Program - Brookhaven National Laboratory

importance in nuclear technology, as they can be used as a diagnostic tool. While the fission process has
been extensively studied since its discovery more than 70 years ago, the energy dependence of the yields
of specific fragments in neutron-induced fission is poorly understood. A new instrument, SPIDER, is
currently being developed to address this issue by measuring the mass, charge, and kinetic energy of fission
fragments as a function of incident-neutron energy. The instrument is based on the 2E-2V method, in
which the velocity and kinetic energy of fragments are measured in coincidence to determine their masses.
Additionally, by using Bragg peak spectroscopy, the charge of a fragment can be identified. A prototype
instrument has been developed, and preliminary results indicate that 1 mass unit resolution is feasible using
this approach. A larger detector array is currently being designed, and will be used at the Los Alamos
Neutron Science Center (LANSCE) to study fission fragment yields from thermal neutron energies up to
at least 20 MeV.
Session KE Integral Experiments
Wednesday March 6, 2013
Room: Central Park West at 1:30 PM
KE 1 1:30 PM
What If Lady Godiva Was Wrong?
John D. Bess, J. Blair Briggs, Margaret A. Marshall
Idaho National Laboratory
The experiment from which benchmark specifications of ”Lady Godiva” were derived consisted of a bare
sphere of highly enriched uranium (HEU) comprised of nested hemispheres. That experiment was performed
in the early 1950s and the critical configuration was evaluated and published in the International
Handbook of Evaluated Criticality Safety Benchmark Experiments in 1995 with the identifier HEU-MET-
FAST-001. The benchmark eigenvalue is reported as 1.000 ± 0.001, which is representative of a very
high quality benchmark experiment. Our current neutronic codes and cross section data are tailored to
provide qualitative results that concur with the Godiva benchmark. But what if our understanding of the
experiment wasn’t perfect? Since 1995, a multitude of additional high-fidelity HEU metal benchmark data
have been evaluated and published, including data for several assemblies that were performed at the Oak
Ridge Critical Experiments Facility (ORCEF) and others at the Russian Federal Nuclear Center - Institute
of Technical Physics (RFNC-VNIITF). Furthermore, the rigor through which benchmark experiments are
examined has increased over the past two decades. Eigenvalue calculations of the HEU metal benchmark
experiments from ORCEF and VNIITF consistently calculate slightly low, possibly indicating that our fast
neutron cross section data for 235 U may not be as well known as hoped. It is recommended that we not just
reevaluate the Godiva benchmark data, but also evaluate a more recent bare critical sphere experiment
performed at ORCEF in 1971.
International Handbook of Evaluated Criticality Safety Benchmark Experiments, NEA/NSC/DOC(95)03,
OECD-NEA, Paris, France (2012).
KE 2 2:00 PM
Shielding Design Calculations for the ESS Target Station High Activated Components
Daniela Ene, Ferenc Mezei
ESS-AB, Sweden
158