ML11313A012
| ML11313A012 | |
| Person / Time | |
|---|---|
| Site: | Rhode Island Atomic Energy Commission |
| Issue date: | 11/01/2011 |
| From: | Tehan T State of RI, Atomic Energy Comm |
| To: | William Kennedy Division of Policy and Rulemaking |
| References | |
| Download: ML11313A012 (4) | |
Text
STATE OF RHODE ISLAND AND PROVIDENCE PLANTATIONS RHODE ISLAND ATOMIC ENERGY COMMISSION Rhode Island Nuclear Science Center 16 Reactor Road Narragansett, RI 02882-1165 Mr. William B. Kennedy, Project Manager Research and Test Reactors Division of Policy and Rulemaking Office of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Washington, D.C. 20555-0001 November 1, 2011 Re: Radiological Incident on October 25, 2011 Docket No. 50-193
Dear Mr. Kennedy:
On October 25, 2011, one of our interns entered the dry gamma room while the core was in the low power section of the pool. We have investigated the circumstances, identified what we believe was the root cause of this radiological incident, and are instituting certain corrective actions as outlined in this letter. Although it is our contention that this was an isolated occurrence, we believe that the root cause of the incident was lack of adequate control over the high radiation area present in the dry gamma room.
The dry gamma room is located on the reactor confinement floor two levels below the control room and pool level. It had sat unused for most of the facility's life and only recently had been reopened to become an experimental facility after extensive test and characterization by staff and students. During the initial test and characterization, a physics student from the University of Rhode Island worked side-by-side with a senior former staff member to ensure that no entries were made while the core was in the low-power section of the pool. Five entries were made without incident (January 11, 2011, February 2, 2011, April 27, 2011, April 28, 2011 and July 25, 2011).
As information concerning radiation levels within the dry gamma room became available, the area adjacent to the entrance was posted as a radiation area. The entrance itself was posted as a high radiation area whenever the core was in the low power section of the pool. Concurrently, shielding needs were evaluated and specific shielding installed.
Radiological data showed that the dry gamma room could be safely accessed when the core was positioned in the high power section of the pool.
By October 25, 2011 sufficient information had been gathered to post the area and establish a labyrinth to shield the entrance. A "Caution - Radiation Area" sign was posted outside the labyrinth providing access to the dry gamma room. The entrance to the high radiation area within the dry gamma room was posted, "Caution - High Radiation Area." A lockable gate had been provided to prevent entry into the dry gamma room. A closed-circuit television monitor viewed from the control room observed the entrance.
Access to the reactor confinement floor was controlled by a locked door and observed from the control room by closed-circuit television. Our preoperational checklist required the dry gamma room to be secured prior to start up. It should be noted that only trained radiation workers are permitted unescorted access to the locked reactor confinement by our procedures. Our radiation safety officer had reviewed the high radiation area controls and judged them to be adequate under 10 CFR 20.1601.
On the morning of October 25, 2011, a senior reactor operator (SRO) was working with an intern to characterize the gamma dose field within the dry gamma room during 100 kilowatt operation in the low-power section of the pool. An ion chamber placed next to the aluminum window was set up to measure that field. A temperature reading was needed to properly calibrate the ion chamber. The temperature was taken and recorded and the SRO and the intern exited the dry gamma room. Contrary to procedures, the gate was left unlocked.
The SRO and the intern climbed to the pool level and prepared to move the reactor core to the low power section of the pool. The intern moved the core to the low power section of the pool under the supervision of the SRO. It should be noted that movement of the core requires turning a hand crank so there isn't any ambiguity about what is being done.
During this movement, the reactor remained safely shut down. The SRO noted that the gate to the dry gamma room was unlocked and directed the intern to go lock it. The SRO continued his preoperational checklist in preparation for start-up.
The intern returned to the reactor confinement floor and, instead of locking the gate as directed, inexplicably re-entered the dry gamma room to confirm the temperature reading that had previously been taken. During the entry, the shut down core was in the low power section next to the aluminum window. Readings taken with the ion chamber measured the gamma present in the dry gamma room at 36 reins per hour from the decay of the fission products within the core. At no time during the entry was the reactor critical.
When the radiation safety officer was told that the intern had entered the dry gamma room while the core was in the low power section of the pool, he immediately recognized the radiological and regulatory implications of the entry, restricted the intern to work not involving exposure to radioactive materials pending the outcome of an emergency reading of his personnel monitoring device and removed his personnel monitoring device for overnight shipment to the vendor. He also started our investigation of the incident by asking the SRO and the intern to provide separate written statements of their actions. He asked the health physicist to make a survey of the area without subjecting himself to the high fields likely to be present in the dry gamma room. Upon completion of his survey, 2
the health physicist reported that he had found the dry gamma room unlocked and had secured it.
The intern estimated his stay time in the dry gamma room as five minutes. The radiation safety officer initially estimated the whole body dose equivalent at 3 rems based upon the intern's estimate of his stay time and the dose rate recorded by the ion chamber within the dry gamma room. The radiation safety officer notified the backup NRC Project Manager and others of the incident in accordance with our technical specifications and 10 CFR 20.
Overnight, emergency reading of the intern's personnel monitoring device by the vendor recorded a deep dose equivalent of 115 millirems, a shallow dose equivalent of 115 millirems and eye dose equivalent of 115 millirems.
As a result of this incident and our subsequent investigation, we have taken and completed or will shortly complete the following corrective actions:
" We immediately banned interns from confinement and work on any nuclear systems pending outcome of our investigation.
- We immediately banned any further use of the dry gamma room until the Nuclear and Radiation Safety Committee is satisfied with our corrective actions.
" A warning system consisting of the ion chamber within the dry gamma room, three strobe lights and a remote readout display will be installed by November 25, 2011. The ion chamber is already present in the dry gamma room. Radiation levels detected by the ion chamber will activate the three strobe lights to warn personnel of the presence of those fields. One of the strobe lights will be visible in the dry gamma room. A second strobe light and a read out will be mounted adjacent to the gate on the "safe" side. The third strobe light will be mounted near the "reactor on" light.
- We retrained our staff on high radiation controls and procedures on October 31, 2011.
- We reviewed intern and student training records and determined that site-specific training on specific tasks could not be verified in all cases. As a result of that audit, we will ensure that all students and interns are fully trained on their site-specific tasks and responsibilities and that that training will be fully documented before they are permitted entry into radiologically-controlled areas of the facility.
" We have developed a new procedure for operation in the low power section of the pool including specific controls for access to the dry gamma room. The procedure is being reviewed by the Nuclear and Radiation Safety Committee and will be considered at its next meeting.
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If you have any questions concerning our actions in this matter, please contact the undersigned.
Respectfully, Terrence N. Tehan Ph.D. Director Rhode Island Atomic Energy Commission I certify under penalty of perjury that the representatis made above t and correct.
Executed on:o.O By:_ ____ ____
Docket No. 50-193 4