RPT 243 Instructional Resources
Module 2: General Radiation Fields
Table of Contents:
Resources Key 2
Module Readings and Homework 2
Primary Scenario “Exposure in Excess of Quarterly Limit during Steam Generator Work” 2
Transfer Scenario “Exposure of Personnel While Repairing In-core Flux Mapping System” 3
Primary Scenario “Exposure to Worker Who Removed Shielding Without Authorization” 3
Transfer Scenario “Exposure to Worker from Reactor Water Cleanup Heat Exchanger Room” 3
Transfer Scenario Original Event Descriptions 4
Transfer Scenario “Exposure of Personnel While Repairing In-core Flux Mapping System” 4
Transfer Scenario “Exposure to Worker from Reactor Water Cleanup Heat Exchanger Room” 8
ACAD References 11
Resources Key
This refers to: / This reference:ACAD / National Academy for Nuclear Training, Uniform Curriculum Guide for Nuclear Power Plant Technician, Maintenance, and Nonlicensed Operations Personnel Associate Degree Programs, ACAD 08-006.
DOE-SG / Office of Environmental, Safety and Health: Radiological Control Technician Training Site Academic Training Study Guide Phase I, Project Number TRNG-0003
Available at: http://nsedu.rnet.missouri.edu/docshare/. File is located under the Docs/General Curriculum/DOE materials folder.
G. / Gollnick, D. (2006). Basic Radiation Protection Technology, 5th Ed. Pacific Radiation Corporation, Altadena, CA.
Module Readings and Homework
Primary Scenario “Exposure in Excess of Quarterly Limit during Steam Generator Work”
Core Concept: Techniques and precautions for minimizing exposure from external area radiation fieldsHomework
Readings / Calculation Items / Non-calculation Items
DOE-SG-Mod. 1.11-6 to 1.11-12 / DOE-SG-Mod. Sample prob. 1.11.05, 1.11.06 / N/A
Core Concept: Techniques and precautions for controlling individual exposures
Homework
Readings / Calculation Items / Non-calculation Items
G., Chap. 15, 687-689
G., Chap. S-1, 746-755
DOE-SG-Mod 1.10-2 to 1.10-5 / N/A / G., Chap. 15, # S-2
Core Concept: Techniques and precautions for responding to overexposure(s) from working in high radiation area(s)
Homework
Readings / Calculation Items / Non-calculation Items
DOE-SG-Mod 2.11-5 – 2.11-7 / N\A / DOE-SG-Mod. 2.11.06
Transfer Scenario “Exposure of Personnel While Repairing In-core Flux Mapping System”
· Refer to readings and homework for primary scenario above.
· The complete text of the event for this scenario is in the section “Transfer Scenario Original Event Descriptions” below.
Primary Scenario “Exposure to Worker Who Removed Shielding Without Authorization”
Core Concept: Enforcement of radiological protection safeguards (procedures, RWPs, briefings) against overexposure(s)Homework
Readings / Calculation Items / Non-calculation Items
G., Chap. 11, 450-452
DOE-SG-Mod 1.10-7 to 1.10-8
DOE-SG-Mod 2.10-3 to 2.10-6 / N\A / G., Chap. 11, # 5
Core Concept: Worker responsibilities for complying with, monitoring and enforcing ALARA practices
Homework
Readings / Calculation Items / Non-calculation Items
G., Chap. 11, 446-449
DOE-SG-Mod 1.10-9 / N\A / DOE-SG-Mod 1.10.05
Transfer Scenario “Exposure to Worker from Reactor Water Cleanup Heat Exchanger Room”
· Refer to readings and homework for primary scenario above.
· The complete text of the event for this scenario is in the section “Transfer Scenario Original Event Descriptions” below.
Transfer Scenario Original Event Descriptions
Use the complete text of these events to assess students’ ability to analyze the event, and apply appropriate safety and response procedures.
Transfer Scenario “Exposure of Personnel While Repairing In-core Flux Mapping System”
Description: Plant personnel received radiation exposure in excess of administrative limits due to a combination of personnel errors, inadequate communications, inadequate procedures, and inadequate training.
A health physics technician also received a radiation exposure in excess of administrative limits due to his inexperience in working in very high radiation areas and a lack of controls to prevent his error. Although the radiation doses were within federal limits, substantially higher doses could have occurred had circumstances been slightly different in these two events.
While conducting in-core flux mapping with the plant operating at 48 percent power, the "A" in-core detector became stuck at 103 inches from the fully withdrawn position. The shift engineer started preparations for repairing the in-core detector. A radiation work permit (RWP) was initiated, and a rad-chem technician was assigned to conduct the pre-job survey. The RWP, survey, and planned containment entry were cancelled when a temporary procedure was written to complete the flux mapping.
When the temporary flux mapping procedure was unsuccessful, the shift engineer reinitiated the repair work. Due to the importance placed upon completing the repairs as soon as possible, an emergency RWP was initiated instead of the normal RWP. An emergency RWP requires a rad-chem technician in attendance at the job site but no RWP paperwork prior to the work. Rad-chem technicians were assigned to perform a pre-job survey for an RWP (type not specified) and additionally were assigned to perform air samples and routine surveys of containment.
Before beginning work, the health physics (HP) foreman briefed the electricians on the radiological requirements of the job stressing that rad-chem technicians were required at the job site, that work was being performed under an emergency RWP, and that normal radiation levels at the in-core drive motors were 5 mrem/hour. The electricians were provided with digital dosimeters set to alarm at 90 mrem.
The rad-chem technicians entered containment about 10 minutes before the electricians. Upon surveying the in-core drive motor area they found the dose rate to be 5000 mrem/hour and promptly left the area. The rad-chem technicians then proceeded to complete the remainder of their assigned tasks.
Upon arriving at the containment entrance, the electricians were informed that the rad-chem technicians were already in containment. The electricians went to the in-core drive motor area and assumed there were no radiation problems because the rad-chem technicians were not present. Although their digital dosimeters alarmed within a short time, the electricians dismissed the alarms based upon the HP foreman pre-job briefing that indicated an expected level of 5 mrem/hour. The amount of work to be done was small, and the job was completed.
In the meantime, the rad-chem technicians left the containment and informed the electrical foreman of the radiation levels at the job site. While the rad-chem technicians were preparing to reenter containment to tell the electricians to leave the in-core drive motor area, the electricians exited the containment. The electricians had received 290 mrem compared to the emergency RWP limit of 100 mrem.
An investigation by the utility identified the following items as the root causes contributing to this event:
Personnel Errors
The electricians violated radiation protection requirements by failing to stop work and exit the area when their dosimeters alarmed.
The shift engineer inadequately assessed job conditions by not determining operable in-core detector positions and unnecessarily initiating an emergency RWP.
The HP foreman failed to properly instruct the electricians and rad-chem technicians. This caused the rad-chem technicians to believe they were performing a pre-job survey for a regular RWP and the electricians to not clearly understand the monitoring requirements at the job site.
Inadequate Communications
Communications between the shift engineer, HP foreman, electricians, rad-chem technicians, and control room personnel were determined to be deficient in that the status of the in-core detectors and the potential for high radiation areas to exist were not discussed.
The rad-chem technicians and electricians were given conflicting information on the type of RWP being utilized and the rad-chem technicians were assigned other work not related to the job.
The control room personnel directly involved with the flux mapping were unaware of the status of containment entry. they did not inform the shift engineer of the detector status and inherent radiation potential.
Inadequate Procedures
Containment access procedure precautions failed to address in-core detector status.
Flux mapping procedures did not provide definitions of the terms "withdrawn", "storage", and "parked" with regard to detector position nor did they provide precautions to follow during containment entries.
The RWP procedure was not in agreement with the station's technical specifications regarding high radiation controls for areas greater than 1000 mrem/hour. Technical specifications required a pre- job survey to be conducted; the RWP procedure did not.
Inadequate Training
HP foreman, rad-chem technicians, and maintenance personnel were not adequately familiar with the in-core detector system and the inherent potential for high radiation to exist.
Maintenance personnel were not adequately trained on digital dosimeter usage.
In addition to taking corrective action to address each of the above concerns, the plant has installed a local, portable radiation monitor in the in-core drive motor area and is reviewing the following areas and activities for potentially large unplanned exposures:
· Access to PWR reactor cavity, in-core detector seal table room, missile barrier, and containment
· Spent fuel and spent resin transfers
Another station
With the plant operating at 90 percent power, surveillance was being performed on the traversing in-core probe (TIP) system. While performing this surveillance the status indication lights for the TIP system ball valve and system ready condition were lost with the TIP probe in the core region. The loss of the system ready light also indicated a loss of power to the logic system that controls TIP movement. This circuit allows TIP movement into the core when certain conditions are satisfied and a control relay is energized. A loss of power to this circuit de-energized the control relay which prevented further TIP movement. Troubleshooting the loss of power problem continued for two hours and while this was in progress the TIP probe remained stuck in the core. In normal operation the probes remain in the core only for a few minutes at a time, as they are moved into and out of the core for flux profile measurements.
The TIP probe finally had to be manually withdrawn from the core to its storage area inside the TIP room using a hand crank on the drive mechanism outside the room. The problem was identified as a faulty solenoid on the ball valve that apparently had burned out and shorted. The short from the solenoid caused the fuses in the logic circuit to open and thus resulted in a loss of power to the indicating lights and control relay.
The ball valve was located in the TIP room that was a high radiation area. In order to enter the room to work on the valve, a radiation work permit (RWP) was required. In accordance with procedure, a health physics technician prepared to survey the area. The results of this survey were to be used in preparation of the RWP. Since the work was occurring on a backshift, only one HP technician was on duty. He acquired the key to the TIP room, and in accordance with a note on the key, he called the radiation protection (RP) department head. The department head informed the technician that dose rates as high as 1000 rem/hour could be encountered.
The HP technician notified the shift supervisor of his intent to enter the TIP room and requested the assistance of auxiliary operators. One auxiliary operator stayed outside the room where he was to time an air sample from the area while the other auxiliary operator stayed behind a shield wall near the door where he monitored radiation with a survey meter. The HP technician entered the room where he first surveyed the walkway through the shield walls with an extender type survey meter. At this point the radiation reading was 200 rem/hour. The meter was again extended into the walkway area, and a reading of 300 rem/hour was obtained. As the probe was extended further, readings dropped off to 50 rem/hour. As the HP technician proceeded further into the room and moved from behind the shield wall with the probe extended, dose rates as high as 800-1000 rem/hour were noted. At this point one of the auxiliary operators moved closer to the HP technician, but after the high dose rates were indicated on the survey meter, both individuals left the area.
The HP technician had been in the TIP room for an estimated 2 minutes before realizing the seriousness of the situation. As the HP technician and auxiliary operator were leaving the area, an HP assistant supervisor who was working late arrived at the TIP room entrance. He had been told earlier by the HP technician that the TIP room was to be surveyed, and he was concerned about the high dose rates in the area. The HP assistant supervisor found that the technician had been in an estimated 300 rem/hour field for about 2 minutes and that the HP technician's 0-500 mrem dosimeter was off scale. The dosimeters of the auxiliary operators indicated that the auxiliary operator who stood at the door received no dose and the auxiliary operator who assisted the technician received approximately 260 mrem. The HP assistant supervisor notified the HP supervisor, who arrived on site and with the HP technician proceeded to the nearest dosimetry processing location. The actual TLD reading for the HP technician was 1.219 rem, 0.1 rem of which was previously acquired.
One of the root causes contributing to this event was the inexperience of the HP technician. He had recently completed 6 months of formal HP training and 6 months of on-the-job training. However, he had not had much experience as an HP technician. He also had no previous experience in the TIP room and thus was not completely aware of the magnitude and sources of radiation that might be expected after the TIP probe and cable had been stuck in the core for a few hours. Considering the lack of experience, better direction, planning, and supervisory involvement were needed.
Station is taking the following steps to prevent reoccurrence:
· The dose rate radiation survey procedure has been modified to include a requirement to withdraw from any area where dose rates exceed 3 rem/hour and contact HP management. Stay times will be calculated prior to reentry.
· A TIP room radiation monitor will be installed.
· Training programs were reviewed and modified as necessary to ensure all HP technicians are sufficiently trained and knowledgeable in light of this event, and that plant personnel are familiar with the presence of dangerous radiation exposure levels within the plant and are familiar with appropriate actions to be taken upon encountering such levels.
· Health physics management was made aware of the need for selecting experienced personnel, when those personnel will be working in areas where HP problems could be dangerous.