4 10 10 i '° r ; 650°F[—«—" />
 
Views
5 years ago

Applying the pulsed ion chamber methodology to full range reactor ...

Applying the pulsed ion chamber methodology to full range reactor ...

utilized. Such an

utilized. Such an examination will not only suggest where, and possibly how, improvement can be made in current systems, but it will also point to the pressing need for a full range, high temperature single sensor system. The first division between neutron sensing systems comes from whether they utilize in-core or ex-core sensors. Examining figure 1-1 we see why such a division exists. There is a difference of a factor of 10 in temperature and a factor of 10 in gamma and neutron fluxes between the two regions. It is apparent that those systems designed for in-core monitoring must be an extremely hearty breed. For this reason, only one of the four major reactor types (PWR, HTGR, LMFBR, and BWR) has the neutron flux level safety control monitors in-core. The BWR, due to its large volume xnd particular design characteristics (large cruciform control rods and boiling water) requires in core flux monitoring for safety reasons. This requirement, coupled with the "lack of dependable in -core systems, together, comprise one of the most difficult problems the BWR engineer faces today. Figure 1-1 also serves to define the upper limit operating specifi- cations for both the in-core and ex-core environment. The lower limits corresponding to reactor shutdown are depicted in figure 1-1 as well. The great, range in reactor power makes the use of a single sensor and circuit impossible with current technology. Thus a detector of any given design is of use only over a specific part of the flux range -md must be complimented with other sensor-circuit designs. Overlapping one or two decades of each design sacrifices part of their useful range but insures smooth transfer of control and safety functions from one control circuit to the next.

1 1 a 4'. J8H8H' '!•! I Jm ' , I fJ4 i L-. : Flux, nv > "*~*^~-^. i 10 iol ;>4 10 10 i '° r ; 650°F[—«— Temperature 180 nnOc. -^ Flux (nv; Y-Field (R/hr) " ^ L. "s4 \ !40 o,., Temperature ( F) N iiOv-^2- !':!K\ intw \\ \V j Thermal Insulation Neutron Sensor Parameters at Power Parameters at Shutdown Figure '1-1. Typical environmental profile for neutron sensors in a PWR at full power ana at. shutdown