Hiroaki Sawahata

Improvement of neutron startup source handling work by developing new transportation container for high-temperature engineering test reactor (HTTR)

ABSTRACT The high-temperature engineering test reactor (HTTR) has three neutron startup sources (NSs) in the reactor core, each of which consists of 252Cf with 3.7 GBq, installed in NS holder and subsequently in a control rod guide block (CR block). The NSs are exchanged at the interval of approximately seven years. The NS holders are transported from the dealers hot cell to the HTTR using a transportation container. The loading work of NS holders to the CR blocks is subsequently carried out in the fuel handling machine maintenance pit of HTTR. Technical issues, which are the reduction and prevention of radiation exposure of workers and the exclusion of falling of NS holder, were extracted from the experiences in the past two exchange works of NSs to develop a safety handling procedure. Then, a new transportation container special to the NSs of HTTR was developed to solve the technical issues while keeping the cost as low as that for overhaul of conventional container. As a result, the NS handling work using the new transportation container was safely accomplished by developing the new transportation container which can reduce the risks of radiation exposure dose of workers and exclude the falling of NS holder.

Development of the maintenance technologies for the future high-temperature gas cooled reactor (HTGR) using operating experiences acquired in high-temperature engineering test reactor (HTTR)

This paper describes the lessons learned of the maintenance technologies, which have been and will be developed by using the high-temperature engineering test reactor (HTTR), which should be expected to apply to the future high-temperature gas cooled reactors (HTGRs). For example, the periodical maintenance for the future HTGRs is planned to carry out in each two years. The duration of periodical maintenance is planned about 60 days to satisfy the availability of operation up to 90%, in which decay heat removal, refueling and maintenances of equipment and components are carried out. As the key issue is to make a practical application of the technologies to the future HTGRs, shortening the duration of the periodical maintenance is expected to be important by excluding the maintenance related to the reactor equipment from the critical path by shifting the time-based maintenance, which is defined to be carried out in certain time interval, to the condition-based maintenance, which is defined to be carried out when a parameter exceeds its criteria, by using the experience and data acquired in HTTR, which is expected to make the maintenance interval significantly longer than that of the time-based maintenance as the operation experiences are accumulated. The maintenance technologies for the reactor system, which have been developed by using HTTR, are categorized as the following. (1) Establishment of the maintenance technologies specific to the HTGRs. (2) Development of the maintenance technologies for the future HTGRs. (3) Efficient maintenance works for the general equipment.