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

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

and gamma induced

and gamma induced ionization, by matching this Detector with one that is sensitive to gammas only, compensation is possible, at least at a given temperature,, as was shown by Cooper. Some of his experimental results are shown in figure 2-6. Conventional in-core ionization chambers suffer greatly from high temperature induced leakage current effects as shewn in figure 2-7. The departure from linearity of the ionization current- as a function of reactor power at low flux levels, results from temperature enhanced leakage current. The PIC method's ability to greatly reduce such current 4 effects was shown by Ellis and Irnani and reported in Markwell's thesis. Figure 2-8 shows their results. The change in signal output for increased temperatures was shown to be due to the change of the recombination coefficient with temperature. However, such a change would complicate the application of the PIC methodology to reactor power measurements. p Fortunately, however, Sanders results indicate that this drawback could possibly be averted in chambers using neon as a fill gas, since neon's recombination coefficient was reported to be independent of temperature over the range of 70°F (25°C) to 572^F (300°C). Even though the previously developad PIC systems were adequate for the proof-of-principle application described above, they fell far short of being prototypic of a practical reactor power measurement system. The 9 bases for such a practical design was set forth by Lllis. The principle technique of his system involved direct analog signs'! processing in com- bination with direct logic system gating resulting in live time feedback range and operational mode control. The major advantage of this approach, in terms of reactor safety and control, would be its fast response time 1 characteristics. However, it would suffer from the inherent disadvantage

-r C5 NT 10 r fc—».~-I 10 ... ''J - 'V/A K////> Ya/// Y//A nde rcompe nsated Ove rcompensa te V/A V///J .// //. Y/ // A ///A V // / ) 7/ / / 7//; /" X /J v///> X, 6 4 2 2 4 DEVIATION FROM TOTAL COMPENSATION ( T lOOv Y 5i0v Y : igure 2-6. Gamma compensation as a function of gamma field strength, ; i) J 10