Chernobyl Nuclear Power Plant

Radiation background in the Administrative building area is in average 65 microrentgens per hour, in the Shelter object's Observation pavilion area - 1,08 myllyrentgens per hour.
Controllable parameters of the Shelter object are within the limits established by Operational Regulations. According to monitoring systems data the maximal value of gamma - radiation rate inside the object has made 3403 Rontgens per hour, temperature near to Fuel Containing Materials is +29 degrees on Celsius. Exceeding of control levels of Shelter object condition parameters is not fixed.

	Home
	News
	Photos
	Download
	Links
	Contacts

Assumptions

Accident at Unit 4 Chernobyl NPP occurred on April, 26, 1986 in 01.23 minutes 40 sec. (Moscow time) during one of a safety systems design tests implementation. This safety system provided usage of staying turbogenerators rotation mechanical energy (so-called stopway) for electric power generation in conditions of two emergency situations superposition. One of them - full loss of NPP electro supply, including MCP and pumps of reactor emergency cooling system (RECS); another - maximal designed accident (MDA) in the design the big diameter pipeline of a reactor circulating contour break has been considered as a reason of which. It was stipulated by the design, that at external power supplies switching-off the electric power, generated by turbogenerators (TG) due to stopway, is supplied for the pumps starting, included in RECS that would provide secured reactor cooling. The proposal on TG stopway usage has been initiated in 1976 by NIKIET – Main Designer of RBMK reactor. This concept has been recognized and included in civil-engineering designs of NPPs with such type reactors.
However Unit 4 of ChNPP, as well as other power units with RBMK, has been accepted in operation without this mode approbation, though such tests should be a component of preoperational tests of the basic design modes of unit. Except for Chernobyl, at NPPs with RBMK- 1000 reactors after their commissioning, design tests on TG stopway use were not carried out. Such tests have been carried out at the Unit 3 of Chernobyl NPP in 1982. They have shown, that requirements on electric current characteristics, generated due to TG stopway, during set time were not observed and completion of TG excitation regulation system was necessary.

It was stipulated by tests programs for 1982-1984 to connect to stopwaied TG one of each of two reactor circulation loops, and by programs for 1985 and April, 1986 - two MCP. Thus emergency situation modelling was stipulated at switched - off by manual RECS valves. It was planed to carry out test at Unit 4 in the afternoon on April, 25 1986 at reactor’s thermal capacity 700 mwt, after that it was planed to stop reactor for scheduled repair works implementation. It should be noted, that the tests program corresponded to requirements effective at that time. Thus, tests should be carried out in a lowered capacity mode for which increased relatively to nominal coolant consumption through a reactor, insignificant coolants underheating up to boiling-point on an input in a core and minimal steam-content are characteristic. These factors have direct impact on accident scale.

Version of accident