CPR1000核电站严重事故重要缓解措施与严重事故序列

CPR1000核电站采用非能动氢气复合器、稳压器卸压功能延伸以及安全壳卸压过滤排放系统作为严重事故的预防和缓解措施,保证在严重事故条件下核电站安全壳的完整性不受损坏,保护环境周围的居民不受核辐射的危害。通过相关严重事故谱分析,选取冷却剂管道热段双段断裂+失去应急堆芯冷却系统、全厂断电、主蒸汽管道断裂+失去喷淋、失水未能紧急停堆的预计瞬态(ATWS)这4种严重事故作为CPR1000核电站的重要严重事故序列,包络了所有安全壳内氢气产生速度快浓度高、安全壳超压、冷却剂系统发生高压熔堆、反应堆不能停堆等最严重的事故。     

49-2泳池堆低温供热全厂断电ATWS事故分析

针对49-2泳池式反应堆(简称49-2泳池堆)用于城市低温供热的工况,选取典型的全厂断电叠加紧急停堆系统失效(全厂断电ATWS)的超设计基准事故,使用RELAP5/MOD3.2程序对其热工水力参数瞬态特性进行分析。结果显示,49-2泳池堆具有很好的负温度反馈效应,事故后,由于燃料和冷却剂温度升高,从而引入一定的负反应性,使反应堆处于次临界状态;同时堆芯通过与堆水池建立自然循环,将衰变热带出,最终依靠自然循环方式将堆芯余热排出至上部大气环境热阱,验证了49-2泳池堆用于城市低温供热的固有安全性。     

49-2泳池堆低温供热全厂断电ATWS事故分析

针对49-2泳池式反应堆（简称49-2泳池堆）用于城市低温供热的工况,选取典型的全厂断电叠加紧急停堆系统失效(全厂断电ATWS)的超设计基准事故,使用RELAP5/MOD3.2程序对其热工水力参数瞬态特性进行分析。结果显示,49-2泳池堆具有很好的负温度反馈效应,事故后,由于燃料和冷却剂温度升高,从而引入一定的负反应性,使反应堆处于次临界状态;同时堆芯通过与堆水池建立自然循环,将衰变热带出,最终依靠自然循环方式将堆芯余热排出至上部大气环境热阱,验证了49-2泳池堆用于城市低温供热的固有安全性。     

先进堆非能动余热排出系统应对全厂断电事故的能力分析

采用RELAP5/MOD程序对先进堆全厂断电事故进行分析计算,论证非能动余热排出系统对事故的缓解能力.分析表明,先进堆在发生全厂断电事故后,完全能够依靠非能动余热排出系统导出堆芯余热,保证反应堆的安全;先进堆非能动余热排出系统的设计总体上是成功的.     

固态熔盐堆全厂断电ATWS事故工况下的堆芯安全探讨

利用修改后的适用于固态熔盐堆的RELAP5/MOD4.0系统分析程序,对固态熔盐堆全厂断电ATWS(Anticipated Transient Without Scram)事故进行了分析。主回路系统进行了合理简化建模,模拟系统在全厂断电ATWS事故时非能动余热排出系统有效与否两种情况下的瞬态响应过程。分析结果表明:非能动余热排出系统在全厂断电ATWS事故初期作用不明显,但长期作用较明显,投入使用后最终将使堆芯温度和主冷却剂温度达到稳定;对于固态熔盐堆来说,即使非能动余热排出系统失效,燃料元件温度上升也很缓慢,给人员干预采取必要措施提供了超过20天的宽限时间。分析结果表明了固态熔盐堆在应对极端事件时具有高的安全性。     

CPR1000非能动应急给水系统瞬态特性分析

利用RELAP5/MOD3.4程序对CPR1000压水堆在全厂断电事故下一回路主要参数的瞬态热工水力特性进行分析，验证CPR1000非能动应急给水系统(PEFWS)对事故的缓解能力。计算结果表明，CPR1000在发生全厂断电事故后，PEFWS完全可及时向蒸汽发生器补水，同时导出堆芯余热，保证反应堆处于安全状态，从而验证CPR1000PEFWS的设计成功。     

ATWS事故工况下的应急初始条件和应急行动水平在核电厂的应用

本文描述了在未能紧急停堆的预期瞬变(ATWS)事故工况下应急初始条件及应急行动水平在PWR核电厂和CANDU核电厂的应用,并对这两种类型核电厂在ATWS事故工况下相同应急初始条件的应急行动水平的不同进行了比较.     

基于CFD的棱柱型模块式高温气冷堆典型事故研究

为验证和评估棱柱型模块式高温气冷堆设计的固有安全性,需针对代表性事故工况开展计算分析。目前针对棱柱型堆芯的模块式高温气冷堆尚缺少专用的事故分析程序。本研究基于通用CFD程序COMSOL针对堆芯活性区域和压力容器建立三维模型,包括燃料和冷却剂通道、石墨慢化剂、侧反射层以及压力容器;非能动余热排出系统采用对流边界条件简化模拟。采用C++编写点堆模块求解中子动力学,并通过动态链接库(DLL)与COMSOL实现耦合。首先计算了正常运行工况下的稳定状态;然后以该结果作为初始条件,选取3个典型事故瞬态工况开展了数值模拟,包括未失压丧失强迫流动冷却(PLOFC)事故、未失压丧失强迫流动冷却且未能停堆(PLOFC+ATWS)事故以及反应性引入且未能停堆(RIA+ATWS)事故;最后针对压力容器壁与非能动余热排出系统的辐射发射率开展了敏感性分析。计算结果表明：在本文分析的事故条件下,燃料最高温度均低于安全限值(1 620℃)且具有较大的裕量,因此均能保证堆芯燃料结构的完整性。对于PLOFC事故,提高非能动余热排出系统的换热能力能显著缓解事故后果,但对于ATWS类事故影响趋势则正好相反,需进一步开展综合分...     

一种非能动余热排出系统设计方案

非能动余热排出系统依靠本身的自然循环特性,应能够在较长时间内提供对堆芯的冷却,保证反应堆的安全。提出一种非能动空气冷却余热排出系统(PRHRS)方案,利用应急冷却水箱作为中间缓冲设备,既可以满足事故初期快速冷却的要求,又能保证非能动余热排出系统在相当长一段时间内的可靠运行。基于自然循环系统特性对所设计的PRHRS系统进行设计计算,并使用RELAP5程序对全厂断电事故下反应堆停堆后PRHRS投入运行的过程进行仿真,以验证设计的合理性。反应堆热工水力动态特性的结果表明,该系统可通过自然循环排出堆芯余热,保证堆芯安全。     

一体化先进堆全厂断电事故下非能动余热排出系统能力分析

中国核动力研究设计院（NPIC）设计的中国一体化先进堆（CIP）余热排出系统是非能动系统。采用RELAP5／MOD程序分析计算该堆全厂断电事故后堆芯核功率、堆芯平均温度、一回路和二回路压力,以及非能动余热排出系统功率随时间的变化,论证了非能动余热排出系统对事故的缓解能力。分析结果表明,CIP在发生全厂断电事故后,完全能够依靠非能动余热排出系统导出堆芯余热,保证反应堆的安全。     

核电站非能动辅助给水系统仿真研究

以先进核电站AP1000为研究对象,在其蒸汽发生器二次侧设计了1套耗汽驱动汽动辅助给水泵的非能动辅助给水系统。使用RELAP5程序计算分析全厂断电事故下设计系统的运行特性,研究其应对事故工况的能力。计算结果表明：全厂断电事故下,设计的非能动辅助给水系统可有效地排出堆芯余热,保证反应堆的安全;由于冷却剂体积收缩,170 min时稳压器排空;该系统可连续运行200 min,排出事故后的大部分堆芯余热。非能动辅助给水系统可作为全厂断电事故后的应急缓解方案。     

Modelica仿真技术在气冷式微型反应堆中的应用

相比传统大型核电厂,微型反应堆各系统功能间紧密耦合且相互制约,传统的分专业解耦设计模式难以应对,需开展全范围的系统仿真。采用Modelica语言建立了气冷式微型反应堆的系统仿真模型,以未能紧急停堆的预期瞬态（ATWS）事故为例开展事故分析计算,并与专业堆芯安全分析结果对比,结果表明反应堆功率变化趋势较为一致,且ATWS事故后仅依靠堆芯温度升高引入的负反应性可实现停堆。本文研究方法为气冷式微型反应堆的全系统建模仿真打下了坚实基础,也为其他类型反应堆的系统建模仿真提供了很好的借鉴作用。      

全厂断电引发的严重事故下蒸汽发生器传热管蠕变失效风险研究

全厂断电引发的严重事故若处置不当,可能发展为长期、高压的严重事故进程,此时堆芯冷却系统中的自然循环在导出部分堆芯余热的同时,也增加了蒸汽发生器（SG）传热管、稳压器波动管以及热管段出现蠕变失效的风险。本文基于两环路设计的秦山二期核电厂设计特点,结合蠕变失效风险模型,对全厂断电引发的严重事故后未能执行“严重事故管理导则中向蒸汽发生器注水（SAG-1）”时SG传热管的蠕变失效风险进行了研究,从而为全厂断电引发的严重事故的负面影响提供量化结果,为技术支持中心（TSC）最终决策提供参考依据。分析结果表明,全厂断电引发的严重事故后16 361 s可能出现蠕变失效;自事故后16 610 s,SG传热管出现蠕变失效的可能性均远低于稳压器波动管与热管段,秦山二期核电厂全厂断电引发的严重事故下因SG传热管蠕变失效而导致安全壳旁通的风险很小。     

Study on severe accident mitigation measures for the development of PWR SAMG

In the development of the Severe Accident Management Guidelines （SAMG）, it is very important to choose the main severe accident sequences and verify their mitigation measures. In this article, Loss-of-Coolant Accident （LOCA）, Steam Generator Tube Rupture （SGTR）, Station Blackout （SBO）, and Anticipated Transients without Scram （ATWS） in PWR with 300 MWe are selected as the main severe accident sequences. The core damage progressions induced by the above-mentioned sequences are analyzed using SCDAP/RELAP5. To arrest the core damage progression and mitigate the consequences of severe accidents, the measures for the severe accident management （SAM） such as feed and bleed, and depressurizations are verified using the calculation. The results suggest that implementing feed and bleed and depressurization could be an effective way to arrest the severe accident sequences in PWR.     

全厂断电事故工况下小型铅铋快堆余热排出能力评价

小型铅铋快堆的非能动余热排出系统（PRHRS）主要是为应对全厂断电（SBO）事故,但目前并不确定该PRHRS能否有效带走堆芯衰变热以保证堆芯安全,因此开展了数值分析研究评价PRHRS的余热排出能力。本文使用RELAP5 4.0程序开展了小型铅铋快堆SBO事故热工水力分析,首先进行稳态计算,之后将稳态结果作为初值进行瞬态计算。研究结果表明：在整个SBO事故中,包壳峰值温度最高为820 K,主容器与保护容器壁面最高温度分别为792 K和769 K,均未超过安全限值,表明此PRHRS可有效应对小型铅铋快堆SBO事故。本文研究可为小型铅铋快堆PRHRS的工程设计奠定技术基础。     

Thermal hydraulic characteristics analysis of direct residual heat removal system for China pressurized reactor

An innovative Direct Residual Heat Removal System (DRHRS) is proposed for Pressurized Water Reactor (PWR) in this paper. The new designed parallel DRHRS is different from traditional Passive Residual Heat Removal System (PRHRS), which is connected to steam generation. The thermal hydraulic transient analysis of the new designed DRHRS for CPR1000 has been carried out using the widely accepted safety analysis software RELAP5. The new designed DRHRS is directly connected to the primary loop, which consists of three independent parallel loops, three intermediate cooling circuits and an air loop. The transient behaviors of passive safety system are studied, and design parameter sensitivity analysis is carried out. Results show that during Station Black_Out (SBO) accident, natural circulations are established stably in passive safety system so that core decay is continuously removed from primary loop. And the new designed DRHRS has the capability of removing residual heat to the atmosphere without any external energy input at different surrounding environmental temperature. In emergency, the DRHRS directly remove core decay heat from reactor outlet, and efficiency of residual heat removal is improved. Moreover, reactor power plant maintains safe even if double-ended rupture of a single tube during SBO accident occurs. Thus, the designed DRHRS has great significance for increasing the degree of inherent safety features of CPR1000.     

Safety analysis of LBLOCA in BDBA scenarios for the Bushehr's VVER-1000 nuclear power plant

This paper presents the results of thermal-hydraulic calculations of a large break loss of coolant accident (LBLOCA) analysis for a VVER-1000/V446 unit at Bushehr nuclear power plant (BNPP). LBLOCA is analysis in two different beyond design basis accident (BDBA) scenarios using the RELAP5/MOD3.2 best estimate code. The scenarios are LBLOCA with station blackout (SBO) and LBLOCA with pump re-circulation blockage which have been evaluated in the final safety analysis report (FSAR) of BNPP. A model of VVER-1000 reactor based on Unit 1 of BNPP has been developed for the RELAP5/MOD3.2 thermal-hydraulics code consists of 4-loop primary and secondary systems with all their relevant sub-systems important to safety analysis. The analysis is performed without regard for operator's actions on accident management. The safety analysis is carried out and the results are checked against the acceptance criteria which are the possibility of using water inventory in the emergency core cooling system (ECCS) accumulators and the KWU tanks for core cooling and the available time to operators before the maximum design limit of fuel rod cladding damage is reached. These kinds of analyses are performed to provide the response of monitored plant parameters to identify symptoms available to the operators, timing of the loss of critical safety functions and timing of operator actions to avoid the loss of critical safety functions of core damage. The results of performed analyses show that the operators have 2.9 and 3.1 h for LBLOCA with SBO and LBLOCA with pump re-circulation blockage scenarios, respectively, before the fuel rod cladding rupture. The results are also compared with the BNPP FSAR data.     

Simulation of the small modular reactor severe accident scenario response to SBO using MELCOR code

Advanced small modular reactors (SMRs) use different design in the systems, structures, components from large reactors for achieving a high level of safety and reliability. In present work, the SMRs severe accident caused by the station blackout (SBO) was modeled and analyzed using MELCOR code, and the simulation of the accident scenario response to SBO was conducted. Based on the steady state calculation, which agrees well with designed values, we introduced the SBO accident for transient calculation. First, the case of the SBO accident without the passive core cooling system (PXS) was calculated. The progression and scenario in the reactor pressure vessel (RPV) and the containment were simulated and analyzed, including the transient response, cooling capacity and thermal-hydraulic characteristics and so on. The station black-out transient in the SMR can be simulated accurately, and the main failure model in the accident process can be concluded. Then three other cases of the SBO accident with different passive safety systems (core makeup tank (CMT), accumulator (ACC), passive residual heat removal system heat exchanger (PRHR HX), automatic depressurization system (ADS)) of the PXS were calculated respectively, and the results for different passive safety systems were compared. The passive core cooling system can not only provide water to the primary coolant system, but also take away the reactor decay residual heat. So in a station black-out transient, we can get more time for restoring AC power, and effectively prevent the accidents such as Fukushima.     

A study on the minimum steam cooling pressure of EOP for BWR power plants

The minimum steam cooling pressure (MSCP) is an important parameter for safe operation of boiling water reactor (BWR)-type nuclear power plant for the anticipated transient without scram (ATWS) scenario with reactor pressure vessel (RPV) water level unknown. Under such situation, the operator is requested to open the safety/relief valves (SRVs) and control the RPV pressure slightly above the MSCP so that adequate core cooling can be maintained. It is derived based on steam cooling strategy.The MSCP, defined to be the lowest RPV pressure at which the covered portion of the core, is capable of generating sufficient steam to preclude peak cladding temperature (PCT) in the uncovered portion of the core from exceeding 1088 K (1500 °F). It is calculated by two parameters - (1) the minimum bundle steam flow (Wg-1500) to maintain PCT < 1088 K (1500 °F) and (2) the number of SRVs available for opening.For current emergency operating procedure (EOP), only one set of MSCP derived based on one value of Wg-1500 for the ATWS condition. Furthermore, it is derived based on decay power of 2.2% rated power. Thus, the current MSCP used for the ATWS accident scenarios was deemed inadequate. The purpose of this paper (work) is to study the MSCP used in the ATWS conditions. For case of ATWS of 13% full power, controlling RPV pressure at MSCP of current approach ends up with core melt. The Wg-1500 is suggested to be replaced by the steam generation rate at minimum steam cooling RPV water level (MSCRWL), which is a function of power level. Simulation result indicates controlling RPV pressure at MSCP is equivalent to controlling the RPV water level at MSCRWL. The revised MSCP is dependent on the ATWS power level.