Use of neutron-absorbers to improve CANDU reactor operating margins

将可燃毒物应用于现有的CANDU天然铀（NU）燃料设计是一种新方法，目前由CANDU业主集团（COG）资助。 由于NU燃料的低过量反应性，中子吸收剂的量预计将被限制在少量。 这意味着对中子经济性的影响相对较小，但燃料性能将得到显著改善。 选择了少量和适当混合的中子吸收剂（在标称重量为24 kg的CANDU燃料棒束中约500 mg吸收剂）。 初步结果表明，初始reactivitypeak的燃料瞬态可以降低足够长的时间，以提高反应堆的运行裕度。 2012年6月在萨斯卡通举行的不扩散研究中心会议上介绍了这一结果。 对CANDU NU燃料棒束进行重新设计，适当地组合一些元件，包括中子吸收剂，可以很好地解决无氙效应的问题，同时降低此后不久出现的钚峰值。 拟议的NSERC项目是为了进一步利用这种概念设计。 使用含有中子吸收剂的燃料棒束提供了一个机会，将大约1%到2%的功率重新分配到较低功率的通道，即整个堆芯的功率重新分配。 推荐的燃料设计之一是将中子吸收体定位在束的端部，如端芯块或端盘。 因此，本建议的第二部分是使用建议的设计来减轻换料期间的末端通量峰值，并使其增量效益符合安全裕度（如果有的话）。 燃料的安全性和性能一直是核电站的重要课题。 如果这个项目是成功的，提高燃料利用率的好处（通过进一步优化加油策略）和安全裕度（通过降低最大通道和束功率）可以实现一个合理的简单的变化。

The proposed application of burnable poisons to existing CANDU Natural Uranium (NU) fuel design is a novel approach and is currentlyfunded under the CANDU Owners Group (COG). Because of low excess reactivityfor NU fuel, the amount of neutron-absorber is expected to be restricted to small quantities. This implies the impact on neutron economywould be relativelyminimal, but the fuel performance would be significantlyimproved. Small amounts and appropriate mixtures of neutron absorbers were selected (approximately500 mg of absorbers in a CANDU fuel bundle having a nominal weight of 24 kg). Preliminary results indicate that the fuelling transient for the initial reactivitypeak can be lowered long enough to improve the reactor's operating margins. This result was presented at the CNS Conference in Saskatoon in June 2012. A redesign of the CANDU NU fuel bundle with an appropriate combination of elements, with some including neutron-absorbers, could well address the issue of the xenon-free effects while lowering the plutonium-peak that occurs shortlythereafter. The proposed NSERC project is to further exploit the use of this conceptual design. The use of fuel bundles containing neutron absorbers offers an opportunityto redistribute approximately1 to 2 % power to lower powered channels i.e. power redistribution across the core. One of the recommended fuel designs is to locate neutron-absorbers at bundle ends, as end pellets or end discs. Hence thesecond part of this proposal is use the proposed design to mitigate end-flux peaking during refueling and to qualify(if any) its incremental benefit to safetymargins. Fuel safety and performance are always important topics to a nuclear utility. If this project is successful, benefits of improving fuel utilization (byfurther optimizing the fuelling strategy) and safetymargins (by lowering the maximum channel and bundle powers) could be realized for a reasonable simple change.