In this paper, a thermal-hydraulics analysis code under non-inertial system was developed by establishing dynamic simulation models of typical ocean conditions and modifying RELAP5 code. Based on the modified code, the effects of the inclination, fluctuation and rolling conditions on the natural circulation characteristics of an integrated PWR were studied. The dynamic input and output interface model of RELAP5 was further established, and RELAP5 was coupled with a two-group three-dimensional neutron kinetics code to realize the improvement of nuclear feedback module in thermal hydraulic code. And the distribution of core flow and power under different motions was analyzed. The results indicate that, the uneven distribution of coolant flow increases with the increasing inclination angle, this trend leads to an uneven distribution of primary coolant flow. The flow fluctuation has a 180° phase difference under rolling conditions, and the reactor power and coolant flow oscillation increases with the increasing rolling period and amplitude. In the case of heaving motion, the peaks of the oscillation amplitude of the flow and power lying in the hottest channel as the additional forces on the fluid of each channel are spatially uniform. The code developed in this paper has the functions of modelling ocean conditions and three-dimensional coupled neutronics/thermal-hydraulics, and can be used as a simulation tool for Floating PWR.

The numerical calculations with and without rolling motions were conducted to investigate the effects of ocean environment on flow and heat transfer of supercritical CO 2 . The AKN k -epsilon model was selected to model the turbulent flow and heat transfer of supercritical fluid. It concludes that the effect of rolling motion on the supercritical CO 2 in LPV region is much greater than that on conventional single-phase fluid. The rolling motion can cause the periodic oscillation of the local heat transfer and suppress the nonuniform heat transfer. The secondary flow is induced by both the rolling motion and buoyancy force. The heat transfer is enhanced gradually as the rolling period decreasing or rolling amplitude increasing, but the corresponding pressure drop varies more violently to affect the stability and controllability of the heat exchanger.

In recent years, nuclear power are widely used in the ship and submarine. Affected by the ocean wave, the bubble dynamic under ocean conditions may be different from stationary condition. In order to investigate the influence mechanism of ocean conditions, the single bubble rising in stagnant liquid under rolling conditions with different frequencies and amplitudes were calculated through CFD method. In present work, the typical ocean conditions such as rolling were realized through dynamic mesh method, this method could simulated the movement of container directly. The Volume-of-fluid (VOF) method was applied to track the interface between liquid and gas phases and the surface tension were calculated by Continuum Surface Force (CSF) method. We can draw the conclusions as follows: (1) the bubble tend to move laterally and periodically under rolling conditions, this may attributed to the additional force caused by rolling motion. (2) the period of lateral movement are in accordance with the rolling period, and the frequency and amplitude of bubble lateral movement may increasing as the decreasing of rolling period. (3) The amplitude of the bubble lateral displacement is proportional to the rolling amplitude. (4)larger bubbles have the higher rising velocity than the small ones, and the larger bubble are easier to break up which may promote the lateral movement.

Studying the diffusion and migration mechanism of radionuclide in an offshore environment under accidental conditions of nuclear power stations is of great significance to emergency decision-making and nuclear accident mitigation. The migration mechanism of radionuclide in the ocean was studied. For the short-term situation, a multi-factor coupled model was established and the effects of turbulent diffusion, decay and adsorption sedimentation on the radionuclide concentration were analyzed. The results show that the radionuclide concentration decreases with turbulent diffusion. In the short-term, the decay of radionuclide has no effect on the concentration of 137Cs, but has a significant effect on the concentration of 131I. The maximum adsorption sedimentation rate of suspended matter to radionuclide is about 1%, which can be neglected in the short-term simulation and needs to be considered in the long-term simulation. The model can better simulate the variation of radionuclide concentration.

For some Pressurized Water Reactors (PWR) operated on automobiles, boats or deep sea vessels, system characteristics is important for understanding their safety during severe accidents. The development of an analysis code and the transient thermal beaviors of a floating nuclear reactor under heaving motion are described in this paper. By modifying the control equations based on the mathematical models of ocean conditions, an ocean condition available system analysis code named RELAP5/GR was developed from RELAP5 MOD3.2 to simulate the transient thermal-hydraulic response of the nuclear reactor systems to the motion conditions in accidents, which is an advanced and independent node programming code. Using the code, the analysis model was established for a small 200MW offshore floating nuclear plants (OFNP). The transient thermal behaviors of the whole system were analyzed in the cases of the station blackout accident under heaving motion conditons. The analysis shows that all the results can be reasonably explained and the code development is successful at this stage.

For electric energy generation, the design organizations of China have developed variants of floating nuclear plants. Depending on the customer requirement one or more power plants could operating in the same sea area at a time. To achieve a high degree of reactor safety, the passive core cooling subsystems is utilized widely on the floating nuclear plants. This paper conducted a preliminary design of the passive residual heat removal system (PRHRS), which is very important for decay hear removal under the ship blackout accident, used on floating nuclear plants. The limitations due to ocean environment including condition of sea wave and wind, space availability and weight limitations have be considered in the design stage. The computation model of PRHRS was established by use RELAP program. The transient behaviors of PRHRS are simulated. The results showed that PRHRS of floating nuclear plants could achieve the function of remove decay heat and keep reactor core safe under the ship blackout accident with the impact of ocean environment.

The FNPP (Floating Nuclear Power Plant) expanded the application field of Integrated Pressurized Water Reactor (IPWR) in the movable marine platform, it is necessary to study the natural circulation flow characteristics in heaving motion on the ocean. From the characteristics of FNPP, by means of THEATRe code which was based on the two-phase drift flux model and was modified by adding module calculating the effect of heaving motion, the simulation model in heaving motion was built. Using the models developed, the natural circulation operating characteristics of natural circulation in heaving motion and the transitions between forced circulation and natural circulation are analyzed. In the case of amplitude limited, the periods of mass flow rate are equal to periods of heaving motion. The oscillation amplitude of mass flow rate increases with the heaving amplitude increase. In the case of period limited, the natural circulation flow rate oscillating amplitude increases with the heaving period increases. The result obtained are not only evaluating FNPP design behavior properly but also pointing out the direction to further optimum design to ensure FNPP operating safety in heaving motion.

More and more attentions have been paid to the impact of the earthquake on the reactor thermal hydraulics after the Fukushima accident. In order to figure out the seismic effect on the flow in primary loop, the natural circulation in primary loop of CPR1000 influenced by earthquake is modeled by learning from the study on natural circulation under ocean conditions. Natural circulation ability at earthquake, which includes longitudinal earthquake and transversal earthquake, is dynamically simulated by a program written with MATLAB, respectively. Besides, the safety of the system is discussed based on the calculated results. The research results show that, once the longitudinal earthquake occurs, in the earlier stage of earthquake, the peak and valley values of the coolant mass flow rate decrease gradually and the amplitude will be a constant as time goes on because of flow fluctuation in seismic condition. On the contrary, as for transversal earthquake, the peak and valley values of the coolant mass flow rate increase gradually in the earlier stage of earthquake. However, the amplitude will be a constant as time goes on, just like that in the longitudinal earthquake. For both of the two conditions, they have the same characteristics. The constant mentioned above grows up with the increase of the earthquake acceleration peak value and the period; the fluctuation period of mass flow rate is generally the same as the period of earthquake acceleration and the mass flow rate changes steadily; the average mass flow rate decreases slightly with the increase of the earthquake acceleration peak value and the period. Both of the vibration period and the peak of seismic wave have disturbing effect on reactor coolant system natural circulation. And the increase of the peak of the earthquake acceleration as well as the period of the earthquake acceleration will reduce the natural circulation ability. In the range of research parameters, the system is considered to be safe according to the calculation results of core coolant temperature.

The floating nuclear power plant (FNPP) is recently received increasing attention in China. The effects of ship motions on the working fluid of marine-type reactor are not only a change of effective gravity, but also an appearance of additional forces, which requires further researches. This paper focuses on the derivation of body force model under 6 typical ocean conditions. The derived model consists of body force terms based on both three-dimensional and one-dimensional momentum equations and can be applied to the pipe with an arbitrary flow direction. For programming calculation, the integrations with respect to spatial and time variables are performed for the body force terms of one-dimensional momentum equations under 6 typical ocean conditions. For verification purpose, the deprived model is implemented into the RELAP5 code and a two-loop single phase natural circulation system is analyzed using the modified RELAP5 code under 6 typical ocean conditions. The calculation results show that the deprived model is reasonable.

At present, simulation research on condenser mostly focuses on the one of power plant. While little attention is paid on the marine one. The marine condenser is different from the one of power plant. One difference between them is that marine condenser limited by the hull space is much smaller than the one of power plant. Another difference is that marine condenser usually runs in condition that steam load changes greatly and frequently. In addition, the temperature of cooling water changes with seasons and maritime space. When the ship makes an ocean-going voyage, the temperature of cooling water varies obviously, which has a negative effect on the control system. Therefore, simulation research to the dynamic characteristic of marine condenser is carried on by this paper. The vacuum and the condensate supercooling degree are the main operating parameters for a condenser. In this paper, a mathematical model for marine condenser is established. The dynamic variation of each parameter is monitored by this model. Then an expert control system is designed. The condenser vacuum and supercooling degree are controlled by the flow rates of cooling water, air-blend and steam jet for deaerating. The deaerating steam bubbles which are not absorbed completely by condensate water, have a negative impaction on the condenser vacuum. The deaerating steam bubbles heating the condensation water to be exactly saturated is calculated. Referring to it, the fluctuation of condenser vacuum is filtered. So the negative influence on condenser control system can be remitted. The temperature of water replenishing is usually lower than that of condensate water in condenser heat well. And the water is replenished into the heat well part. So water replenishing would increase the supercooling degree of condensate water. This paper adopts the simulation experiment method to gain the expert knowledge of condenser control. According to power level, inlet temperature of cooling water, the messages of operating modes and sensors, the control system regulates the regulating valves for turbo circulating pump of cooling water, air extractor and steam jet deaerator to change the flow rates of cooling water, air-blend and steam jet for deaerating, so as to achieve automatic control of condenser vacuum and supercooling degree. Finally, two PID controllers are added as well, to counteract the adverse effect, enhance anti-interference ability and optimize control performance of intelligent control system. Simulations of varying load and cooling water temperature are done. Results show that the intelligent control system could effectively control condenser vacuum and supercooling degree under different power level and variable temperature of cooling water condition.

A new Offshore Floating Nuclear Plant (OFNP) concept with high potential for attractive economics and an unprecedented level of safety is presented, along with an overview of work done in the area of security. The OFNP creatively combines state-of-the-art Light Water Reactors (LWRs) with floating platforms such as those used in offshore oil/gas operations, both of which are well-established technologies which can allow implementation on a time scale consistent with combating climate change in the near future. OFNP is a plant that can be entirely built within a floating platform in a shipyard, transferred to the site. OFNP eliminates earthquakes and tsunamis as accident precursors; its ocean-based passive safety systems eliminate the loss of ultimate heat sink accident by design. The defense of an OFNP poses new security opportunities and challenges compared to land-based plants. Such a plant can be more easily defended by virtue of the clear 360 degree lines of sight and the relative ease of identifying surface threats. Conversely the offshore plant is potentially vulnerable to underwater approaches by mini-submarines and divers. We investigate security considerations of the OFNP applicable to two potential plant options, an OFNP-300 with a 300 MWe reactor, and an OFNP-1100 with an 1100 MWe reactor. Three innovative security system approaches could be combined for the offshore plant. The first is a comprehensive detection system which integrates radar, sonar and unmanned vehicles for a long distance overview of the vicinity of the plant. The second approach is the use of passive physical barriers about 100 meters from the plant, which will force a fast-moving power boat to lose speed or stop at the barrier allowing the plant security force more time to respond. The third approach takes advantage of the offshore plant siting and the monthly or biweekly rotation of crew to reduce the total on-plant and onshore security force by using the off-duty security force on the plant as a reserve force. Through the use of these approaches, the OFNP-300 should be able to achieve a similar security cost (on a per Megawatt basis) as land-based plants of similar or somewhat larger power rating. Due to non-linear scaling of cost, the security cost of the OFNP-1100 has the potential to be reduced significantly compared to its land-based equivalents.

A theoretical model for flow instability in parallel rectangular channels under ocean conditions was established using lumped method based on the homogeneous model. The model consists of flow instability under static condition, the model of additional forces generated by ocean conditions, the constitutive and numerical models. The effect of ocean conditions was introduced through additional forces in the momentum equation generated by ocean conditions. The code was validated with the experimental data of flow instability under static conditions. Then the margin of flow instability, the threshold power and the periods of the system under static condition was calculated as a basis condition for comparison. The effect of the heaving condition on flow instability will be analyzed analytically. Besides these, the effect of asymmetric heating and throttling under heaving condition will be shown.

After Fukushima nuclear accidents, China timely started national nuclear emergency coordination mechanism, and the national nuclear emergency organizations carried out effective response, strengthened communication with IAEA, widely collected all kinds of related information, carried out the monitoring on the land, sea, air, and ocean, predicted the accident consequence, and increased public communication. On all kinds of nuclear facilities, governments required the urgent circular-self safety assessments by each operators, and organized safety inspection groups to comprehensive on-site safety supervision and inspection. Safety inspection thought China overall nuclear safety condition was controllable, and safety was guaranteed. Meanwhile, safety improvements of NPPs considered the external disaster warning and operational, waterproof ability evaluations and improvements of important buildings, etc. China reported China radiation monitoring data to IAEA emergency center, and organized Chinese nuclear emergency expert delegation to develop technical exchanges with Japanese experts. From fukushima nuclear accident response experiences, China national nuclear emergency response ability should continue to increase according to the national nuclear energy scale: (1) Nuclear emergency response professional capacity needs to increase and professional quantity also need to increase. (2) Nuclear emergency response technique and ability needs to emphasize, and the practicability, systematic and integration of nuclear emergency response system also need to emphasize. (3) The operation mechanism and guarantee conditions of national nuclear emergency response system should be further to take attention and should be continuous to improve.

On March 11, 2011, Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Plant (NPP) was hit by a tsunami caused by the Tohoku-Pacific Ocean Earthquake, resulting in nuclear accidents in Units #1 to #4. With the aim of improving the safety of NPPs worldwide, we summarize the lessons that have been learned following a thorough analysis of the event and make specific proposals for improving the safety of such facilities. The author has been involved in investigating the causes of the accidents and developing countermeasures for other NPPs in Japan as a member of the Committee for the Investigation of Nuclear Safety of the Atomic Energy Society of Japan [1], an advisory meeting member of NISA with regard to technical lessons learned from the Fukushima Daiichi NPP accidents, and a Safety Evaluation Member of NISA for the other NPPs in Japan [2].

The natural kinetic motion of oceans, rivers, and other bodies of water is a promising resource for sustainable power production. Rotor-based marine and hydrokinetic (MHK) turbines generate electricity from river, tidal, and other water currents, operating analogously to wind turbines in air. An MHK rotor designer can draw upon a vast body of general purpose and wind power specific airfoils, but application specific hydrofoils can more optimally meet the needs of MHK power. We present the MHKF1 family of hydrofoils, designed upon experience drawn from wind turbine airfoils and incorporating hydro-specific considerations. The MHKF1 hydrofoils were developed to balance the following design objectives: (1) basic hydrodynamic performance with lift to drag ratio (l/d) as a key metric, (2) limited sensitivity to soiling because of biofouling concerns and the high cost of maintenance in the marine environment, (3) sufficient thickness for structural efficiency, (4) good stall characteristics, (5) hydrodynamic and geometric compatibility such that the different hydrofoils of the family can be applied on the same rotor blade, (6) low susceptibility to cavitation, and (7) low susceptibility to singing. While the first five criteria are common to wind turbine airfoil design, the last two are specific to operation in water. Cavitation, the formation of bubbles within a fluid, can have numerous detrimental effects including erosion of impinged surfaces, degraded performance, vibration, and noise. The minimum surface pressure of the MHKF1 hydrofoils were managed to reduce the likelihood of cavitation. Singing, a hydroacoustic/hydroelastic phenomenon of the trailing edge of hydrofoils, results in noise and vibration. To suppress singing, trailing edge thicknesses were increased and hydrofoil variants were designed with “anti-singing” profiles. The MHKF1 hydrofoils were developed with a combination of inverse and direct design methods using XFOIL and various routines for parameterizing hydrofoil geometries and surface velocity distributions. Performance was further evaluated with OVERFLOW, a Reynolds averaged Navier Stokes computational fluid dynamics code.

The flowing characteristics of turbulent flow in rectangular channels in rolling and heaving motions are investigated theoretically with FLUENT code. The flowing model of turbulent flow in rectangular channels in rolling and heaving motion is established. The effects of several turbulent models and parameters on the flow are analyzed. In rolling motion, the velocity profile in channel center is more averaged. The mixing coefficient can be strengthened significantly in rolling motion. The effect of heaving motion on turbulent flow is more limited than that of rolling motion. The turbulent kinetic energy and fluctuating velocity in rolling motion are greater than that in heaving motion and steady state. The effect of rolling motion on the turbulent flow can be depressed by the tube wall.

In this paper, the flow oscillation in the parallel multichannel system has been studied under ocean condition with RELAP5/MC. A double-channel boiling system model is built using the code RELAP5/MC and it is proved to be capable of simulating the instable phenomena. The influences of rolling, heaving and inclination on the flow oscillation have been analyzed. The result shows that the effect of lengthways rolling on the oscillation in parallel channels can be ignored. The influence of athwartships rolling and heaving reveals resonance effect, that is, when the rolling cycle is close to the oscillation cycle and half cycle respectively, the oscillation would happen earlier, when the difference between the cycles is large, the impact of rolling can also be ignored. The influence of inclination on the oscillation in parallel channels is feeble.

Marine reactor would be influenced by ocean conditions such as rolling, inclination and heaving which made system coolant fluctuate and changed the ability of natural circulation of the system. The paper summarizes the study of effects of ocean conditions upon flow characteristics of natural circulation, including the researches of Japan, South Korea and China. The result shows that the ocean conditions have some effects upon natural circulation, and the structure of the loop would affect the experiment result. Generally, Inclination would reduce the ability of natural circulation, the larger the inclination angle, the more decrease the ability of natural circulation. Rolling would cause core flow rate oscillation and the amplitude of oscillation increases as rolling angle increase and rolling period decrease. Heat transfer in the core is enhanced by the rolling motion and the enhancement is thought to be caused by the internal flow due to rolling motion. The flow oscillation caused by rolling motion would overlap the density wave oscillation which made the system more instable. Heaving would also cause core flow rate oscillation and the amplitude of oscillation increases as heaving acceleration increase and heaving period increase. It is also found that the improved RETRAN procedure can be used to simulate the thermal-hydraulic characteristics of marine reactor under ocean conditions. The parameters of the current experiment have some differences with the actual condition of the marine reactor, so some further research should be done.

A safety assessment code, DecDose, for decommissioning of nuclear facilities has been developed, based on the experiences of the decommissioning project of Japan Power Demonstration Reactor (JPDR) at Japan Atomic Energy Research Institute (now Japan Atomic Energy Agency). DecDose evaluates the annual exposure dose of the public and workers according to the progress of decommissioning of the plant, and also evaluates the public dose at accidental situations including fire and explosion. The public dose at normal situations during decommissioning is evaluated from the amount of radionuclides discharged from the plant to the atmosphere and the ocean. The amounts of radionuclides discharged depend on which and how activated and/or contaminated components and structures are dismantled. The amount is predicted by using the radioactive inventory given by the plant. The filtration efficiency of the ventilation system and decontamination factors of the liquid waste treatment system of the plant are also considered. Both of the internal dose caused by inhalation and ingestion of agricultural crops and seafood, and the external dose by radioactive aerosols airborne and radioactive deposition at soil surfaces are calculated for all of possible pathways. Also included in the external dose are direct radiation and skyshine radiation from waste containers which are packed and temporarily stored in the in-site building. For external dose of workers, the radiation dose rate from dismantling contaminated components and structures is calculated using the dose rate library which was previously evaluated by a point kernel shielding code. In this condition, radiation sources are regarded to be consisted of two parts; one is a dismantling object of interest, and the other is the sum of surrounding objects. Difference in job type or position is taken into account; workers for cutting are situated closer to a dismantling component, other workers help them at some distance, and the supervisor watches their activities from away. For worker’s internal dose, the radionuclide concentrations in air for individual radionuclides are calculated from a dismantling condition, e.g. cutting speed, cutting length of the dismantling component and exhaust velocity. A calculation model for working time on dismantling was developed using more segmented WBS (work breakdown structure). DecDose was partially verified by comparison with measured the external dose of workers during JPDR Decommissioning Project. The DecDose is expected to contribute to utilities in formulating rational dismantling plans and to the safety authority in estimating conservativeness in safety assessment of licensing application or risk-based regulatory criteria.

Avoiding CO 2 emissions while meeting global energy needs is a far greater challenge than most commentators and governments appreciate. Even the Intergovernmental Panel on Climate Change has offered no scenario that would stabilize atmospheric levels. The capacity of the oceans to absorb CO 2 is limited to about 40% of the level of emissions in 1990. Shared equitably among the present-day world population, per capita emissions of 35% of the current European average would only return the world to 100% of 1990 emission levels. Yet world population will probably grow by 25% by 2050 and, between 1990 and 2007, global emissions increased by 29%. Our current global trajectory is hurtling us toward ever-higher levels, perhaps even disaster. Consequently, near-zero-emitting sources are the only approaches to energy generation that should be deployed. Nuclear power, with its immense energy density, is the only available source that qualifies for widespread deployment. Existing alternative options are not and cannot effectively contribute (see e.g. MacKay, 2008). The weakness in wind is the need for back-up and supplementation, not so much from its short-term fickleness but its seasonal variability. Carbon capture and storage would have to achieve far higher levels of capture than currently seem feasible. Hydroelectricity has limited remaining potential as well as needing careful deployment to avoid collateral emissions. Aggressive conservation and efficiency measures reduce but do not solve the growth in energy demand and usage. Global economic downturns provide temporary relief but huge social political pain, and energy supply security concerns remain unresolved issue for many countries, even today. Of course nuclear alone would face an overwhelming challenge. We shall need to deploy massive improvements in the efficiency with which energy is used. Solar power in various forms has promise and could have a substantial role at lower latitudes in consistently sunny areas though photovoltaic electricity is still a high-cost option. Geothermal and various forms of ocean-derived energy have development potential. However, we argue that worldwide deployment of 5000 to 10 000 nuclear reactors by 2050 is the only clearly accessible pathway to CO 2 stabilization that exists today. This will require extension of the resource beyond once-through cycles and so the deployment of advanced reactor types. But it is doable, it is affordable, and our planet must plan to accomplish this deployment.