Pressure vessel HWRs

HWRs of the pressure vessel type have been designed and constructed in Sweden, Germany, and Argentina. The main references of this line are the Agesta reactor in Sweden (shutdown), the MZFR reactor in Germany, and the Atucha-1 and Atucha-2 reactors in Argentina. 

In Sweden, the first pressure vessel pressurized HWR was constructed at Agesta. This was a project that combined the objectives of two separate concepts one for a district heating reactor and the other for a heat and power reactor. The pressure vessel reactor was conceived as a 65 MWth prototype plant that was to supply district heating and electricity (10 MWe). The reactor was located in an imderground chamber excavated in solid rock and serviced a suburb of Stockholm. The reactor operated with a good degree of reliability. Operation was interrupted over the summer months when district heating was not required. The reactor was shut down in 1975 and decommissioned because it had ceased to be an economical source of power. 

A unique feature of pressure tube HWRs is large volumes of heavy water or light water surrounding the fuel channels and the calandria vessel, respectively. These water volumes provide an inherent means for removal of decay heat from the core during BDBA that progresses to severe core damage. The two water sources are the heavy water moderator... 

SYNOPSIS Swedish HWRs use D2O as moderator and coolant and pressure vessels. The Agesta PHWR has operated since 1963/64 with very low D2O leakage and high availability. Commissioning of the Marvlken 200 MWe BHWR Is due for early 1969 Features of these units and of designs for commercial BHWRs are discussed. 

Current designs for large BHWRs use concrete pressure vessels and a project for building a model vessel In Sweden by Scandinavian funds has started. Discussion of economic and technical parameters Indicated that expected trends for the cost of uranium, plutonium, fuel fabrication and reprocessing and the size of units all favour the economics of natural uranium HWRs In general and the highly neutron economic BHWRs in particular. 

Thus given continuity in the current development and construction programme -which requires the decision in the near future to order some commercial size plant - and adequate information to purchasers and planners, HWRs should conquer a significant share of tlie world s reactor markets. In this process, concrete pressure vessel BHWRs with their high bum-up with natural uranium, relatively simple circuit with few components, unlimited outputs, and relation to the technology of an established reactor system should play their part. 

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