Induced nuclear reactions: processes – systems – and elements – Reactor protection or damage prevention – Pressure suppression and relief
Reexamination Certificate
1995-11-09
2001-06-19
Behrend, Harvey E. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Reactor protection or damage prevention
Pressure suppression and relief
C376S299000
Reexamination Certificate
active
06249561
ABSTRACT:
FILED OF THE INVENTION
This invention relates generally to safety systems for boiling water nuclear reactors and, more particularly, to a combination primary containment cooling and residual heat removal steam condenser system.
BACKGROUND OF THE INVENTION
Boiling water nuclear reactors (BWRs) typically utilize active safety systems to control and mitigate accident events. Such safety systems transport reactor decay heat to the ultimate heat sink, which is normally sea or fresh water. Active safety systems, for example, have both high-pressure and low-pressure pumping equipment. Such active systems require maintenance and surveillance testing of the safety related equipment. In addition, the pumps and other equipments typically require AC power to operate.
An alternative to an active safety system is a passive system. Totally passive safety systems have been studied for use in BWRs because of their merits in reducing maintenance and surveillance testing of the safety-related equipment, and in eliminating the need for AC power, thereby improving the reliability of BWR operation and safety. Simplified BWRs (SBWRs) have been configured to include totally passive safety features that provide more resistance to human error in accident control and mitigation.
There are, however, some tradeoffs when employing totally passive safety systems in BWRs. Due to their passive nature, the totally passive system, when configured in accordance with nuclear standards of system separation and diversity, substantially add to plant size and cost. Therefore, passive system applications to BWRs have been limited to small- and medium-sized plants having up to about 1000 MWe output.
A combination active and passive system is described in U.S. Pat. No. 5,426,681, which is assigned to the present assignee and incorporated herein, in its entirety, by reference. The system described in the above referenced patent provides many advantages, however, such system has separate passive containment cooling systems (PCCS) units and separate reactor heat removal steam condenser (RHR-CND) systems. Such separate systems are located in separate compartments of a condenser pool and add to the plant size and cost.
It would be desirable to provide a safety system for a nuclear reactor which is highly reliable and satisfies safety requirements yet has fewer safety components. For example, it would be desirable to provide PCCS and RHR-CND systems which perform the same functions as known PCCS and RHR-CND systems yet require less space and few components than such known systems.
SUMMARY OF THE INVENTION
These and other objects are attained by a combination primary containment cooling system and residual heat removal condenser (PCCS-CND) operable in a containment cooling mode and in a reactor vessel cooling mode are described. In the containment cooling mode, the PCCS-CND interfaces with the primary containment vessel (PCV) through an isolation valve, and upon receipt of a high drywell pressure signal, the valve opens allowing the steam in the PCV to flow to the PCCS-CND where it condenses. The decay heat is transferred to the condenser pool.
In the reactor pressure vessel (RPV) cooling mode, the PCCS-CND interfaces with the RPV through isolation valves. Upon receipt of a high temperature signal from the suppression pool or through an operator action, the isolation valves are opened allowing the steam in the RPV to flow to the PCCS-CND where it condenses. As in the containment cooling mode, the decay heat is transferred to the condenser pool.
The combination PCCS-CND performs both functions of containment cooling and reactor vessel cooling. The number of components required to satisfy the BWR safety requirements of decay heat removal therefore is reduced, resulting ultimately in reducing plan size and cost. In addition, the subject PCCS-CND can be used to provide backup depressurization of the RPV, and provide backup heat removal and inventory control for events such as station blackout and reactor isolation. Further, the steam condensate from the subject PCCS-CND is allowed to discharge to either the suppression pool or to a collection tank located in the PCV. The collected condensate can be utilized as a source of water inventory for flooding the lower drywell during a postulated severe accident, or back to the reactor vessel for long term core cooling.
REFERENCES:
patent: 5082619 (1992-01-01), Sawyer
patent: 5102617 (1992-04-01), Gluntz et al.
patent: 5158742 (1992-10-01), Dillmann
patent: 5169595 (1992-12-01), Cooke
patent: 5282230 (1994-01-01), Billig et al.
patent: 5295168 (1994-03-01), Gluntz et al.
patent: 5345481 (1994-09-01), Oosterkamp
patent: 5349616 (1994-09-01), Nakayama et al.
patent: 5377242 (1994-12-01), Carlton et al.
patent: 5377243 (1994-12-01), Hill
patent: 57-69289 (1982-04-01), None
patent: 4098198 (1992-03-01), None
Armstrong Teasdale LLP
Behrend Harvey E.
General Electric Company
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