Whether or not nuclear ship has economic benefit is a fundamental matter to judge the social incentive to realize the practical use of nuclear ships. To evaluate the economics of nuclear ships, the construction and operation costs of nuclear and conventional ships have been studied and compared as parameters of the ship’s speed, containers’ capacity in terms of TEU (Twenty — feet Equivalent Unit), etc. Figure 5 shows the comparison of RFR (Required Freight Rate, $/TEU : Operation cost to transport one container) between two container ships of 6,000 TEU and 30 knots (one uses reactors equipped with two MRXs of total power 348MWth and the other a diesel engine), in case of Asia — North America route, commissioned for 20 years from the year 2015. The quantity of container transport through this route is the largest among the the world’s three biggest sea routes (Routes of Asia-North America, Europe — North America and Asia-Europe). The crude oil price is assumed to be $36/bbl. averaged within the service period. This figure shows, (a) The capital cost of the nuclear ship is about 2 times larger than that of the diesel ship, (b) On the other hand, the fuel cost of the nuclear ship is about 1/2 of that of the

Ship Speed (knots)

Fig.6 RFR as a function of ship speed

diesel ship, (c) The environmental cost of the diesel ship accounts for 22% of the RFR. The cost study of nuclear and conventional ships shows that the situation becomes more favorable for nuclear ships as increasing of the speed and the load. Figure 6 indicates the RFR as a function of ship speed. Over 28 knots, the nuclear ship holds an economically dominant position over the diesel ships, because the diesel ships must have higher environmental costs.

3. R&D work

To realize nuclear ships with commercial use, it is necessary to obtain an economical, safe and reliable reactor system. In addition, the supplementary items such as the international agreement on safety, the preparation of the maintenance yard, etc., should be solved. R&D programs on nuclear ships have been proposed and being performed to solve technical subjects so that the nuclear ships will be put into commercial use in the future.

(1) Experimental study on thermal-hydraulics

To study the hydrothermal behavior in the water-filled CV, especially steam condensation characteristics, a small scale test facility (volume ratio : about 1/300 of MRX) has been fabricated and fundamental experiments on the following behavior are in progressC5>, (a) thermal and hydraulic responses in both the RPV and the water-filled CV under LOCAs, (b) evaluation of mechanical loads generated by LOCAs, and (c) capability of natural circulation and decay heat removal. Furthermore, to confirm the function of the safety features such as an integral PWR with a water filled CV and passive safety systems, a large scale synthetic test facility is planned. The thermal power of the facility is 5MW (1/20 of the MRX), however the height is same as that of the MRX because it is most important to simulate accurately the natural circulation condition. Experiments on board are planned to obtain the behavior under the ship inclination and oscillation.

(2) Development of components

The components of in-vessel type CRDMs such as the motor, the latch magnet, etc., have been developed <6>, and the function and reliability tests using the full mock-up CRDMs are planned. The water-proofed design is being performed for the components and the thermal insulator placed in the water- filled CV.

(3) Automatic control system

It is important to reduce the number of reactor operators from the view of the ship’s economy. From this standpoint and to enhance the ship’s safety, highly automated control systems have been studied which will be adopted and will cover the whole operations during normal, abnormal and accident conditions. This system consists of control and diagnostic systems as shown in Fig. 7. The control systems generate control signals for control equipments, for example, control rods, pressure control valves, flow control valves, etc., in accordance with the reference signals (demand signal) and signals of each measured parameter. If a difference exists between the signals of the reference and the parameter, a control signal is generated based on the operational procedure and changes the parameter to the demand conditions. The diagnostic systems are provided to monitor the malfunction of the systems and

the plant operating conditions. For the operational procedures, the optimization is made based on the operator’s knowledge and the learning AI.

(4) Development of nuclear ship simulator

The nuclear ship simulator NESSY (Nuclear Ship Engineering Simulation System) has been developed in JAERI and used for the simulation of the nuclear ship "Mutsu" so farC7:>. It can simulate both the behaviors of the reactor systems and the ship motions. Mutual interactions can be analyzed for the situations such as changes of the reactor power, the steam generator water level, etc., due to the ship motions caused by waves or the navigator’s maneuvering.

The accuracy of the system has been verified with the operation data of the "Mutsu" and it is proved that this system is a very useful tool for developing advanced marine reactors<e>. Modifications of the models and the parameters are being made for the MRX reactors since 1995.

4. Conclusion

An advanced marine reactor, MRX, has been designed to be more compact and lightweight with enhanced safety. The engineered safety is accomplished through a simplified system which is suitable in particular for a marine reactor, since it must be operated by limited number of crews. The LOCA analysis shows that the core flooding is maintained passively even taking into account the ship inclination. The one-piece removal method is proposed to keep the maintenance and refueling works short and safe. This method also makes the ship’s decommissioning easy and enables us to reuse the reactor after the ship’s life. The economic evaluation shows that for container ships of 6000 TEU traveling over 28 knots, the nuclear ships will hold an economically dominant position after 20 years from the present time, because the diesel ships must have higher environmental costs. In addition to the design study, extensive R&D activities are being performed. These can contribute largely to the realization of the nuclear ship in commercial use in the future. Considering that the MRXs are small size reactors with highly safe capabilities and transferable ones, they have a wide variety of uses in the energy supply system.

Reference

(1) A. Yamaji and K. Sako : Shielding Design to Obtain Compact Marine Reactor, J. Nucl. Sci. Technol., Vol. 31, No. 6, 1994.

(2) K. Sako, et al. : Advanced Marine Reactor MRX, Int. Conf. on Design and Safety of Advanced Nuclear Power Plants, Oct. 1992, Tokyo, Japan.

(3) T. Hoshi, et al. : R&D Status of an Integral Type Small Reactor in JAERI, ICONE-3, Apr. 1995, Kyoto, Japan.

(4) A. Yamaji, et al. : Core Design and Safety System of Advanced Marine Reactor MRX, ibid.

(5) T. Kusunoki, et al. : Steam Condensation Behavior of High Pressure Water’s Blowdown Directory into Water in Containment under LOCA, ibid.

(6) Y. Ishizaka, et al. : Development of A Built-in Type Control Rod Drive Mechanism (CRDM) for Advanced Marine Reactor MRX, Int. Conf. on Design and Safety of Advanced Nuclear Power Plants, Oct. 1992, Tokyo, Japan.

(7) T. Kusunoki, et al. : Development NESSY (Nuclear Ship Engineering Simulation System) and Its Application to Dynamic Analysis, ibid.

(8) M. Ochiai, et al. : Present Status of Nuclear Ship Engineering Simulation System, The 1994 SCS Simulation Conference, Apr. 1994, San Diego, U. S.A.