Induced nuclear reactions: processes – systems – and elements – Fission reactor material treatment – Post accident impurity or contaminant removal
Reexamination Certificate
1999-04-14
2001-06-12
Jordan, Charles T. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Fission reactor material treatment
Post accident impurity or contaminant removal
C376S313000, C376S293000, C055S318000, C055S399000
Reexamination Certificate
active
06246739
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to nuclear reactors, and more particularly, to a passive aerosol retention device for reducing the offsite radiation dose resulting from particulate aerosols during a severe accident.
One known boiling water nuclear reactor includes a reactor pressure vessel and a primary containment vessel. The primary containment vessel includes a lower, an upper drywell, and a passive containment cooling system. The upper drywell is separated from the lower drywell by the reactor pressure vessel skirt and support. Circular vents permit communication between the lower and upper drywells. The primary containment vessel surrounds the reactor pressure vessel and can withstand pressure generated by the reactor pressure vessel during reactor accident conditions and to contain any radioactive aerosols that may be generated during a severe accident condition. Particularly, the reactor pressure vessel is positioned within the primary containment vessel, which contains pressure resulting from accidents including a Loss-Of-Coolant Accident (LOCA), and severe accidents.
During a theoretical case of a severe accident, interactions of the corium with structural materials may cause the generation of radioactive aerosols, primarily in the lower drywell. These aerosols are subsequently transported into the upper drywell through the connecting vents by a steam and non-condensable gas flow. Recirculatory flows between the upper and lower drywell tend to distribute the aerosols between the upper and lower drywells. A certain percentage of the aerosols are retained in the upper drywell due to agglomeration and deposition on the containment surface. A portion of the aerosols are transported to the suppression pool via the passive containment cooling system. Some of the insoluble particulate aerosols deposit in the tubes and headers of the passive containment condenser (PCC) unit, thereby degrading the PCC heat removal capability and the overall containment heat removal performance.
Another portion of the aerosols in the upper drywell escape via leakage paths which may develop during a severe accident. The leakage of aerosols from the containment vessel is an important contributor to the offsite radiation dose. In addition, a resuspension of the aerosols agglomerated and deposited on the containment walls and in the PCC tubes and headers may occur which have an effect on the aerosol concentration in the upper drywell.
It would be desirable to provide a mechanism to minimize the offsite radiation dose and improve containment heat transfer capability during a severe accident by reducing the aerosol concentration in the upper drywell.
BRIEF SUMMARY OF THE INVENTION
Passive aerosol retention apparatus positioned in the connecting vents of a nuclear reactor are described. The aerosol retention apparatus minimizes aerosol transport from the lower drywell to the upper drywell of the reactor. The retention apparatus includes a substantially cylindrical housing and a flow modulator positioned inside the housing and extending at least partially from a first end to a second end of the housing. The flow modulator includes a helically shaped baffle positioned in the housing so as to be coaxial with the housing. The baffle is coupled at each end to the housing by attachment bars.
In one embodiment, the diameter of the helical baffle is less than the inside diameter of the housing. The angle formed by the intersection of the helical baffle and a radial plane extending perpendicular to a longitudinal plane, is about 30 to about 60 degrees. The longitudinal plane passes through the longitudinal axis of the housing.
The aerosol retention apparatus is positioned in the connecting vents that are located between the lower and upper drywell. In operation, the helical baffle of the aerosol retention apparatus imparts a rotational component to the steam, gas and aerosol mixture as the mixture flows from the lower drywell to the upper drywell. The resulting tangential acceleration imparted to the aerosol particles causes the aerosol particles to be thrown against the inside surface of the housing of the apparatus. The insoluble aerosol particles then may adhere to the inside surface of the housing or drop back into the lower drywell. The aerosol particles that impact the housing, agglomerate and build-up on the inside surface of the housing and then flow back into the lower drywell because only a thin layer of aerosol particles can be maintained on the vertical inside surface of the housing.
REFERENCES:
patent: 2970669 (1961-02-01), Bergson
patent: 3593496 (1971-07-01), Merrill
patent: 3813854 (1974-06-01), Hortman
patent: 4567941 (1986-02-01), Coppolani et al.
patent: 4571323 (1986-02-01), Costes
Galtman Jimmy Frank
Khorana Shyam Satinder
Armstrong Teasdale LLP
General Electric Company
Jordan Charles T.
Mun K. Kevin
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