United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

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

HPPOS-299 PDR-9306220283

Title: Technical Assistance Request, SteriGenics

International, Authorization to Increase the Limit on Pool

Water Conductivity

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


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


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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