Prospects of small and medium sized power reactors in Pakistan

To alleviate power shortages already being experienced and the impending crisis in the coming years, Pakistan is making all out efforts to harness the conventional sources of power production. However, the anticipated increase in generating capacity by the turn of this century shall not be sufficient to meet the moderately rising demand of power. Under these circumstances the only option is to get more power from nuclear plants.In this paper the existing electric power situation in Pakistan as well as the future requirements are briefly described. Suggestions are made to cope with the situation and the prospects of nuclear power in general, and of small and medium sized power reactors in particular, are discussed.     

Possible design improvements and a high power density fuel design for integral type small modular pressurized water reactors

The study evaluates potential weaknesses and possible improvements for integral type small modular pressurized water reactor designs. By taking International Reactor Innovative and Secure (IRIS) as the reference design and keeping the power output as the same, a new fuel and reactor design were proposed. The proposed design relocates the primary coolant pumps and the pressurizer outside the reactor pressure vessel (RPV). Three recirculation lines and jet pumps/centrifugal pumps are introduced to provide the coolant circulation similar to Boiling Water Reactor designs. The pressurizer component is expected to be similar to the AP600 design. It is located at one of the recirculation lines. The new fuel assembly adopts 264 solid cylindrical fuel pins with 10 mm diameter and 2.3 m height, arranged at a hexagonal tight lattice configuration. Large water rods are introduced to preserve the moderating power and to accommodate finger type control rods. The resulting fuel can operate with 104.5 kW/l power density while having substantially higher margin for boiling crisis compared to typical large PWRs. Full core neutronic analysis shows that 24-month cycle length and 50 MWd/kg burnup is achievable with a two-batch refueling scheme. Furthermore, the fuel behavior study shows that the new fuel with M5 type Zircaloy cladding show fairly acceptable steady state performance. A preliminary Loss of Coolant analysis shows that the new design could be advantageous over IRIS due to its low ratio of the water inventory below the top of the active fuel to total RPV water inventory. The proposed reactor pressure vessel height and the containment volume are 30% lower than the reference IRIS design.     

Burnup management simulator for small and medium sized reactors

We propose a novel burn up management simulator scheme which would maximize the discharge burn up of Small and Medium Sized Reactors (SMR) by optimum choice of Fuel Cycle Length (FCL). In this simulator, the objective being to maximize the burn up of all the subassemblies of the reactor so that burn up loss in them is a minimum and the plant availability factor is maximized. The simulator can be used both for the conventional batch refueling as well as the once through cycle schemes. Further, the designer has the option to choose a particular FCL depending upon the percentage loss in burn up.     

Development of medium and small sized reactors: DMS

Nuclear power is expected to become the main source for electric power generation in Japan for the reasons of energy security and prevention of CO₂ emission. In addition, the slowdown of recent electric power demand and the liberalization of the electric power market are accelerating medium and small sized reactor development. (Hida and Ito, 2003) Furthermore, the needs of medium and small sized reactors have become greater in foreign countries where electric grid systems are weak. Under these circumstances, Hitachi has developed DMS's (Double MS: Modular Simplified & Medium Small Reactors) as 400 MWe class LWR's supported by The Japan Atomic Power Company. (Moriya et al., 2003) In addition, DMS's have been designed based on proven technology that requires no large-scale development, and can therefore be introduced in the market in near future.     

The status of development of small and medium sized reactors

Several IAEA Member States have shown their interest in reactor designs, having a smaller power rating [100–500 MW(e) range] than those generally available on the international market. These small and medium sized power reactors are of interest either for domestic applications or for export into countries with less developed infrastructure. There are different developments undertaken for these power reactors to be ready for offering in the nineties and beyond.The paper gives an overview about the status and different trends in IAEA Member States in the development of small and medium sized reactors for the 90's and provides an outlook for very new reactor designs as a long term option for nuclear power.     

Design and safety optimization of ship-based small nuclear power reactors

Design and safety optimization of ship-based nuclear power reactors have been performed. The neutronic and thermo-hydraulic programs of the three-dimensional X–Y–Z geometry have been developed for the analysis of ship-based nuclear power plant. Quasi-static approach is adopted to treat seawater effect and quasi-static approach is also employed to treat neutronic aspect during safety analysis.

The reactors are loop type lead–bismuth-cooled fast reactors with nitride fuel and with relatively large coolant pipe above reactor core, the heat from primary coolant system is directly transferred to water–steam loop through steam generators. The power level is 100–200 MW th and excess reactivity is about 1$. Three types of core were investigated in the optimization process: balance, tall, and pancake with five values of Z–Y size ratio.

As the optimization results, the core outlet temperature distribution is changing with the elevation angle of the reactor system. The pancake core type has larger temperature distribution change as the elevation angle changes due to the sea wave. The natural circulation capability is good for safety. However, large driving head of natural circulation may cause large temperature fluctuation as the elevation angle changes.     

Iaea activities for innovative small and medium sized reactors (SMRs)

The renewed interest in many Member States in the development and application of Small and Medium Sized Reactors (SMRs) is reflected in the increased activities of the IAEA's (the Agency's) Nuclear Power Technology Development Section (NPTDS) for this trend. The paper gives an overview, summarizes intermediate result, and presents major findings of the NPTDS activities for innovative SMRs, including the preparation of new Status Report on Innovative SMR Designs, dedicated Report on Small Reactors without On-Site Refuelling and Coordinated Research Project for the Development of Small Reactors without On-Site Refuelling.     

The prospect of mox fuel based PbBi cooled small nuclear power reactors

Safety performance of MOX fuel based PbBi cooled small fast power reactors has been analyzed and discussed. Though the thermal conductivity of MOX fuel is not large relative to that of nitride or metal fuel, but by proper combination of relatively small power density and relatively large natural circulation it can compensate fuel temperature decrease with coolant temperature increase smartly during unprotected loss of flow accident. Under such condition, accident analysis discussed in this paper show that under unprotected total loss of flow (ULOF) accident the reactor can survive inherently using combination of reactivity feedback. For unprotected rod run out transient over power (UTOP) accident the MOX reactor can overcome external reactivity by smaller power increase compared to that of nitride fueled reactors case. In this case doppler feedback plays much more important role compared to radial expansion component. So the MOX fueled small power reactors discussed here can survive both UTOP and ULOF accident with still enough temperature margin.     

Modeling of the High Pressure Core Spray Systems with fuzzy cognitive maps for operational transient analysis in nuclear power reactors

In this paper the application of fuzzy cognitive maps (FCM) to model a risk scenario for Nuclear Power Plants (NPP) in a Boiling Water Reactor (BWR) is presented, specifically for failure modes and effects analysis of High Pressure Core Spray System (HPCS) during loss of reactor coolant inventory transients. A simplified model of the HPCS is analyzed with the fault tree analysis technique in order to compare this results with those obtained with the FCM and show consistency with the results, although this process is not a validation of the FCM techniques. The decision making in an NPP is a complex process, because of the numerous elements involved in its operation, and the permanent attention demanded by its maintenance. This is the first step in the development of an expert system that will help in the decision making process, through the design of the knowledge representation and the design of reasoning with FCM to automate the decision making process.     

Market potential of small and medium-size nuclear reactors as combined heat and power plants in Europe

The preliminary results are presented concerning a study launched by the Commission of the European Communities to assess the potential market of small and medium-size nuclear reactors through EC Member countries. The study was aimed at identifying those factors that may have a role in shaping the eventual deployment and diffusion of this class of nuclear reactors. In a first phase, attention focused on modular high-temperature gas-cooled reactors that would be installed to produce low-temperature heat and power. Federal Republic of Germany, Italy and France are the countries for which the investigation has been completed. The time span of interest is up to the year 2020. Referring to this horizon, an appraisal has been made of the number of nuclear units which could come on line to cope with energy demand and their timing. Through the study a distinction is made between technical potential, economic potential, and effective market potential. It is understood indeed that both economic competitiveness towards other energy sources and also institutional or organizational factors may restrict the market which could become accessible and would be covered by the new nuclear plants.     

Operating experience with pressurised components of German light-water reactors

Operating experience of pressurised components is reported on the basis of 19 light-water reactors operating in Germany. The design basis and materials have demonstrated their worth. Licenses are not limited in time, and the major regulatory effort is directed to continuous improvement in plant safety. Technical issues for long-term operation as evaluation of operating experience, plant monitoring, replacement of components are addressed. The basic safety concept as the design basis for the pressurised components is illustrated by some of its details. The main results from the analysis of operating experience are mentioned. Plant monitoring and inspections are important measures to ensure the integrity of the components and to maintain the safety level of the plant. The expansion of the monitoring system may allow a reduction in the scope of inspections.     

Nuclear power plant operational diagnostics and control

Before the end of the present century, a significant proportion of the world's needs for electrical energy will be supplied by nuclear power plant. The capital invested in these stations, as opposed to their operating costs, will be considerable. For this reason and to ensure their optimal and safe operation, both as individual units and in a generating network, computer based on-line monitoring, identification and control techniques will be associated with each nuclear plant.