Shielding Facility

As a result of the above decision, the MTR biological shield now contains a 6- by 6-ft hole which will be filled, for the present, with,closely packed barytes blocks. However, in the hope that eventually this facility may be used for a thermal column or other experiments, the following steps have been taken to permit removal of the concrete blocks without danger of.overexposure to radiation  

The 6- by 6 ft hole will have a well-anchored steel liner. During construction this liner will be provided with tapped holes so that at some future time lead plates can be fastened to it as each layer of concrete blocks is removed. 

The inner end of the hole is covered by a quickly removable boral sheet. 

Means are provided for raising a. 2-in. lead door up between the thermal shield plates to cover the- hole. 

The preliminary design of the shielding facility as planned in November, 1949 is fully described in ORNL CF-49 12 30.  

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Another medical use of radioisotopes, such Co, is to irradiate certain tissues within the body. An intense source of Co in a heavily shielded facility provides a highly coUimated beam of y-rays that impinge on a tumor in order to kill its cells. 

Experimental Methods of Investigation. All of the aclinide elements are radioactive and, except for thorium and uranium, special equipment and shielded facilities are usually necessary for their manipulation. 

The contamination due to 232U in the recovered 233U product leads to intense gamma radiation, which requires specially designed shielded facilities during fuel reprocessing and fuel fabrication. 

It should be noted that one of the most significant characteristics of the actinides is their radioactivity all isotopes are radioactive, although some have half-lives of greater than 1 x 10 years. Precautions must be taken in their handling, ranging from the use of special enclosures (HEPA-filtered exhaust hoods, negative-pressure gloveboxes) to the use of shielded facilities. 

The east wall of the reacjtor has. access to a. thermal c.pl m . which is provided with nine horizontal and two vertical access holes. Depending upon future demands, space is available through the west waT-l- for a shielding facility or another thermal column. 

The experimental shielding facility would be designed by ORNL. 

Two important experimental facilities, the thermal column and the shielding facility (see Sections 3.1 and, 3.2j, require that a section approximately 6 by 6 ft be removed from.the east and west thermal-shield side plates. Two components are added to the thermal-shield design by.these facilities (1) the neutron window, and (2) the neutron-absorbing curtain. The locations of these components may be visualized by referring to Figs. 2.B and C. When the 6- by 6-ft hole is cut in the thermal shield, it becomes necessary to replace... 

Provisions have also been made for installation of a curtain on the west side of the thermal shield at the. face of the shielding facility however, no curtain or lifting mechanism will be furnished initially. 

In this way it is hoped that the concrete blocks can be removed and graphite or other material stacked in during reactor shutdown. In addition, a deep water shield tank is set into the floor immediately in front of the shielding facility hole. 

Shell, W. E., MTR Design Report on Experimental Shielding Facility, ORNL CF 49 12 30, December 8, 1949. 

An obvious disadvantage of RAA separations is that samples often have to be treated in shielded facilities or in hot cells because of the radioactivity. 

In the new standard, the sections on administrative and technical practices are generally satisfactory. How ever, some items might be qualified. SRP s nuclear safety specialists aren t simply "advisors to supervision" they furnish directions rather than advice. The standard permits relaxed safety criteria inf shielded facilities, but we see ho benefit in taking advantage of this. It might be said that if controls can be relaxed in the shielded case, they are excessively conservative for the unshielded case. As a personal point of view, an incident in a shielded area is intolerable even though it hurts no one, because it casts doubt on ability to control the operation. 

Moderation control in operations with fissile material makes some proposals technically feasible and can result in significant cost savings in others. Often designs can be simplified and processes made more efficient. However, there are many problems and pitfalls both in calculations and implementation. Therefore, current criticality safety philosophy at the Idaho Chemical Processing Plant (ICPP) permits moderation control only within shielded facilities capable of containing the consequences of an accidental criticality. This requirement was imposed midstream in the development of several projects and necessitated Some redesign. I will discuss... 

Nuclear Criticality Safety in Shielded facilities—ANS-8.10, Bryan F. Gore (PNL)... 

A number of different ways were originally considered for removing the loops. The initial methods were to use the reactor refuelling machine or a heavily shielded facility constructed on the reactor cap. The loops (Figure 6) are so constructed that they could be drawn into such a facility and then size reduced ready for disposal. For various reasons, including the lack of a suitable repository for the cut tubes, a decision was taken to delay loop removal until after the RDM had been installed. As a consequence the loops must now be removed using remotely-deployed tooling mounted on the reactor internals. 

All of the actinide elements, with the exception of uranium and thorium, are radioactive to such a degree that handling requires spedal equipment and shielded facilities [9,10]. The special containment and manipulation techniques for work with the actinide elements are necessitated by the potential health hazards to the investigator and other occupants of the laboratory. Containment in the form of glove boxes is now standard, and these are available through normal commercial channels. Shielded facilities are more specialized, and, for the most part, are found in laboratories devoted to the study or processing of the actinide elements. 

By operating the reactor at a suitable power level, the foils may be irradiated to activities proportional to the spatial distribution of neutron flux within the water in the shielding facility. 

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