ELOG RH-ISAC

Testing was performed on August 9th on the ISAC nuclear ventilation system to determine if the existing ventilation system can achieve the required cell depressions for both SHC and NHC under all expected configurations and if a proposed modification to the DDC control system can provide acceptable stability and response time for the system. The proposed control system observes the lower of the SHC depression or the NHC depression + 10% (to avoid stability issues), and adjusts the dampers to try to achieve 250Pa (1.00" WC) depression in the area it is observing. With the proposed control system the SHC and NHC dampers are programmed to be at the same position, but can be tuned with a bias between them if required to achieve all ventilation requirements. The NHC and SHC dampers are programmed with a limit at 90% of the fully-open position. There is a damper in the ducting system in the section of duct after the SHC and NHC legs join together; this is set at 50% open, and was not adjusted during the the tests. Test summary and results are listed below:

1. Prior to switching to SHC+NHC control mode, the flow rate and depression of the SHC was measured with the lid on: 266Pa cell depression, damper 47% open, duct flow 417cfm. The lid was opened and the measurements repeated: 35Pa, damper 90% open, duct flow 630cfm (results in 83ft/min, 0.42m/s average flow velocity across HC module opening)

2. The control system was switched to the new SHC+NHC single control loop system. Measurements were taken with both hot cell lids closed. SHC: 246Pa, damper 72% open, 350cfm flow rate. NHC: 257Pa, damper 72% open, 510cfm flow rate. The ventilation fan speed was then increased from 53Hz to 57Hz (maximum speed is 60Hz). Measurements were taken with both hot cell lids closed. SHC: 257Pa, damper 51% open, 353cfm flow rate. NHC: 257Pa, damper 51% open, 515cfm flow rate.

3. The SHC module port lid was opened and the NHC lid left closed. SHC: 37Pa, damper 90% open, 462cfm (results in 61ft/min, 0.31m/s average flow velocity across HC module opening). NHC: 249Pa, damper 90% open, 551cfm.

4. The NHC module port lid was opened and the SHC lid closed. SHC: 203Pa, damper 90%, 360cfm. NHC: 33Pa, damper 90%, 648cfm (results in 85ft/min, 0.44m/s average flow velocity across HC module opening). The fan speed was then increased to 60Hz (max speed) to see if the depression setpoint for the SHC could be achieved in this configuration. SHC: 231Pa, damper 90%, 389cfm. NHC: 29Pa, damper 90%, 705cfm (results in 93ft/min, 0.47m/s average flow velocity across HC module opening)

5. Both SHC and NHC module port lids were opened and the fan was left at 60Hz. SHC: 31Pa, damper 90%, 448cfm (results in 59ft/min, 0.30m/s average flow velocity across HC module opening). NHC: 29Pa, 90% damper, 669cfm (results in 88ft/min, 0.45m/s average flow velocity across HC module opening)

For all tests the control system arrived at a stable depression value in less than 5 minutes, and thereafter exhibited only minor fluctuations.

The HEPA filter in the SHC leg of ducting has not been changed since commissioning of the facility (~15 years), and the SHC charcoal filters have not been changed since installation approximately 5 years ago. The SHC pre-fitler located inside the cell was changed in January 2016. When these are changed (which should be done before commissioning of the NHC ventilation system), the difference between SHC and NHC flow rates should decrease, and the SHC depression with NHC open should increase (likely up to the 250Pa setpoint).

Conclusion: The new SHC+NHC single control loop system effectively controls the system under all conditions tested. The existing ventilation system achieved the required NHC depression (250Pa, from RS 50, Document #131915) with both cells closed, and with SHC open only. The same depression for SHC with both cells closed was achieved with both cells closed, but only reached 231Pa w/ NHC open (203Pa at 57Hz fan speed). It is expected that 250Pa can be easily achieved in the final system because the NHC will be better sealed than in its current condition, the damper in the shared SHC/NHC leg can be opened further, there will be greater flow through the SHC leg after changing the HEPA and charcoal filters, and the system can be tuned to better balance the SHC and NHC flow rates. RS51 states "the ventilation system should maintain an average air flow velocity of 0.5m/s across the opening into the hot cell". This is almost achieved with the NHC open, but SHC only had 0.3m/s average flow velocity. It should be possible to increase both to > 0.5m/s by further opening the shared leg damper and tuning the system to have more balanced flow rates. At the very least, both SHC and NHC should have > 0.42m/s average flow velocity to match what is currently achieved in SHC only mode (measured in test step #1), which to date has not allowed contamination to escape out the top of the hot cell. Depending on what flow velocity is deemed acceptable, after commissioning it may be possible to have both the SHC and NHC open concurrently based on the results of Test 5. At the time of commissioning, the SHC/NHC damper bias and NHC air inlet damper should both be tuned to achieve as similar depression and flow rate conditions as possible for both cells, and to meet all requirements in the RS document.

Duct flow rate was calculated assuming that measured flow velocity at the center of the duct is 90% of average duct velocity. The duct ID at the sample location is 7.75", the hot cell opening size used for SHC and NHC module opening flow velocity calculations was 33" x 33".

Duct flow velocity measurements were taken using a thermal anemometer (Model number: 9555-P, Serial number: 9555:1108059 Rev. 2.11.0, Last calibrated by Rob Walker on April 29, 2016).

After completion of the tests the system was restored to it's original configuration and the ISAC target hall was swiped for contamination: none found. No EF12 trips occurred during these tests.