PSFC Safety Committee

PSFC Safety Committee


Plasma Science and Fusion Center

Office of Environment, Safety, and Health


190 Albany Street, NW21 2nd floor
617-253-8440 (Catherine Fiore)
617-253-8917 (Matt Fulton)
617-253-5982 (Bill Byford)
617-258-5473 (Nancy Masley)
Fax 617-252-1808

Be Safe or Die


Maintenance Procedure for Diborane Gas System

PFC-CH-95005

Author: Catherine L. Fiore, Chris Reddy, Joe Bosco

Version: Version 1.1 Released 1/22/96 by C. Fiore. Reviewed by J. Irby, E. Marmar

Date: 1/22/96

Computer filename: User9:[fiore.text.esh]diborane_maintain_pro\.tex

System: Diborane Gas System

Person responsible: C. Fiore, C. Reddy

Introduction

It has been surmised that an effective way to coat the walls of the Alcator C-Mod vacuum vessel with a thin layer of boron is to create a gaseous discharge in diborane gas inside the vacuum vessel. Diborane is highly toxic and flammable, and presents an explosion hazard. The gas delivery system must be of high integrity and leak free. Leak detection and remote control are essential. Procedures for handling, maintenance, process, and emergency response are required, as is training of any personnel directly or peripherally involved with using this material.

Scope/Purpose

This document covers the maintenance requirements for the Alcator C-Mod Diborane facility.

Consequences of procedural failure.

Failure to adequately maintain the diborane system could result in leakage of diborane gas into the cell or into the diborane housing, which could lead to fire or explosion, or to personnel exposure to toxic gas. Diborane is immediately dangerous to life and health at 40 ppm, and an explosion hazard at 9000 ppm.

Definitions

Responsibilities

Required Equipment

Required Materials

Assumptions and Prerequisites

Procedure for maintenance of the diborane monitors

Please refer to the "TLD-1 Toxic Gas Detector: Operating Instructions" for more information. Change chemical tape on diborane monitors. This must be done every two weeks during operation of the diborane monitors.

  1. Turn the Tape Load Lever to the "open" (9 o'clock) position, and remove the Chemcassette from the locator post. Pull the Take-up Reel cover off the Take-up Reel, slip off the used Chemcassette tape and discard.

  2. To load in a fresh tape, make sure that the Tape Load Lever is in the "open" (9 o'clock) position. Pull approximately 12 inches of tape out of the fresh Chemcassette. Place the end of the tape in the slot on the Chemcassette Take-up Reel cover. Thread the Chemcassette tape through the Detector Head, Capstan Assembly, and adn over the Guide Post. Push the fresh Chemcassette (with the raised lettering facing you) on the Chemcassette Locator Post and secure with the screw cover. Also push the Take-up Real cover into place. Rotate the assembled Take-up Reel on or two turns to take up any slack. Turn the Tape Load Lever to the "closed" (6 o'clock) position.
Check function of the diborane monitors. (Perform prior to installation of diborane bottle, and every 2 weeks while diborane is in the cell.)

  1. Turn the Tape Load Lever to the "open" (9 o'clock) position, remove the Chemcassette, and press the Alarm Test Key. The green System Status Indicator will flash.

  2. Insert the test card with position#1 centered in the Detector Head; be sure that the colored chip on the test card faces up and that the card is inserted fully into the Detector Head.

  3. Close the Tape Load Lever and press the Alarm Test Key. The instrument will beep once.

  4. Open the Tape Load Lever and reverse the Test Card, centering position #2 in the Detector Head.

  5. Close the Tape Load Lever and press the Alarm Test Key. If all electronics and optical systems are operating properly, the instrument will go into an alarm condition, with both the audible and visual alarms activated and the alarm relay energized. Check that the process gas valve has closed.

  6. Open the Tape Load Lever and press the Alarm Reset Key. Rethread the Chemcassette Detection Tape and turn the Tape Load Lever to the closed (6 o'clock) position. The test is now complete.

  7. Repeat steps 1-6 for the second monitor.
Change Internal Flow Filter (Yearly). Consult Manual.

Procedure for Purge System Maintenance

Replace Venturi Nitrogen Gas. To be done when the gas bottle pressure falls to 500 PSI.

  1. This should be done only when the diborane is not present in the process gas lines, and the diborane bottle valve is closed.

  2. Close the valves on the nitrogen bottles and open PV1 to release the pressure from the system. Close the regulator REG3 and MV3 and close the valve on the nitrogen bottle.

  3. Disconnect the nitrogen bottles (outside the gas cabinet on the right) and remove them.

  4. Replace the bottles, and open the bottle valves. Set the REG3 to 100 Psi and open MV3.
Replace Helium Purge Gas. To be done when the gas bottle pressure falls to 500 PSI.

  1. This should be done only when the diborane is not present in the process gas lines, and the diborane bottle valve is closed.

  2. Close the valve on the helium bottle. Open PV1, PV2 and PV4 to release the pressure, then close the regulator REG2 and MV2. Open the gas cabinet. Disconnect the helium bottle (on the right) and remove it.

  3. Replace the bottle, and open the bottle valve. Set the REG2 to 30 Psi and open MV2.

Test procedure

Refer to the "Test Procedure for the Diborane Gas System" for performing these tests.

  1. Helium leak check the diborane gas lines. Perform prior to beginning of any boronization campaign, and whenever an opening in the diborane gas lines has occurred.

  2. Test the diborane safety system performance. Perform prior to beginning of any boronization campaign.

  3. Test the system performance in helium. Perform prior to beginning of any boronization campaign.

Training

Those responsible should review these procedures in detail, and should receive training in toxic gas hazards, and SCBA usage.

Cross references

Distribution

E. Marmar, J. Irby, C. Reddy, R. Clifford, J. Bosco, B. Childs,

References