steam volume. During the discharge process water may be drained
discontinuously. The bigger the pipe diameter, the more the
discharged quantity. The total drain water quantity is more than for the
opening of the safety valve at the same discharge orifice diameter.
(3) For the discharge from the water volume, the drain quantity is
more than that of a drain from the steam volume. All water above thepipe opening will be drained. When the level is lower than the opening of the pipe, the drain quantity depends on the height difference between the liquid level and the opening of the pipe. In a certain range the bigger the height difference, the smaller the drain quantity. Under the conditions of our tests, when the height difference is more than 5cm, its effect on the quantity can be negligible.
References
1. Ma Changwen, Bo Jinhai, Za Meisheng and Others:
" Safety experimental study for the Nuclear Heating Reactor" ,
INET Report, 1991,2.2. Ja Haijun
Safety experimental study on the Boron injection system of the
5MW Heating Reactor, doctoral thesis. 1991, INET, Tsinghua Univ.OPERATIONAL, MANUFACTURING AND DECOMMISSIONING ASPECTS
CAREM: OPERATIONAL ASPECTS, MAJOR XA9745988
The paper presents the design related aspects of operation and maintenance of the CAREM reactor and the principal features of its main components.
The paper covers three main topics: operational aspects, major components and maintainability
Operational aspects
A strong negative thermal coefficient, the use of burnable poisons to compensate burnup and no use of soluble boron for reactivity control characterized reactor control.
Hydraulically driven control rod drives are fully contained in the pressure vessel.
The following research and development activities are being carried on:
A critical facility for testing main core characteristics is in final construction stage.
A full scale model of control rod drives is currently under test.
A full scale model of one steam generator will be constructed and tested.
Major components
Pressure vessel: The empty pressure vessel weights 100 tons. This fact facilitates both its manufacturing and transport. Internals and steam generators will be mounted on site. Being the reactor self-pressurized, no pressurizer is included.
Steam Generators: Twelve once-through steam generators are symmetrically placed inside the pressure vessel. Specific design aspects are discussed in the paper.
Containment: The containment is of pressure suppression type. Second shutdown system, pressure relief tank, and equipment and installation for manual reactor refueling and for handling of RPV internals, are all placed inside the containment.
Provisions are also made for accommodating RPV internals during refueling and maintenance operations.
Maintainability
Lay-out: The balance of plant lay-out is conventional. For nuclear island layout, attention has been paid to the fact that the containment will not be accessible during reactor operation. This fact imposes special demands on equipment reliability, that will assure high plant availability.
In service inspection: it is currently under study. Inspection of pressure vessel welds will follow standard practices. Inspection of steam generators will be performed by conventional eddy-current techniques adapted to tube geometry. Other in-service inspections required by ASME XI, SS-50-SG-O2, and local regulatory authorities, are being evaluated, most of them being similar to the standard for non-integrated reactors.
Fuel and waste handling: manual refueling of the reactor implies changing 31 fuel elements (approx. 70 kg each) per year. Spent-fuel-pool capacity covers seven years of operation; afterwards, dry spent fuel element storage is considered.
Decommissioning: The CAREM concept does not impose specific conditions on plant decommissioning.
1. INTRODUCTION
CAREM reactor features have been described elsewhere /!/. This paper deals with detailed engineering aspects of its design, that point to important differences between the CAREM, and conventional non-integrated PWRs.
The main aspects to be discussed are:
- Operational aspects, including reactor control and control devices.
- Major components engineering: reactor vessel, steam generators and containment vessel
- Maintainability, as related to lay-out, in-service inspection, fuel and waste handling, and decommissioning.
The R&D status corresponding to each item is mentioned when convenient.
2. OPERATIONAL ASPECTS 2.1 Concept of reactor control
Two characteristics of CAREM reactor core design will be discussed:
- strong negative temperature coefficient - no soluble boron for burnup compensation
The stron negative temperature coefficient enhances the self-controlling features of the PWR: the reactor is practically self-controlled and need for control rod movement is minimal. In order to keep a strong negative temperature coefficient during the
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whole operational cycle, it is necessary to do without soluble boron for burnup compensation. Burnup reactivity compensation is obtained with burnable poisons, i.e.
gadolinium oxide dispersed in the uranium oxide fuel. Nonetheless, soluble boron is used to compensate cold-hot reactivity difference (the strong negative temperature coefficient means that a large difference in reactivity must be compensated between cold and hot states). Soluble boron is also used as a back-up of the safety shutdown rods: if the protection system of the plant orders to shut reactor down, and safety rods fail to do so, the reactor is shutdown by boron injection.
The effect the two core design features have on burnup, tend to cancel each other. A strong negative temperature coefficient means that fuel arrangement is not optimum from the reactivity point of view, but this charecteristic is compensated by the fact that power density in the core is lower than normal for PWRs. As a consequence, fuel temperature is lower, and the reactivity at hot state is higher.