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Standardization of portable assay instrumentation: the neutron-coincidence tree

Description: Standardization of portable neutron assay instrumentation has been achieved by using the neutron coincidence technique as a common basis for a wide range of instruments and applications. The electronics originally developed for the High-Level Neutron Coincidence Counter has been adapted to both passive- and active-assay instrumentation for field verification of bulk plutonium, inventory samples, pellets, powders, nitrates, high-enriched uranium, and materials-testing-reactor, light-water-reactor, and mixed-oxide fuel assemblies. The family of detectors developed at Los Alamos National Laboratory and their performance under in-field conditions are described. 16 figures, 3 tables.
Date: January 1, 1983
Creator: Menlove, H.O.
Partner: UNT Libraries Government Documents Department

Description and performance characteristics for the neutron Coincidence Collar for the verification of reactor fuel assemblies

Description: An active neutron interrogation method has been developed for the measurement of /sup 235/U content in fresh fuel assemblies. The neutron Coincidence Collar uses neutron interrogation with an AmLi neutron source and coincidence counting the induced fission reaction neutrons from the /sup 235/U. This manual describes the system components, operation, and performance characteristics. Applications of the Coincidence Collar to PWR and BWR types of reactor fuel assemblies are described.
Date: August 1, 1981
Creator: Menlove, H.O.
Partner: UNT Libraries Government Documents Department

Implementation of the active neutron Coincidence Collar for the verification of unirradiated PWR and BWR fuel assemblies

Description: An active neutron interrogation technique has been developed for the measurement of the /sup 235/U content in fresh fuel assemblies. The method employs an AmLi neutron source to induce fission reactions in the fuel assembly and coincidence counting of the resulting fission reaction neutrons. When no interrogation source is present, the passive neutron coincidence rate gives a measure of the /sup 238/U by the spontaneous fission reactions. The system can be applied to the fissile content determination in fresh fuel assemblies for accountability, criticality control, and safeguards purposes. Field tests have been performed by International Atomic Energy Agency (IAEA) staff using the Coincidence Collar to verify the /sup 235/U content in light-water-reactor fuel assemblies. The results gave an accuracy of 1 to 2% in the active mode (/sup 235/U) and 2 to 3% in the passive mode (/sup 238/U) under field conditions.
Date: January 1, 1982
Creator: Menlove, H.O. & Keddar, A.
Partner: UNT Libraries Government Documents Department

Field test and evaluation of the passive neutron coincidence collar for prototype fast reactor fuel subassemblies

Description: The passive neutron Coincidence Collar, which was developed for the verification of plutonium content in fast reactor fuel subassemblies, has been field tested using Prototype Fast Reactor fuel. For passive applications, the system measures the /sup 240/Pu-effective mass from the spontaneous fission rate, and in addition, a self-interrogation technique is used to determine the fissile content in the subassembly. Both the passive and active modes were evaluated at the Windscale Works in the United Kingdom. The results of the tests gave a standard deviation 0.75% for the passive count and 3 to 7% for the active measurement for a 1000-s counting time. The unit will be used in the future for the verification of plutonium in fresh fuel assemblies.
Date: August 1, 1982
Creator: Menlove, H.O. & Keddar, A.
Partner: UNT Libraries Government Documents Department

Field test and evaluation of the IAEA coincidence collar for the measurement of unirradiated BWR fuel assemblies

Description: The neutron coincidence counter has been field tested and evaluated for the measurement of boiling-water-reactor (BWR) fuel assemblies at the ASEA-ATOM Fuel Fabrication Facility. The system measures the /sup 235/U content per unit length of full fuel assemblies using neutron interrogation and coincidence counting. The /sup 238/U content is measured in the passive mode without the AmLi neutron interrogatioin source. The field tests included both standard production movable fuel rods to investigate enrichment and absorber variations. Results gave a response standard deviation of 0.9% for the active case and 2.1% for the passive case in 1000-s measurement times. 10 figures, 2 tables.
Date: December 1, 1982
Creator: Menlove, H.O. & Keddar, A.
Partner: UNT Libraries Government Documents Department

Manual for the Portable Handheld Neutron Counter (PHNC) for Neutron Survey and the Measurement of Plutonium Samples

Description: We have designed a portable neutron detector for passive neutron scanning measurement and coincidence counting of bulk samples of plutonium. The counter will be used for neutron survey applications as well as the measurement of plutonium samples for portable applications. The detector uses advanced design {sup 3}He tubes to increase the efficiency and battery operated shift register electronics. This report describes the hardware, performance, and calibration for the system.
Date: November 1, 2005
Creator: Menlove, H.O.
Partner: UNT Libraries Government Documents Department

Passive neutron assay of heterogeneous waste drums using the segmented Add-a-Source method

Description: We have developed passive neutron detectors that include the Add-a-Source (AS) technique to improve the accuracy of the nondestructive assay of plutonium in large waste containers. We have improved the AS by incorporating multiple positions for the {sup 252}Cf source on the exterior of a 200-L drum. The multiple positions give a better coverage of the drum and have the effect of segmenting the matrix as a function of fill height. We have applied the multiposition AS to the assay of drums with heterogeneous matrix combinations of concrete, polyethylene, wood, paper, and metal. The measurement errors caused by the matrix significantly reduced by the AS technique and anomalous shielding material in the drum can be flagged for more detailed investigation.
Date: July 1, 1995
Creator: Menlove, H.O.
Partner: UNT Libraries Government Documents Department

Moisture corrections in neutron coincidence counting of PuO/sub 2/

Description: Passive neutron coincidence counting is capable of 1% assay accuracy for pure, well-characterized PuO/sub 2/ samples that contain plutonium masses from a few tens of grams to several kilograms. Moisture in the sample can significantly bias the assay high by changing the (..cap alpha..,n) neutron production, the sample multiplication, and the detection efficiency. Monte Carlo calculations and an analytical model of coincidence counting have been used to quantify the individual and cumulative effects of moisture biases for two PuO/sub 2/ sample sizes and a range of moisture levels from 0 to 9 wt %. Results of the calculations suggest a simple correction procedure for moisture bias that is effective from 0 to 3 wt % H/sub 2/O. The procedure requires that the moisture level in the sample be known before the coincidence measurement.
Date: January 1, 1987
Creator: Stewart, J.E. & Menlove, H.O.
Partner: UNT Libraries Government Documents Department

Direct fissile assay of highly enriched UF/sub 6/ using random self-interrogation and neutron coincidence response

Description: A new nondestructive method for direct assay of /sup 235/U mass contained in Model 5A uranium hexafluoride (UF/sub 6/) product storage cylinders has been successfully tested in the laboratory and under field conditions. The technique employs passive neutron self-interrogation and uses the ratio of coincidences-to-totals counts as a measure of bulk fissile mass. The accuracy of the method is 6.8% (1 sigma) based on field measurements of 44 Model 5A cylinders, 11 of which were either only partially filled or contained reactor return material. The cylinders contained UF/sub 6/ with enrichments from 5.96% to 97.6%. Count times were 3 to 6 min depending on /sup 235/U mass. Samples ranged from below 1 kg to over 16 kg of /sup 235/U. Because the method relies primarily on fast neutron self-interrogation, complete sampling of the UF/sub 6/ takes place. This feature alleviates inhomogeneity problems and offers increased assurance of the presence of stated amounts of bulk fissile material as compared with current verification methods.
Date: January 1, 1983
Creator: Stewart, J.E. & Menlove, H.O.
Partner: UNT Libraries Government Documents Department

High-level neutron coincidence counter (HLNCC): users' manual

Description: This manual describes the portable High-Level Neutron Coincidence Counter (HLNCC) developed at the Los Alamos Scientific Laboratory (LASL) for the assay of plutonium, particularly by inspectors of the International Atomic Energy Agency (IAEA). The counter is designed for the measurement of the effective /sup 240/Pu mass in plutonium samples which may have a high plutonium content. The following topics are discussed: principle of operation, description of the system, operating procedures, and applications.
Date: June 1, 1979
Creator: Krick, M.S. & Menlove, H.O.
Partner: UNT Libraries Government Documents Department

International safeguards: experience and prospects

Description: IAEA safeguards have been applied to over 95% of the nuclear material and facilities outside of the nuclear weapon states. The present system of nonproliferation agreements implemented by IAEA safeguards likely will not be changed in the foreseeable future. Instruments used for nondestructive analysis are described: portable multichannel analyzer, high-level neutron coincidence counter, active well coincidence counter, and neutron coincidence collar. 7 figs. (DLC)
Date: January 1, 1982
Creator: Keepin, G.R. & Menlove, H.O.
Partner: UNT Libraries Government Documents Department

Channel coincidence counter: version 1

Description: A thermal neutron coincidence counter has been designed for the assay of fast critical assembly fuel drawers and plutonium-bearing fuel rods. The principal feature of the detector is a 7-cm by 7-cm by 97-cm detector channel, which provides a uniform neutron detection efficiency of 16% along the central 40 cm of the channel. The electronics system is identical to that used for the High-Level Neutron Coincidence Counter.
Date: June 1, 1980
Creator: Krick, M.S. & Menlove, H.O.
Partner: UNT Libraries Government Documents Department

Accurate plutonium waste measurements using the sup 252 Cf add-a- source technique for matrix corrections

Description: We have developed a new measurement technique to improve the accuracy and sensitivity of the nondestructive assay (NDA) of plutonium scrap and waste. The 200-{ell} drum assay system uses the classical NDA method of counting passive-neutron coincidences from plutonium but has added the new features of add-a-source'' to improve the accuracy for matrix corrections and statistical techniques to improve the low-level detectability limits. The add-a-source technique introduces a small source of {sup 252}Cf (10{sup {minus}8} g) near the external surface of the sample drum. The drum perturbs the rate at which coincident neutrons from the {sup 252}Cf are counted. The perturbation provides the data to correct for the matrix and plutonium inside the drum. The errors introduced from matrix materials in 200-{ell} drums have been reduced by an order of magnitude using the add-a-source technique. In addition, the add-a-source method can detect unexpected neutron-shielding material inside the drum that might hide the presence of special nuclear materials. The detectability limit of the new waste-drum assay system for plutonium is better than prior systems for actual waste materials. For the in-plant installation at a mixed-oxide fabrication facility, the detectability limit is 0.73 mg of {sup 24O}Pu (or 2.3 mg of high-burnup plutonium) for a 15-min. measurement. For a drum containing 100 kg of waste, this translates to about 7 nCi/g. This excellent sensitivity was achieved using a special low-background detector design, good overhead shielding, and statistical techniques in the software to selectively reduce the cosmic-ray neutron background.
Date: January 1, 1992
Creator: Menlove, H.O.
Partner: UNT Libraries Government Documents Department

Neutron collar calibration for assay of LWR (light-water reactor) fuel assemblies

Description: The neutron-coincidence collar is used for the verification of the uranium content in light-water reactor fuel assemblies. An AmLi neutron source is used to give an active interrogation of the fuel assembly to measure the /sup 235/U content, and the /sup 238/U content is verified from a passive neutron-coincidence measurement. This report gives the collar calibration data of pressurized-water reactor and boiling-water reactor fuel assemblies. Calibration curves and correction factors are presented for neutron absorbers (burnable poisons) and different fuel assembly sizes. The data were collected at Exxon Nuclear, Franco-Belge de Fabrication de Combustibles, ASEA-Atom, and other nuclear fuel fabrication facilities.
Date: March 1, 1987
Creator: Menlove, H.O. & Pieper, J.E.
Partner: UNT Libraries Government Documents Department

Calculation of fast-neutron induced-fission multiplication in large PuO/sub 2/ samples

Description: Fast-neutron multiplication in large PuO/sub 2/ samples has been studied using both Monte Carlo computer codes and the coincidence correlation equations developed by K. Boehnel and N. Ensslin. Samples covering the mass range from 0.1 to 7.2 kg of plutonium have been measured and the multiplication results were compared with the theoretical predictions. The results are in agreement within the uncertainties in the sample characteristics. A parametric study was performed to determine the effect of sample density and moisture variation on the neutron multiplication.
Date: December 1, 1986
Creator: Menlove, H.O. & Rinard, P.M.
Partner: UNT Libraries Government Documents Department

Portable neutron measurement technique for the assay of /sup 235/U in LWR fuel assemblies

Description: An active neutron interrogation technique has been developed for the measurement of the /sup 235/U content in fresh fuel assemblies. The method employs an AmLi neutron source to induce fission reactions in the fuel assembly and coincidence counting of the resulting fission reaction neutrons. When no interrogation source is present, the passive neutron coincidence rate gives a measure of the /sup 238/U via the spontaneous fission reactions. The system can be applied to the fissile content determination in HWR, BWR, and LWR fuel assemblies for accountability, criticality control, and safeguards purposes.
Date: January 1, 1981
Creator: Menlove, H.O. & Krick, M.S.
Partner: UNT Libraries Government Documents Department

The development of {sup 3}He neutron detectors for applications in high level gamma-ray backgrounds

Description: To measure high-level-activity scrap and waste, it is necessary to use neutron detectors that are insensitive to the high gamma-ray background. We have developed a combination of {sup 3}He tubes and custom preamplifiers to provide the high efficiency associated with {sup 3}He detectors with good gamma-ray rejection. We have preamplifiers with short time constants in the signal processing to help separate the neutron signals from the slower risetime gamma signals. We have compared AMPTEK (A-111) preamplifiers with Precision Data Technology (PDT 110A) preamplifiers with experimental tests for gamma rejection and radiation damage. Hot cell radiation tests using a 4.5 Ci radium source were performed using {sup 10}B and {sup 3}He detectors to evaluate relative efficiency and the ability to separate neutrons and gamma rays. The AMPTEK A-111 and PDT-110A amplifiers were exposed to gamma doses between {approximately}0.1 R/h and 1500 R/h to observe where the gamma pileup would interfere with the neutron counting. The conclusion is that both amplifiers can operate in gamma fields up to {approximately}500 R/h with modest loss of neutron efficiency. This is valid for the case of only one {sup 3}He tube (30-cm active length) connected to a single amplifier. If an amplifier services multiple tubes or longer tubes, the gamma rejection will get worse. Studies are in progress to determine the lifetime of the amplifiers and {sup 3}He tubes in the high-radiation fields.
Date: December 1, 1995
Creator: Menlove, H.O. & Beddingfield, D.H.
Partner: UNT Libraries Government Documents Department

Design study for MOX fuel rod scanner for ATR fuel fabrication. Phase I: Design of active neutron scanner. Phase II: Design of passive neutron scanner. Phase III: Design of passive gamma-ray scanner

Description: An active neutron fuel-rod scanner has been designed for the assay of fissile materials in mixed oxide fuel rods. A {sup 252}Cf source is located at the center of the scanner very near the through-hole for the fuel rods. Spontaneous fission neutrons from the californium are moderated and induce fissions within the passing fuel rod. The rod continues past a combined gamma-ray and neutron shield where delayed gamma rays above 1 MeV are detected. The authors used the Monte Carlo neutron-photon (MCNP) code to design the scanner and review optimum materials and geometries. Applications of the rod scanner include accountability of fissile material for safeguards applications, quality control of the fissile content in a fuel rod, and the verification of reactivity potential for mixed oxide fuels. A passive neutron fuel-rod scanner has been designed for the assay of the plutonium in mixed oxide fuel rods. The {sup 240}Pu-effective is measured by counting the spontaneous fission neutrons using a high-efficiency thermal-neutron detector. This passive neutron detector would be combined with a high-resolution gamma-ray system (HRGS) measurement to obtain the total plutonium from the plutonium isotopic ratios. A passive gamma-ray scanner has been designed for the measurement of the {sup 241}Am and plutonium uniformity in mixed oxide fuel rods. The passive gamma-ray emissions from {sup 241}Am (60 keV) and plutonium (150-400 keV) are used to verify the unformity of the fuel enrichment zones and to check for any pellets that are out of specification. The fuel rod is moved through the interior of an NaI(Tl) or a bismuth germanate detector to measure the passive gamma-ray emissions. A tungsten sleeve collimator is used in the through-hole to improve the pellet-to-pellet spatial resolution. The same detector is used to verify the plutonium uniformity in the pellets with a 13-mm tungsten collimator. The low-resolution passive ...
Date: September 1, 1997
Creator: Griffith, G.W. & Menlove, H.O.
Partner: UNT Libraries Government Documents Department

Applications of curium measurements for safeguarding at large-scale reprocessing plants

Description: Safeguarding the plutonium passing through a large-scale reprocessing plant (such as one with 800 t of uranium per year) involves nondestructive assay measurements for plutonium at key points. The gamma-ray and neutron signals from the plutonium are generally hidden by the much larger backgrounds from fission products and actinides, so indirect measurements are routinely used. The intense neutron emission rate from spent fuel is from curium. In a spent fuel assembly at the head-end of a plant, the curium neutrons are used to deduce the amount of plutonium present. Coincidence and multiplicity counting are alternative ways to measure neutrons from spent fuel; they have advantages over total neutron counting in certain conditions and offer new opportunities for examining assemblies. New uses for measurements of curium`s neutrons are proposed to safeguard waste streams. From a year`s work at a large-scale plant, 4 to 7 kg of plutonium can remain in leached hulls and 4 to 22 kg of plutonium can remain in the vitrified high-level liquid waste. While the plutonium in these wastes has the safeguards advantage of being dilute, it is important to verify (a) that the many kilograms involved are in fact present and (b) that the declared masses are not higher than the actual amounts so that more concentrated plutonium cannot pass through the plant by masquerading as waste. Curium measurements on spent fuel assemblies, the accountability tank, and leached hulls would form a safeguards system around all the inputs and outputs of a plant`s head-end where the plutonium is always intimately mixed with the curium. A neutron measurement of the vitrified waste would help identify the presence of a diversion path upstream because essentially all of the curium measured in the spent fuel assemblies should also be found in the vitrified waste (on a batch basis). 7 ...
Date: August 1, 1997
Creator: Rinard, P.M. & Menlove, H.O.
Partner: UNT Libraries Government Documents Department

Application of curium measurements for safeguarding at reprocessing plants. Study 1: High-level liquid waste and Study 2: Spent fuel assemblies and leached hulls

Description: In large-scale reprocessing plants for spent fuel assemblies, the quantity of plutonium in the waste streams each year is large enough to be important for nuclear safeguards. The wastes are drums of leached hulls and cylinders of vitrified high-level liquid waste. The plutonium amounts in these wastes cannot be measured directly by a nondestructive assay (NDA) technique because the gamma rays emitted by plutonium are obscured by gamma rays from fission products, and the neutrons from spontaneous fissions are obscured by those from curium. The most practical NDA signal from the waste is the neutron emission from curium. A diversion of waste for its plutonium would also take a detectable amount of curium, so if the amount of curium in a waste stream is reduced, it can be inferred that there is also a reduced amount of plutonium. This report studies the feasibility of tracking the curium through a reprocessing plant with neutron measurements at key locations: spent fuel assemblies prior to shearing, the accountability tank after dissolution, drums of leached hulls after dissolution, and canisters of vitrified high-level waste after separation. Existing pertinent measurement techniques are reviewed, improvements are suggested, and new measurements are proposed. The authors integrate these curium measurements into a safeguards system.
Date: March 1, 1996
Creator: Rinard, P.M. & Menlove, H.O.
Partner: UNT Libraries Government Documents Department

Plutonium nitrate bottle counter manual

Description: A neutron coincidence counter has been designed for plutonium nitrate assay in large storage bottles. This assay system can be used in the reprocessing plant or in the nitrate-to-oxide conversion facility. The system is based on the family of neutron detectors similar to the high-level neutron coincidence counter. This manual describes the system and gives performance and calibration parameters for typical applications. 4 references, 11 figures, 9 tables.
Date: March 1, 1984
Creator: Menlove, H.O.; Adams, E.L. & Holbrooks, O.R.
Partner: UNT Libraries Government Documents Department

Birdcage neutron coincidence counter manual

Description: A thermal neutron coincidence counter has been constructed for the assay of fast critical assembly fuel plates stored in birdcages. Standard coincidence counting electronics are used. This manual describes the birdcage, the measurement system, and its performance characteristics. 3 refs.
Date: July 1, 1985
Creator: Krick, M.S.; Menlove, H.O. & Ramalho, A.
Partner: UNT Libraries Government Documents Department