Lessons Learned from the Holdup Measurement Program at the K-25 Site Richard Hagenauer ORTEC
Richard Mayer United States Enrichment Corporation
The K-25 Site Includes Five Large Gaseous Diffusion Buildings K-31 K-27
K-33 K-25
K-29
Uranium deposits from 0.2% to 93% 235U Buildings shut down in 1964 (K-25 and K27) and 1985 (K-29, K-31, K-33) NDA Survey began in 1987
Each Building Included Many Repetitive Parts as well as Auxiliary Equipment
Building Unit • groups of cells
Cells • groups of stages
Stages • Enrichment process equipment
Auxiliary equipment, piping also present
Building K-25
NDA Survey Objectives
Initial objective was nuclear criticality safety (NCS) • Plant engineers retiring, concerned about possible deposits of NCS significance
Objectives expanded to include • NMC&A • Safeguards
Data currently used to support D&D
Calibration and Analysis Methods Evolved Over Time
Detectors were calibrated by positioning activity within the process equipment. • In 1987, no user-friendly software available. • MCNP code was too cumbersome for routine use. • This approach had serious shortcomings, and was very inflexible.
NDA Engineers Developed In-House Software and Calibration Methods
Model deposits Detection efficiency Attenuation correction Estimate uranium quantity Enrichment
Maps Were Used to Identify the Location Of Activity
Maps had schematics of process equipment and interconnecting piping Measurement personnel used the maps: • as a guide to the locations and identifiers of process equipment, • as a guide to piping locations and names, • to record scan values for piping and process equipment
Four NDA Measurement Techniques Were Developed
In 1987, no standardized methods existed for gaseous diffusion plant holdup measurements • Developed methods with assistance from Los Alamos NDA personnel Scanning • NaI detector coupled to a ratemeter Quantitative gamma-ray • NaI detector coupled to a scalar, then MCA Neutron • Shielded Neutron Assay Probe (SNAP), slab Isotope Identification • HPGe coupled to MCA
Gamma-Ray Measurements Were Used to Quantify Some Deposits
Most sensitive measurement technique Attenuation (wall, matrix, self) could be severe Evolved over time • NaI • HPGe – use spectrum to estimate selfattenuation
High Purity Germanium Detectors Helped Identify Unexpected Nuclides
Neutron Measurements Also Used for Quantification
Least sensitive measurement technique Neutrons are emitted from weak spontaneous fission of 238U and 19F(α,n)22Na reactions Neutron signal not reduced by thick steel, matrix, or large U deposits Best technique for compressors, large converters, large deposits
All Compressors Were Measured with Neutron Detectors
Compressors contain large amounts of metal • Neutrons pass through metal well • Gamma-rays are severely attenuated
Deposits could build up at specific locations • Neutrons pass through uranium well • Gamma rays can be severely attenuated
Major Complications
Neutrons scatter (“bounce”) like crazy!!!! • • •
Background difficult to accurately measure Field of view often includes several items Spallation affected larger items (~60,000 lb steel in largest converters)
Neutron specific activity for uranium compounds not well known • UF6 + H20 makes UO2F2 + HF maybe • References for NSA for 234UO2F2 vary by 40%
Gamma-ray attenuation was severe, difficult to estimate for many deposits Comparisons of NDA to cleanout data very limited – uncertainty estimates uncertain
Lessons Learned
Data will be used for unintended purposes Document, document, and then document some more Experienced analysts are needed to plan measurements, interpret results Validate the measurements to develop proper uncertainties Design QA programs to check important instrument parameters, minimize down time Be prepared for a massive amount of data Obtain engineer plans that establish the flow of nuclear material through the enrichment process
New Portable Hardware Makes Life Easier For New Holdup Programs
New Software Is Very Helpful
Modeling software (Isotopic, ISOCS, etc.) Enrichment software (PC/FRAM, MGA+) Holdup remeasurement software (HMS4) Still no commercial software for neutron holdup Represents blessing and curse • Easier to produce results • Permits personnel without proper training, expertise to produce results of poor quality
Summary
Nobody said holdup measurements would be easy and they are not! New hardware and software does make it easier for the next holdup program Much development work is still needed
