Health Phys. Abstracts，Volume 121,Number 3

DevelopmentofaFissionNeutronSpectrumfromaD-TNeutronGeneratorbySpectrumSubtractionTechnique

Wade W. Scates1, Bradley J. Schrader2, Konner M. Casanova3

(1.Criticality Safety Engineering Department, Idaho National Laboratory, P. O. Box 1625, Idaho Falls, ID 83415-3458;2.Radiation Safety Department, Idaho National Laboratory, P. O. Box 1625, Idaho Falls, ID 83415-3405;3.Criticality Safety Engineering Department, Idaho National Laboratory, P. O. Box 1625, Idaho Falls, ID 83415-3458)

Abstract:Californium-252 (252Cf) is considered essential by the National Institute of Standards and Technology for the calibration of neutron instrumentation and dosimetry. Californium-252 has a relatively short half-life of 2.645 y; consequently, it must be replaced frequently to produce an adequate neutron flux for calibration. The user community is currently looking for a replacement for252Cf. The patented technology described herein has a high probability of being that replacement. A preferred method to replace252Cf would use an affordable and easily maintained neutron source that generates neutrons in an energy spectrum as close to that of252Cf as possible. Deuterium-tritium (D-T) neutron generators are both affordable and easily maintained, which makes them highly attractive for replacing252Cf. The patented technology discussed in this paper simulates the252Cf fission spectrum through a D-T neutron generator by using spectral subtraction. The primary spectrum is built using principally (n,xn) and (n,n′) reactions in a variety of materials. In conjunction with the primary spectrum, an engineered background spectrum is generated using a second set of materials. This engineered background spectrum corrects for differences between the primary and desired spectra. This subtraction technique generates a spectrum very similar to252Cf while maintaining a reasonable flux. Further, by choosing different scattering materials, any fission spectrum can be matched, including the thermal and epithermal components. This flexibility expands the potential use of this technology beyond simulating252Cf to any desired neutron spectrum below 14 MeV.

Keywords:252Cf; calibration; safety standards; spectrometry; neutron

Health Phys. 121(3):181-192; 2021

EvaluationofMigrationRadiologicalEquivalenceforDualComponentNuclearWasteinaDeepGeologicalRepository

V. K. Ivanov1,2, E. V. Spirin2, A. N. Menyajlo1, S. Y. Chekin1, S. S. Lovachev1, A. M. Korelo1, K. A. Tumanov1, V. M. Solomatin2

(1.A. Tsyb Medical Radiological Research Center, branch of NMRRC of Ministry of Health, Russian Federation, Obnins;

2.Joint Stock Company PRORYV, Moscow)

Abstract:The paper is concerned with the issue of achieving the radiological equivalence (the equivalence of radiation risks) of radioactive waste of nuclear reactors and corresponding mass of natural uranium, taking into account the different migration ability of radionuclides in geological formations and soil. This migration radiological equivalence is being investigated for the deep burial of radioactive waste in the case of the development of a two-component nuclear power system with the concurrent use of thermal neutron reactors and fast neutron reactors. Calculations were performed of radiation doses and radiation risks of cancer death arising from consumption of drinking water from a well above a disposal site. The radiation risk relating to a two-component nuclear power system is lower than that from natural uranium; i.e., after reaching the radiological equivalence (100 y of storage) over the timescale of 109y, the principle of migration radiological equivalence is satisfied. It would take 106y after radioactive waste disposal to reach the migration radiological equivalence if only thermal reactors were operated. As regards consumption of well drinking water, the radiation risk does not exceed 10-5y-1for a two-component nuclear power system, while being 10-3y-1(socially unacceptable level) for a power system using only thermal reactors. Radionuclides241Am,239Pu, and240Pu in drinking water make the main contribution to the doses and radiation risks of people for 104y after the disposal of radioactive waste.

Keywords: internal dose; external dose; radiation risk; waste disposal; uranium

Health Phys. 121(3):193-201; 2021

PeakEfficiencyofNaIDetectorandCoincidenceSummingFactorforDifferentCylindricalSourcesUsingGeant4Simulation

Jamila S. Alzahrani, Aljawhara H. Almuqrin1

(1.Physics Department, College of Science, Princess Nourah Bint Abdulrahman University, Saudi Arabia)

Abstract:Geant4 simulation is used to calculate peak efficiency and correct the effect of coincidence summing in detecting volumetric gamma-ray sources; this simulation was applied to a standard152Eu source with different volumes as a test case. The source is a liquid cylindrical shape of various volumes. Peak efficiency was calculated using two tracks in the Geant4 simulation: single-energy track and “monoenergetic Track” without coincidence summing. Here, the energy of the source is known, and the track of radionuclides, including the coincidence summing, depends on the decay scheme of the radioactive source. The ratio between the peak efficiency of the two tracks gives us the correction factor (CF). The experimental method was used to calculate the peak efficiency and was amended by the correction factor computed with Geant4 tracks. The results showed a good agreement between experimental efficiency after correction and free-summing simulated efficiency. The comparison indicated that the present method is valid and useful for voluminous gamma-ray sources.

Keywords: correction factor; detector； scintillation; gamma radiation; radiation safety

Health Phys. 121(3):202-208; 2021

DoseAssessmentforTechnologicallyEnhancedNaturallyOccurringRadioactiveMaterialsDisposalinLandfills

Emily A. Caffrey1, Arthur S. Rood2, Helen A. Grogan3, John E. Till4, Kurt Herman5

(1.Radian Scientific, LLC, 806 Wells Ave SE, Huntsville, AL 35801;

2. K-Spar, Inc., 4835 W Foxtrail Lane, Idaho Falls, ID 83402;

3. Cascade Scientific, Inc., 1678 NW Albany Avenue, Bend, OR 97703;

4. Risk Assessment Corporation, 417 Till Road, Neeses, SC 29107;

5. Gradient, One Beacon St., 17th Floor Boston, MA 02108)

Abstract:Technologically enhanced naturally occurring radioactive material (TENORM) is gaining notoriety in the public sector, as the oil and gas industry looks for disposal locations for its slightly radioactive waste streams. Due in part to both the lack of federal regulations on the disposal of TENORM and the lack of permitted landfills that are designated for TENORM waste, occasionally it ends up being unknowingly placed in municipal landfills. It was alleged that a municipal landfill in Kentucky accepted 1.05×106kg of TENORM over approximately 8 mo starting in July 2015. This matter is still in litigation, and many facts, including whether the material in question actually constituted TENORM, are still in dispute. The authors had no means available to independently verify the actual composition of the material. Therefore, for purposes of this article only, we assume that the material in question did constitute TENORM. This qualification allows us to evaluate potential doses while respecting the litigation process. Doses from the disposals and for two remediation alternatives, (1) closure-in-place and monitoring and (2) excavation and redisposition of waste, were evaluated, taking into consideration the landfill construction, local geology and hydrology, meteorology, background radiation, population distribution, and current and future land uses. This study outlines appropriate methods for calculating doses to potential receptors for a variety of exposure pathways that are broadly applicable to municipal or chemical/hazardous waste landfills. As this study demonstrates, doses to landfill workers and members of the public are low, both during the disposal and for the remediation alternatives evaluated, and well below regulatory limits. Removal of the materials does not reduce present day doses, and it presents other risks that outweigh any benefit from the long-term dose reduction.

Keywords: dose assessment; naturally occurring radioactive materials; risk assessment; waste management

Health Phys. 121(3):209-224; 2021

PrenatalX-rayExposureandtheRiskofDevelopingPediatricCancer—ASystematicReviewofRiskMarkersandaComparisonofInternationalGuidelines

Fleur Wit, Colinda C.J.J. Vroonland, Harmen Bijwaard

Abstract:Since the first Oxford Survey of Childhood Cancer’s results were published, people have become more aware of the risks associated with prenatal exposure from diagnostic X rays. As a result, it has since been the subject of many studies. In this review, the results of recent epidemiological studies are summarized. The current international guidelines for diagnostic X-ray examinations were compared to the review. All epidemiological studies starting from 2007 and all relevant international guidelines were included. Apart from one study that involved rhabdomyosarcoma, no statistically significant associations were found between prenatal exposure to X rays and the development of cancer during 2007-2020. Most of the studies were constrained in their design due to too small a cohort or number of cases, minimal X-ray exposure, and/or data obtained from the exposed mothers instead of medical reports. In one of the studies, computed tomography exposure was also included, and this requires more and longer follow-up in successive studies. Most international guidelines are comparable, provide risk coefficients that are quite conservative, and discourage abdominal examinations of pregnant women.

Keywords: health effects; exposure; radiation; pregnancy; X rays

Health Phys. 121(3):225-233; 2021

Time-temperatureThresholdsandSafetyFactorsforThermalHazardsfromRadiofrequencyEnergyabove6GHz

Kenneth R. Foster1, Marvin C. Ziskin2, Quirino Balzano3

(1.Department of Bioengineering, University of Pennsylvania;

2.Department of Radiology, Temple University Medical School, 3420 N. Broad Street, Philadelphia, PA 19140;

3.Department of Electrical and Computer Engineering, University of Maryland, College Park, MD 20742)

Abstract:Two major sets of exposure limits for radiofrequency (RF) radiation, those of the International Commission on Nonionizing Radiation Protection (ICNIRP 2020) and the Institute of Electrical and Electronics Engineers (IEEE C95.1—2019), have recently been revised and updated with significant changes in limits above 6 GHz through the millimeter wave (mm-wave) band (30-300 GHz). This review compares available data on thermal damage and pain from exposure to RF energy above 6 GHz with corresponding data from infrared energy and other heat sources and estimates safety factors that are incorporated in the IEEE and ICNIRP RF exposure limits. The benchmarks for damage are the same as used in ICNIRP IR limits: minimal epithelial damage to cornea and first-degree burn (erythema in skin observable within 48 h after exposure). The data suggest that limiting thermal hazard to skin is cutaneous pain for exposure durations less than ≈20 min and thermal damage for longer exposures. Limitations on available data and thermal models are noted. However, data on RF and IR thermal damage and pain thresholds show that exposures far above current ICNIRP and IEEE limits would be required to produce thermally hazardous effects. This review focuses exclusively on thermal hazards from RF exposures above 6 GHz to skin and the cornea, which are the most exposed tissues in the considered frequency range.

Keywords: review paper; exposure limits; nonionizing radiation; safety standards

Health Phys. 121(3):234-247; 2021

EffectsofAutomationforEmergencyOperatingProceduresonHumanPerformanceinaNuclearPowerPlant

Tao Qing1,2, Zhaopeng Liu2, Yaqin Tang1, Hong Hu1, Li Zhang1, Shuai Chen3

(1.Institute of Human Factors & Safety Engineering, Hunan Institute of Technology, Hengyang, P.R. China;

2.State Key Laboratory of Nuclear Power Safety Monitoring Technology and Equipment, China Nuclear Power Engineering Co., Ltd, Shenzhen of Guangdong Province, P.R. China;

3.School of Nuclear Science and Technology, University of South China, Hengyang, P.R. China)

Abstract:The digitization of the control systems in the main control room of a nuclear power plant has changed the operators’ role in coping with accidents and has thus brought about new human factor problems. This article focuses on the procedures that are used for guiding the emergency operating procedures in a nuclear power plant, and experimentally investigates the effects of the digitization of procedures on operators’ mental workload and situation awareness. In these experiments, the procedures at three different levels of automation, namely, paper-based procedures (PBPs), electronic procedures (EPs), and computer-based procedures (CBPs), are used as the independent variables. According to the experimental results, using these procedures at a high level of automation enables the operator to exhibit favorable operational performance with a decreased mental workload; however, the operator’s situation awareness (SA) is decreased. The research results presented here can provide a reference level for optimally setting the level of automation of the emergency operating procedures in a nuclear power plant and provide support for the optimization of a corresponding HRA (Human Reliability Analysis) model.

Keywords: operational topics; exposure; radiation; health effects; nuclear power plant

Health Phys. 121(3):261-270; 2021