The scope and contents of the procedures for maintenance of integral reactors, developed in OKBM meet the requirements of national regulatory documentation. Thereby the following peculiarities of the integral reactor are taken into account:

— presence of the guard vessel; .

— location of steam-generators (heat exchangers) in the reactor vessel.

A complex of special devices for scheduled servicing and, if necessary, for repair and reconditioning work which account for the peculiarities of integral reactor lay-out has been developed and tested in AST-500 reactor conditions.

As for inspection of metal and welded joints the following measures are provided in the design:

— periodic visual inspection with video recording of the part of the reactor vessel visible in the zones between heat exchangers with the help of a periscope and of the whole surface when the heat exchangers (SG) are removed;

— periodic eddy current and ultrasonic inspection of the welding and main metal of the reactor vessel in the core zone:

— periodic outside visual and ultrasonic inspction of the reactor vessel with the help of a rotational device and a universal self-propelled device;

— periodic radiographic inspection of the welds of nozzles and penetrations in the upper part of the reactor;

— periodic inspection of the main metal and welds of the reactor vessel using test sample;

— periodic visual inspection of the state of in-vessel devices on removal from the reactor.

The strength and leak-tightness of the structures is confirmed by:

— periodic hydraulic tests of the reactor and heat exchangers of the primary and secondary circuits (steam generators) ;

— periodic pneumatic tests of the guard vessel.

In RP power operation, constant control monitoring of the reactor and guard vessel leak-tightness is provided by measuring the GV environment parameters (pressure, activity, gas content), also acoustic-emission methods of inspection are used.

Constant monitoring of primary-secondary circuit heat exchanger (SG) leak — tightness at RP power operation is performed by measuring the activity and gas content of the secondary circuit medium.

In the event of heat exchanger (SG) loss of tightness the leaking section is looked for, the leaking part is plugged or (if necessary) the whole section is substituted with the help of special devices.

Analysis and discussion of the decisions made by operating staff experts have shown their acceptability during operation.

Arrangements for monitoring the AST-500 reactor vessel

When the problems of scheduled servicing and repair are considered, the problem of the cleating to operate the plant before the end of its lifetime should also be discussed.

One of the advantages of the integral reactor is that it is simple from the point of view of technology and radiation to remove it from operation. The presence of a thick water layer between the core and reactor provides low radiation levels from the structures. It allows performance of dismantling work in the reactor cavity using standard equipment without using special means of protection and unique mechanical arms, very soon after reactor shut down and core unloading. The main pan of the equipment is low radioactive or even not radioactive and may be dismantled in the same way as at industrial plants. The mass of in-reactor equipment with high radioactivity, which is dismantled by standard means is 2% of the mass of the reactor unit.

In conclusion it should be mentioned, that the results of OKBM work on the reactor plants NDHP, NCP, VPBER show, that an integral lay-out of the reactor gives additional, new possibilities for NPP increase of safety in comparison with loop-type plants. The difficulties of operational servicing, caused by compactness are overcome when highly reliable in-reactor equipment is used. .