Vessel Vent Research Articles

Method of Analyzing Criteria for Primary Containment Vessel Venting and Protective Measures for Public Risk Reduction

Method of Analyzing Criteria for Primary Containment Vessel Venting and Protective Measures for Public Risk Reduction

Hydrogen gas dispersion studies for hydrogen fuel cell vessels I: Vent Mast releases

We report modeling results for hydrogen releases associated with deploying hydrogen fuel cell technology on vessels. This first paper (I) considers hydrogen releases through the vessel Vent Mast from 250-bar hydrogen gas storage tanks, the type of tanks being used for the first hydrogen vessels. A manifolded 10-tank hydrogen storage system, holding 278 kg of hydrogen, can be emptied in ∼10 min for maintenance purposes, with a pressure reduction to half the original pressure (125 bar) realized in 2 min if a rapid pressure reduction is needed, for example in the event of a fire. The time profile for filling a tank is also of interest so as not to exceed the tank thermal limits. The calculations show that a manifolded 10-tank array can be filled with hydrogen to 250-bar pressure in ∼2 h from a 350-bar hydrogen refueling trailer without exceeding the 85 °C temperature limit typical of Type IV hydrogen tanks.Computational fluid dynamic (CFD) modeling shows that when the hydrogen is released out of the 10-tank array and into the Vent Mast in a 5-mph wind blowing horizontally, the effect of the wind on the hydrogen dispersion strongly depends on the hydrogen exit speed. For high release speeds (∼800–900 m/s), the hydrogen flow is strongly momentum-driven, and there is modest cross-wind influence. For low hydrogen exit speeds (∼10 m/s), the hydrogen is readily entrained in the wind flow and blown sideways, with the downstream flammable envelope rising at a positive angle to the horizontal due to buoyancy. To capture the influence of a wind with a downward component (e.g., created by a downdraft near a building), a calculation of a low-velocity (8.6 m/s) hydrogen release was performed with a 5-mph wind pointed downward at a 45° angle. The results show that despite the buoyancy of hydrogen, the wind blows the hydrogen substantially downward for low hydrogen speeds exiting the Vent Mast.

Recovery of vacuum condition and plasma performance after vessel vent in EAST tokamak

The plasma recovery after vessel vent is studied in the EAST 2019 spring campaign. The removal of condensate water is important for the fully superconducting tokamak. The low-Z impurities are mostly removed after a baking cycle for 200 h and GDC for 111 h. About 49% of H2 and 40% of H2O molecules are removed in this phase. The clean ultra-high vacuum pressure is re-obtained to 3.0 × 10−6 Pa. In a follow-up process, about ~550 shots with an accumulated plasma duration of 4100 s are carried out to further remove implanted impurities. In the initial discharge stage, the removal rates of H2 and H2O particles are 4.7 × 1021 molecules/(m2·h) and 3.1 × 1021 molecules/(m2·h), respectively, which are ~4 times higher than that during D2/He-GDC and baking. About 31% of H2 and H2O impurities are removed due to the effect of initial plasma shots. And the repeatable plasma shots are achieved with the decrease of impurity level. The results provide reference for the arrangement of recovery plan after vacuum failure of EAST, ITER, CFETR and superconducting fusion devices.

Metallurgical Failure Investigation of Cracking of a Vent Nozzle on a Pressure Pulsation Dampener of a Natural Gas Compressor

Abstract A leakage occurred in the area of the weld of a vent nozzle in the pressure pulsation dampener of a natural gas compressor. It was caused by a crack adjacent to the weld on the side of the pipe. A metallurgical failure investigation was ordered to identify the mechanism that caused the damage. The defective pressure pulsation dampener was brought back to the welding manufacturer for repair. The crack that caused the leakage was opened and the pipe was detached from the shell by the vessel manufacturer. A sample of the pipe containing the crack edge on the side of the pipe was brought to the laboratory for examination. A fatigue crack which initiated at the outer surface of the pipe was identified as the metallurgical cause of the failure. No indications of weld defects were found. In the damaged area, the microstructure at the outer surface of the vessel's vent nozzle presents a number of damage-promoting features such as small surface ruptures and scale residues (which will lead to an increased notch effect there) as well as decarburization and coarse grain. The design of the vessel's nozzle at the shell of the pressure pulsation dampener does not seam very suitable for dynamic loading. Also taking into account the poor surface quality of the pipes, the vessel's nozzles are insufficiently dimensioned for the present loading condition which clearly comprises dynamic elements. It was recommended to review the design and to apply adapted repair measures.

Dimension of the forced vessel water level based on subcooling margin of core outlet coolant in CPR1000 nuclear power plants

The core cooling and monitoring system (CCMS) supplies the sub-cooling margin (ΔTSAT) and the pressure vessel water level (L VSL) information for State Oriented Procedure (SOP) to identify the core cooling state in post-accident conditions, as some special accidents such as the rupture of the vessel vent line will lead to both train A and train B L VSL measurements failure, the forced L VSL values have to be designed and set in the CCMS to ensure the correct diagnosis of primary system state in these scenarios. Considering the inherent relationship between ∆TSAT and L VSL from the point of view of thermal-hydraulics, the forced L VSL values are dimensioned based on ∆TSAT while taking into consideration the presence of non-condensable gases in primary system and the operating state of reactor coolant pumps. These values have been practically applied in CPR1000 nuclear power plants.

Video analysis of dust events in full-tungsten ASDEX Upgrade

Fast video data recorded during seven consecutive operation campaigns (2008–2012) in full-tungsten ASDEX Upgrade have been analyzed with an algorithm developed to automatically detect and track dust particles. A total of 2425 discharges have been analyzed, corresponding to 12 204 s of plasma operation. The analysis aimed at precisely identifying and sorting the discharge conditions responsible of the dust generation or remobilization. Dust rates are found to be significantly lower than in tokamaks with carbon PFCs. Significant dust events occur mostly during off-normal plasma phases such as disruptions and particularly those preceded by vertical displacement events (VDEs). Dust rates are also increased but to a lower extent during type-I ELMy H-modes. The influences of disruption energy, heating scenario, vessel venting and vessel vibrations are also presented.

Identification and mitigation of stray laser light in the Thomson scattering system on the Madison Symmetric Torus (MST).

The Thomson scattering diagnostic on the Madison Symmetric Torus (MST) records excessive levels of stray Nd:YAG laser light. Stray light saturates the 1064 nm spectral channel in all polychromators, which prevents absolute electron density measurements via Rayleigh scattering calibration. Furthermore, stray light contaminates adjacent spectral channels for r/a ≥ 0.75, which renders the diagnostic unable to make electron temperature measurements at these radii. In situ measurements of stray light levels during a vacuum vessel vent are used to identify stray light sources and strategies for reduction of stray light levels. Numerical modeling using Zemax OpticStudio supports these measurements. The model of the vacuum vessel and diagnostic includes synthetic collection optics to enable direct comparison of measured and simulated stray light levels. Modeling produces qualitatively similar stray light distributions to MST measurements, and quantifies the mitigation effects of stray light mitigation strategies prior to implementation.

Assessment of W7-X plasma vessel pressurisation in case of LOCA taking into account in-vessel components

This paper presents the analysis of W7-X vacuum vessel response taking into account in-vessel components. A detailed analysis of the vacuum vessel response to the loss of coolant accident was performed using lumped-parameter codes COCOSYS and ASTEC. The performed analysis showed that the installed plasma vessel venting system prevents overpressure of PV in case of 40mm diameter LOCA in “baking” mode. The performed analysis revealed differences in heat transfer modelling implemented in ASTEC and COCOSYS computer codes, which require further investigation to justify the correct approach for application to fusion facilities.

G101 福島第一原子力発電所事故対応の概要(OS8 軽水炉・新型炉・原子力安全)

Fukushima Daiichi Nuclear Power Station lost all off-site power sources immediately after the earthquake which occurred at 14:46 on March 11, 2011.But the important safety features were retained for their safety functions with back-up power supply even after the earthquake. However the eventual flooding of the site caused by tsunami resulted in loss of all power sources, which led to the failure of cooling the reactor cores. As ad hoc measures such as alternative water injection using fire engines and primary containment vessel venting by assembling temporary equipment and manual operation were attempted. But core damage could not be prevented and hydrogen explosion occurred. Based on the identified lessons learned of the causes and issues that could not stop the accident, action plans are developed and are presented in this paper.

Basic concept of a near future BWR

This paper shows a basic concept of a near future boiling water reactor (BWR) aiming at evolutional safety and cost savings with minimum change from the current advanced BWR (ABWR). The plant output is uprated to 1500 MWe from 1356 MWe. This power uprate can bring about potential of 11% cost saving per MWe base. Safety improvement as a next generation large reactor is also achieved. The advanced reinforced concrete containment vessel (ARCCV) is used for the containment vessel to improve safety for severe accidents. The peak pressure of the containment at severe accidents can be kept close to the design pressure. The advanced passive containment cooling system (APCS) is also provided and can accomplish no primary containment vessel (PCV) venting. The advanced emergency core cooling system (AECCS) consists of four divisions in the front line. The advanced passive cooling system (APCS) is also provided. The combination of the four divisional emergency core cooling system (ECCS) and the passive safety system improves the plant performance in probabilistic safety assessment (PSA). This plant concept is designed based on the heritage of the current ABWR. No more major research and development (R&D) are necessary. Therefore, construction and operation is possible in the early 2010s.

A new closed vessel for determining the ballistic performance of high energy solid and liquid gun propellants

A new closed vessel, designed and build by Cranfield University under contract to the UK Defence Evaluation and Research Agency (DERA), is described. The jacketed vessel, which can be operated at high pressure (500 MPa) and has the capability of firing liquid monopropellants, is fitted with a single instrumented head and a detachable liner. The internal surface profile of the combustion chamber is shaped so as to prevent the build up of shock waves which can occur between parallel surfaces and this feature leads to improved output signal quality. Vessel venting following a firing is carried out by remote control via a proprietary air-actuated high pressure valve. The vessel can be fitted with optical windows or converted to a vented device for gas erosion studies.

Impurity and particle recycling reduction by boronization in JT-60U

In JT-60U boronization using decaborane was carried out. Boronization reduced the oxygen impurity in OH discharges and shortened the wall conditioning after the vacuum vessel vent and consequently enabled JT-60U to produce clean plasmas easily except for NB heated plasmas. After boronization, particle recycling was reduced drastically in OH and NB discharges. High confinement plasmas were obtained including high β p mode and H-mode discharges. In the latest boronization part of divertor plates were replaced with B 4C coated tiles with a B 4C thickness ∼ 300 μm. After introducing B 4C divertor tiles, an explosive generation of boron particles from the tiles was observed. By the combined effects of boronization with decaborane and boron generation from B 4C tiles, oxygen impurity was so low that oxygen line signals were reduced to noise levels after the latest boronization. On the other hand, boron burst from the B 4C tiles restricted the operation of JT-60U.