Venting Strategies Research Articles

Effect of hydrogen blending on ammonia/air explosion characteristics under wide equivalence ratio

In order to evaluate the effect of mixing hydrogen on the explosive characteristics of ammonia, this work explored the evolution of explosion overpressure and flame propagation characteristics of ammonia/hydrogen/air mixture under different hydrogen blending ratios in closed pipelines through experimental research. Experimental results show that as the hydrogen blending ratio increase, the instability of flame increases, and flame surface changes from smooth to wrinkled. Flame propagation undergoes the evolution of jellyfish-shaped/near-spherical, finger-shaped, plane-shaped, irregularly protruding flame and tulip flame. Flame surface area is constantly changing, accompanied by violent flame tip velocity pulsations. The maximum explosion pressure and the maximum explosion pressure rise rate are consistent with the evolution law of adiabatic flame temperature. They first increase and then decrease with increase of the equivalence ratio, and their peak value appears near the equivalence ratio of 1.1. On the contrary, the explosion duration and rapid combustion period first decrease and then increase with increase of equivalence ratio, and decrease monotonically with increase of hydrogen blending ratio. The conclusions obtained in this work will contribute to the structural design of flame arresters and the formulation of explosion venting strategies during the preparation, transportation and utilization of ammonia/hydrogen mixtures.

Discussion

Discussion

Assessment of Filtered Containment Venting Strategies for Mitigating Severe Accident Consequences at a Generic Single-Unit CANDU

Abstract In many jurisdictions, filtered containment venting systems are an integral part of severe accident management guidelines but are normally only used as a last resort, to be manually activated when the containment pressure approaches the containment failure limit. This approach fails to utilize the capability of the filtered venting system to better control containment pressure throughout an accident and to create capacity for possible future pressurization based on the accident progression. In this paper, smart venting strategies are explored, using a generic single-unit Canada Deuterium Uranium (CANDU) (660 MWel) plant model in MAAP-CANDU, as a means to mitigate the consequences of a severe accident. These strategies are able to account for both current conditions as well as possible future pressurization. The use of strategic venting offers an improvement in maintaining containment integrity, as well as reducing I-131 releases to the environment by about 10% to 31% compared to last-resort venting while being feasible for manual operator actions. Overall, this comprehensive analysis demonstrates the capability of a smart venting strategy paired with a filtered containment venting system as an active mitigation tool.

CARC13: Early Low Pulsatility in VA-ECMO is Associated with Acute Brain Injury

Background: Pulse pressure (or pulsatility) is a dynamic marker of cardiovascular function and is often decreased in patients on veno-arterial extracorporeal membrane oxygenation (VA-ECMO), which provides non-pulsatile flow. We explored the impact of pulse pressure on development of acute brain injury (ABI) in VA-ECMO patients. Methods: We retrospectively analyzed all adult (≥18 years old) patients receiving VA-ECMO at a single tertiary care center between 7/2016 and 1/2021. All patients received routine neurocritical care consultations with standardized neuromonitoring. ABI included intracranial hemorrhage, ischemic stroke, hypoxic ischemic brain injury, cerebral edema, seizure, and brain death. Blood pressure (BP) was recorded every 15 minutes during the first 24 hours after ECMO initiation. Pulse pressure (systolic minus diastolic pressure) was categorized as: very low (<10mmHg), low (1029mmHg), moderate (30-44mmHg), and high (≥45mmHg). Multivariable logistic regression, controlling for baseline illness severity, operative characteristics, and left ventricle (LV) venting strategy, was performed for the association of pulse pressure with ABI. LV venting strategies included intra-aortic balloon pump (IABP), percutaneous ventricular assist device, right superior pulmonary vein, and left ventricle apex vents. Results: We collected 9,179 pressure measurements from 123 VA-ECMO patients (median age=63, 63% male), of which 41 (33%) experienced ABI. Demographics, baseline clinical characteristics, and pre-ECMO arterial blood gases were not significantly different between those with and without ABI. Those with ABI had a lower median pulse pressure than those without (20 mmHg vs. 32, p=0.038). In a multivariable model controlling for cannulation site, preECMO lactate, and left ventricle venting strategy, low (adjusted odds ratio/aOR=7.04, 95%CI: 1.72-28.82, p=0.007) and very low pulse pressure (aOR=5.14, 95%CI: 1.18-22.34, p=0.029) were associated with ABI (Figure 1). In a model with the same covariates, every 10-mmHg decrease in pulse pressure was associated with a 1.29 increased adjusted odds of ABI (95%CI: 1.00-1.65, p=0.047) (Figure 2). In a sensitivity analysis, adjusting for systolic BP yielded similar associations between pulse pressure and ABI, suggesting pulse pressure acts independently of BP in mediating ABI. Conclusions: Decreased pulsatility in the first 24 hours of VA-ECMO was associated with ABI. Special attention should be given to management practices which sustain sufficient pulse pressure early during ECMO. Figure 1. Forest plot for multivariable model of pulse pressure and acute brain injury (ABI), with the covariates of central cannulation, lactate on ECMO day 1, and left ventricle venting strategy. Covariates are not shown in the figure. Dots represent adjusted odds ratios and brackets represent 95% confidence intervals. Low and very low pulse pressure were associated with increased odds of ABI. This model had a C-index of 0.76. Figure 2. Multivariable logistic regression model with pulse pressure treated as a continuous variable, with the covariates of central cannulation, lactate on ECMO day 1, and left ventricle venting strategy. The adjusted relative odds of acute brain injury decrease as pulse pressure increases.

MO598: Coping Strategies During the COVID-19 Pandemic: Influence of Patient Activation in People Living With Kidney Disease

BACKGROUND AND AIMSPatient activation refers to the knowledge, skills and confidence needed to manage one's health [1]. Higher patient activation is associated with better health outcomes in long-term conditions [2] such as kidney disease (KD). The COVID-19 pandemic has presented a myriad of additional challenges for people living with KD. Individuals may display different coping strategies in response to stressful and difficult circumstances such as health management during the pandemic [3]. Our group conducted a multicentre survey to evaluate the impact of the pandemic on kidney patient experiences, lifestyle and health care. As part of this larger study, we hypothesized that higher patient activation may be associated with more effective coping strategies. The purpose of this analysis was to explore coping styles utilised during the pandemic across different levels of patient activation in people with nondialysis CKD (ND-CKD) and kidney transplant recipients (KTR).METHOD214 ND-CKD and KTR participants [50.9% male, mean age 60.71 (SD 14.15) years, 56.1% KTRs] completed the Patient Activation Measure (PAM-13). Participants were categorised into ‘low’ and ‘high’ activation based on their PAM-13 score (levels 1–2 as low; 3–4 as high). Coping strategies were assessed using the Brief-COPE questionnaire and categorised into adaptive coping (active coping, information support, positive reframing, planning, emotional support, humour, acceptance and religion) and maladaptive coping (venting, self-blame, self-distraction, denial, substance use and behavioral disengagement) strategies. Chi-square tests were conducted to compare coping strategies used by low- and high-activated patients.RESULTSMost participants were classified as having ‘high’ activation levels (n = 164, 77%). Table 1 shows the three most frequently used adaptive and maladaptive coping strategies across activation levels. A significantly greater proportion of those with high activation used acceptance (P = 0.006), active coping (P = 0.045) and positive reframing (P = 0.031) as coping strategies. No significance was observed between maladaptive coping strategies and activation level.Adaptive coping strategiesMaladaptive coping strategiesHigh activationLow activationHigh activationLow activation1Acceptance (79.5%)Acceptance (58.5%)Self-distraction (53%)Self-distraction (47.6%)2Religion (60.5)Religion (30.8%)Behaviour Disengagement (37.5%)Substance Use (40%)3Active Coping (48.2%)Information Support (30%)Substance Use (31.6%)Self-Blame (37.5%)CONCLUSIONThe most commonly reported coping strategy was ‘acceptance’ for individuals with high and low activation. The findings suggest that a higher proportion of people with high patient activation used adaptive coping strategies. Worryingly, regardless of activation level, about a third of participants used substance use (i.e. alcohol and drugs) as a form of coping. Identifying people with lower activation in KD can indicate the need for additional support to help them cope in challenging circumstances. Interventions to improve activation may assist in developing effective coping strategies.

Intra‐Aortic Balloon Pump for Left Ventricular Unloading in Veno‐Arterial Extracorporeal Membrane Oxygenation: The Last Remaining Indication in Cardiogenic Shock

Intra‐Aortic Balloon Pump for Left Ventricular Unloading in Veno‐Arterial Extracorporeal Membrane Oxygenation: The Last Remaining Indication in Cardiogenic Shock

Modelling airborne transmission of SARS-CoV-2 using CARA: risk assessment for enclosed spaces.

The COVID-19 pandemic has highlighted the need for a proper risk assessment of respiratory pathogens in indoor settings. This paper documents the COVID Airborne Risk Assessment methodology, to assess the potential exposure of airborne SARS-CoV-2 viruses, with an emphasis on virological and immunological factors in the quantification of the risk. The model results from a multidisciplinary approach linking physical, mechanical and biological domains, enabling decision makers or facility managers to assess their indoor setting. The model was benchmarked against clinical data, as well as two real-life outbreaks, showing good agreement. A probability of infection is computed in several everyday-life settings and with various mitigation measures. The importance of super-emitters in airborne transmission is confirmed: 20% of infected hosts can emit approximately two orders of magnitude more viral-containing particles. The use of masks provides a fivefold reduction in viral emissions. Natural ventilation strategies are very effective to decrease the concentration of virions, although periodic venting strategies are not ideal in certain settings. Although vaccination is an effective measure against hospitalization, their effectiveness against transmission is not optimal, hence non-pharmaceutical interventions (ventilation, masks) should be actively supported. We also propose a critical threshold to define an acceptable risk level.

Analysis of venting strategies and hydrogen concentration evolution during a station blackout in a BWR-6 containment using GOTHIC 8.3

After the Fukushima accident, the interest on hydrogen combustion hazard management has increased considerably. Many European nuclear plants reinforced their strategies for severe accident management with the installation of Passive Autocatalytic Recombiners (PARs) and Filtered Containment Venting Systems (FCVS), among others. In this study, the hypothesis of considering a preventive venting to try to reduce the hydrogen combustion risk is analyzed for a BWR-6 Mark III containment. The scenario chosen was the in-vessel phase of a Station Blackout accident. Cases with and without PARs have been tested.The venting action has been tested at different conditions to clarify its impact on the hydrogen concentration in the containment. One novelty of this study is to consider the difference between measuring the hydrogen concentration values present in the containment in the venting pipe rather than in the instrumentation position. The purpose is to try to understand the decisions that an operational crew can take with the instrumentation available and analyze the differences by modifying the location of the plant instrumentation.For the numerical analysis, numerous simulations have been carried out using a BWR containment model with GOTHIC 8.3. It has been observed that hydrogen concentration depends to a great extent on the containment venting strategy. The main conclusion is that the venting strategy, if properly performed, can reduce the risk associated with hydrogen for BWR-6 containments. During a SBO scenario, an early venting increases considerably the hydrogen combustion hazard, even in the cases with PARs.

ELSO Interim Guidelines for Venoarterial Extracorporeal Membrane Oxygenation in Adult Cardiac Patients.

ELSO Interim Guidelines for Venoarterial Extracorporeal Membrane Oxygenation in Adult Cardiac Patients.

Wireless Ventilation Measurement in 3D Printed Sand Molds

Additive Manufacturing is enabling the casting of complex geometries directly from digital design data, including 3D-scanned and reverse-engineered structures and even functionally graded lattices. By ink jetting binder into a bed of sand layer-by-layer, dimensionally precise sand molds and cores can be printed to serve as soft tooling for sand casting. However, the related increase in geometry complexity can lead to challenges in ensuring casting quality and yield. One recently explored remedy is to introduce sensors (the Internet of Things) to enable the collection of a diversity of data at difficult-to-access locations in molds in order to measure temperature, pressure, moisture, and core shift. This effort has explored measuring barometric pressure at strategic locations to evaluate the ventilation design of internal cores. Optimized and measurable ventilation can be leveraged to improve the quality of castings by reducing porosity and improving surface finish. By measuring the pressures that accumulate within cores due to binder decomposition, new ventilation designs and strategies—enabled with complex, 3D printed fluidic channels—can be explored. In this work, two castings with different metal temperatures were poured and internal pressures were measured and compared to simulations demonstrating that wireless disposable sensors can be used to measure pressure and that the measured pressure correlated with venting strategies now possible with 3D printed sand cores.

Prevention and treatment of pulmonary congestion in patients undergoing venoarterial extracorporeal membrane oxygenation for cardiogenic shock.

Cardiogenic shock is still a major driver of mortality on intensive care units and complicates ∼10% of acute coronary syndromes with contemporary mortality rates up to 50%. In the meantime, percutaneous circulatory support devices, in particular venoarterial extracorporeal membrane oxygenation (VA-ECMO), have emerged as an established salvage intervention for patients in cardiogenic shock. Venoarterial extracorporeal membrane oxygenation provides temporary circulatory support until other treatments are effective and enables recovery or serves as a bridge to ventricular assist devices, heart transplantation, or decision-making. In this critical care perspective, we provide a concise overview of VA-ECMO utilization in cardiogenic shock, considering rationale, critical care management, as well as weaning aspects. We supplement previous literature by focusing on therapeutic issues related to the vicious circle of retrograde aortic VA-ECMO flow, increased left ventricular (LV) afterload, insufficient LV unloading, and severe pulmonary congestion limiting prognosis in a relevant proportion of patients receiving VA-ECMO treatment. We will outline different modifications in percutaneous mechanical circulatory support to meet this challenge. Besides a strategy of running ECMO at lowest possible flow rates, novel therapeutic options including the combination of VA-ECMO with percutaneous microaxial pumps or implementation of a venoarteriovenous-ECMO configuration based on an additional venous cannula supplying towards pulmonary circulation are most promising among LV unloading and venting strategies. The latter may even combine the advantages of venovenous and venoarterial ECMO therapy, providing potent respiratory and circulatory support at the same time. However, whether VA-ECMO can reduce mortality has to be evaluated in the urgently needed, ongoing prospective randomized studies EURO-SHOCK (NCT03813134), ANCHOR (NCT04184635), and ECLS-SHOCK (NCT03637205). These studies will provide the opportunity to investigate indication, mode, and effect of LV unloading in dedicated sub-analyses. In future, the Heart Teams should aim at conducting a dedicated randomized trial comparing VA-ECMO support with vs. without LV unloading strategies in patients with cardiogenic shock.

Hemodynamic Changes With Left Ventricular Venting In Patients Supported With Va-ecmo For Cardiogenic Shock

Introduction Despite the ability to provide full pulmonary and biventricular support for severe or refractory cardiogenic shock (CS), a recognized limitation of veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is the increase in left ventricular afterload and its associated adverse effects on the myocardium. Limited data exists regarding the relative efficacy of typical left ventricular venting (LVV) strategies to address this issue. Methods We retrospectively reviewed 31 consecutive patients at our institution initially treated for severe or refractory CS with VA-ECMO who then underwent LVV from 01/01/17 - 12/31/19. Patients with alternate MCS devices implanted prior to VA-ECMO and those with post-cardiotomy CS were excluded. Clinical characteristics, baseline risk stratification scores and serial hemodynamic assessments were collected at 0, 24 and 48 hours. Results Twenty-six (84%) patients underwent LVV with Impella (E-I) and 5 (16%) with atrial septostomy (E-S). Patients in the E-S cohort were younger (mean age 37 vs. 52, p=0.02).There were no significant differences between the E-S and E-I cohorts with regards to baseline CARDShock scores (5 vs. 4; p=0.06), SOFA scores (10 vs. 9; p=0.89), index hemodynamic assessments, and mean time to LVV (32 vs. 31 hours; p=0.60). We also did not detect a significant difference in total time on the mechanical ventilator between the E-S and E-I patients (19 vs. 10 days; p=0.19). At 48 hours following LVV, there was no significant difference in changes in mean lactate, pulmonary artery diastolic pressure (PA-D), right atrial pressure (RA), cardiac power output (CPO) or pulmonary arterial pulsatility index (PAPi) between the E-S and E-I cohorts. Thirty-day survival in the E-S and E-I cohorts were 80% (4/5) and 50% (13/26), respectively (p=0.35). Conclusions Changes in hemo-metabolic profiles at 48 hours were similar between VA-ECMO patients who underwent LVV with E-S vs. E-I. There was a trend toward a greater reduction in PA-D with E-S vs. E-I. Larger prospective studies are needed to identify effective LVV strategies that optimize hemodynamics and improve long-term outcomes in these complex patients.

Experimental study on aerosol behavior in water pool scrubbing under severe accident conditions

In severe accident of nuclear power plant, large quantities of steam and radioactive aerosol may release to the containment. Meanwhile, hydrogen may be generated by zirconium-steam reaction and released to the containment and mixed with steam and air to form a flammable mixture (H2, H2O, Air) which might combust even explode to generate mechanical and thermal load on containment. In this situation, timely containment venting strategies (CVS) is an important and effective measure to release the containment atmosphere to decrease the pressure. In order to remove the radioactive aerosol particles and cool the high temperature mixture, the containment atmosphere are vented to the water pool. This paper mainly investigated the behavior of aerosol scrubbing in water pool. The effects of submergence depth, aerosol particle diameter and aerosol concentration were preliminary studied by conducting a series of experiments. The results illustrate that the scrubbing efficiency of gas jet injection into water pool almost larger than 90%. And the aerosol particle diameter and submergence depth have significant influence on decontamination factor (DF). This paper provide data basis and reference to the subsequent work.

A computational methodology for estimation of aerosol retention in a sand-bed based filtering system for severe accident venting strategies

A computational methodology to estimate the capacity of aerosol particle retention in a filter- ing system based on sand bed is described in this work. This methodology uses a combination of computational fluid dynamics and mechanistic models in the calculation procedure. The methodology is applied to venting actions during a severe accident in a BWR Mark II primary containment. The SALOME and OpenFoam platforms were used to generate the geometric and numerical models of a full scale model of a sand bed filtering system. The Eulerian/Lagrangian approach was used to determine the steady-state of a compressible turbulent flow through a porous media and to compute the aerosol particle transport, respectively. Collection efficiency was calculated by means of a mechanistic model based on the capture efficiency of a single grain. The obtained Eulerian results include velocity, pressure, and temperature fields inside the filtering systems. The Lagrangian tracking of aerosol particles showed that particles crossing the coarser sand tend to accumulate initially on the periphery of the filter. The parametric studies showed that mass-flows of up to 4.7 kgs?1 satisfy the constraint of 1.1 bar pressure drop across the sand depth. Additionally, the efficiency of 99.5 % of retention was determined for 1.0 ?m aerosol particles in the 0.6 mm sand grain zone, for a gas velocity m of ms?1.

Study of hydrodynamics performance of a multi-venturi filtering system for BWR severe accident venting strategies

The aim of this project was to determine the capacity of a multi-venturi scrubber filtering system to cope with vented gas mass-flow rate coming from a BWR Mark II primary containment during a long-term station blackout. The multi-venturi filtering system CFD models were developed in the environment of the open source platforms SALOME and OpenFoam. The first geometrical model was created based on the dimensions of a well-known experimental setup, and the results of the pressure drop along the streamwise co-ordinate showed a maximum difference of 10 % in relation to the experimental values for different cases of liquid to gas mass ratios. Then a full scale multi-venturi model was developed. To study the performance of this system during conditions expected in a severe accident, a gas mixture similar to that occurring in a BWR Mark II containment at venting pressure was used as inlet gas. The gas mass-flow that can be cleansed by individual venturis and the pressure required to activate those venturis were computed. The pressure drop profiles in each sector were also determined as the function of different liquid loadings. The results showed good agreement with the capacity of the design taken as the reference model.

Optimal Strategy and Timing of Left Ventricular Venting During Veno-Arterial Extracorporeal Life Support for Adults in Cardiogenic Shock: A Systematic Review and Meta-Analysis.

Veno-arterial extracorporeal life support (VA-ECLS) is widely used to treat refractory cardiogenic shock. However, increased left ventricular (LV) afterload in VA-ECLS can worsen pulmonary congestion and compromise myocardial recovery. Our objectives were to explore the efficacy, safety, and optimal timing of adjunctive LV venting strategies. A systematic search was performed on Medline, EMBASE, PubMed, CDSR, CCRCT, CINAHL, ClinicalTrials.Gov, and WHO ICTRP from inception until January 2019 for all relevant studies, including LV venting. Data were analyzed for mortality and weaning from VA-ECLS on the basis of timing of LV venting, along with adverse complications. A total of 7995 patients were included from 62 observational studies, wherein 3458 patients had LV venting during VA-ECLS. LV venting significantly improved weaning from VA-ECLS (odds ratio, 0.62 [95% CI, 0.47-0.83]; P=0.001) and reduced short-term (30 day; risk ratio [RR], 0.86 [95% CI, 0.77-0.96]; P=0.008) but not in-hospital (RR, 0.92 [95% CI, 0.83-1.01] P=0.09) or long-term (6 months; RR, 0.96 [95% CI, 0.90-1.03]; P=0.27) mortality. Early (<12 hours; RR, 0.86 [95% CI, 0.75-0.99]; P=0.03) but not late (≥12 hours; RR, 0.99 [95% CI, 0.71-1.38]; P=0.93) LV venting significantly reduced short-term mortality. Patients with LV venting spent more time on VA-ECLS (3.6 versus 2.8 days, P<0.001), and mechanical ventilation (7.1 versus 4.6 days, P=0.013). With the exception of hemolysis (RR, 2.18 [95% CI, 1.58-3.01]; P<0.00001), overall adverse events did not differ. LV venting, especially if done early (<12 hours), appears to be associated with an increased success of weaning and reduced short-term mortality. Future studies are required to delineate the importance of any or early LV venting adjuncts on mortality and morbidity outcomes.

Left ventricular distension and venting strategies for patients on venoarterial extracorporeal membrane oxygenation.

Venoarterial extracorporeal membrane oxygenation (VA ECMO) is an established method of short-term mechanical support for patients in cardiogenic shock, but can create left ventricular (LV) distension. This paper analyzes the physiologic basis of this phenomenon and treatment methods. This is a retrospective review of the existing literature on VA ECMO and LV distension. We undertook a PubMed review of all peer-reviewed papers focusing on VA ECMO, LV distension, and LV venting. We reviewed these papers and synthesized our findings. We also will discuss the various methods of LV venting and venting strategies we use at Columbia. LV distension is becoming an increasingly appreciated aspect of caring for patients on VA ECMO support. The literature demonstrates that the consequences of failing to anticipate, recognize, and treat LV distension are grave, and will worsen an already distended and hypocontractile LV. Myocardial recovery will be hindered, and LV thrombus formation more likely. Early recognition and aggressive management of LV distension is paramount in helping care for this critically ill patient population.

유아의 자아지각과 정서조절전략이 또래 수용에 미치는 영향

The purpose of this study is to investigate the effect of children’s self-perception and the emotion control strategies on a child"s peer acceptance. The participants for this study were 120 preschool children (57 boys, 63 girls) that were attending classes for four year olds at 4 daycare centers and 1 kindergarten in Seoul and Gyeong-gi province, respectively. A peer rating scale was used to assess peer acceptance (Asher et al., 1979). A Puppet Interview was employed to assess global self-esteem (Cassidy, 1988). A children"s coping strategy checklist was further used to assess emotion regulation strategies (Eisenberg et al., 1993). The data collected was analyzed by t-tests and multiple regression. The child"s self-perception and emotion regulation strategies explained significantly a child"s peer acceptance. Boys who had more positive perception of self-worth were well accepted by peers. Girls who displayed more positive coping and venting strategies were well accepted by peers.

Analysis of containment venting strategy under severe accident conditions

Under severe accidents without containment heat removal, the containment integrity can be challenged due to over-pressurization by the steam and non-condensable gas generation. Containment filtered venting has been considered as an effective measure to avoid or delay the containment failure by over-pressurization. In order to minimize the environmental effects and maximize the effectiveness of filtered venting, it is critical to initiate venting in timely manners with sufficient discharge flow rate. It is also important to optimize the vent line size to prevent additional risk of leakage and to minimize the space and the cost requirement. In this study, the various venting strategies are investigated with respect to possible release flow characteristics. First of all, the accident scenarios representing the core meltdown accident with containment pressurization are selected by reviewing relevant literature. With those scenarios, thermal hydraulic behaviors in the containment and the discharge flow depending on the different venting strategies (i.e. vent line size and vent initiation pressure) are analyzed. MAAP5 model for the OPR1000 Korean nuclear power plant has been used for simulation.

RPV Depressurization Strategy Analysis for Chinshan Nuclear Power Plant by Using MAAP5

When an accident occurs, operators in nuclear power plants (NPPs) must follow emergency operating procedures (EOPs) or severe accident management guidelines (SAMGs). However, EOPs and SAMGs are symptom-based procedures and guidelines to cope with severe transients and accidents. Operators depend on real-time operating parameters of NPPs to perform each action in EOPs or SAMGs. When a beyond-design-basis accident like the Fukushima Daiichi accident of 2011 occurs, EOPs or SAMGs cannot be performed effectively without adequate information. One lesson learned from the Fukushima accident is that such a situation requires advance preparation regarding the key indicators, the water supply, reactor pressure vessel (RPV) depressurization, and containment venting strategies so actions can be performed with limited manpower and time. After the Fukushima accident, Taiwan Power Company established ultimate response guidelines (URGs) and has implemented them in three operating NPPs. An URG is an event-based guideline developed to manage accidents caused by a compound disaster beyond the design basis. The purpose of this study is to find out the differences of RPV depressurization strategies between EOPs and URGs and to discuss the effect of different RPV depressurization strategies on fuel integrity. The plant responses and accident physical phenomena are simulated using MAAP5. The results show that the RPV water level should be maintained as high as possible and the RPV pressure should be controlled sufficiently low at the beginning of RPV emergency depressurization to avoid core uncovery and assure fuel integrity. The URG provides the better RPV depressurization strategy to respond to a beyond-design-basis accident and mitigate an anticipated severe accident consequence as early as possible.