先进非能动核电厂DEDVI事故热工水力模拟分析

采用Relap5/Mod3.4程序建立了先进非能动核电厂的事故分析模型,包括反应堆冷却剂系统(RCS)、简化的二回路系统和专设安全设施。针对小破口失水事故(SBL,OCA)中的直接安注管双端断裂事故(DEDVI)进行分析,并着重对SBLOCA现象识别和排序表(PIRT)中对其影响较大的液滴夹带进行敏感性分析。分析结果表明,对直接安注管双端断裂事故,破口和自动卸压系统(ADS)能够有效地使反应堆冷却剂系统降压,堆芯补水箱(CMT)、安注箱(ACC)和安全壳内置换料水箱(IRWST)能够迅速实现堆芯补水,确保堆芯冷却。对液滴夹带的敏感性分析表明,对于位置较高的第4级ADS,喷放流量对液滴夹带模型比较敏感,使用均相流模型计算时,其液相流量显著高于非均相流模型。     

AP1000核电厂直接注射管线双端断裂小破口失水事故计算

基于压水堆最佳估算程序RELAP5/MOD3.3,对AP1000核电厂冷却剂系统和非能动堆芯冷却系统进行建模分析,得到在直接注入管线发生双端断裂事故下,系统压力、破口流量、系统水装量等关键参数的瞬态变化,计算结果与西屋公司采用NOTRUMP程序的计算结果基本一致。分析表明:AP1000的非能动专设安全设施能有效对一回路进行冷却和降压,防止堆芯过热,验证了AP1000发生DVI双端断裂事故后的安全性。     

波动管小破口失水事故实验研究

在模块化小型反应堆非能动安全系统综合模拟实验装置上进行波动管小破口尺寸失水事故实验,研究波动管小破口失水事故过程中的热工水力现象和非能动安全系统运行特性。模块化小型反应堆发生失水事故后,压力平衡管和安注管线内流体的密度差可以驱动堆芯补水箱(CMT)内的冷流体注入反应堆压力容器,压力平衡管裸露后CMT安注流量出现波动;安注箱(ACC)的安注对事故初期的堆芯冷却效果显著;经自动卸压系统卸压后,内置换料水箱(IRWST)可以对堆芯进行持续稳定的安注和冷却。研究结果表明:波动管小破口失水事故中,非能动安注系统可以对堆芯进行有效注水,并带走堆芯衰变热量。     

ACME台架PRHR管线破口位置敏感性试验研究

为研究先进非能动（AP）型核电厂在非能动系统失效条件下的安全性能,利用我国先进堆芯冷却机理整体试验台架（ACME）开展了非能动余热排出（PRHR）管线破口失水试验研究,分析了主要的试验进程和破口位置对事故过程各阶段关键参数的影响。结果表明,ACME PRHR管线破口试验进程与冷管段小破口失水事故（SBLOCA）进程基本一致,再现了非能动核电厂自然循环阶段、自动卸压系统（ADS）喷放阶段和安全壳内置换料水箱（IRWST）安注阶段的安全特性;在不同破口位置的试验中,非能动堆芯冷却系统（PXS）均可保证堆芯得到补水,堆芯活性区始终处于混合液位以下;破口位置对ACME LOCA事故进程、反应堆冷却剂系统（RCS）初期降压速率、PRHR热交换器（HX）流量、喷放流量、堆芯液位、IRWST安注流量等参数具有显著影响,对堆芯补水箱（CMT）和蓄压安注箱（ACC）安注流量的影响较小。      

DVI管小破口失水事故实验研究

在模块化小型反应堆非能动安全系统综合模拟实验装置上进行了压力容器直接注入（DVI）管小破口失水事故实验,研究了DVI管小破口失水事故过程中的热工水力现象和非能动安全系统运行特性。研究结果表明：模块化小型反应堆DVI管小破口失水事故中,非能动安全系统可对堆芯进行注水,有效导出堆芯衰变热量,保护堆芯安全。     

DVI安注技术在三环路压水堆的应用研究

本文针对某三环路压水堆核电厂提出采用压力容器直接注入（DVI）技术的安注系统简化设计方案。采用RELAP5/SCDAP-SIM和CATHARE-GB程序分别分析了对安注系统功能执行要求最高的DVI管道断裂事故及反应堆冷却剂冷管段双端剪切断裂事故，研究该简化设计方案的可行性和有效性。分析结果表明，在DVI管道发生断裂的事故工况下，安注系统有足够的冗余性保证燃料温度不会明显上升。在RCS主管道发生大破口包括双端剪切断裂事故工况下，通过DVI注入可明显延长安注箱注入时间、提高安注箱水装量的有效利用率，仅利用中压安注泵和安注箱即可完成安注功能的执行，不再需要低压安注子系统。DVI技术的应用大大简化了安注系统设计，电厂的安全性和经济性得到共同提升。     

非能动堆芯冷却系统LOCA下冷却能力分析

本文基于机理性分析程序建立了包括反应堆一回路冷却剂系统、专设安全设施及相关二次侧管道系统的先进压水堆分析模型,对典型的小破口失水事故和大破口失水事故开展了全面分析。针对不同破口尺寸、破口位置的失水事故,分析了非能动堆芯冷却系统（PXS）中非能动余热排出系统（PRHRS）、堆芯补水箱（CMT）、安注箱（ACC）、自动卸压系统（ADS）和安全壳内置换料水箱（IRWST）等关键系统的堆芯注水能力和冷却效果。研究表明,虽然破口尺寸、破口位置会影响事故进程发展,但所有事故过程中燃料包壳表面峰值温度不超过1 477 K,且反应堆堆芯处于有效淹没状态。PXS能有效排出堆芯衰变热,将反应堆引导到安全停堆状态,防止事故向严重事故发展。     

基于DVI管失水事故试验的CATHARE程序模拟评价

采用CATHARE程序对直接注入(DVI)管失水事故(LOCA)试验进行了数值模拟。研究发现:DVI管LOCA中系统卸压、非能动安注、堆芯冷却等主要过程和物理现象得到了较好的模拟。一回路系统压力、堆芯补水箱(CMT)安注流量、安注箱(ACC)安注流量、内置换料水箱(IRWST)安注流量以及堆芯流体温度等参数的计算结果和试验数据符合较好。研究结果表明,CATHARE程序可以用于失水事故下非能动安注系统瞬态特性模拟分析。     

PRHRS隔离阀前后破口事故对非能动堆芯冷却系统的影响分析

对于AP型核电站小破口失水事故(SBLOCA)试验进程，国内外有较为一致的认识，但对于相同尺寸破口在不同破口位置对试验进程、非能动堆芯冷却系统的影响仍需进一步研究。本文利用大型非能动堆芯冷却整体试验台架ACME开展了非能动余热排出系统（PRHRS）隔离阀前后破口事故试验工况研究，并以堆芯补水箱（CMT）侧冷管底部破口事故工况作为对比工况。试验结果表明：ACME开展的PRHRS隔离阀前后破口事故模拟工况事故进程符合典型SBLOCA进程，堆芯始终处在良好的冷却状态，非能动堆芯冷却系统的安全性得到有效验证；相同破口尺寸工况下，不同破口位置对事故进程有一定的影响，其中破口位置对CMT液位、安注流量的影响较为关键。对比工况中，PRHRS设备换热量也有较大不同，冷管破口和隔离阀后破口工况较隔离阀前破口工况换热量更大，但PRHRS换热管内部流动换热机理需进一步研究。     

小型堆破口失水事故初步研究

为验证中国广核集团小型堆方案设计,尤其是其中非能动安全注入系统的初步设计,基于RELAP/SCDAPSIM程序,建立了小型堆的一、二回路系统和非能动安全注入系统模型,模拟计算了冷管段0.04 m等效直径破口、冷管段0.2 m等效直径破口、直接注入管道双端断裂、自动卸压系统误启动等LOCA工况。计算结果表明,一回路可实现有效的冷却和降压,堆芯不会过热,验证了其非能动安全注入系统的设计合理性和反应堆系统的安全性。     

A numerical investigation of SBLOCA scenario in nuclear heating reactor

Small break loss of coolant accident (SBLOCA) is one of the most important severe accidents in nuclear heating reactor. Nuclear heating reactor designed by Tsinghua University, whose primary loop is integrated layout and designed without main pump. The initial water volume in the reactor vessel is important to determine whether the reactor will be cooled or not as no safety injection system is designed for coolant makeup during the whole scenario. This paper simulates SBLOCA in nuclear heating reactor based on RELAP5. Transient behavior of relevant thermal parameters is specifically analyzed. Moreover, investigation also has been made on SBLOCA scenario based on different residual heat removal correlations and found the long-term residual heat removal capacity is decisive in determining the loss of coolant. The mathematical form of residual heat removal correlation is specifically deducted and can be widely applied to different situations. The envelope line that differentiates the region whether the core is safe or not under different maximum PRHRS capacity is also given.     

Detailed evaluation of coolant injection into the reactor vessel with RCS depressurization for high pressure sequences

A coolant injection into the reactor vessel with depressurization of the reactor coolant system (RCS) has been evaluated as part of the evaluation for a strategy of the severe accident management guidance (SAMG). Two high pressure sequences of a small break loss of coolant accident (LOCA) without safety injection (SI) and a total loss of feedwater (LOFW) accident in Optimized Power Reactor (OPR)1000 have been analyzed by using the SCDAP/RELAP5 computer code. The SCDAP/RELAP5 results have shown that only one train operation of a high pressure safety injection at 30,000 s with indirect RCS depressurization by using one condenser dump valve (CDV) at 6  min after implementation of the SAMG prevents reactor vessel failure for the small break LOCA without SI. In this case, only one train operation of the low pressure safety injection (LPSI) without the high pressure safety injection (HPSI) does not prevent reactor vessel failure. Only one train operation of the HPSI at 20,208 s with direct RCS depressurization by using two SDS valves at 40 min after an initial opening of the safety relief valve (SRV) prevents reactor vessel failure for the total LOFW.     

Evaluation of the RCS depressurization strategy for the high pressure sequences by using SCDAP/RELAP5

As part of the evaluation for a severe accident management strategy, a reactor coolant system (RCS) depressurization in optimized power reactor (OPR)1000 has been evaluated by using the SCDAP/RELAP5 computer code. An indirect RCS depressurization by a secondary depressurization by using a feed and bleed operation has been estimated for a small break loss of coolant accident (LOCA) without a safety injection (SI). Also, a direct RCS depressurization by using the safety depressurization system (SDS) has been estimated for the total loss of feed water (LOFW). The SCDAP/RELAP5 results have shown that the secondary feed and bleed operation can depressurize the RCS, but it cannot depressurize the RCS sufficiently enough. For this reason, a greater direct RCS depressurization by using the SDS is necessary for the 1.35 in. break LOCA without SI. A proper RCS depressurization time and capacity leads to a delay in the reactor vessel failure time from 7.5 to 10.7 h. An opening of two SDS valves can depressurize the RCS sufficiently enough and the proper RCS depressurization time and capacity leads to a delay in the reactor vessel failure time of approximately 5 h for the total LOFW. An opening of one SDS valve cannot depressurize the RCS sufficiently enough.     

大型非能动压水堆核电厂安全注射系统旋启式止回阀阻力变化对长期堆芯冷却影响分析

大型非能动压水堆核电厂在发生失水事故(LOCA)后的长期堆芯冷却阶段依靠重力向堆芯注入应急冷却水,其注射管线上设置的旋启式止回阀的阻力可随流量变化,管线的阻力可能将非预期地增加。根据旋启式止回阀阻力特性,为失水事故最佳估算系统分析程序添加相应的计算功能,对压力容器直接注射(DVI)管线双端断裂事故后长期堆芯冷却工况进行了计算分析。结果表明:安全注射管线上旋启式止回阀阻力变化对大型非能动压水堆核电厂LOCA后长期冷却的影响较小;在安全裕量不足的情况下,旋启式止回阀的阻力特性将影响到非能动注射管线的安全注射功能的执行。     

Detailed Evaluation of RCS Boundary Rupture during High-Pressure Severe Accident Sequences

A depressurization possibility of the reactor coolant system (RCS) before a reactor vessel rupture during a high-pressure severe accident sequence has been evaluated for the consideration of direct containment heating (DCH) and containment bypass. A total loss of feed water (TLOFW) and a station blackout (SBO) of the advanced power reactor 1400 (APR1400) has been evaluated from an initiating event to a creep rupture of the RCS boundary by using the SCDAP/RELAP5 computer code. In addition, intentional depressurization of the RCS using power-operated safety relief valves (POSRVs) has been evaluated. The SCDAPRELAP5 results have shown that the pressurizer surge line broke before the reactor vessel rupture failure, but a containment bypass did not occur because steam generator U tubes did not break. The intentional depressurization of the RCS using POSRV was effective for the DCH prevention at a reactor vessel rupture.     

模块式小堆超压风险及设计优化研究

模块式小堆采用带直流蒸汽发生器（OTSG）的一体化堆芯设计。OTSG具有传热面积大、设备体积小、蒸汽品质高的优点,然而因其二次侧水装量小、热惯性差,当反应堆发生二次侧排热减少时,反应堆冷却剂系统（RCS）可能存在超压风险。紧凑的一体化布置使得堆芯应对冷却剂受热膨胀的能力减弱,进一步增大RCS超压风险。本文采用RELAP5程序对模块式小堆的超压风险进行了研究。研究结果表明,模块式小堆在二次侧排热减少事故中会出现RCS超压现象,其中汽轮机事故停机导致的超压后果最为严重。波动管的流通面积对于RCS压力有着显著影响,合理地设计波动管流通面积可缓解RCS超压。