29 août 2014
Une source de plutonium 239 de 60 nanocuries a chuté de son conteneur et s’est rompue. Une mesure de contamination alpha a montré la présence d’une contamination du sol à 200 coups/minute. Deux personnes, à proximité de l’accident, présentaient une contamination alpha de 0,17 dpm. Selon la NRC, l’accident n’aurait pas dû être déclaré car l’activité de la source de plutonium 239 était 5 fois inférieure à la limite annuelle d’incorporation...
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Event Number : 50420
Licensee : NATIONAL INST OF STANDARDS & TECH
City : GAITHERSBURG State : MD - County : MONTGOMERY
Event Date : 08/29/2014 - Event Time : 16:00 -
Emergency Class : NON EMERGENCY 10 CFR Section : 70.50(b)(1) - UNPLANNED CONTAMINATION
Event Text
UNPLANNED CONTAMINATION INCIDENT IN THE RESEARCH REACTOR FACILITY
At approximately 1600 EDT on 08/29/14, a 60 nanocurie Pu-239 wafer source dropped from its holder during change out following neutron irradiation in building 235 (Research Reactor Test Facility). The wafer struck the floor and cleaved in half. Radiation surveys confirmed alpha contamination of approximately 200 counts per minute. The area was decontaminated, resurveyed and released.
The licensee will notify their NMSS PM (Naquin) and the State of Maryland Department of Environment as a courtesy.
* * * UPDATE AT 1840 EDT ON 08/30/14 FROM TOM O’BRIEN TO STEVE SANDIN VIA EMAIL * * *
"Follow-up to the dropped source (Pu-239 RS# 87-0039(4) on 8/29/14)) at NG-6MAll personnel involved have been evaluated, with the exception of two nasal swipes, on two separate individuals not directly involved with the incident, but near the location, reporting about 0.17 dpm alpha each, all surveys find the personnel to be clear of contamination. It is believed the two 0.17 dpm nasal swipes are statistically not different than zero, follow-up measurements will be done to confirm this. Even if we assume them to be positive, the resulting estimated dose from these measurements would be on the order of 10 mrem.
"The NG-6M instrument area has been surveyed and cleared for normal use. All contamination swipe surveys of the floor, tools, furniture and equipment potentially involved in this incident have been found to be clean. With the exception of one alpha instrument survey, all surveys with alpha and beta/gamma survey instruments have found levels less than or equal to background. The one survey where positive indication was found was performed at the source drop location, directly underneath where the source fell. This survey was done after the source was retrieve. Initially measured about 200 cpm alpha contamination and very localized, the spot was carefully deconned and subsequent surveys found to be less than or equal to background. All swipes of this spot were also found to be clean.
"The source has been safely retrieved, secured and is locked in our safe in A134. No removable contamination was found on the source containers or during retrieval of the source. Gamma spectrum measurements of the retrieved source, detecting the Am-241 trace nuclide, and correlating this activity by know nuclide ratios find that the Pu-239 activity of the source is within good agreement of the original activity of the source (2190 Bq). While this confirmation has many errors incorporated into it, it is the best measurement we can make at this time, that along with the negative findings of any removable contamination to speak of, and visual inspections of the source, I conclude that to the best of my knowledge, the source material is intact on the broken source substrate pieces, inside the source container. Careful follow-up measurements would need to be performed to confirm this for certain, but based on the info I have at present this is my conclusion."
Notified R1DO (Mangan), NMSS EO (Stablein) and NMSS PM (Naquin).
* * *RETRACTION PROVIDED FROM TOM O’BRIEN TO JEFF ROTTON AT 1425 EDT ON 09/04/2014 * * *
"Upon detailed review of the incident data NIST is requesting retraction of this notification on the basis that 70.50 (b)(1)(i) and (ii) are not applicable to this event and therefore no 24 hour (or other notification) was required. Access to the contaminated area was restricted for less than 24 hours. Additionally, at the time of initial reporting on 8/30/2014, the most conservative annual limit on intake (ALI) was used as the chemical composition was not yet known. As of today, 9/3/2014, we have confirmed that the radioactive material is in the form of PuO2. This additional information indicates that the involved quantity of radioactive material was less than five times the lowest ALI for Pu-239.
"Since the initial report of 8/30/2014, there has been no other contamination detected. The nasal-swab measurements were analyzed for a longer time period and have been determined to be less than the minimum detectable activity.
"NIST is evaluating the incident for lessons learned and extent of conditions and will advise [NRC] Region I and our [NRC] Project Manager of the outcome.
"Licensee also requested that the first sentence of the [original] Event Text be corrected as indicated below as the source was not subjected to neutron irradiation. ’At approximately 1600 EDT on 08/29/14, a 60 nanocurie Pu-239 wafer source (that was going to be used to calibrate an instrument detector) dropped from its holder during transfer in building 235 (Research Reactor Test Facility).’"
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