Titolo della tesi: FINAL DESIGN of the Safety-relevant Chilled Water System (CHWS-1) of ITER Plant
The PhD activity, discussed in this document, was conducted between 2018 and 2021 in a collaboration between DIAEE of Sapienza University of Rome and the ITER Organization.
The purpose of this work is to develop the Final Design of the Safety-relevant Chilled Water System (CHWS-1) of ITER plant. In particular, the study will be oriented towards the thermal-hydraulic design in connection with its safety functional analysis.
Chilled Water System (CHWS-1) is an ITER safety cooling system comprised of two independent and segregated trains (CHWS-1A and CHWS-1B), which provide cooling water to components located in Tokamak and Hot Cell Complexes.
It is a Safety Important System which operation is needed for the proper functioning of Protection/Safety Important Activities (PIA) & Components (PIC/SIC).
The performed analyses have the object of determine, develop and validate the operating procedures and required I&C to be implemented in CHWS-1. These operations have been developed by combining the thermal-hydraulic modelling with the simulation of I&C during normal and abnormal scenarios (incident and accident events). Particular emphasis is given to CHWS-1 accident detection and mitigation system following the ITER SIC Requirements.
First part of the work consists in defining CHWS-1 all possible operating scenarios, perform sizing calculations of all the system components and execute relevant steady-state simulations. For this propose, several CHWS-1 models were creating using the thermo-hydraulic software AFT Fathom9 based on the system stage approaches (First Plasma (FPO) and Post First Plasma (PFPO-I & PFPO-II) Operations).
Sensitivity analysis on critical aspects of the system were performed based on these Fathom Models.
All the safety functions assigned to CHWS-1 were identified along with their performance requirements. Functional Analysis was developed with a structured top-down approach, starting from the System Requirements deducing the Basic functions until components needed to fulfil the requirements.
All the Postulated Initiated Events (PIEs) are considered, in order to identify the required safety functions.
Each function was analysed to identify its importance to safety, equipment protection etc.
The actuators and the sequence of the actions to be performed, either automatically or manually, are described.
In order to verify the postulated accident management strategy and the defined CHWS-1 instrumentation and control (I&C), a simplified RELAP5-3D model of CHWS-1B was developed.
Based on the pre-determined relevant PIEs, three transient scenarios were analysed: LOCA Accident in the DTR, Pipe Leakage in the System, VV-PHTS HX Incident/Accident.
The simulation results are studied to analyse and verify the system behavior as well as eventually implement its design, studying the required actions to reach and maintain a safe state after the given events.
With respect to the events studied, the CHWS-H1 Design & Operation was demonstrated, justified and validated in compliance with ITER SIC Requirements and CHWS-1 SIC Classification.