Severity
Near-Miss
Leak
No
Ignition
No

Liquid Waste Disposition Projects (LWDP) has experienced repetitive events involving Hydrogen Monitor/LFL Analyzer degradations over the last year. There have been 12 reportables in the last two years. As a result, a determination was made to issue a recurring occurrence report referencing management concern as its reporting criteria.

Engineering has recently made significant progress in further defining issues and potential corrective actions necessary to address the lower flammability limit (LFL) failures. The engineering path forward to resolution of this issue addresses potential failure contributors, among these are: Drift - This phenomenon is being closely assessed. Initial tests indicate the monitor power supply may be a significant contributor to instability resulting from the effects of temperature. Calibration Issues - Vendor-supplied parts and fabricated parts may be introducing small variations that, when eliminated, could improve reliability. Premature Sensor Degradation - Potential caused by increased surveillance frequency (i.e., normal performance of calibration surveillance).

The engineering path forward takes specific actions over the next several weeks that are aimed at better defining the contributors to monitor failure. Program improvements are underway to address these issues and provide resolution. The final product is targeting a more predictive approach to hydrogen monitor/analyzer performance.

The recurrent reportable events are dominated by a certain tank. This tank has operating characteristics that differ from most waste tanks because of its association with the in-tank precipitation process. The tank is subject of an engineering study. The performance of the actions specified in the path forward document will be able to provide a more in-depth look at the overall issues with hydrogen monitors than this analysis can. The path forward ultimately will address monitor dependability and use for all LWDP waste tanks.

Background:
The hydrogen monitors in use in the LWDP tank farms have been the primary means of detecting the levels of hydrogen and benzene in the waste tanks since installation years ago. Over the lifetime of their service, failures of components within the monitor periodically occur. This continues even to this present time. As the tank farm facilities have operated over the years, various specifications and controls for operation have been placed into effect with regard to the hydrogen monitors. These specifications and controls were intended to ensure the natural generation of hydrogen gas within the waste tanks did not and does not reach explosive levels. Historically, the hydrogen monitors have been expected to operate with a very narrow range. The monitors were expected to maintain their calibration to within + - 2% LFL. This range was selected based on a general belief that it was conservative and appropriate for operation. There was no calculated technical basis for the + - 2% LFL assumption. An uncertainty calculation was approved to add expanded required accuracy limits to the LFL Monitor surveillances. The original + - 2% range was expanded to + - 6% LFL.

Corrective actions include evaluation of the current LFL monitor trending and analysis program to determine if the program needs to be improved. Include an evaluation and development of criteria that can be used to predict LFL monitor failures such as cal-to-cal changes and PI monitoring. Implement the improvements, as required.

Perform an LFL monitor procedure consistency review. Include procedures for FTF and HTF LFL monitors.

Evaluate the need for a replacement for the currently installed LFL monitors as compared to providing better temperature control in the existing LFL monitor enclosures, expanding the use of portable LFL instrumentation, or eliminating the sensor/transmitter 1.5 gain setting. Develop a temporary modification to test the replacement monitor, as necessary.

The currently installed LFL monitors utilize technology that is approximately 20 years old. A more modern technology should result in more stable operation of the LFL monitors. In addition, the current vendor no longer manufactures the currently installed LFL monitor controllers (that provide the %LFL display). The vendor now manufactures a new model. When the facility's existing spare parts are depleted, a replacement controller will have to be provided.

A potential replacement LFL monitor has been identified and is currently undergoing testing at the lab. For its operation, it relies upon a modern, electronic, solid-state sensor/transmitter system to provide a consistent display and signal output instead of the older technology currently used by the facility. Preliminary test results indicate that the replacement monitor is accurate, more stable, and easier to calibrate than the currently installed system. Both the potential replacement monitor and a monitor like the currently installed monitor were subjected to varying temperature and humidity conditions in an environmental chamber. During the tests, the replacement monitor was more stable and accurate than the currently used monitor.

Incident Date
May 24, 2004
Equipment
  • Safety Systems
  • Measurement / Sensing Device
Damage and Injuries
Probable Cause
When Incident Discovered
Lessons Learned

Utilize a Six Sigma Black Belt to statistically evaluate LFL monitor reliability and determine the failure rate based on the existing technology.

Revise the tank uncertainty calculation and surveillance to include a wider "Required Accuracy" range like the other tanks LFL monitors "Required Accuracy" ranges.

Evaluate minimizing the "Calibration Staff" for the LFL monitors, i.e., establish a small qualified crew of maintenance personnel who are allowed to calibrate the LFL monitors.

Also, submit DSA change request to require installed monitors only when tanks are in agitation e.g., slurry pump operation, salt dissolution, interstitial liquid removal. When in static state, utilize the portable LFL measurement instrumentation. With appropriate basis, this could result in elimination of installed LFL monitoring equipment on specified tanks.