Pressure Suppression Research Articles

Thermal stratification and mixing in a Nordic BWR pressure suppression pool

The pressure suppression pool of a Nordic Boiling Water Reactor (BWR) serves as a heat sink to condense steam from the primary coolant system in normal operation and accident conditions. Thermal stratification can develop in the pool when buoyancy forces overcome the momentum created by the steam injection. In this case, hot condensate forms a hot layer at the top of the pool, reducing the pool cooling and condensation capacity compared to mixed conditions. The Effective Heat Source and Effective Momentum Source (EHS/EMS) models were previously proposed to model the large-scale pool behavior during a steam injection. In this work, we use CFD code of ANSYS Fluent with the EHS/EMS models to simulate the transient behavior of a Nordic BWR pool during a steam injection through spargers. First, a validation against a Nordic BWR pool test with complete mixing is presented. Prediction of the pool behavior for other possible injection scenarios show that stratification can occur at prototypic steam injection conditions, and that the hot layer temperature above the injection point can be non-uniform. In cases with significant steam condensation inside the sparger pipes, the 95 °C pool temperature limit for the Emergency Core Cooling System (ECCS) pumps was reached ∼7 h after the beginning of the blowdown.

Status of ITER Safety Issues

The decree authorizing the creation of the ITER facility was published on November 9, 2012, with the provisions adopted having been considered mostly acceptable. However, it is the first fusion facility of this kind to require a creation decree and the design of some of the systems had not yet been finalized. Moreover, while some equipment, with their associated safety requirements, are indeed classic and well known, others are uncommon and their safety requirements, although considered acceptable, are requesting justification.Therefore, the decree was supported by about 200 requests, which have to be met during the facility startup schedule. This paper takes stock of the current situation and presents the current status of the main expected answers, taking into account the design evolution which has been further proposed by the operator (e.g., the new vacuum vessel pressure suppression system, etc.).Some safety issues have already been considered as solved (the tokamak support design, accident within the neutral beam cell, etc.). Others are estimated not to be completely satisfactory (e.g., explosion within the vacuum vessel). Before moving on to commissioning, a few issues are still pending (detritiation system efficiency, radiation protection, etc.) and additional studies regarding the final design are expected (hot cells, tritium and waste buildings, etc.).

Initial configuration studies of the upper vertical port of the European DEMO

In the current pre-concept phase of the European DEMO, integration studies of the systems in the Upper Port area are being carried out. In DEMO, the Upper Port of the Vacuum Vessel is extraordinarily large to allow for the vertical extraction of the Breeding Blanket segments. This requires a number of components inside and outside the port to be integrated with tight space constraints: The Upper Port structure and its annexes, the adjacent Toroidal and Poloidal Field Coils, the Thermal Shields, the piping connection to the Vacuum Vessel Pressure Suppression System, the Shield Plug and its inserts, the feeding pipework of the in-vessel components and part of the Breeding Blanket supporting structures.Apart from functional aspects, the design of these components is driven by considerations of structural integrity, maintainability and irradiation shielding, which are mutually competing in many areas. Several studies were conducted on the design of the Upper Port and the required configuration of the components within. The present article describes the development approach, the studied options and the respective results, the identified issues as well as the proposed engineering solutions, in particular with respect to the mechanical design of the Upper Port and the integrated Shield Plug.

Experimental analysis of steam condensation patterns within a pressure suppression system operating at sub-atmospheric pressure conditions

For some specific applications, the pressure suppression systems should be maintained at sub-atmospheric pressure, such as in fusion plants systems. This operation conditions differ considerably from those experienced in the suppression pools of BWR operating at atmospheric pressure.The steam condensation in water at sub-atmospheric conditions is not sufficiently known, if not at all; therefore its effectiveness has to be investigated experimentally. In fact the steam condensation at sub-atmospheric pressure requires a subcooling capacity 2.5 times higher than that at atmospheric pressure.In consideration of that, a low scale experimental facility was designed and built at the University of Pisa. More than 350 steam condensation tests were performed in broad influencing parameters range (e. g. pressure within the condensation tank, water temperature and steam mass flux) to study of effectiveness of the steam condensation. In doing that, different sparger configurations (with single or multiple holes) were considered to check possible interference of condensing steam jets and bubble coalescence.Results indicate a high efficiency of condensation for all the examined conditions. The 3D map of the condensation regimes demonstrate they are dependent only on the downstream exit pressure, the water temperature and the steam mass flux per hole.

Experimental study on penetration characteristic of submerged steam jet in quiescent water

AbstractThe direct contact condensation is an effective way to rapid depressurization for light water reactor, such as pressure suppression pool, for which the characteristic of steam plume is a key parameter to evaluate the efficiency of depressurization. In this paper, a series of visualization experiments are described which investigate the characteristic of steam plume, the influence of jetting direction, air mass fraction, water temperature, diameter of jet on the steam plume were analyzed. The results show that, the dimensionless steam plume length increased with the increase of inlet pressure and water temperature for pure steam submerged jet, a correlation was set up to predict the dimensionless penetration length and the predicted errors were within the band of ±15%. Furthermore, the penetration length decreased with the rise of air mass fraction due to buoyancy force, the penetration length increased with the increase of inlet pressure, and the jet penetration length for vertical jet is longer than horizontal jet about 25% at the same inlet pressure and air mass fraction.

Development of plant concept related to tritium handling in the water-cooling system for JA DEMO

The conceptual design of Japan’s fusion demonstration plant (JA DEMO) is now being developed. In this paper, an overall plant system concept related to tritium handling in the water-cooling system is developed to give a concrete shape to the present JA DEMO concept as an electric power plant. The basic condition of tritium permeation from the in-vessel components to the primary cooling system is evaluated to be 5.7 g-T/day. The tritium concentration of the primary coolant is assumed to be 1 TBq/kg similar to the heavy water reactor condition. The capacity of the water detritiation system (WDS) is assessed, and the bypass feed water from the primary cooling loop is evaluated to be 94 kg/h under the tritium extraction efficiency of 0.96. Based on those specific parameters, the existing WDS in the heavy water reactor is found to be applicable to that of JA DEMO. Configuration of the primary heat transfer system (PHTS) is also discussed. Based on the heavy water reactor experience, tritium permeation through a steam generator (SG) to the secondary cooling system in PHTS is evaluated at 11.77TBq/year/loop (318 Ci/year/loop), which is found to be less than the restricted amount of tritium disposal for a pressurized water reactor in Japan. The key effect of the heavy water reactor experience is reduction of tritium permeation by oxide layer formed on SG pipes. Finally, a confinement concept of tritium release from PHTS is discussed under the condition of ex-vessel loss of coolant accident (LOCA). A pressure suppression system is installed to prevent the upper tokamak hall from pressurizing at the ex-vessel LOCA, and the tritium leakage from the upper tokamak hall is consequently restrained. The resultant early public dose at the plant site boundary can be reduced to 1.8 mSv, which is negligibly smaller than 100 mSv of the no-evacuation limit recommended by IAEA.

An interpretation of Fukushima-Daiichi Unit 3 plant data covering the two-week accident-progression phase based on correction for pressure data

ABSTRACT Water columns were adopted in the pressure measurement system of Fukushima-Daiichi Unit 3 to compensate for evaporation/condensation during normal operation. Some of these water columns evaporated partially during the accident condition jeopardizing correct understanding on actual pressure. Through inter-comparison of reactor pressure vessel (RPV) and suppression chamber (S/C) pressures with drywell (D/W) pressure, such water-column-change effect was evaluated. From this evaluation, correction for the specific effect was developed for RPV and S/C pressure data. With this corrected pressure, slight pressure difference among RPV, S/C, and D/W during the accident transient was evaluated. This information of pressure difference was then integrated with other available data, such as water level, containment atmosphere monitoring system, and environmental dose rate in the Fukushima-Daiichi site, into an interpretation of accident progression behavior focusing on RPV and primary containment vessel pressurization/depressurization and radioactive material release to environment. It is suggested that dryout of in-vessel and ex-vessel debris was likely causing pressure decrease on one hand, and S/C water poured into pedestal heated by relocated debris was a likely cause of pressurization on the other hand. Cyclic reflooding of pedestal debris and its dryout was likely leading to the cyclic pressure change lasting several times until the final debris reflooding.

Experimental study on the condensation of sonic steam in the underwater environment

Abstract Steam jet condensation is of great importance to pressure suppression containment and automatic depressurization system in nuclear power plant. In this paper, the condensation processes of sonic steam jet in a quiescent subcooled pool are recorded and analyzed, more precise understanding are got in direct contact condensation. Experiments are conducted at atmospheric pressure, and the steam is injected into the subcooled water pool through a vertical nozzle with the inner diameter of 10 mm, water temperature in the range of 25–60 °C and mass velocity in the range of 320–1080 kg/m2s. Richardson number is calculated based on the conservation of momentum for single water jet and its values are in the range of 0.16–2.67. There is no thermal stratification observed in the water pool. Four condensation regimes are observed, including condensation oscillation, contraction, expansion-contraction and double expansion-contraction shapes. A condensation regime map is present based on steam mass velocity and water temperature. The dimensionless steam plume length increase with the increase of steam mass velocity and water temperature, and its values are in the range of 1.4–9.0. Condensation heat transfer coefficient decreases with the increase of steam mass velocity and water temperature, and its values are in the range of 1.44–3.65 MW/m2°C. New more accurate semi-empirical correlations for prediction of the dimensionless steam plume length and condensation heat transfer coefficient are proposed respectively. The discrepancy of predicted plume length is within ± 10% for present experimental results and ± 25% for previous researchers. The discrepancy of predicted condensation heat transfer coefficient is with ± 12%.

Treatment of purulent-inflammatory complications in a combat gunshot trauma

Purpose of the study. Justification of the effective treatment tactics of the wounded with the gunshot fractures of the long bones.
 Materials and methods. The examination and treatment of 123 wounded with gunshot fractures were performed. All wounded were divided into 3 groups according to clinical observation. For the first clinical group the traditional treatment of the combat fractures with osteometallosynthesis out of injury zone was done. In the second group, treatment was added with negative pressure therapy. In the third clinical group Wounded got a VAC-associated therapy with the proposed of counter-drainage of wounds with the flow-washing irrigation with antiseptic solutions Decasan + 3% hydrogen peroxide. A bacteriological study of the wounds` exudates was carried out, and the sensitivity of microorganisms to antibiotics was determined.
 Results. The assay of microbiological investigation of the wounds of patients, which got explosive and mineexplosive injuries, demonstrated a predominance gramnegative microflora in the wound microbiocenoses such as Acinetobacter spp. (53% of cases) and Pseudomonas spp. (15% of cases). Gram-positive cocci were isolated from 22,2% of cases. The analysis of the antibiotic sensitivity data of gram-negative nonfermentative rods showed a high level of resistance to most antibacterial. All strains of acinetobacteria and pseudomonads were susceptible to polymyxin B and colistin, but resistant to unprotected and protected aminopenicillins (amoxicillin/clavulanate, ampicillin/ sulbactam). Acceleration of regenerative processes in the wound under the influence of VAC-therapy (formation of healthy granulations, disappearance of edema) in patients with negative pressure suppression (II HS, III HS) led to a reduction of hospitalization period, which took in average 7,8 ± 1,2 days, that was 5,2 ± 0,8 days less than in a control group. In the third group of wounded, a mixture of Decasan and 3% hydrogen peroxide in the proportion of 3 : 1 was used for rinsing of wounds. On the third day tissue edema decreased in 94,45% of the wounded in that observation group, while in the second clinical group it was observed in 88,89% of patients. The duration of the hydration phase in the wound process was reduced to 5,7 days. The period of complete healing of the wounds was shorter for 2,5 days. The period of indoor stay of the wounded of this group in the hospital decreased from 14,97 to 10,8 days.
 Conclusions. Prevalence of gram-negative microorganisms in a gunshot wound and their high degree of resistance to antibiotics should be noticed when one takes a decision about empirical antibiotic therapy in the wounded. Observed clinical results of the proposed negative pressure therapy with counter-drainage of wounds by setting of flow-washing irrigation with a mixture of antiseptics Decasan and 3% hydrogen peroxide allow recommending this scheme for treatment of wounded with gunshot fractures of long bones.

Computational Optimal Boundary Control for Water Pressure Suppression Arising in a Fluid Flow System Modeled by Hyperbolic PDEs

In this paper, we propose an efficient computational boundary control strategy for reducing water pressure shock effects generated by the suddenly operation of the valve closure located at the end of a fluid flow pipeline. First, we model the dynamic of the fluid flow transmission system as a coupled hyperbolic partial differential equations (PDEs), and then the water pressure suppression problem is formulated as a finite-time PDE-constrained optimal control problem. Second, we directly parameterize the time-varying boundary control input as a set of basic piecewise-quadratic functions which are needed to be optimized, the penalty function method is also introduced to deal with the inequality control constraint. As a result, the original PDE-constrained problem is transformed as a sequence of parameter optimization problems which can be easily solved by using existing gradient-based methods such as sequential quadratic programming (SQP). The exact gradient formulas of the cost function are derived analytically by using adjoint-based sensitivity analysis method. Finally, numerical simulations are illustrated to demonstrate our designed computational optimal boundary controller can significantly reduce the water pressure shock and fluctuation in the fluid flow transmission system.

The Study of Pressure Suppression in Transmission Pipelines by Orifice

The Study of Pressure Suppression in Transmission Pipelines by Orifice

Investigation on steam contact condensation injected vertically at low mass flux: Part I pure steam experiment

Steam direct contact condensation in subcooled water is an inevitable process in pressure suppression system of advanced light water reactor. Ten pure steam experiments have been performed in the range of steam mass flux 5–80 kg/m2 s and water temperature 19–96 °C. The steam condensation behave, fluid oscillation and pressure oscillation are recorded and analyzed. Prominent small bubbles are observed on the bubble surface due to the Rayleigh-Taylor instability. Vortex ring appears after aspherical bubble collapses. The upper threshold of chugging is identified by temperature data acquired continuously. The amplitude and frequency of fluid oscillation are obtained and compared with previous correlations. Two typical pressure wave shapes of continuous oscillation and pulse oscillation are identified. The pulse oscillation is induced by steam bubble collapse and observed at low water temperature. The maximum pressure pulse peak is about 1 MPa measured in the nozzle and 0.1 MPa in the pool. The pressure oscillation intensity in the water pool increases first, then decreases rapidly, and then increases slowly. It has a maximum at water temperature about 55–75 °C and the related temperature increases with the increment of the steam mass flux. The pressure oscillation dominant frequency is analyzed and compared with available correlations.

Investigation of vibrations caused by the steam condensation at sub-atmospheric condition in VVPSS

Fusion technology deployment passes through the design of safety systems aimed to protect the Vacuum Vessel (VV) from pressurizing accidents event such as LOVA (Loss Of Vacuum Accident) or the failure of the Tokamak Water Cooling System (TWCS) causing the LOCA (Loss Of Coolant Accident). One of important safety systems of the ITER plant is the Vacuum Vessel Pressure Suppression System (VVPSS), which is designed to protect the VV by the steam condensation at sub-atmospheric pressure conditions in Suppression Tanks.The aim of this study is to investigate vibrations phenomenon, originated during the steam-water direct contact condensation (DCC) at sub-atmospheric conditions, and determine any correlations between the steam jet dynamic and water temperature (TW), steam mass flux (GS) and downstream pressure (PW).According to the thermal hydraulic conditions characterising the DCC, vibrations may evolve because of the latent heat of the phase change (large amount of heat transmitted quickly to the water).In the paper also presents the numerical investigations performed by means of proper FEM code, the set-up procedure and the experimental activity carried out at Lab. B. Guerrini of DICI- University of Pisa. This latter allowed correlating the different steam condensation regimes (chugging, condensation oscillation, etc.) to the acceleration and force, to be in turn used to determine the strength capacity of the VVPSS.

Frequency analysis of chugging condensation in pressure suppression pool system with pattern recognition

Abstract Direct contact condensation (DCC) phenomena in boiling water reactor (BWR) pressure suppression pool systems need to be understood to properly assess the performance of the pool as a heat sink and as a safety critical structure. Condensation oscillations in the form of chugging are challenging to predict by computational fluid dynamics (CFD) methods but safety relevant because of associated high dynamic loads on in-pool structures and the pool itself. Recently, new measurement methods for CFD validation purposes have become available. One of these techniques is visual observation using the high-speed cameras and suitable data processing method. Pattern recognition is a well suited technique for the determination of large oscillating bubble dynamics in a pressure suppression pool. In this work, the formation and collapse of the steam bubbles in chugging condensation mode are evaluated by using the pattern recognition algorithm. The pattern recognition algorithm is based on video material recorded during the direct contact condensation experiment DCC-05 of the PPOOLEX test facility. The formation speed, the shape and size of the steam bubbles and the acceleration of collapsing bubbles are estimated with the algorithm. Fast Fourier transform (FFT) is used for frequency analysis of the pattern recognized data. The frequencies found are compared to the frequency data of the pressure transducers collected during the experiment and to the previous results of the NEPTUNE_CFD simulations of the same experiment. The frequency analysis shows that the chugging frequencies of the steam bubbles range from 1 to 3 Hz, as predicted. Also the natural frequencies of the bubbles are visible around 53 Hz. Another frequency spike was observed close to the 125 Hz. This frequency is close to the mechanical resonance frequencies of the suppression pool and the blowdown pipe. Because of neither the pressure suppression pool nor the blowdown pipe are visible to the pattern recognition, the spike of the higher frequencies is most likely from the interfacial area of the bubble which resonates with the suppression pool system, affecting rapid condensation at a certain point.

Hydrogen cloud explosion evaluation under inert gas atmosphere

This paper is aimed at evaluating the hydrogen cloud explosion under inert gas atmosphere experimentally and numerically. The results demonstrate that only under Ar, N2 and CO2 atmosphere, the lean and stoichiometric hydrogen flame tends to be unstable. The Markstein length of Ar, N2 and CO2 is less than zero and the decreasing order is Ar, N2 and CO2. Except for CO2, the average flame propagation velocity, maximum explosion pressure, maximum pressure rise rate, positive pressure impulse and explosion pressure attenuation decrease monotonously in the order of He, Ar and N2. For various equivalence ratios and inert gases, the explosion pressure releases into the far field at the sound speed and attenuates with distance. Due to the fact that the explosion pressure is closely related to laminar burning velocity, the explosion pressure suppression by inert gas is revealed by analyzing the factors affecting laminar burning velocity. As equivalence ratio increases, the adiabatic flame temperature plays a more important role in affecting laminar burning velocity than thermal diffusivity. For different inert gases, the effect of thermal diffusivity on laminar burning velocity is obviously greater than adiabatic flame temperature. Besides, the third-body effect of various inert gases increases gradually until Φ = 1.4. and then decreases with increasing equivalence ratio. For a given equivalence ratio, the increasing order of third-body effect is He, Ar and CO2.

Prevention of hydrogen accumulation inside the vacuum vessel pressure suppression system of the ITER facility by means of passive auto-catalytic recombiners

Hydrogen safety is a relevant topic for both nuclear fission and fusion power plants. Hydrogen generated in the course of a severe accident may endanger the integrity of safety barriers and may result in radioactive releases. In the case of the ITER fusion facility, accident scenarios with water ingress consider the release of hydrogen into the suppression tank (ST) of the vacuum vessel pressure suppression system (VVPSS). Under the assumption of additional air ingress, the formation of flammable gas mixtures may lead to explosions and safety component failure.The installation of passive auto-catalytic recombiners (PARs) inside the ST, which are presently used as safety devices inside the containments of nuclear fission reactors, is one option under consideration to mitigate such a scenario. PARs convert hydrogen into water vapor by means of passive mechanisms and have been qualified for operation under the conditions of a nuclear power plant accident since the 1990s.In order to support on-going hydrogen safety considerations, simulations of accident scenarios using the CFD code ANSYS-CFX are foreseen. In this context, the in-house code REKO-DIREKT is coupled to CFX to simulate PAR operation. However, the operational boundary conditions for hydrogen recombination (e.g. temperature, pressure, gas mixture) of a fusion reactor scenario differ significantly from those of a fission reactor. In order to enhance the code towards realistic PAR operation, a series of experiments has been performed in the REKO-4 facility with specific focus on ITER conditions. These specifically include operation under sub-atmospheric pressure (0.2–1.0 bar), gas compositions ranging from lean to rich H2/O2 mixtures, and superposed flow conditions.The paper gives an overview of the experimental program, presents results achieved and gives an outlook on the modeling approach towards accident scenario simulation.

Turbulent pressure of magnetoconvection for slow and rapid rotation

Motivated by recent simulations of sunspot formation, we extend the theory of the pressure difference between magnetized and nonmagnetized gas by Dicke to include rotating turbulence. While the (vertical) background field provides a positive‐definite magnetic pressure difference between the magnetized and the unmagnetized gas, Reynolds stress and Maxwell stress of turbulence strongly modify this result. With the quasilinear approximation, we demonstrate that the influence of the turbulence differs between the high‐conductivity and the low‐conductivity limits. Sufficiently small magnetic Reynolds numbers lead to magnetic pressure suppression, where indeed the pressure excess can even assume negative values. Box simulations of magnetoconvection subject to a vertical magnetic field carried out with the Nirvana code confirm this overall picture. They also demonstrate how a global rotation reduces the negative magnetic pressure effect. For rapid rotation, the total magnetic pressure difference caused by large‐scale magnetic fields and turbulence even fully disappears for small field strengths. Magnetic fields of moderate strength thus neither reduce nor enhance the turbulence pressure of rapidly rotating convection. Consequences of this phenomenon for star‐formation efficiency are briefly discussed.

Experimental investigation of steam condensation in water tank at sub-atmospheric pressure

Abstract The International Thermonuclear Experimental Reactor (ITER) Vacuum Vessel Pressure Suppression System (VVPSS) limits the Vacuum Vessel (VV) internal pressure, in case of loss of coolant (LOCA) or other pressurizing accidents from the in-vessel components, to 150 kPa (abs). This is key safety function because a large internal pressure could lead to a breach of the primary confinement barrier. Safety is ensured by discharging the steam evolved during the accident event to the VVPSS suppression tanks where it is condensed. Steam condensation occurs at sub-atmospheric pressure condition. Moreover, being this latter not standard for traditional nuclear systems, this investigation is quite new (not studied in detail before) and deals with an experimental investigation of the direct contact condensation at VVPSS prototypical thermal-hydraulic conditions. To the purpose, a small-scale experimental rig was properly designed and built at Lab. B. Guerrini of DICI-University of Pisa as well as different temperature, pressure and steam mass (flow rate per hole) conditions and sparger patterns have been investigated. The experimental test matrix is also presented in this study. The obtained results show high efficiency of condensation for all examined conditions. The main condensation regimes at sub-atmospheric pressure conditions were identified. In addition, a comparison was done between the condensation regimes experimentally determined and those available in the literature, which were obtained at atmospheric pressure. Finally, results demonstrated to be representative of the real configuration at ITER reactor.

Modelling an in-vessel loss of coolant accident in the EU DEMO WCLL breeding blanket with the GETTHEM code

One of the accidents to be analyzed for the operation of the EU DEMO tokamak reactor is the in-vessel Loss-Of-Coolant Accident (LOCA), in which a postulated rupture in the First Wall causes a rapid pressurization of the Vacuum Vessel (VV). To avoid rupture of the VV, a VV Pressure Suppression System (VVPSS) is used, which is aimed at removing the coolant from the VV, preserving its integrity and safely storing the coolant together with the radioactive products contained therein. A system-level tool for the analysis of thermal-hydraulic transients in tokamak fusion reactors, called GEneral Tokamak THErmal-hydraulic Model (GETTHEM), is under development at Politecnico di Torino. This paper presents the GETTHEM module developed for the description of the EU DEMO VVPSS, in the case of a water-cooled Breeding Blanket concept; the code validation against experimental data coming from the Ingress of Coolant Event campaign performed in Japan is shown. The tool is then applied to a parametric analysis relevant for an EU DEMO in-VV LOCA, and the results are presented and discussed.

Thermal Hydraulic Safety Assessment of LLCB Test Blanket System in ITER Using Modified relap/scdapsim/mod4.0 Code

This work attempts to investigate the thermal hydraulic safety of lithium lead ceramic breeder (LLCB) test blanket system (TBS) in International Thermonuclear Experimental Reactor (ITER) with the help of modified thermal hydraulic code relap/scdapsim/mod4.0. The design basis accidents, in-vessel and ex-vessel loss of coolant of first wall (FW) of test blanket module (TBM) are analyzed for this safety assessment. The sequence of accidents analyzed was started with postulated initiating events (PIEs). A detailed modeling of first wall helium cooling system (FWHCS) loop and lithium lead cooling system (LLCS) is presented. The analysis of steady-state normal operation along with 10 s power excursion before the accident is also discussed in order to better understanding of initial condition of accidents. The analysis discusses a number of safety concerns and issues that may result from the TBM component failure, such as vacuum vessel (VV) pressurization, TBM FW temperature profile, passive decay heat removal capability of TBM structure, pressurization of port cell and Tokomak cooling water system vault annex (TCWS-VA) and to check the capability of passive safety system (vacuum vessel pressure suppression system (VVPSS)). The analysis shows that in these accident scenarios, the critical parameters have reasonable safety margins.