Loss Of Sink Research Articles

Analysis on the Role of RSG-GAS Pool Cooling System during Partial Loss of Heat Sink Accident

RSG-GAS is a 30 MW reactor that is mostly used for radioisotope production and experimental activities. Recently, it is regularly operated at half of its capacity for efficiency reason. During an accident, especially loss of heat sink, the role of its pool cooling system is very important to dump decay heat. An analysis using single failure approach and partial modeling of RELAP5 performed by S. Dibyo, 2010 shows that there is no significant increase in the coolant temperature if this system is properly functioned. However lessons learned from the Fukushima accident revealed that an accident can happen due to multiple failures. Considering ageing of the reactor, in this research the role of pool cooling system is to be investigated for a partial loss of heat sink accident which is at the same time the protection system fails to scram the reactor when being operated at 15 MW. The purpose is to clarify the transient characteristics and the final state of the coolant temperature. The method used is by simulating the system in RELAP5 code. Calculation results shows the pool cooling systems reduce coolant temperature for about 1 K as compared without activating them. The result alsoreveals that when the reactor is being operated at half of its rated power, it is still in safe condition for a partial loss of heat sink accident without scram.

Integral effect test on station blackout (SBO) scenario with steam generator tube rupture (SGTR) in ATLAS facility

Station blackout (SBO) is one of the most important design extension conditions (DECs) because a total loss of the heat sink leads to a core uncovery or damage without any proper operator action. During a long transient of an SBO, a steam generator tube rupture (SGTR) accident can occur when a steam generator tube is exposed to a superheated steam flow. In this study, a prolonged SBO with an SGTR occurrence was experimentally investigated by performing an integral effect test with the ATLAS facility. For the transient simulation, the tube rupture was simulated when the core water level became below the top of the active core. As an accident management measure, the auxiliary feedwater was supplied to the intact steam generator when the maximum heater surface temperature started to show an excursion behavior. The experimental results showed that a single tube rupture could not sufficiently reduce the primary system pressure before the injection of the auxiliary feedwater. A delayed supply of the auxiliary feedwater after an excursion of the heater surface temperature successfully cooled the primary system until the end of the transient, where inflow of the coolant from the pressurizer contributed to a recovery of the coolant inventory in the core. The natural circulation flow characteristics in the primary system showed an oscillating behavior depending on the heat removal rate of the steam generators. This integral effect test data can be used to evaluate the prediction capability of safety analysis codes and identify code deficiencies in predicting an SBO transient with an SGTR occurrence.

Phosphorus more than temperature controls the phytoplankton community in a deep quarry lake: a combined field and laboratory approach

Phytoplankton community structure and their abiotic drivers are seldom studied in quarry lakes. We monitored the phytoplankton and physical and chemical conditions of a deep quarry lake for more than a year. The lake was meromictic and phosphorus concentrations remained low year-round. The phytoplankton community was dominated by a small Cosmarium species, identified by molecular techniques, which persisted throughout the year. Laboratory experiments were additionally performed to test which abiotic factors control the phytoplankton community of the lake: nutrients, water temperature, or their interaction. An increase of phosphorus alone increased biomass and changed the community structure, selecting low temperature adapted species, while higher temperature alone and increase in nitrates alone had no effect. Higher temperature associated with nutrient input increased biomass and led to a third community structure dominated by fast growing species with low sedimentation loss. Cosmarium sp. dominated treatments without phosphorus inputs at all temperatures but was easily outcompeted in phosphorus-replete conditions. The thermo-tolerance of Cosmarium sp., associated with a high affinity for phosphorus and low sinking losses, allows this species to dominate in situ year-round. Results from both in situ and laboratory experiments indicated that phosphorus exerts a stronger control than temperature on the phytoplankton community of the quarry lake during the entire year, similar to natural lakes.

Analysis of lead-cooled fast reactor using a core simulator

The Lead-cooled Fast Reactor (LFR) is a novel reactor concept, the core of which can be simulated by developing a dynamic model. The model consists of 3 sub-models; a block for reactor kinetics, thermal hydraulics and the reactivity feedback calculations. By implementation of the LFR core simulator, the response of the reactor has been shown for various test inputs. Certain events have been simulated in the LFR core (unprotected transient of overpower, loss of heat sink, loss of flow and a SCRAM shutdown). A sensitivity analysis has been performed and it is observed that the LFR core power is the most sensitive to changes in the average coolant temperature. A stability analysis has been performed to show that the LFR core has a stable configuration (for its normal operating conditions). Similarly, a noise analysis has revealed that the output parameters have the most adverse effect in case of a Gaussian noise being introduced in the reactivity of the core.

Dynamic Safety Analysis of a Subcritical Advanced Burner Reactor

A customized dynamic safety model is developed and used to analyze the safety characteristics of the Subcritical Advanced Burner Reactor (SABR), a fast transmutation reactor driven by a tokamak fusion neutron source. Loss-of-flow accidents (LOFAs), loss–of–heat sink accidents (LOHSAs), and loss-of-power accidents (LOPAs) are analyzed taking into account the effects of feedback mechanisms, control rod insertion, and terminating electrical power to the neutron source. The core avoids fuel melting and coolant boiling without corrective action for 50% (failure of one of two pumps) loss of heat sink (LOHSA) and loss of flow (LOFA). For 100% (failure of both pumps) LOFAs, LOHSAs, and LOPAs without corrective action, coolant boiling (1156 K)/fuel melting (1473 K) occur at about 25 s/36 s, 35 s/84 s, and 25 s/36 s, respectively, after pump failure unless corrective control action is taken before this time, in which case the core power can be reduced to the decay heat level by shutting off the plasma power source. The present passive heat removal system is not sufficient to remove the decay heat, and both fuel melting and coolant boiling ultimately occur in the 100% LOFAs and LOHSAs (failure of both pumps) in either the primary or secondary system indicating the need to provide other means for decay heat removal.

Solving the Spent Nuclear Fuel Problem by Fissioning Transuranics in Subcritical Advanced Burner Reactors Driven by Tokamak Fusion Neutron Sources

The Georgia Tech concept of the Subcritical Advanced Burner Reactor (SABR) spent nuclear fuel (SNF) transmutation reactor and supporting analyses to date are summarized. SABR is based on the fast reactor physics and technology prototyped in Experimental Breeder Reactor-II (EBR-II) and proposed for the Integral Fast Reactor and the PRISM Reactor and on the tokamak fusion neutron source physics and technology that will be prototyped in ITER. Preliminary fuel cycle calculations indicate that subcritical operation would enable a proliferation-resistant fuel reprocessing cycle that would safely accommodate fuel with up to 100% TRU content and that introduction of SABRs in a 1-to-3 power ratio with light water reactors would reduce the required SNF high-level waste repository capacity (defined on the basis of decay heat released) by a factor of 10 to 100. Preliminary dynamic safety calculations indicate that SABRs could be shut down to the decay heat level by turning off the plasma heating power without core damage in loss of heat sink, loss of flow, and loss of power accidents, but that additional decay heat removal capability is needed in the case of total loss of primary or secondary system pumping power.

Updating of local blockage frequency in the reactor core of SFR and PRA on consequent severe accident in Monju

ABSTRACTFuel subassemblies of sodium-cooled fast reactors (SFRs) are densely arranged and have high power densities. Therefore, the local fault has been considered as one of the possible initiating events of severe accidents. In the conventional analyses for the license of Japanese prototype SFR (Monju), according to the local fault evaluation under the condition of one sub-channel flow blockage in the analyses of design basis accident (DBA), it was confirmed that the pin failures were limited locally without severe core damage. In addition, local flow blockage of 66% central planar in the subassembly was historically investigated as one of the beyond-DBAs. However, it became clear that these deterministic analyses were not based on a realistic assumption by experimental studies. Therefore, probabilistic risk assessment on local fault which was initiated from local flow blockage was performed reflecting the state-of-the-art knowledge in this study. As a result, damage propagation from local fault caused by local flow blockage in Monju can be negligible compared with the core damage due to anticipated transient without scram or protected loss of heat sink in the viewpoint of both frequency and consequence.

Transient Safety Analysis of a Transportable Fluoride-Salt-Cooled High-Temperature Reactor Using RELAP5-3D

A transportable fluoride-salt-cooled high-temperature reactor (TFHR) design with 20-MW(thermal) rated power and 18-month fuel cycle is proposed for off-grid applications. One of the design goals of the compact reactor core is potential transport by truck, rail, or air. Full-core thermal-hydraulic analyses and improvements using three-dimensional computational fluid dynamics (CFD) were performed previously to demonstrate the feasibility of a TFHR design at a nominal power of 20 MW(thermal). In this paper, the best-estimate system code Reactor Excursion Leak Analysis Program (RELAP5-3D) is adopted to study the transient behavior of this TFHR design and the safety characteristics of the primary loop system during accident conditions. The modeling results of the steady state were verified using CFD results with consideration of radial heat conduction between heat transfer unit cells. Four most challenging accidents of anticipated transient without scram were analyzed, as well as parametric studies of some key factors. These accidents include unprotected reactivity insertion accident (URIA), unprotected loss of heat sink (ULOHS), unprotected loss of flow (ULOF), and a combination accident of ULOF and ULOHS. The results indicate that transient temperature limits are not exceeded during the most severe accidents. They indicate satisfactory transient performance of the TFHR design. The transient temperature limit of structure material Hastelloy N, based on embrittlement phenomena, poses the most limiting constraint due to the small temperature margin of about 20 K in the accident combination of ULOF and ULOHS. Overall, TFHR is a sound reactor design from a thermal-hydraulic viewpoint.

Secondary Effects of Glyphosate Action in Phelipanche aegyptiaca: Inhibition of Solute Transport from the Host Plant to the Parasite

It is currently held that glyphosate efficiently controls the obligate holoparasite Phelipanche aegyptiaca (Egyptian broomrape) by inhibiting its endogenous shikimate pathway, thereby causing a deficiency in aromatic amino acids (AAA). While there is no argument regarding the shikimate pathway being the primary site of the herbicide's action, the fact that the parasite receives a constant supply of nutrients, including proteins and amino acids, from the host does not fit with an AAA deficiency. This apparent contradiction implies that glyphosate mechanism of action in P. aegyptiaca is probably more complex and does not end with the inhibition of the AAA biosynthetic pathway alone. A possible explanation would lie in a limitation of the translocation of solutes from the host as a secondary effect. We examined the following hypotheses: (a) glyphosate does not affects P. aegyptiaca during its independent phase and (b) glyphosate has a secondary effect on the ability of P. aegyptiaca to attract nutrients, limiting the translocation to the parasite. By using a glyphosate-resistant host plant expressing the “phloem-mobile” green fluorescent protein (GFP), it was shown that glyphosate interacts specifically with P. aegyptiaca, initiating a deceleration of GFP translocation to the parasite within 24 h of treatment. Additionally, changes in the entire sugars profile (together with that of other metabolites) of P. aegyptiaca were induced by glyphosate. In addition, glyphosate did not impair germination or seedling development of P. aegyptiaca but begun to exert its action only after the parasite has established a connection to the host vascular system and became exposed to the herbicide. Our findings thus indicate that glyphosate does indeed have a secondary effect in P. aegyptiaca, probably as a consequence of its primary target inhibition—via inhibition of the translocation of phloem-mobile solutes to the parasite, as was simulated by the mobile GFP. The observed disruption in the metabolism of major sugars that are abundant in P. aegyptiaca within 48 h after glyphosate treatment provides a possible explanation for this inhibition of translocation and might reflect a critical secondary effect of the herbicide's primary action that results in loss of the parasite's superior sink for solutes.

Modeling of natural circulation for the inherent safety analysis of sodium cooled fast reactors

The paper discusses a set of developed integrated one-dimensional models of thermal-hydraulic processes that contribute to the removal of decay heat in a BN-type reactor. The assumptions and constraints involved in one-dimensional equations of unsteady natural convection in closed circuits have been analyzed. It has been shown that the calculated values of the primary circuit sodium temperature and flow rate in conditions with a loss of heat sink and with a forced circulation of the primary coolant are in a reasonable agreement with the results of a benchmark experiment in the PHENIX reactor. The model makes it possible to assess the effects general thermophysical and geometrical parameters and the selected technology have on the efficiency of passive heat removal by the natural coolant convection in the reactor tank and in the emergency heat removal system's intermediate circuit and by the heat transfer through the reactor vessel. The model is a part of an integrated algorithm used to assess the inherent safety level of advanced fast neutron reactors and is intended primarily to develop, at the early conceptual design stage, the recommendations and requirements with respect to the reactor equipment parameters leading to an increase in the reactor inherent safety. The model will be used to identify the set of quantitative thermal-hydraulic criteria that have an effect on the dynamics of emergency transients leading to a potential loss of integrity by the reactor safety barriers, and to formulate such limits for the defined criteria as would cause, if observed, the requirement for the safety barrier integrity to be met under any combination of the accident initiating events.

Stationary liquid fuel fast reactor SLFFR — Part II: Safety analysis

Safety characteristics have been evaluated for the stationary liquid fuel fast reactor (SLFFR) proposed for effective burning of hazardous TRU elements of used nuclear fuel. In order to model the geometrical configuration and reactivity feedback mechanisms unique to SLFFR, a multi-channel safety analysis code named MUSA was developed. MUSA solves the time-dependent coupled neutronics and thermal-fluidic problems. The thermal-fluidic behavior of the core is described by representing the core with one-dimensional parallel channels. The primary heat transport system is modeled by connecting compressible volumes by liquid segments. A point kinetics model with six delayed neutron groups is used to represent the fission power transients. The reactivity feedback is estimated by combining the temperature and density variations of liquid fuel, structural material and sodium coolant with the corresponding axial distributions of reactivity worth in each individual thermal-fluidic channel. Preliminary verification tests with a conventional solid fuel reactor agreed well with the reference solutions obtained with the SAS4A/SASSYS-1 code. Transient analyses of SLFFR were performed for unprotected transient over-power (UTOP), unprotected loss of heat sink (ULOHS) and unprotected loss of flow (ULOF) accidents. The results showed that the thermal expansion of liquid fuel provides sufficiently large negative feedback reactivity for passive shutdown of UTOP and ULOHS. The ULOF transient is also terminated passively with the negative reactivity introduced by the gas expansion modules installed at the core periphery. The maximum coolant temperatures have sufficient margins to the sodium boiling point for all three unprotected transient scenarios.

Analyses of Feedwater Trip With SBO Sequence of VVER1000 Reactor

In the Czech Republic, as a follow-up, a consortium of research organizations and universities has decided to simulate selected stress tests’ scenarios, in station blackout (SBO) and the loss of ultimate heat sink (LoUHS), with the aim to verify the national stress report and to analyze time response of respective source term releases. These activities are carried out in the frame of the project prevention, preparedness, and mitigation of consequences of severe accident (SA) at Czech NPPs in relation to lessons learned from stress tests after Fukushima, financed by the Ministry of Interior. The Research Centre Rez has been working on a methods for estimation of leakages and consequences of releases (MELCOR) model for VVER1000 nuclear power plant (NPP) starting with a plant systems nodalization. The aim was to benchmark the MELCOR model with the validated TRAC/RELAP advanced computational engine (TRACE) model, first comparing the steady state and continuing in a long-term SBO plus another event until the beginning of the SA. The presented work is based on the previous paper from the ICONE 23rd Conference hosted in Japan. It focuses mainly on the comparison of the thermohydraulics of the two models created in MELCOR and TRACE codes as outcome of the “Fukushima project.” After that, preliminary general results of the SA progression showing the hydrogen production and the relocation phenomena will be shortly discussed. This scenario is considered closed after some seconds to the break of the lower head. It is important to note that this paper is a substantial update of a previous one (Mazzini et al., 2015, “Analyses of SBO Sequence of VVER1000 Reactor Using TRACE and MELCOR Codes,” 23rd International Conference on Nuclear Engineering (ICONE23)) and although it contains the same descriptive sections, all the results are new.

Tailoring the response of Autonomous Reactivity Control (ARC) systems

The Autonomous Reactivity Control (ARC) system was developed to ensure inherent safety of Generation-IV reactors while having a minimal impact on reactor performance and economic viability. In this study we present the transient response of fast reactor cores to postulated accident scenarios with and without ARC systems installed. Using a combination of analytical methods and numerical simulation, the principles of ARC system design that assure stability and avoids oscillatory behavior have been identified. A comprehensive transient analysis study for ARC-equipped cores, including a series of Unprotected Loss of Flow (ULOF) and Unprotected Loss of Heat Sink (ULOHS) simulations, were performed for Argonne National Laboratory (ANL) Advanced Burner Reactor (ABR) designs. With carefully designed ARC-systems installed in the fuel assemblies, the cores exhibit a smooth non-oscillatory transition to stabilization at acceptable temperatures following all postulated transients. To avoid oscillations in power and temperature, the reactivity introduced per degree of temperature change in the ARC system needs to be kept below a certain threshold the value of which is system dependent, the temperature span of actuation needs to be as large as possible.

Transient behavior of ASTRID with a gas power conversion system

The present article is dedicated to preliminary transient studies carried out for the analysis of the system overall behavior of the ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration) demonstrator developed in France by CEA and its industrial partners. ASTRID is foreseen to demonstrate the progress made in SFR technology at an industrial scale by qualifying innovative options, some of which still remain open in the areas requiring improvements, especially safety and operability. Among the innovative options, a gas power conversion systems (PCS) is envisaged. In this innovative PCS, the working gas is nitrogen whose flow rate delivers power to a turbine driving with the same shaft two compressors (low and high pressure) separated by an intercooler. The other part of the work delivered by the gas is used to drive the alternator that produces electricity. The main objective of such a PCS consists in avoiding physically the possibility of a sodium/water reaction with the secondary circuit but the impact of this PCS on the control of incidental and accidental transients has also been studied. The main purpose of the studies presented in the paper is to assess the dynamic behavior of ASTRID including a gas PCS with the CATHARE2 code. The first transient presented deals with a loss of off-site power and has been calculated for the gas PCS but also for a classical steam/water PCS for comparison purpose. Then typical transients of gas system have been investigated. Several families of initiating events affecting the PCS are studied: breaches in the ternary circuit, a loss of power supply, a loss of main heat sink and the spurious opening of the turbine by-pass valve. Regarding this last transient, sensitivity studies have shown that an adequate design of the turbomachine by-pass lines allows a control of the event without shutdown. Moreover, regulating actions following the scram are also investigated in order to take benefit of the PCS in order to remove the decay heat.

Design study of long-life small modular sodium-cooled fast reactor

Summary This paper presents a new design for a small modular sodium-cooled fast reactor core with an optimized lifetime and reactivity swing through the analysis of various breed-and-burn strategies and its neutronic analyses in terms of active core movements, isotopic mass balance, kinetic parameters, and inherent safety. The new core design aims at a power level of 260 MW with a long lifetime of 30 years without refueling and a reactivity swing smaller than 1000 pcm. Starting from five initial candidate cores with various breed-and-burn strategies, an optimum core was selected from a combination of the two candidates that shows a proper breeding behavior with the optimized uranium enrichment in the low-enriched uranium region and the optimized size of the blanket region. The depletion analysis of the new core provides various reactor design parameters such as the core multiplication factor, breeding ratio, heavy metal mass change, power distribution, and summary of neutron balance. In addition, the perturbation analysis provides the reactor kinetic parameters and reactivity feedback coefficients for the inherent safety analysis of the core. The integral reactivity parameters of the quasi-static reactivity balance analysis demonstrate that the new core is inherently safe in cases of unprotected loss of flow, unprotected loss of heat sink, and unprotected transient over power. Copyright © 2016 John Wiley & Sons, Ltd.

The influence of rapid urbanization and land use changes on terrestrial carbon sources/sinks in Guangzhou, China

Complex changes in carbon sources and sinks caused by rapid urbanization have been observed with extensive changes in the quantity, structure, and spatial pattern of land use types. Based on the modified Carnegie-Ames-Stanford Approach model and on gray relational analysis, we analyzed the influence of land use changes on carbon sinks and emissions in Guangzhou from 2000 to 2012. The aim was to identify suitable options for built-up land expansion that would allow for minimal carbon losses. The key results were as follows: (1) Built-up land increased by 118.91% in Guangzhou city over the study period, with this expansion taking the form of concentric circles extending around the old Yuexiu district. (2) Carbon emissions over the period of analysis significantly exceeded carbon sink capabilities. The total carbon sink decreased by 30.02%, from 535.40×103t to 374.6×103t. Total carbon emissions increased by 1.89 times, from 13.73×106t to 39.67×106t; 80% of carbon emissions were derived from energy consumption. (3) There were large differences in the extent of carbon sink losses at different scales of built-up land expansion and land use change. In Guangzhou, the loss of carbon sink is small when cultivated land (though not prime farmland) and water bodies are converted to built-up land on a small scale. The loss of carbon sink is much smaller when grasslands are converted to built-up land on a large scale. However, forested land, which has excellent carbon sink functions, should not be converted. (4) Changes in carbon sinks were mainly affected by natural factors and land urbanization. Changes in carbon emissions were mainly affected by population urbanization, economic urbanization, and land urbanization. (5) To achieve “economical and intensive use of land”, “urban growth boundary” and “ecological red lines” should be determined for government policies on land use management. These factors have great significance for “increasing carbon sinks and reducing carbon emissions” in urban ecological systems.

Carbon dynamics of China’s forests during 1901–2010: The importance of forest age

The forest ecosystem plays a significant role in long-term carbon sequestration. The magnitude of a forest carbon sink is determined by the combination of intrinsic biotic factors (i.e. forest age) and extrinsic environmental driving factors (i.e. temperature, precipitation, nitrogen deposition). The mechanism of how forest age affects the carbon balance is still unclear. Furthermore, forest age is a useful surrogate variable for analyses of the impact of disturbances on forest carbon and an important parameter for assessing carbon mitigation potential of forests at regional scale. Without considering forest age, large uncertainties exist in the simulating forest carbon cycle at regional scale. In this study, we analyzed the effect of forest age information on carbon uptake of China’s forests based on a process-based model (Integrated Terrestrial Ecosystem Carbon budget, InTEC model) in the last century, with integration of two forest age maps at 1 km spatial resolution which were derived from inventory data and remote sensing AVHRR NDVI. Inter-annual variability of net primary productivity in China’s forests during 1901–2010 based on InTEC model coupled with inventory data and remote sensing data was similar with each other. Meanwhile, the comparison approach indicated that the errors of 5 years in forest age might cause uncertainties of 25% in simulated net ecosystem productivity of China’s forests. We also discussed the significance of forest age in ecosystem process-based model and the uncertainties of carbon balance of China’s forest ecosystem during 1901–2010. Besides, the hypothesis assumed that no large-scale deforestation occurred since1950s and mature forests (and older forests) were covered the whole China. We adjusted forest age structure for different forest types and regions to simulate the effect of changes in forest age on distribution of carbon balance in China. The important finding is that the loss of carbon sink in China’s forests induced by disturbances (i.e. deforestation, afforestation or natural disturbances) is about 3.80 Pg C during last century. Based this hypothesis, China’s forests in the last two decade manifested a large carbon sink (0.23 Pg C a - 1). Currently, many process-based models are not capable of reflecting the impact of land disturbances because the explicit forest age information are lacking. Our study incorporated the forest age in models successfully and explored the effect of forest age on the simulating carbon balance of forests. The application of forest age in large-scale carbon modeling can improve the accuracy of simulated carbon dynamics and explore the uncertainties in carbon cycle models.

Sinking loss should be taken into account while studying the dynamics of Microcystis under light-availability control

In-situ light-availability control is commonly used to suppress Microcystis blooms in nutrient-rich water resources. It has been suggested that the reduction of column cyanobacterial biomass could mostly be attributed to the inhibition of photosynthesis. However, sinking loss may be another factor influencing the column cyanobacterial biomass. To further investigate the mechanism of this reduction, a mixing-static water column experimental apparatus was designed to simulate the reduction of Microcystis biomass under light-availability control. Under light-shading plus mixing, the reduction of Microcystis in the water column was attributed to both intrinsic biomass loss and sinking loss. Comparatively, under light-shading without mixing, the Microcystis accumulated in surface water, maintaining a continuously increase of intrinsic biomass. Meanwhile, the sinking loss increased as the water column became static, even exceeding the increase of intrinsic biomass, suggesting that sinking loss was the main mechanism for the reduction under light-shading. Further investigation indicated that both intrinsic growth rate and sinking loss rate varied in response to available light. Accordingly, a hypothesis is represented that the loss of column biomass and the shift in dominant species under light-availability control are primarily attributed to the combined effects of intrinsic biomass change and sinking loss, which both respond to available light.

Natural circulation experiments in a non-uniform diameter lead bismuth loop and validation of LeBENC code

Experimental studies are carried out on natural circulation in a Lead Bismuth Eutectic (LBE) loop. The loop mainly consists of a heated section, air heat exchanger, valves, various tanks and argon gas control system. All the components and piping are made of SS316L. The dissolved oxygen in the LBE is monitored online by an Yttria Stabilised Zirconia (YSZ) oxygen sensor and controlled during the operation of the loop. In this paper the details of the loop and experimental studies carried out with heater power levels varying from 900 W to 5000 W are described. The temperature range of LBE during the experiments was 200 °C–500 °C. The maximum heat loss in the piping is kept less than 20% of the main heater power. Steady state experimental studies are carried out at different power levels and the LBE flow rate was found to be varying from 0.095 kg/s to 0.135 kg/s. The analysis and results of the performance of the heat exchanger with air and water as the secondary coolants are also discussed in the paper. Transient studies were carried out to simulate various events like heat sink loss, step power change and secondary side coolant flow rate change and reported in the paper. In the start up experiments, where the flow is started from stagnant condition of LBE, the time required for starting of natural circulation is found to be 600 s, 400 s and 240 s with power level of 1200 W, 2400 W and 3000 W respectively. The results are compared with available correlation and prediction of computer code LeBENC.

Fundamental safety strategy against severe accidents on prototype sodium-cooled fast reactor

ABSTRACTThe accident categories of severe accidents (SAs) for prototype sodium-cooled fast reactor (SFR) which need proper measures were investigated through the internal event probabilistic risk assessment (PRA) and event tree analysis for the external event and six accident categories, unprotected loss of flow (ULOF), unprotected transient over power (UTOP), unprotected loss of heat sink (ULOHS), loss of reactor sodium level (LORL), protected loss of heat sink (PLOHS) and station blackout (SBO), were identified. Fundamental safety strategy against these accidents is studied and clearly stated considering the characteristics and existing accident measures of prototype SFR, and concrete measures based on this safety strategy are investigated and organized. The sufficiency of these SA measures is confirmed by comparing the evaluated core damage frequency (CDF) and containment failure frequency (CFF) to the target value, 1×10−5 and 1×10−6 per plant operating year, respectively, which were selected based on the IAEA's safety target. However, the target value of CDF and CFF should be satisfied considering all the SAs caused by both internal and external events. External event PRA for prototype SFR is now under evaluation and we set out to satisfy the target value of CDF and CFF considering both internal and external events.