World Association of Nuclear Operators 
Moscow Centre
WANO – MC
25 Ferganskaya st, Moscow, 109507, Russia
Phone. +7 495 376 15 87
Fax: +7 495 376 08 97
info@wanomc.ru	
REQUEST
to provide technical and organizational information
via WANO

1.	NPP/Organization: Tianwan NPP	
2.	Information request topic: 
During the shutdown cooling process of VVER unit, the steam side isolation of steam generator was triggered because the saturation temperature difference between primary and secondary circuits was greater than 75 ℃.	
3.	Information request objective: 
During the shutdown cooling process of VVER unit, the problem that the regulating performance of the normal spray control valve of the pressurizer decreased triggered the saturation temperature difference between the primary and secondary circuits to be greater than 75 ℃, which led to the steam side isolation of the steam generator.	
4.	Problem description: 
During the shutdown cooling process of VVER unit, the average temperature of the primary circuit was about 146 ℃, and the pressure fluctuation of the primary circuit was caused by the decline of the regulation performance of the normal spray control valve of the pressurizer, which triggered the saturation temperature difference between the primary circuit and the secondary circuit to be greater than 75 ℃, and finally led to the steam side isolation of the steam generator.	
5.	Specific questions: 
1. Is there any similar case happened in your station? If yes, could you please offer us a short report of the event?
2. The root cause of the decline of the regulating performance of the regulating valve and the corresponding corrective measures.
3. Contributing factors and specific improvement measures.	
6.	Organizations proposed for distribution of this request: 
All VVER plants	
7.	Department – request initiator: 
Nuclear safety department	
8.	Contact details of the requester: 
 Mr. Sun Fengping  email: sunfp@cnnp.com.cn	
9.	Request date: 16/03/2021