Decay Tank Research Articles

A new approach to determine abnormality of radioactive discharges from pressurized water reactors and to derive abnormality indicators correlated with a specific causal event

Abstract A novel methodology to analyze the trend of radioactive effluent data from nuclear power plants (NPPs) has been proposed to estimate the possibility of abnormal releases of radioactive materials, and to identify sensitive radionuclides with high correlation to specific events and abnormal releases. Actual discharge data including abnormal releases for 21 years (1,610 reactor-years) from 62 US and 22 Korean pressurized water reactors were collected. A release correlation factor (RCF) was newly proposed as a quantitative indicator of the abnormality of radioactive discharges based on annual discharge data from each NPP. The probability of correct estimation of abnormality using the RCF for a test case ranges 27–36 %, and such a modest estimation power was ascribed to the relatively low contribution (i.e., about 12 %) of a specific causal event to the annual radioactivity release. Through this, the feasibility of the RCF for estimating the abnormality of radioactive discharges was demonstrated. The RCF was derived for three types of causal events, and subsequently the sensitive radionuclides to each specific event were derived as 88Kr, 137Xe, and 138Xe for leakage from gas decay tank, 3H for leakage from steam generator’s power operated relief valve, and 85Kr, 88Kr, 133Xe, 133mXe, 3H and 14C for leakage from defected spent fuel during handling. The new approach proposed in this study is to be used to suppose the significant unreported abnormality in radioactive effluent data and the potential causal event, which may contribute to improving the safety and performance of radioactive effluent control as necessary.

Institutional Experience of Routine Radiation Surveillance of Delay and Decay Tanks Facility in a Department Having High-dose Iodine Therapy Unit.

Radioactive solid and liquid waste generated by patients after high-dose iodine therapy may lead to significant radiation exposure if not properly handled. This study was conducted to monitor the radiation exposure along the sewerage drainage system of the high-dose iodine therapy ward and to rule out leakage if any, that might pose a potential radiation hazard to the general public (sewerage workers) and radiation health professional. The sewerage drainage system from isolation wards has multiple gate valves to regulate sewerage flow from the high-dose iodine therapy ward into delay and decay tanks (DDT) built, especially for the purpose. Radiation surveillance was done using a Geiger-Muller counter-based survey meter at 11 different locations on a weekly basis for 12 weeks. A total of 26 patients underwent high-dose iodine ablation therapy during the study period in our department, with the highest recorded radiation exposure rate in the sewerage draining system in the 9th week of patient admission. This was at the common gate valve junction (location B) that directed sewerage waste from all four isolation rooms into the common pipeline leading to DDT. Minimal radiation exposure was recorded within Atomic Energy Regulatory Board -prescribed limits with no evidence of leakage. A routine radiation survey is an important component of overall radiation safety in the nuclear medicine department, including sewerage delay tank facilities, which helps keep the radiation exposure to acceptable levels by identifying timely leakage.

Monitoring and fault detection: a comparative study using computational intelligence techniques

In this work, two different Computational Intelligence Techniques were used to provide a comparative study by using Neural Networks and Neuro-fuzzy applied in Monitoring and Fault Detection in sensor of an experimental reactor. Both methodologies were developed and tested using a model composed by 9 variables: N2 (% power), T3 (pool water temperature), T4 (decay tank inlet temperature), T7 (primary loop outlet temperature), T8 (secondary loop inlet temperature), T9 (secondary loop outlet temperature), F1M3 (primary loop flowrate), F2M3 (secondary loop flow rate) and R1M3 (nuclear dose rate). It was used data from the first week experimental reactor IEA-R1 operation from October 2012 in both Monitoring Systems, which was divided in subsets in a following way: 60% for training, 20% for tens and 20% for validation. The results obtained using Neuro-fuzzy were better than the ones with Neural Networks.

Radiological study of a wastewater treatment plant associated with radioiodine therapy at a hospital in West Java, Indonesia

Nuclear medicine (NM) services in Indonesia have rapidly developed due to the increasing number of patients, and this growth has been supported by standardized regulations in the field, including the management of solid waste generated. However, multiple reports indicate that licensing control does not regulate liquid waste disposal from patient excretions to protect personnel and the community from radiopharmaceutical exposure. One of the radiopharmaceuticals commonly used in NM and having the longest half-life among the radiopharmaceuticals used in NM is iodine 131(I-131). Thus, this study used a high-purity germanium detector to measure iodine-131 (I-131) activity in liquid waste from decay tanks, temporary collection channels, the hospital’s wastewater treatment plant (WWTP) outlet, and six points around the NM service and liquid waste treatment unit. Concentration measurements in three decay tanks were carried out sequentially every 12 h for 3 d, corresponding to the therapy period. The results showed that the I-131 activity levels in the decay tanks and temporary collection channels, before being mixed with liquid waste from other units, were 95.9 × 106 ± 4.4 × 106 Bq m−3. At the point where the liquid waste from other units was mixed, the activity level decreased significantly to 472 680 ± 22 160 Bq m−3, which was below the clearance level of 107 Bq m−3. However, the recorded concentration exceeded the standard for environmental radioactivity at the hospital’s WWTP outlet, namely 37 670 ± 2040 Bq m−3. The measurement results for I-131 in the air in the open space for two nuclear buildings was above the standard at 1.3 ± 0.27 Bq m−3. According to the RESRAD simulation, based on the initial dose taken from the liquid waste treatment outlet point, the accumulation of doses and the risk of cancer among workers and the community decreased within 3 months after the maximum exposure.

IEA-R1 Renewed Primary System Pump B1-B Nozzles Stress Analysis

The present report is a summary of the structural analysis of the pump nozzles applying the finite element method by using the Ansys computer program. The IEA-R1 RR is an open pool-type moderated and cooled by light water using beryllium/graphite as a reflector. The reactor can reach up to 5MW of thermal power cooled by the primary and secondary systems. The primary coolant system consists of a piping arrangement, a decay tank, two pumps, and two heat exchangers. The primary pump B1-B presented some failures requiring refurbishment by a new one. The pump used in the IEA-R1 must meet the requirements inherent to the nuclear installation, in addition to the operational requirements for rotating equipment, such as flow and pressure, and structural integrity of the body and nozzles. The supplier specified the type of pump suitable for the System. The pump furnished granted mechanical allowable loads for the nozzles that were lower than the loads imposed by the piping on the nozzles. To enable the installation of the pump in the primary circuit, new support was inserted in the piping system next to the pump minimizing efforts and deformations. A piping stress analysis was carried out to obtain the new efforts imposed on the nozzles. For validation of the motor pump set, a verification of the nozzles was done compared with API 610 standard loads, and the allowable loads of the provider. Finally, a structural analysis of the pump nozzles with the new loads was developed using the finite element method. The calculated stresses meet the limits prescribed by the ASME code; therefore, the new B1-B Pump is approved for operation at the IEA-R1 Nuclear Research Reactor primary circuit.

Optimization in Designing the Series-Wound Decay Tanks of Radioactive Wastewater

Optimization in Designing the Series-Wound Decay Tanks of Radioactive Wastewater

Design of a Low-Resolution Gamma-ray Spectrometer for Monitoring Radioactive Levels of Wastewater

Wastewater containing radioactive materials is stored in decay tanks, which are typically installed in basements to restrict public access. Specific activity is measured by a gamma spectroscopy system or a gamma counter for several hours per sample before discharge. To simplify the sample collection and measurement procedures before draining, the specific activity conversion coefficient for converting a measured value from a 1.5″ NaI (Tl) detector installed on a tank into specific activity was calculated. The experimental calibration was performed in a test water tank with a volume of 14 L filled with diluted reference source 18F, which is most commonly used in hospitals. The specific activity of the test water was measured with a gamma spectroscopy system using a high-purity germanium detector calibrated with certified reference materials. The change in the conversion coefficient according to the change in the volume of the water tank was corrected based on a Monte Carlo calculation. Finally, it was determined whether the minimum detectable activity (MDA) of this system was lower than that of the draining standard. The counts for the specific activity conversion factor and MDA were evaluated as 5.5389 × 1010 and 2.09 × 105 for 18F and for the one-hour count, respectively. The MDA was lower than the standard value. Thus, this system can be used for discharge determination.

Démarche d’optimisation des modalités de gestion des déchets lors des traitements au 177Lu-oxodotréotide (Lutathera®)

This paper provides an experience report on the handling and disposal procedures of waste contaminated with Lutetium-177 (177Lu, Lu-177) that have been established in the context of peptide receptor-targeted radionuclide therapy with 177Lu dotatate (Lutathera®). Treatments are administered in a dedicated infusion room within the nuclear medicine department where dry waste is separated and collected into appropriate containers. The expected duration of storage in decay was extrapolated from the results of a 2-year iterative measurement study for each type of waste. Effluents from hot sinks are collected in decay tanks whose radioactive concentration measured when closed as full is used to calculate the duration of storage required before discharge. Lu-177 activity eliminated by renal excretion for the 6hours after injection of the radiopharmaceutical was evaluated from the analysis of urine samples. First micturitions are directed to three septic tanks whose efficacy was estimated comparing Lu-177 activity at the inlet and at the outlet of the system. Results of six-monthly controls performed by continuous measurement of radioactive concentration in wastewater were used to evaluate the fraction of the total activity administered annually that is finally discharged into the main sewage system and to define guide values. The impact of hospital radioactive discharge to sewers for the workers exposed at different steps of wastewater treatment was assessed using the numerical model called CIDRRE developed by the Institute of Radiation protection and Nuclear Safety (IRSN).

Remediation of decay tanks for high-activity radioactive waste

Remediation of decay tanks for high-activity radioactive waste

Remediation of decay tanks for high-activity radioactive waste

The paper aims to present the remediation of decay tanks for high-activity radioactive waste in UJV Řež Ltd. From 1961 to 1991, two decay tanks for high-activity radioactive waste were built in order to lower the activity over time. The paper shows procedures and technologies used for liquidation of contaminated fluid, and solid waste from both tanks as well as decontamination of surfaces of tanks and building. During the remediation works, was pursued monitoring of the environment in the areas nearby the locations of environmental burden. Throughout the remediation works T.G. Masaryk Water Research Institute p.r.i. monitored surroundings ground water and activity in nearby river Vltava.

Evaluation of the Pump Capability of the Primary Cooling of TRIGA 2000 Research Reactor

The TRIGA 2000 research reactor has been operating since mid 2000. Currently, there are plans to convert the reactor core from cylindrical fuel element to plate type fuel element. The conversion process is expected to not change too many existing systems, including the primary cooling systems. For this reason, it is necessary to evaluate the pump capability of the primary cooling system. Based on experimental studies, then merging with the existing installation system head, it has been obtained the main and the redundant pump mass flow rate of 45 and 45.5 kg/s, respectively. The pump capability decreased by around 5 % compared to the results of its commissioning. If the two pumps are combined in parallel, the combined mass flow rate can increase to 62 kg/s. The existing primary pumps cannot be used for primary cooling system if the reactor core is converted into a plate type, even though both pump are installed in parallel. These results need to be considered in designing a new core of the Bandung TRIGA 2000 research reactor with primary cooling systems that are slightly modified because they have to add the decay tank.

Assessment of Radiation Exposure and Radioactivity from the Liquid Discharge in a Nuclear Medicine Facility.

Aim:Radionuclide imaging and therapies produce radioactive liquid waste that may lead to significant radiation exposure to the general public. The study aims to assess the radiation exposure rate to public sewerage from a modified delay tank facility. We shall also evaluate the exposure rates and overall radioactivity at several points.Materials and Methods:After having appropriate permission from the AERB, we measured the radiation exposure from the radionuclide therapy ward. Ward has three isolation beds and a single delay and decay tank of a capacity of 7500 liters. Effluents from the delay tank are processed at the filtration plant of the institute and subsequently released in the public sewerage. We obtained samples from several sites to determine discharged radioactivity.Results:A total of 38 patients received 129.4 ± 42 mCi (Range 40- 200) radioiodine therapy during the study. Discharge of the tanks was done two times during the study. The radioactivity discharges into aeration plant were 89.2 and 71.2 mCi that correspond to 440.05 and 351 MBq/m3, respectively. This was diluted by the aeration tank (6 million liters). Finally, at the discharge time, the radioactivity in the discharge was 1.6 and 1.5 MBq/m3, respectively. The highest exposure rates were 14 μSv/h near the delay tank, which rapidly decreased on moving to the surrounding.Conclusion:Our study indicates that the addition of the dilution method and close monitoring may significantly reduce the radiation exposure and overall radioactivity release from the facility. Old facilities that do not have space to add up the tank capacity may get a benefit from it. A small change in the practice, such as admitting patients alternate months or providing extra decay time for radioactive waste, may lead to a cost-effective alternative.

Experimental study on air ingression and residence time of a small-scale decay tank for a research reactor

An air ingression phenomenon in a pool-type research reactor was observed in small-scale experiments, assuming that a pipe on the upstream of a decay tank was ruptured. The air and water formed a two-phase flow on the upstream of the decay tank, and the air was trapped in the decay tank, occupying its upper volume. The trapped air could be detected by measuring the differential pressure between the inlet and outlet of the decay tank. Also, the shortest residence time of water during the normal operation was measured to verify the decay tank’s design adequateness. The measured residence time in the small-scale experimental facility is used to estimate the residence time in a real-scale decay tank by a dimensional analysis with a dimensionless kinetic pressure. The estimated residence time is in good agreement with the CFD result from the particle-tracking and unsteady UDS methods.

OA203] Assessment of radiation exposure in a newly formed nuclear medicine department

Purpose In an oncology nuclear medicine department, radioisotopes are not only used for tumor detecting, staging, evaluation of therapy response but also for therapeutic purposes. This study documents the radiation exposure of departmental staff, related to cyclotron operation and service during the production and injection of 18F radiopharmaceuticals for PET/CT examination. In addition, it investigates exposure in a multiple holding tank system used for the storage of 131I waste generated from patients undergoing thyroid therapy, in order to optimize environmental protection procedures. Methods Measurements for the dose rates of neutrons and photons in the room of ABT-BG-75 self-shielded mini-cyclotron were recorded during bombardment for 18F-FDG production using a neutron detector and a scintillation dosimeter. The correlation between the duration of bombardment and required time to reach a dose rate equal to background level was investigated. An electronic dosimeter was used to record staff exposure for 18F production, dispensing, administration and imaging using PET-CT. Finally, the decay rate of 131I waste was measured using a dose rate meter positioned in the decay tank system of the radioactive iodine isolation ward. Results The time required for the cyclotron room to reach background level following completion of bombardment (3 × 50 min each) was approximately 2 h. The dose rate from neutrons was found to be negligible and from photons was less than 7.5 μ Sv/h. Therefore, personnel can safely enter the room during bombardment. The staff mean whole-body dose per 18F-administered patient was 1–2 μ Sv, depending on patient condition. The values obtained from the 131I radioactive waste stored in a delay tank system were comparable with theoretical values. Conclusion This study is useful for optimizing radiation exposure in an oncology nuclear medicine department. It is shown that during 18F production exposure is mostly attributed to photons. The level of the dose permits staff entry into the cyclotron room. Staff responsible for administration received 1–2 μ Sv per 18F-patient, considered to be on the lower end of the acceptable limit for a radiation worker. The study also documents the decay rate of 131I waste over the period which the suggested activity level for release in the environment is reached.

Assessment of N-16 activity concentration in Bangladesh Atomic Energy Commission TRIGA Research Reactor

Abstract An assessment for determining N-16 activity concentrations during the operation condition of Bangladesh Atomic Energy Commission TRIGA Research Reactor was performed employing several governing equations. The radionuclide N-16 is a high energy (6.13 MeV) gamma emitter which is predominately created by the fast neutron interaction with O-16 present in the reactor core water. During reactor operation at different power level, the concentration of N-16 at the reactor bay region may increase causing radiation risk to the reactor operating personnel or the general public. Concerning the safety of the research reactor, the present study deals with the estimation of N-16 activity concentrations in the regions of reactor core, reactor tank, and reactor bay at different reactor power levels under natural convection cooling mode. The estimated N-16 activity concentration values with 500 kW reactor power at the reactor core region was 7 . 40 × 10 5 Bq / cm 3 and at the bay region was 3 . 39 × 10 − 5 Bq / cm 3 . At 3 MW reactor power with active forced convection cooling mode, the N-16 activity concentration in the decay tank exit water was also determined, and the value was 4 . 14 × 10 − 1 Bq / cm 3 .

CFD Analysis of a Decay Tank and a Siphon Breaker for an Innovative Integrated Passive Safety System for a Research Reactor

An innovative integrated passive safety system for a research reactor is proposed in this study to improve the safety of the research reactor. This integrated system has three functions in the facility as a decay tank, siphon breaker, and long-term cooling tank. This paper also deals with the process of designing and optimizing the decay tank and the siphon breaker of the integrated passive safety system. At first, the decay tank was designed and improved step by step, while considering the computational fluid dynamics analysis results. Consequently, we could satisfy the design requirements of the decay tank. In addition, the performance of a new type of siphon breaker that was installed in the final decay tank model was tested. We designed an 18-inch diameter siphon breaker at the top of the decay tank’s third section, and we could observe the breaking of the siphon that prevented the occurrence of a severe accident in the research reactor. By locating the siphon breaker at the third section of the decay tank, we could also use the coolant of the front three sections for long-term cooling of the research reactor.

Design evaluation of decay tank for a pool-type research reactor from the required minimum flow residence time point of view

A decay tank shall be designed to provide enough flow residence time to ensure that the N-16 activity decreases before the coolant leaves the decay tank's shielding room. However, when a proper criterion for the flow residence time in a decay tank is not presented, the tank would be oversized/undersized. In this paper, design evaluation for a decay tank is performed by investigating the effect of the fluid distribution along the residence time on the total dose rate and the required minimum flow residence time. The evaluation is also carried out to resize the predesigned decay tank.

Estimation of flow residence time in a decay tank for a pool type research reactor using CFD

A decay tank shall be designed to provide enough flow residence time to ensure that the N-16 activity decreases before the coolant leaves the decay tank's shielding room. Therefore, estimation of the residence time in a decay tank is necessary before the conclusion of such a design. To estimate the flow residence time in a decay tank, the transport equation of a user-defined additional variable, which has a time unit and zero kinematic diffusivity, is solved using steady and unsteady assumptions. The minimum flow residence time is compared with that of an analytic method with an assumption of a uniform flow in a decay tank, and a particle tracking method. For the simulations, a commercially available CFD code, ANSYS-CFX, is used. When comparing the results, the unsteady simulation is seen to be much more efficient approach than steady simulation to obtain the minimum flow residence time of the decay tank.

The Large Angle Photon Veto System for the NA62 Experiment at CERN

The NA62 experiment at CERN SPS aims at measuring-100 events of the very rare decay K + →π + ννˉ (BR∼8.5xlO∼ 10 ). It poses stringent requirements on PID capabilities to reject the overwhelming π + π 0 (63%) and Kμ 2 (21%) backgrounds. The photon veto system must provide a rejection factor of 10∼ 8 on π 0 decays. As a main γ veto detector, the NA48 liquid Kripton calorimeter will be used. To have full geometrical acceptance up to 50 mr, a set of 12 veto stations should be placed along the vacuum decay tank, with an inefficiency <10∼ 4 in a wide energy range (200 MeV-35 GeV). Good energy resolution (∼10% at 1 GeV) for threshold definition, good time resolution (∼1 ns) to be used at the trigger level, sensitivity to MIP for calibration with muons of the beam halo are needed. A moderate segmentation in the azimuthal angle is desirable, for reducing the counting rate and providing information on the γ direction. We performed an intense R&D program on three solutions: “spaghetti” calorimeter, lead/scintillator sandwich calorimeter, and original re-use of the existing barrel of the OPAL lead-glass e.m. calorimeter. Studies have been performed at the Frascati BTF beam and all three meet the efficiency requirements. The final choice uses a peculiar radial arrangement of lead-glasses in rings. Front-end electronics has been designed to cover the tree orders of magnitude of the signal, contributing to the trigger, and integrated in the general TDAQ, while keeping low cost and simplicity. The first five full veto stations have been constructed. Two tests have been done and problems found fixed. We will discuss about R&D for the technology choice, LAV construction, test beams results and simulation performance.

Radioactivité résiduelle avant vidange des cuves de décroissance de déchets liquides : bilan annuel d’un service de médecine nucléaire hospitalier au Luxembourg

Residual radioactivity within decay tanks in an in-hospital clinical nuclear medicine unit reflects the specific typology of the concerned unit. To learn how to improve management of emptying the tanks, measures of residual radioactivity over the year 2009 have been compared to prevailing legal norms in Luxembourg. Legal norms have in no case been outpassed. A minimal residual radioactivity, below legal thresholds, has been often found (84%). It concerned 131I, 99mTc and 111In. This is why management of radioactive decay tanks may be continued unchanged.