Today, on February 22, 2013, the First Deputy Chairman of the State Nuclear Regulation Inspectorate of Ukraine (SNRIU), the Principal State Supervisor for Nuclear and Radiation Safety of Ukraine, Mikhail Gashev visited Chernobyl NPP.

The objective of the visit was to hold meeting on issues regarding investigation of the event occurred on February 12, 2013, in ChNPP Unit 4 Turbine Hall and development of the corrective measures; progress on construction of new ventilation stack (NVS), as well as issues on management of damaged spent nuclear fuel (DSNF).

A specific attention was paid to investigation of the event occurred on February 12, 2013. The First Deputy Chairman of SNRIU, the Principal State Supervisor for Nuclear and Radiation Safety of Ukraine, inspected the site of occurrence, visited workplaces of operating personnel, where he got familiar with the records of the operating logs (including those of February 12, 2013). He was also demonstrated with operation of radiation and seismic monitoring subsystems of the Integrated Automated Shelter Monitoring System, including data of February 12.

Mikhail Gashev visited Unit 2 Central Hall (CH-2), where he became familiar with progress on ChNPP Unit release from spent nuclear fuel (SNF), including damaged one.

Following the visit, there was held a meeting with participation of SSE ChNPP managers, during which the First Deputy Chairman of SNRIU, the Principal State Supervisor for Nuclear and Radiation Safety of Ukraine, was reported on investigation progress regarding partial collapse of a part of roof and walls of Unit 4 Turbine Hall, being held by ChNPP commissions, and he was provided with action plan on mitigating roof breakdown and potential hazards for available structures and personnel.

Pursuant to the findings of the Commissions, which were investigating the occurrence causes, this incident “did not create the hazard to health and life, did not create the hazard to the environment, did not result in stoppage of production work and is not considered as an accident”.

The Commissions consider that the possible cause of the collapse of Turbine Hall roof fragment and eight wall panels became the collapse of a truss due to combination of negative factors, namely: lack of data on actual damages of the truss and roof decking during the accident of 1986, as well as because of the fact that structures of the additional roof are rested upon the deaerator stack’s columns, which undergone the heavy destructions during the 1986 accident.

Some other negative factors are also given in the findings. At that the experts emphasize that the snow load on the Turbine Hall roof as of the date of the collapse did not exceed the values established by the ChNPP design and operational documentation. “The main cause that made it impossible to prevent the collapse of the specified structures was absence of the possibility to carry out visual inspection of technical state of the structures due to the absence of safe accesses and very hazardous radiation situation” – emphasized in the Commissions’ findings.

In general the experts draw a conclusion on relative stability of the bearing structures adjacent to the collapsed one, and the possibility of their further use provided that the roof is reconstructed.

It is recommended to carry out a survey of Unit 4 Turbine Hall structures involving specialized organizations with the purpose to obtain reliable data on technical state of the structures similar to the collapsed one with the subsequent implementation of technical solutions on reduction of the probability of the collapse of the Turbine Hall bearing structures.

The experts also recommend dismantling the collapsed wall panels in two stages with the purpose to exclude overload of the structures, and reconstructing the collapsed roof section with the purpose to close the containment facility ambit, exclude spread of radioactive substances into the environment and prevent penetration of atmospheric precipitations into the Turbine Hall premises.

Currently, the works on removing debris originated due to collapse of a part of wall structure and roof of ChNPP Unit 4 Turbine Hall come to an end. The works are performed by SSE ChNPP personnel efforts.
As the works supervisor Aleksandr Khimach, Deputy Head of the Shelter (New Safe Confinement) Operation Shop, said, the ChNPP specialists developed an individual work program to remove fragments of building structures. On February 19, the large fragments were removed. Gathering and removal of the small parts is now being completed.

Today, February 22, 2013, Joint Venture "Novaraka" restarted work in the Shelter object local zone to prepare the site for construction of New Safe Confinement technological building (NSC).
Works on installation of NSC arch metal constructions and cladding in free access area were restarted earlier, on February 20.
Thus, construction of New Safe Confinement, suspended by JV "Novarka" after an abnormal event at Unit 4 Turbine Hall is underway in full.