Session 1.3. System Design and Validation

Session 1.3. covered the topic of system design and validation and included five papers, two from India and three from France. The topics presented included seismic qualification of the shutdown mechanism, design of fuel handling systems and detailing of the gas conversion system vis-a-vis the conventional Rankine cycle steam–water system. Details of the presentations are given below.

S. Raghupathy (India) covered the details of seismic qualification of the diverse safety rod drive mechanism for the prototype fast breeder reactor. Two independent and diverse shutdown systems are provided in the reactor and the diverse safety rod, along with its drive mechanism, forms part of the second shutdown system. Details of the experimental seismic qualification tests carried out on the mechanism in stagnant water were presented. Tests were carried out on a special test facility and excitation was affected using hydraulic actuators. The mechanism was supported at the top, similar to that in the reactor, and the diverse safety rod was supported at the bottom of a structure simulating the grid plate. Excitations were given at three locations, namely, the mechanism support, the subassembly support and the subassembly button location.

The input time history derived from the theoretical seismic analysis was applied. The qualification tests included measuring the increase in the free fall time, the critical parameter governing the drop and insertion of the diverse safety rod in its bottom position. Tests were carried out on two seismic levels, namely, the Operation Base Earthquake (OBE) and Safe Shutdown Earthquake (SSE). The measured value of the increase in free fall time was 180 and 205 ms under OBE and SSE, respectively. The details of the test set-up, instrumentation and methodology of the test were also presented. It was indicated that adequate margin exists on the free fall time, ensuring positive safe shutdown of the reactor under seismic conditions.

D. Planq (France) covered the progress made in the gas Power Conversion System (PCS) development for the ASTRID reactor. The gas PCS was studied as an alternative to avoid the possible sodium–water reactions in the steam PCS. Though the steam PCS was selected as the reference option in the conceptual design phase ending 2015, the alternative gas PCS was studied in detail during 2016–2017 to bring it to a par with the steam PCS. The system uses the nitrogen Brayton thermodynamic cycle and includes sodium gas heat exchangers, heat recuperator coolers, in addition to the multistage gas turbine. The presentation covered the various stages of evolution of the design, beginning in 2012, and the steps taken to improve the gross thermal efficiency of the system to 38.3% by 2017. The improvements made to the turbine design up to 2017 were highlighted. The details of the important components in the system such as the sodium gas heat exchanger, recuperator and pre-coolers and intercoolers along with the system layout were covered and the main domains of qualification requirements were also discussed.

D. Barbier (France) presented the operational aspects of the gas PCS in the same session.

Details of the methodology of operation of the GSS PCS for turbine power control, maintaining the sodium temperature at steam generator outlet, turbine trip, decay heat removal, normal start-up, shutdown, scram, operation at house load, frequency control and the means to maintain gas inventory in the system were presented. The ongoing studies to increase the flexibility and increase the net efficiency of the cycle and the additional thermohydraulic studies planned for addressing incidents were also highlighted. Overall, the two presentations brought out the salient technical details and results of ASTRID studies carried out for the gas PCS.

F. Dechlette (France) presentation covered the French viewpoint on the ASTRID fuel handling system. In-vessel handling is proposed using two rotatable plugs and one straight pull machine located in the small rotatable plug, along with a fixed offset arm type machine located in the large rotatable plug. For ex-vessel handling out of the reactor vessel, an A-frame loading/unloading lock is used. A significant highlight of the design is the provision of the external buffer zone in sodium, which is interfaced with the reactor vessel. This helps to facilitate transfers between the buffer zone and the reactor vessel during fuel handling, resulting in significant reduction in fuel handling time. The exchange of fresh/spent fuel to and from the buffer zone is envisaged during reactor operation and the presentation brought out the requirements of the leak-tight airlock to enable this operation, which is being studied. The presentation also covered the details of sodium cleaning of the handling flask used to transfer from buffer zone to washing pits and the R&D related to sodium washing and future confirmatory studies required to firm up the concepts chosen.

S. Raghupathy (India) covered the details of component handling systems for future fast breeder reactors (FBRs) (twin unit 600 MW(e) FBRs-1/2) in India. The presentation highlighted the fuel handling and special handling system details for FBRs-1/2 as compared to the prototype FBR (PFBR). The experiences gained during testing of the principal fuel handling machines of the PFBR, i.e. the transfer arm and the inclined fuel transfer machine were explained. The commonality, as well as significant differences of the handling equipment with respect to the PFBR, were discussed in the presentation. The concept of in-vessel storage at the periphery of the core and ex-vessel storage in the water pool is retained. The significance of the increase in offset arm length by ~200 m and the change in ex-vessel handling equipment as a replacement for the in-vessel transfer machine was explained. Details of a unique layout of component handling equipment in fuel and decontamination buildings, which facilitates sharing of the equipment between the twin units was also presented. This had resulted in significant economy, with savings of 46% in material consumption and a reduction in overnight cost by ~2%.

Overall, the presentations made during the session were both interesting and technically illuminating. The topics of the presentations summarized the current status and efforts made by France and India for the design and validation of certain key systems of current and future FBRs. The session was very lively with active discussion of the topics.

TABLE 3. PRESENTATIONS FROM SESSION 1.3. – SYSTEM DESIGN AND VALIDATION Chair: S. Raghupathy and S. Rukhlin

Id Presenter Country Title

CN245-344 PPT-344

S. Raghupathy (Invited)

India Experimental seismic qualification of diverse safety rod and its drive mechanism of prototype fast breeder reactor CN245-285

PPT-285

D. Plancq France Progress in the ASTRID Gas Power Conversion System development

CN245-395 PPT-395

F. Dechelette France ASTRID fuel handling route for the basic design

CN245-314 PPT-314

S. Raghupathy India Component handling system: PFBR and beyond

CN245-468 PPT-468

D. Barbier France Main operation procedures for ASTRID gas power conversion system