Engineering safety feature actuation systems

In order to reduce radionuclide transportation from the primary to the secondary cooling system, containment isolation valves should be installed. These valves will be automatically closed by the signal detecting the heat transfer tube rupture of IHX. Meanwhile, the current engineered safety features actuating system is not designed to detect the rupture since the scenario did not impact on the reactor safety of the original HTTR. Therefore, a detection method of heat transfer tube rupture of IHX should be established. 

The strategy of detection method establishment is to apply the simple and reliable method since it would comprise the engineered safety featured actuation system. 

ESF Engineered Safety Feature Actuation System ESFAS... 

Common requirements for the reactor protection system, engineered safety features actuation system and emergency load sequencer on one side, and for the reactor limitation system on the other side have been set forth in the following areas ... 

The next point which makes the digital solution more vulnerable from common causes is eventual aggregation of different safety systems automation into one actuation system - e.g. Reactor Trip System (RTS) and Engineered Safety Features Actuation System (ESFAS), RTS + Reactor Limitation System C S). 

The Main Steam Line Isolation System (see Section 10.3.2 for more details) is composed of portions of the Main Steam System and the Engineered Safety Features Actuation System. Discussed here are those portions of these systems that respond to a Main Steam Isolation Signal, as defined in Section 7.3. A discussion of radiological considerations is provided in Section 12.3. 

Each of the four main steam lines is provided with a power-actuated Main Steam Isolation Valve designed to stop flow from either direction when it is tripped closed. Each valve is located outside containment and is provided with means of actuation from the Engineered Safety Features Actuation System, meeting the requirements of IEEE Standard 279. 

A. The Main Steam Isolation Valves are capable of isolating the steam generators within 5.0 seconds after receiving a signal g from the Engineered Safety Features Actuation System. In the event of a steam line break, this action prevents continuous uncontrolled steam release from more than one steam generator. Protection is offered for breaks inside or outside the containment. 

In case of unsafe conditions the reactor protection system takes over and automatically scrams the reactor and actuates the relevant safety systems. The reactor protection system includes the reactor trip system and the engineered safety features actuation system. 

The engineered safety features actuation system is a limit protection system. When a serious accident occurs in the plant, it actuates the corresponding engineered safety systems to provide emergency cooling for the reactor core so as to ensure containment integrity and to prevent radioactive contamination. The actuation system consists of five parts safety injection actuation, steam line isolation actuation, feedwater line isolation actuation, containment spray actuation, containment isolation actuation system. 

The Plant Protection System (PPS) consists of the Reactor Protection System (RPS) and the Engineered Safety Features Actuation System (ESFAS) (see CESSAR-DC Section 7.1.1.1). 

The System 80+ Standard Design has a Main Feedwater Isolation System (see CESSAR-DC Section 10.4.7.2.2) to protect the SGs from overfill. The system includes redundant remotely operated isolation valves in each main feedwater line to each SG. The valve actuation system (see CESSAR-DC Section 7.3.1.1.10.3) is composed of redundant trains A and B, and each train s instrumentation and controls are physically and electrically separate from and independent of those of the other train. A failure of one train will not impair the action of the other. The main feedwater isolation valves are automatically actuated by a Main Steam Isolation Signal (MSIS) from the Engineered Safety Features Actuation System (ESFAS, see CESSAR-DC Section 7.3.1). High SG water level, in a 2-out-of-4 logic, is one of the initiators for the MSIS. The main feedwater isolation valves can be in-service tested in accordance with ASME Code Section XI, Subsection IWV. A Technical Specification (CESSAR-DC Chapter 16) will establish testing requirements for the valve actuation system. These requirements will also be incorporated into the plant maintenance procedures. 

Engineering safety feature actuation systems (ESFAS)... 

USNRC IN 93-38, "Inadequate testing of engineered safety features actuation systems," dated May 24,1993. 

Classified as Engineered Safety Features Actuation Systems or are relied upon to support operation of an actuation system for Engineered Safety Features within design limits. 

Cepin, M., Riddle, S. Object Modelling and Safety Analysis of Engineered Safety Features Actuation System, Technical Report TR IS AT 96/11 University of Newcastle upon Tyne (December 1996)... 

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