Ian C Gauld

Isotopic Depletion and Decay Methods and Analysis Capabilities in SCALE

Abstract The calculation of fuel isotopic compositions is essential to support design, safety analysis, and licensing of many components of the nuclear fuel cycle—from reactor physics and severe accident analysis to back-end fuel cycle issues, including spent-fuel storage and transportation, reprocessing, and radioactive waste management. Versions of the ORIGEN code, developed by Oak Ridge National Laboratory, have been used worldwide for isotopic depletion and decay analysis for more than three decades. The supported version of ORIGEN, maintained as the depletion analysis module for SCALE 6, performs detailed time-dependent isotopic generation and depletion for 1946 nuclides for reactor fuel and activation analysis. Stand-alone ORIGEN calculations can be performed using cross-section libraries developed for a wide range of reactor types and fuel designs used worldwide, including light water reactors UO2 and MOX, CANDU, VVER 440 and 1000, RBMK, and graphite reactors. Alternatively, within SCALE 6, ORIGEN can be automatically coupled to two-dimensional discrete ordinates or three-dimensional Monte Carlo transport solvers that provide problem-dependent cross sections for use in the ORIGEN depletion calculation. The hybrid ability to function as either a stand-alone or coupled depletion code provides ORIGEN advanced capabilities to simulate a broad range of applications for various reactor systems. The nuclear data libraries in ORIGEN have been significantly improved recently, using modern ENDF/B nuclear data evaluations. The most recent developments in SCALE 6.1 include the addition of ENDF/B-VII decay data, energy-dependent fission yields, and fine-group ORIGEN neutron cross sections based on the JEFF-3.0/A special purpose activation files. Advanced methods and data for neutron and gamma source energy spectral analysis are also available in the current version of the code. The ORIGEN code and associated nuclear data libraries have been extensively validated against experimental data that include spent nuclear fuel isotopic assay data for actinides and fission products, radiation source spectra, and decay heat measurements.

STUDY OF FUKUSHIMA DAIICHI NUCLEAR POWER STATION UNIT 4 SPENT-FUEL POOL

A study on the Fukushima Daiichi nuclear power station spent-fuel pool (SFP) at Unit 4 (SFP4) is presented in this paper. We discuss the design characteristics of SFP4 and its decay heat load in detail and provide a model that we developed to estimate the SFP evaporation rate based on the SFP temperature. The SFP level of SFP4 following the March 11, 2011, accident is predicted based on the fundamental conservation laws of mass and energy. Our predicted SFP level and temperatures are in good agreement with measured data and are consistent with Tokyo Electric Power Company evaluation results.

Analysis of Experimental Data for High Burnup PWR Spent Fuel Isotopic Validation - Vandellos II Reactor

This report is one of the several recent NUREG/CR reports documenting benchmark-quality radiochemical assay data and the use of the data to validate computer code predictions of isotopic composition for spent nuclear fuel, to establish the uncertainty and bias associated with code predictions. The experimental data analyzed in the current report were acquired from a high-burnup fuel program coordinated by Spanish organizations. The measurements included extensive actinide and fission product data of importance to spent fuel safety applications, including burnup credit, decay heat, and radiation source terms. Six unique spent fuel samples from three uranium oxide fuel rods were analyzed. The fuel rods had a 4.5 wt % {sup 235}U initial enrichment and were irradiated in the Vandellos II pressurized water reactor operated in Spain. The burnups of the fuel samples range from 42 to 78 GWd/MTU. The measurements were used to validate the two-dimensional depletion sequence TRITON in the SCALE computer code system.

SCALE 5.1 Predictions of PWR Spent Nuclear Fuel Isotopic Compositions

The purpose of this calculation report is to document the comparison to measurement of the isotopic concentrations for pressurized water reactor (PWR) spent nuclear fuel determined with the Standardized Computer Analysis for Licensing Evaluation (SCALE) 5.1 (Ref. ) epletion calculation method. Specifically, the depletion computer code and the cross-section library being evaluated are the twodimensional (2-D) transport and depletion module, TRITON/NEWT,2, 3 and the 44GROUPNDF5 (Ref. 4) cross-section library, respectively, in the SCALE .1 code system.

Approach for Validating Actinide and Fission Product Compositions for Burnup Credit Criticality Safety Analyses

Abstract This paper describes a depletion code validation approach for criticality safety analysis using burnup credit for actinide and fission product nuclides in spent nuclear fuel (SNF) compositions. The technical basis for determining the uncertainties in the calculated nuclide concentrations is comparison of calculations to available measurements obtained from destructive radiochemical assay of SNF samples. Probability distributions developed for the uncertainties in the calculated nuclide concentrations were applied to the SNF compositions of criticality safety analysis models by the use of a Monte Carlo uncertainty sampling method to determine bias and bias uncertainty in the effective neutron multiplication factor. Application of the Monte Carlo uncertainty sampling approach is demonstrated for representative criticality safety analysis models of pressurized water reactor spent fuel pool storage racks and transportation packages using burnup-dependent nuclide concentrations calculated with Standardized Computer Analyses for Licensing Evaluation (SCALE) 6.1 and the Evaluated Nuclear Data File/B (ENDF/B) Version VII nuclear data. The validation approach and results support a recent revision of the U.S. Nuclear Regulatory Commission Interim Staff Guidance (ISG)-8.

Coupling a transient solvent extraction module with the separations and safeguards performance model.

A past difficulty in safeguards design for reprocessing plants is that no code existed for analysis and evaluation of the design. A number of codes have been developed in the past, but many are dated, and no single code is able to cover all aspects of materials accountancy, process monitoring, and diversion scenario analysis. The purpose of this work was to integrate a transient solvent extraction simulation module developed at Oak Ridge National Laboratory, with the SSPM Separations and Safeguards Performance Model, developed at Sandia National Laboratory, as a first step toward creating a more versatile design and evaluation tool. The SSPM was designed for materials accountancy and process monitoring analyses, but previous versions of the code have included limited detail on the chemical processes, including chemical separations. The transient solvent extraction model is based on the ORNL SEPHIS code approach to consider solute build up in a bank of contactors in the PUREX process. Combined, these capabilities yield a much more robust transient separations and safeguards model for evaluating safeguards system design. This coupling and the initial results are presented. In addition, some observations toward further enhancement of separations and safeguards modeling based on this effort are provided, including: items to be addressed in integrating legacy codes, additional improvements needed for a fully functional solvent extraction module, and recommendations for future integration of other chemical process modules.

Nondestructive Assay Data Integration with the SKB-50 Assemblies - FY16 Update

A project to research the application of non-destructive assay (NDA) techniques for spent fuel assemblies is underway at the Central Interim Storage Facility for Spent Nuclear Fuel (for which the S ...

GAMMA DOSE RATE NEAR A NEW (252)Cf BRACHYTHERAPY SOURCE

Abstract A new generation of medical grade 252Cf sources was developed in 2002 at the Oak Ridge National Laboratory. The combination of small size and large activity of 252Cf makes the new source suitable to be used with the conventional high-dose-rate remote afterloading system for interstitial brachytherapy. A recent in-water calibration experiment showed that the measured gamma dose rates near the new source are slightly greater than the neutron dose rates, contradicting the well established neutron-to-gamma dose ratio of approximately 2:1 at locations near a 252Cf brachytherapy source. Specifically, the MCNP-predicted gamma dose rate is a factor of two lower than the measured gamma dose rate at the distance of 1 cm, and the differences between the two results gradually diminish at distances farther away from the source. To resolve this discrepancy, we updated the source gamma spectrum by including in the ORIGEN-S data library the experimentally measured 252Cf prompt gamma spectrum as well as the true 252Cf spontaneous fission yield data to explicitly model delayed gamma emissions from fission products. We also investigated the bremsstrahlung X-rays produced by the beta particles emitted from fission product decays. The results show that the discrepancy of gamma dose rates is mainly caused by the omission of the bremsstrahlung X-rays in the MCNP runs. By including the bremsstrahlung X-rays, the MCNP results show that the gamma dose rates near a new 252Cf source agree well with the measured results and that the gamma dose rates are indeed greater than the neutron dose rates.