United States Nuclear Regulatory Commission - Protecting People and the Environment

Technical Assistance Request, SteriGenics International, Authorization to Increase the Limit on Pool Water Conductivity

HPPOS-299 PDR-9306220283

See the memorandum from J. E. Glenn to J. A. Grobe dated October 13, 1992.

This memo responds to a technical assistance request from Region III, dated May 20, 1992, regarding the request of SteriGenics International (formerly, Radiation Sterilizers, Inc.) to increase the limit on pool water conductivity from 10 to 20 microsiemens per centimeter (mS/cm). By memorandum dated June 20, 1992 (Enclosure 1), NMSS asked the Office of Nuclear Regulatory Research (RES) for its recommendation. We discussed the issue of pool water conductivity during drafting of the final version of the proposed 10 CFR Part 36. The guidance provided below reflects these discussions; SECY-92-323, "Final Rule on "Licenses and Radiation Safety Requirements for Irradiators" Enclosure 2); and RES' reply to our June 20, 1992 memorandum (Enclosure 3).

The 10-mS/cm value is that recommended by the American National Standards Institute (ANSI), is also the values in the proposed 10 CFR Part 36, and is a current condition of the SteriGenics license. Region III asked the licensee to justify its request. The licensee's response includes the following points:

  1. Conductivity greater than 10 mS/cm will not cause long-term or accelerated corrosion of stainless steel used to fabricate cobalt sources.

  2. The 10-mS/cm values was chosen based on the level of conductivity attainable with Atomic Energy of Canada (AECL) water purification systems.

  3. The are occasions when the 10-mS/cm value may be exceeded; e.g., during source loading.

  4. The license previously used the 20-mS/cm value.

It is important to maintain good water quality in a pool-type irradiator. The water must be clear in order for the operator to see the position and location of the sources, to identify source serial numbers, and to find objects which may be dropped into the pool. The water quality must be such that it does not accelerate corrosion of the radioactive sources and does not damage the pool structure.

As indicated in Enclosure 3, the RES metallurgist endorsed the use of 20 mS/cm as an upper limit on conductivity under normal circumstances for 316L or 321 stainless steel, provided that there are no crevices on the source or between the source and the source holder. He expressed concern that localized areas in crevices on the sources or between the source and source holder could contain water with very much higher conductivity values that could accelerate corrosion.

With regard to SteriGenics' request concerning pool conductivity, Region III may amend the SteriGenics license to require the following:

  1. Pool water purification system must be run sufficiently to maintain conductivity of the pool water below 20 mS/cm under ordinary circumstances;

  2. If pool water conductivity rises above 20 mS/cm, the licensee shall take prompt corrective actions to lower the pool water conductivity and shall take corrective actions to prevent recurrences;

  3. The licensee shall measure the pool water conductivity frequently enough, but no less than weekly, to assure that the conductivity remains below 20 mS/cm [Note: The licensee may use trend analysis or other similar statistical methods to demonstrate that "conductivity remains below 20 microsiemens per centimeter"];

  4. The conductivity meter must be calibrated at least annually;

  5. Records of conductivity measurements and calibration of conductivity meters must be maintained for three years from the date of the measurement or calibration;


  6. SteriGenics' sources are encapsulated in a material resistant to general corrosion and to localized corrosion, such as 316L stainless steel or other material with equivalent resistance; AND

  7. SteriGenics verifies that there are no crevices on the sources or between the source and source holder that would promote corrosion on a critical area of the source.

Regulatory references: License Conditions

Subject codes: 5.0, 10.2

Applicability: Source Material

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