The out-of-core counting subsystem was tested for response to scrams from high power levels (900 watts and 300 watts), using both types of out-of-core fission chambers; i. e., the large 3-inch-diameter chamber (chamber No. 6) and the small 1-inch-diameter chamber (chamber No. 7). The output of the subsystem was monitored before and after the scram. Shown in Figure 8-12 is the decay curve for chamber No. 7 (sensitivity ~0. 1 counts/sec per nv). This curve indicates a constant slope after t = +4 minutes of 81 sec/ecade (186 sec/decade).

Shown in Figure 8-13 is the decay curve for chamber No. 6 (sensitivity ~0. 7 counts/sec per nv). This curve shows a constant slope after t = +3. 5 minutes of 78. 3 sec/ecade (180 sec/ decade). The response of the counting subsystem to rapid mechanical withdrawal at intermediate power levels (30 watts and 300 watts) was determined. The flux level at the detector was equiva­lent to an approximate full-scale reading on the subsystem. At this level the subsystem electronic response time is considered very short compared to the mechanical withdrawal time. ■

Chamber No. 7 was withdrawn four times at a. power level of 30 watts (see Figure 8-14 .

through 8-17). The average mechanical withdrawal time was 1. 5 seconds. The average time between the completion of the withdrawal and the time when the counting subsystem output reached its final value was 0. 75 second. Two withdrawals of chamber No. 7 were made at a power level of 300 watts (see Figures 8-18 and 8-19). The average mechanical withdrawal time for these withdrawals was 1. 22 seconds. The average time between the completion of the withdrawal and the time when the counting subsystem reached its final value in this case was 1. 42 seconds. These times are not known with great precision; the possible error includes a 1-second scaler integrating time.

Chamber No. 6 was withdrawn once at a power level of 100 watts (chamber No. 6 could not be reinserted with the reactor at power). The withdrawal time for this test (see Figure 8-20) was approximately і second, arid the counting subsystem reached its final value alter a delay of 1 second from the time that the withdrawal was completed.

In all cases above, no noise transient phenomena were evident, either on the withdrawals or the subsequent reinsertion. •

dr.