cooperative monitoring: Background radiation studies

We describe an assembly of detectors that quantifies the background radiation present at potential above ground antineutrino detector development and deployment sites. Antineutrino detectors show great promise for safeguard applications in directly detecting the total fission rate as well as the change in fissile content of nuclear power reactors. One major technical challenge that this safeguard application must overcome is the ability to distinguish signals from antineutrinos originating in the reactor core from noise due to background radiation created by terrestrial and cosmogenic sources. To date, existing detectors increase their ability to distinguish antineutrino signals by being surrounded with significant shielding and being placed underground. For the safeguard’s agency, this is less than optimal, increasing the overall size and limiting the placement of this system. For antineutrino monitoring to be a widely deployable solution, we must understand the backgrounds found above ground at nuclear power plants that can mimic the antineutrino signal so that these backgrounds can be easily identified, separated, and subtracted rather than shielded. The design, construction, calibration, and results from the deployment of these background detectors at a variety of sites will be presented.

Background Radiation Studies for Future Above-Ground Antineutrino Detectors.

We will describe an assembly of radiation detectors that quantifies the gamma, muon, and fast and thermal neutron fluxes present at potential above ground antineutrino detector sites. Antineutrino detectors show great promise for reactor safeguards applications, due to their ability to monitor thermal power and/or fissile content. One of the major technical challenges that this safeguard application faces is the ability to distinguish signals from antineutrinos originating in a reactor core from noise due to background created by terrestrial and cosmogenic radiation. To date, antineutrino experiments have increased the signal to noise in their detectors by surrounding the experiments with significant shielding and placing them underground. For the safeguards agency, this is less than optimal, as it increases the overall size of the device and limits the range of possible deployment locations. Placing reactor monitoring antineutrino detectors at, or near, the surface would greatly increase the range of possible deployment locations. In order to investigate designs that would allow this, we must understand the backgrounds found above ground that can mimic the antineutrino signal so that these can be easily identified, separated, and subtracted rather than shielded. The design, construction, calibration, and results from the deployment of this background measurement system at a variety of sites will be presented.

The deployment of three prototype detectors for reactor monitoring and safeguards

Fission reactors emit large numbers of antineutrinos and this flux may be useful for the measurement of two quantities of interest for reactor safeguards: the reactors power and plutonium inventory throughout its cycle. The high antineutrino flux and relatively low background rates means that simple cubic meter scale detectors at tens of meters standoff can record hundreds or thousands of antineutrino events per day. Such antineutrino detectors would add online, quasi-real-time bulk material accountancy to the set of reactor monitoring tools available to the IAEA and other safeguards agencies with minimal impact on reactor operations. Our LLNL/SNL collaboration has deployed a total of three prototype safeguards detectors at a reactor in Southern California in order to test both the method and the practicality of its implementation in the field. Results from these detectors will be presented, and their respective advantages and disadvantages described. LLNL-POST-404014 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory in part under Contract W-7405-Eng-48 and in part under Contract DE-AC52-07NA27344. Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.