Development of HWRs

In 1965 the government requested the CNEA to prepare a feasibility report on the construction of an NPP in the region were most of the population and industry were concentrated. The CNEA’s report showed the feasibility of installing a nuclear power plant and the Atucha site was selected.

In 1966 the CNEA was authorized to start the bidding procedure and 17 offers were received. By the end of 1967 the decision was taken. The construction of Atucha-1 started in 1968 and the plant was connected to the grid in 1974. The main supplier was Siemens AG, from Germany, and the design was a pressure vessel design, moderated and cooled by heavy water, with natural uranium fuel, based on Siemens-KWU PWRs and the German pressurized heavy-water reactor MZFR. Local industry participation in the project was about 40%. The reactor has operated well, with an overall load factor of about 70%. The thermal reactor power of Atucha-1 is 1179 MW, the generator output is 357 MWe and the net plant power totals 335 MWe.

In 1972 it was decided to construct a second NPP in Embalse, province of Cordoba. The call for bids followed the same trend of the Atucha-1 and a 50% minimum local industry participation was requested. In March 1973, the offer of a 600 MWe natural uranium-HWR with pressure tubes, made jointly by Canadian and Italian firms was selected. A very wide technology transfer agreement was negotiated between Argentina and Canada, and signed in March 1974. Different reasons caused both delays in the construction and only partial fulfillment of the technology transfer agreement. CNEA became in 1979 the main contractor for the assembly works, and Argentine firms were responsible for the assembly of many systems. The plant entered into commercial service in 1984. The reactor has operated well, with an overall load factor of about 84%.

The reactor is of a CANDU600 type. The moderator and coolant are heavy water. The fuel channel are horizontal pressure tubes. The moderator is at low pressure and separated from the coolant. The thermal reactor power is 2.109 MW, generator output is 648 MW(e) and net plant power totals 600 MW(e).

In 1979 a call for offers for the third NPP, to be built next to the Atucha-1, was issued. Argentina was requesting a NPP, a heavy-water production plant, and the constitution of a joint company between CNEA and the supplier, who would become architect-engineer for the construction of the present and future nuclear plants in the country. The German and Swiss offer of a 700 MW(e) version of the Atucha-1 pressure vessel reactor and a heavy-water production plant was selected. In 1981 the architect-engineering company ENACE was formed as a joint venture with Germany, and construction of the Atucha-2 started.

Argentine suffered economic crisis, the project was delayed, and construction was formally stopped in 1994. The Argentine nuclear sector was restructured. A state-owned shareholder company, Nucleoelectrica Argentina SA (NA-SA), was created for the operation of the two nuclear stations and the construction and subsequent operation of the third one. In August 2006 the government decided to re-start construction of Atucha-2 under NA-SA management. The first connection to the grid is expected in 2014. Participation of the local industry was very important.

The Atucha-2 was developed from the Atucha-1 design by Siemens-KWU. Many of the components have a conceptual design identical to those of Atucha-1, while the plant layout and other features are derived from the design of the pre-Konvoi and Konvoi 1300 plants. The thermal reactor power is 2.160 MW, the generator output is 745 MWe and the net plant power totals 692 MW(e).

In the 1980s the Empresa Nuclear Argentina de Centrales Electricas (ENACE) designed the ARGOS PHWR 380. Its flow diagram and main technical characteristics were practically the same as those of Atucha NPPs. It had 60 vertical hydraulically actuated absorver rods. The spent fuel pool was located within the reactor building and different fuel options were considered. Its safety design was mainly based on probabilistic safety criteria. Also in the 1980s the Direction de Centrales Nucleares of CNEA designed the TPA 700/300. These were both based on the CANDU 600 and aimed at allowing important local participation. The fuel of Atucha-1 was originally natural uranium but it was substituted by 0.85% enriched uranium in order to reduce fuel costs. The exit burnup was increased from 6 to 11 MW d/kg U.

CNEA has developed under the Combustible Avanzado para Reactores Argentinos (CARA) project an advanced fuel element concept for HWR, specially designed to fit Argentinean fuel-cycle requirements. Atucha-1 and Embalse have quite different designs for the fuel elements. Both NPPs use on-load refueling, but they differ in the number and length of the refueled elements. In Embalse a CANDU reactor type, with a total of 12 fuel elements, 6 meter long channel, two fuel elements are refueled at a time. In Atucha-1 a pressure vessel design, moderated and cooled by heavy water, each vertical channel has one single fuel bundle of about 5 m in length for its active portion, hung by its upper part. Atucha-1 is fueled on-power by a fueling machine that sits above the reactor.

The main objectives of CARA were:

the fuel element could be used in both reactor types;

• NPP performance enhancement;

• thermal-hydraulic and thermal-mechanic extra margins;

• negative void coefficients;

• cost and spent fuel reduction.

This advanced fuel element for HWR has collapsible cladding, 100 cm length and 52 fuel pins. In 2012 a Canadian patent was issued (Florido et al., 2012).

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