UNITED STATES

NUCLEAR REGULATORY COMMISSION 

OFFICE OF NUCLEAR REACTOR REGULATION 

WASHINGTON, D.C. 20555-0001

August 24, 2006

NRC INFORMATION NOTICE 2006-19: LEAKING FUEL ELEMENT CAUSES FALSE

INDICATION OF STEAM DRYER LEAKAGE IN

BOILING-WATER REACTOR

ADDRESSEES

All holders of operating licenses for boiling-water reactors, except those who have permanently

ceased operations and have certified that fuel has been permanently removed from the reactor

vessel.

PURPOSE

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform

addressees of the potential false indication of a steam dryer leak caused by a leaking fuel

element. It is expected that recipients will review the information for applicability to their

facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions

contained in this information notice are not NRC requirements; therefore, no specific action or

written response is required. 

DESCRIPTION OF CIRCUMSTANCES

On February 10, 2006, the licensee at River Bend Station shut down the unit to perform steam

dryer inspections based on suspected steam dryer damage as indicated by high moisture

carryover (NRC Inspection Report 05000458/2006002, Agencywide Documents Access and

Management System (ADAMS) Accession No. ML061250505).

The saturated steam that exits the reactor vessel of a boiling-water reactor contains a small

amount of liquid water entrained in the steam flow (i.e., moisture carryover) that is transported

through the main turbines to the condenser hotwell. Because the liquid water (i.e., reactor

coolant) that is entrained in the steam flow contains sodium-24 (Na-24), the amount of moisture

carryover may be calculated based the concentration of Na-24 in the condenser hotwell. Over

a 60-day period, the gamma spectroscopy results for condenser hotwell samples showed a

steady increase in Na-24. Because such an increase is normally an indication of steam dryer

damage, the licensee shut down the unit to inspect the dryer. Upon inspection, the licensee

found no detectable damage to the steam dryer.

ML062330295
IN 2006-19

Page 2 of 2

Upon further investigation, the licensee determined that the apparent increase moisture

carryover was the result of inaccurate Na-24 measurements. Degraded fuel caused leakage of

iodine-135 (I-135) into the reactor coolant that impacted the Na-24 analysis. The predominant

gamma energy for Na-24 is 1368.5 keV which is close to gamma energy of 1367.9 keV for

I-135. The licensee sets up the gamma spectroscopy equipment by inputting a “library” of

isotopes and their energy level for only those isotopes that the licensee expects could be

present in meaningful quantities. The sample analysis results produced by the gamma

spectroscopy software reflects only those isotopes the licensee inputs into the isotope library. 

Because the quantity of I-135 in normal reactor coolant (without failed fuel) is negligible, the

licensee did not include I-135 in the isotope library. Therefore, for the condenser hotwell 

sample, although the gamma spectroscopy sensor detected the gamma from I-135, the gamma

spectroscopy software determined the gamma was from Na-24 because Na-24 was included in

the isotope library and has a gamma energy close to that of I-135. This resulted in a false high

indication of Na-24. As a corrective action, the licensee added I-135 to the gamma

spectroscopy equipment isotope library to facilitate distinction between I-135 and Na-24. 

DISCUSSION

Fuel failures have a significant impact upon the radionuclide composition of reactor water and

associated systems and could impact the gamma spectroscopy analyses for both chemistry

and radiation protection purposes. In order to obtain accurate analysis results, plants operating

with failed fuel can modify their gamma spectroscopy analysis libraries to reflect the change in

radio isotopic composition. Accurate analysis results are particularly important when the

quantity of an isotope is tied to particular plant actions or responses, including post-accident

responses. 

CONTACTS

This IN requires no specific action or written response. Please direct any questions about this

matter to the technical contact listed below. 

/RA/ by John W. Lubinski

Ho K. Nieh, Acting Director

Division of Policy and Rulemaking

Office of Nuclear Reactor Regulation

Technical Contact: Wayne Sifre, RIV

 817-860-8193

 E-mail: wcs@nrc.gov

Note: NRC generic communications may be found on the NRC public Website,

http://www.nrc.gov, under Electronic Reading Room/Document Collections.