Induced nuclear reactions: processes – systems – and elements – Seal arrangements – Between pressure vessel cover and vessel or portion thereof
Reexamination Certificate
1999-09-14
2002-02-26
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Seal arrangements
Between pressure vessel cover and vessel or portion thereof
C376S203000, C376S206000, C376S283000, C376S461000
Reexamination Certificate
active
06351510
ABSTRACT:
THE BACKGROUND OF THE INVENTION
The present invention relates to a nuclear reactor plant comprising a casing enclosing a primary space, a reactor vessel arranged in the primary space, a reactor core provided in the reactor vessel, and an upper space provided above the primary space, the reactor core being separated from the upper space by means of an openable cover arrangement
Such nuclear reactor plants are known and these have proved to function in a satisfactory manner. During shut-down of such a plant for revision and maintenance, the cover arrangement is removed. Consequently, the reactor core is completely submerged in water. It is of course important from a security point of view to be able to keep the water in the reactor vessel during the whole period of shut-down in order to prevent radiation from the reactor core from reaching the environment and in order to prevent the temperature of the reactor core from exceeding an unallowable level, which may lead to the melting of the reactor core.
During such a shut-down of the reactor and during certain types of service work at the reactor, such as for instance regarding the pumps provided at the bottom portion of the reactor vessel, it may under certain circumstances happen that water in He reactor vessel starts to leak In case of an unfortunate scenario, this may involve emptying of the reactor vessel by such an amount of water that the water level in the reactor vessel comes below the level of the reactor core. Furthermore, if the openings and passages, which normally are provided in the containment into the space below the reactor vessel, are not properly closed, the water leaking from the reactor vessel will, in addition, disappear out of the containment. It is to be noted that during shut-down and revision work, these openings and passages are normally open in order to give access to maintenance staff and transport of material.
At such a water loss in the reactor vessel, it might thus happen that the temperature in the reactor core rises to such a level that the core melts at an open reactor containment.
SUMMARY OF THE INVENTION
The object of the present invention is to remedy the problems mentioned above and in particular to provide a reactor plant by which a water loss in the reactor vessel may be prevented in a secure and passive manner.
This object is obtained by the nuclear reactor plant initially defined and characterized in that the casing is designed in such a manner that the primary space is completely closed against the environment at least to a level corresponding to the most highly located part of the reactor core, and that the upper space is arranged to house a volume of a liquid, which volume is sufficiently large to permit the filling of the primary space with the liquid to a level reaching at least the most highly located part of the reactor core. Since the casing according to the invention is completely closed at its lower part and thus does not comprise any openings or passages, the water which in case of an accident possibly may leak out from the primary space is prevented from leaving the casing below the most highly located part of the core. Since the openable cover arrangement is removed when the reactor plant is shut down for revision and maintenance, the liquid in the upper space will flow down into the reactor vessel. With the liquid volume available in the upper space, it is thus possible to ensure that the reactor core always will be submerged in liquid even if the bottom of the reactor vessel would be open. Consequently, it is possible by the measures according to the invention to prevent in a completely passive manner, i.e without the provision of any external force or measure, the uncovering of the reactor core.
According to an embodiment of the invention, the primary space is limited downwardly by a floor member and a cavity which is open upwardly and extends downwardly from the floor member, the reactor vessel at least partly being provided within the cavity. In such a manner, the volume of the primary space which surrounds the reactor vessel may be reduced. Thereby, the reactor vessel is advantageously provided in the primary space in such a manner that it extends downwardly into the cavity to such a level that the most highly located part of the reactor core is located in the cavity below the floor member. Such a cavity may be defined by a bottom portion and a wall portion which delimit completely the cavity from the surrounding parts of the casing up to the level at which the floor member is located. In such a manner, the cavity will be completely closed against surrounding parts of the spaces located within the casing, ie. the cavity lacks any passages through which water, which at an accident possibly may leak, may leave the cavity. However, at least one transport passage may extend between the lower part of the cavity and the part of the primary space located above the floor member. Such a transport passage may comprise means for the transport of people and material. In such a manner, the space below the reactor vessel is accessible and it is possible to perform work on reactor components located at the underside of the reactor vessel.
According to a further embodiment of the invention, the casing also encloses a secondary space which is separated from the primary space and provided below the floor member and arranged to house a cooling medium Thereby, at least one channel ma y extend through the floor member and connect the primary space and secondary space, the channel having an orifice provided in the secondary space and arranged to be located in the cooling medium.
According to a further embodiment of the invention, the primary space is accessible from outside via an openable passage extending through the casing at a level located above the floor member.
According to a further embodiment of the invention at least one reactor component is sealingly and releasably provided in a through-going opening at a bottom portion of the reactor vessel. Such a reactor component may comprise at least one of a pi device arranged to recirculate liquid in the interior of the reactor vessel, and a drive member arranged to displace a control rod into and out of the reactor core for controlling the nuclear reaction in the reactor core.
According to a further embodiment of the invention, the cover arrangement comprises a first cover arranged to close an upper limiting wall of the primary space and the second cover arranged to close the reactor vessel.
Further features and advantages of the nuclear reactor plant according to the invention appear from the following description of different embodiments.
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Bredolt Ulf
Engström Johan
Ivung Bengt
ABB Atom AB
Carone Michael J.
Connolly Bove & Lodge & Hutz LLP
Richardson John
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