RACA Journal June 2016 - Page 59

Getting Technical Continued from page 55 construction to final commissioning and synchronising into the power grid, have escalated far faster and risen much further than envisaged at the initial time of planning for expansion of the national grid. Base load nuclear stations generating 1 100MWe or more are no longer affordable for many developing and smaller countries. Recognising this change in the outlook for future new power stations, the major suppliers, planning in conjunction with the International Atomic Energy Agency (IAEA) and the World Nuclear Association (WNA) are now concentrating on developing and constructing much smaller compact nuclear power units. These smaller units generate less than 300 MWe, run on specially processed and shaped fuel components as shown in Figure 1 and are known as SMRs, or small modular reactors. According to recent IAEA and WNA reports there are currently approximately 50 SMRs under construction of various designs and power outputs ranging from 300 MWe down to less than 10 MWe. One of the leading designs is a Chinese constructed HTR-PM which stands for High Temperature Reactor-Pebble Bed Modules. It would seem, therefore, that China has continued developments of the original German pebble bed based designs since the South African PBMR project ended in 2010. SMRs are not low-cost, small versions of the established larger reactors. However, there are several projected cost advantages that go hand in hand with numerous probable and possible technical and safety improvements for the smaller SMRs. According to the IAEA, the simplicity of many of the SMR designs means that manufacturing can be carried out in specialist factories where quality control of the product can be more easily ensured prior to delivery to site by road or rail. Selection of suitable sites will also be easier since they will be far smaller including mandatory safety considerations such as minimum size emergency zones. Construction times of power stations using one or more pre-manufactured reactors will also be simpler requiring times from site selection to commissioning at half or even less than the five to 10 years which has been the case for adding nuclear base load stations and synchronising them into power grids. No doubt objectors to nuclear power will continue to demonstrate and demonstrations may even appear to be increasing although this will probably be attributable more to the growing number of SMRs being installed. One aspect of SMRs that objectors will not be able to demonstrate against is their green credentials which are on similar levels to other sustainable energy sources such as solar. In fact, nuclear is the currently the only green technology capable of continuous supply of grid level modular base load electrical power. For their physical size, SMR nuclear reactors produce prodigious amounts of heat at high temperatures of around 1 200°C which can be potentially applied in an unlimited range of industrial www.hvacronline.co.za Figure 3. Cross sectional depictions of two types of SMR designs under development. processes to replace inefficient electrical heating installations, which would have the added benefit of removing these electrical demands from grids. One particular large scale opportunity for SMR heating is desalination of water by distillation. Benefits from SMRs within the field of HVAC in the built environment will probably be mostly for heating as such. District heating has long been applied in Europe and other northern hemisphere countries which have considerably longer and colder winters than South Africa. SMRs look particularly suitable for district off-grid CHP units as they are not reliant on a continuous fuel supply compared to thermal units needing coal, gas or diesel at massively high running costs such as the back-up supply units around South Africa have recently demonstrated. Available heat may also favour absorption cooling as it has already done in trigeneration systems. Nuclear safety, as discussed earlier, has been vastly improved. The deliberate cooling shut-down test run on nuclear fuel particles dispersed in pebble form demonstrated that temperatures will not rise to levels where meltdowns can occur which automatically also precludes any possibilities of nuclear explosions. These improvements in safety are being increasingly recognised by anti-nuclear groups whose emphasis is now not so much concerned with technology but with assurances that proper safety measures will, in fact, be implemented and maintained. Dealing with the waste residues from nuclear fuels is a complex problem which is most likely to be solved in stages as relevant technologies and practical means continue to improve. For example, some of the components of stored nuclear fuel w aste are beginning to be re-used in experimental reactors. One proposed use of SMR heat which seems a bit like ‘chasing its own tail around’ is manufacturing hydrogen gas for supply to fuel cells to produce – electricity. However, this is simply an improvement on current fuelling which is mostly natural gas that fuel cells have to reform into hydrogen by a process which is costly and highly maintenance intensive. RACA RACA Journal I June 2016 57