SGHWR

As explained in Section II, in a depressurization accident to a gas-cooled reactor (and to some water reactors, e.g., the steam generating heavy water reactor—SGHWR) there is a possibility that can temperatures might rise to about 1000 C at which point some cans could fail through their internal gas pressure. Laboratory experiments in which pre-irradiated fuel elements... 

The purpose of this section is to compare the features of the RBMK reactor operated at Chernobyl with reactor types pertinent to the UK. It will be recollected that the RBMK covers a large number of reactors and the comparisons made are indeed with Chernobyl No. 4. The UK reactors covered are in three classes the commercial reactors now built and operated or in commission (Magnox and Advanced Gas-cooled Reactor (AGR)) the prototype Steam Generating Heavy Water Reactor (SGHWR) and Prototype Fast Reactor (PFR) that have comparable performance to commercial reactors and the proposed Pressurised Water Reactor (PWR) or Sizewell B design which, it... 

Table 6.2 makes a direct comparison of some design features. Here the SGHWR and PFR figures are for the actual prototypes with indication of proposed operating improvements. 

SGHWR thermal UO2 2-8% Zircaloy heavy water water (67) 272-280 pressure tube ... 

Only the SGHWR and RBMK under comparison have a direct cycle of light water coolant to the turbine and therefore the admission of somewhat radioactive steam. Both of these types have additional circulation... 

Appendix 12D Visit to the Atomic Energy Establishment Winfrith SGHWR Station... 

Dr Holmes, Director of Winfrith, welcomed the Group. The morning was devoted to the Winfrith reactor—the prototype SGHWR—including... 

The Group were interested in visiting SGHWR because it is a direct cycle pressure tube reactor, with some superficially similar features to the Chernobyl reactor. The moderator is, however, heavy water rather than graphite as at Chernobyl. Control is by pumping boric acid solution into liquid shutdown tubes and dumping heavy water moderator. 

The UKAEA reactors are not formally licensed by the Nil, although they are required to maintain a standard of safety equivalent to that of licensed sites. Dr Peckover of SRD explained how SRD monitored the safety of operations and reported independently to the Chairman of the Authority on this. Nevertheless, as for all industrial plant in the UK, the responsibility for safety lay with the line management on the site concerned. A convenient table contrasting important characteristics of the SGHWR and the Chernobyl... 

In conclusion, the Working Group gained a clear picture of how SGHWR functions as a result of the tour and the presentations. The differences in design and in safety culture between SGHWR and what is believed to have been the case at Chernobyl were elucidated. It is clear that a Chernobyl-type accident could not occur at SGHWR. 

Steam Generating HWR (SGHWR) started operation in 1968 with a designed output of 100 MWe. The use of light water coolant and heavy water moderator means that with the choice of the appropriate fuel-to-moderator ratio, the void coefficient could be made to... 

Similar results on the chemical state of the corrosion products in the reactor water were reported from other BWR circuits, e. g. the reactor water of the British Steam Generating Heavy Water Reactor (SGHWR) (Bridle et al., 1986), where the insoluble iron essentially appeared as a-Fe203, containing minor amounts of Fe304. In this case, approximately 50% of the Co present in the reactor water was attached to the suspended solids, with the remainder being in a ionic dissolved state similar ratios between the particulate and the dissolved state were obtained for Co. 

One of the most frequently reported decontamination processes is the Lomi process (Low Oxidation State Metal Ions), which was originally developed by the British CEGB for removal of corrosion product deposits from the fuel bundles of the Steam Generating Heavy Water Reactor (SGHWR). Since Fe " always is the... 

Although the results obtained in full-system decontaminations at Candu plants as well as at the SGHWR reactor proved to be encouraging, there are sufficient... 

Experiments performed in an SGHWR loop showed that specimens of stainless steel SS 304, Inconel 600 and Zircaloy-4, previously decontaminated with the Lomi or the NP/Lomi processes, recontaminate within a few months to their preceding activity levels (Bridle et al., 1986). Surfaces which had been decontaminated with the Lomi process alone experienced a faster recontamination than those treated with the NP/Lomi process. This difference may be explained by the fact that application of the NP/Lomi process results in a complete removal of the surface oxide layer, leaving behind a surface which shows less tendency to attract suspended corrosion product particles. 

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