Application of the Local Coincidence Veto Technique to Holdup Measurements in Glove Boxes

The Local Coincidence Veto (LCV) technique was originally developed by Los Alamos National Laboratory to reduce cosmic ray background (thus lowering detection limits) for large passive neutron waste crate counters. The original LCV technique had a custom electronics circuit that accepts the first neutron pulse from a given amplifier, but blocks the following coincidence pulses for a time interval (~128 µs) long enough to exclude pulses from the original fission event. It was recognized that the same technique – elimination of localized neutron events- could be used to make the response from the walls and from the interior regions of a glove box more uniform than is obtained using traditional neutron hold-up techniques. As the uncertainty associated with plutonium positioning within a glovebox is a dominant term for hold-up measurements, the LCV technique has the potential to greatly improve neutron hold-up measurements for glove boxes. The basis of the hold-up LCV technique is to divide the glove box detector system into many separate preamplifier/detector tube modules. Each of the preamplifier modules can count the first neutron that arrives from a spontaneous fission event but it is gated off for the next ~128 µs so the same preamplifier cannot count the following “coincidence” neutrons from the same fission event. This paper summarizes hold-up LCV measurement results on a laboratory glove- box test-bed at LANL that was developed in conjunction with Japan Nuclear Fuel Limited. The efficacy obtained on the laboratory system in reducing the uncertainty contribution from plutonium positioning effects is also presented.