Regulatory Guide 8.38
| ML003739558 | |
| Person / Time | |
|---|---|
| Issue date: | 06/30/1993 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| References | |
| DG-8006 RG-8.038 | |
| Download: ML003739558 (15) | |
U.S. NUCLEAR REGULATORY COMMISSION June 1993
)REGULATORY GUIDE
OFFICE OF NUCLEAR REGULATORY RESEARCH
REGULATORY GUIDE 8.38 (Draft was issued as DG-8006)
CONTROL OF ACCESS TO HIGH AND VERY HIGH RADIATION AREAS
IN NUCLEAR POWER PLANTS
A. INTRODUCTION
Appendix A to this guide contains procedures for good operating practices for underwater divers that are recommended for licensees. These practices have evolved, in part, from instances in which propez con Section 20.1101, "Radiation Protection Pro trols were not in place or were not implemented. Ap grams," of 10 CFR Part 20, "Standards for Protection Against Radiation," requires licensees to develop and pendix B summarizes past experiences with very high implement a radiation protection program appropriate and potentially very high radiation areas so that his torical, yet pertinent, information is readily accessible to the scope of licensed activities and potential haz to users, especially to newer personnel.
ards. Section 20.2102 requires licensees to document these programs. An important aspect of a radiation Any information collection activities mentioned protection program at nuclear power plants. is the in in this regulatory guide are contained as requirements stitution of a system of controls that includes proce in 10 CFR Part 20, which provides the regulatory ba dures, training, audits, and physical barriers to pro sis for this guide. The information collection require tect workers against unplanned exposures in high and ments in 10 CFR Part 20 have been approved by the very high radiation areas. Specific requirements appli Office of Management and Budget, Approval No.
cable to controlling access to high radiation areas are 3150-0014.
in 10 CFR 20.1601, and additional requirements to prevent unauthorized entry into very high radiation
B. DISCUSSION
areas are in 10 CFR 20.1602. This regulatory guide describes methods acceptable to the NRC staff for im Requirements intended to prevent inadvertent, plementing these requirements. unwarranted, and potentially dangerous overexpo sures of individuals at facilities licensed by the NRC
are provided in 10 CFR 20.1601 and 20.1602. A
framework of graded radiation protection procedures Underwater divers are being used more often for is recommended in this guide to ensure that the con inspections and maintenance in reactor cavities and trols for access to high and very high radiation areas spent fuel pools. These underwater operations require at nuclear power plants are appropriate to the radia careful planning, proper work methods, and specific procedures because of the potential for significant tion hazard during both normal operations and ab overexposures from irradiated fuel elements and irra normal operational occurrences.
diated reactor components and structures that act as Dose rates in areas of nuclear power plants acces high-level radiation sources. sible to individuals can vary over several orders of USNRC REGULATORY GUIDES Written comments may be submitted to the Regulatory Publications Branch, DFIPS, ADM, U.S. Nuclear Regulatory Commission, Washing Regulatory Guides are issued to describe and make available to the pub ton, DC 20555.
lic such information as methods acceptable to the NRC staff for Imple menting specific parts of the Commission's regulations, techniques The guides are Issued in the following ten broad divisions:
used by the staff in evaluating specific problems or postulated acci dents, and data needed by the NRC staff in its review of applications for 1. Power Reactors 6, Products
2. Research and Test Reactors 7. Transportation permits and licenses. Regulatory Guides are not substitutes for regula
3. Fuels and Materials Facilities 8. Occupational Health tions, and compliance with them Is not required, Methods and solutions
4. Environmental and Siting 9, Antitrust and Financial Review different from those set out in the guides will be acceptable if they pro S. Materials and Plant Protection 10. General vide a basis for the findings requisite to the issuance or continuance of a permit or license by the Commission. Copies of issued guides may be purchased from the Government Printing Office at the current GPO price. Information on current GPO prices may be obtained by contacting the Superintendent of Documents, US.
This guide was Issued after consideration of comments received from Government Printing Office, Post Office Box 37082, Washington, DC
the public. Comments and suggestions for Improvements in these 20013-7082, telephone (202)512-2249 or (202)512-2171.
guides are encouraged at all times, and guides will be revised, as ap Issued guides may also be purchased from the National Technical Infor propriate, to accommodate comments and to reflect new Information or mation Service on a standing order basis. Details on this service may be experience. obtained by writing NTIS, 5285 Port Royal Road, Springfield, VA 22161.
magnitude. High radiation areas, where personnel 6. Frequency for updating radiation work per can receive doses in excess of the regulatory limits in mits (RWPs) or their equivalent, and a relatively short time, require special controls. Very 7. Placement of measuring and alarming do high radiation areas require much stricter monitoring simeters.
and controls since failure to adequately implement ef fective radiological controls can result in radiation 1.2.2 Administrative procedures should address doses that result in a significant health risk. the management oversight and specific control meas ures needed for entry into high and very high radia For the purpose of this guide, a high radiation tion areas. The procedures should include the process area is defined as an area, accessible to individuals, for gaining entry to these areas, such as the control in which radiation levels could result in an individual and distribution of keys.
receiving a deep dose equivalent in excess of 0.1 rem
(1 mSv) in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> at 30 centimeters from the radia 1.2.3 Procedures for activities that can greatly in tion source or from any surface that the radiation crease in-plant radiation levels (i.e., the withdrawal of penetrates. A very high radiation area means an in-core detectors, thimble tubes, or transversing in area, accessible to individuals, in which radiation lev core probes from the reactor) should provide for noti els could result in an individual receiving an absorbed fication of personnel likely to authorize or have ac dose in excess of 500 rads (5 grays) in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> at 1 cess to affected areas.
meter from a radiation source or from any surface that the radiation penetrates. An accessible area is 1.2.4 Procedures should provide for timely sur defined as one that can reasonably be occupied by a veys to identify and post with precautionary notices major portion of an individual's whole body, which is the areas and systems that may become high or very high radiation areas, especially when in-plant changes defined in 10 CFR 20.1003.
(e.g., spent fuel transfer operations) could alter the ambient radiation levels.
C. REGULATORY POSITION
1.2.5 Procedures should be provided to verify, at
1. PROGRAM ELEMENTS least on a weekly basis, that proper controls such as posting and barriers are in place for restricting access Licensees are required by 10 CFR 20.1101 to de to high and very high radiation areas.
velop and implement a radiation protection program appropriate to the potential radiation hazards in their 1.3 Training facility. Because of the potential for overexposure in The types of controls required for entry into high high and very high radiation areas, it is important that and very high radiation areas should be included in licensees have effective programs for controlling ac training for radiation workers (both initial and re cess to these areas. There have been instances of per qualification training). Areas in the plant that are sonnel inadvertently entering these areas because of known to have the potential for becoming very high inadequate controls on access. radiation areas should be specifically identified.
The following elements should be included in the plant procedures and practices for access control to 1.4 Communications be sure that personnel are protected in high and very Good communication is essential among all de high radiation areas. partments concerned with entry into high and very high radiation areas to prevent excessive and unwar
1.1 Management Control ranted radiation exposures. This communication is especially important among personnel in known po Facility management has the responsibility for de tential or existing very high radiation areas, such as veloping, implementing, and enforcing access control reactor cavities, spent-fuel transfer areas, spent-fuel procedures for high and very high radiation areas. pools, and other reactor components and tanks. The access control program should include procedures
1.2 Procedural Controls and provisions for the use of equipment to ensure adequate communication. The group or department
1.2.1 Access control procedures for high and responsible for radiation protection should be notified very high radiation areas should address at least the prior to any entry into a very high radiation area.
following areas:
1.5 Physical Controls
1. Job planning, Physical barriers (such as chain-link fencing or
2. Radiation protection coverage, fabricated walls) may be used to prevent unauthor
3. Survey techniques and frequencies, ized personnel access to high and very high radiation areas. Physical barriers surrounding high radiation ar
4. Training of workers, eas should be sufficient to prevent inadvertent entry
5. Prework briefing, (e.g., a 2-meter [6-foot] fence, with worker training
8.38-2
and signs or procedures to deter climbing, may be tion area, inaccessible. The following guidelines apply adequate for controlling access to a high radiation to shielding used for the purpose of controlling ac area). Physical barriers should, to the extent practica cess.
ble, completely enclose very high radiation areas suf ficient to thwart1 undetected circumvention of the
1. The shielding should not be readily removable.
barrier (i.e., fencing around very high radiation areas Blankets, bricks, or other portable shielding that should extend to the overhead and preclude anyone could be moved by hand would be readily remov from climbing over the fencing). Entrances or access able; however, shielding requiring a hoist or points to these areas should be controlled, as de crane to move would not be considered readily scribed in Regulatory Positions 2 through 4. Physical removable.
controls should be established that do not preclude personnel access to these areas when access is re
2. If the shielding is removable, it should be posted quired to respond to emergencies. with a warning sign such as: "Warning, do not Implicit in the definition of an entrance or access remove. Dangerous radiation levels may result."
point to a high radiation area is that the opening (or portal) itself is accessible to personnel. Openings in 3. If the shielding is removable, local radiation physical barriers around a high radiation area are not monitors with audible and visible alarms should required to be controlled as entrances if exceptional be installed to warn personnel of the high expo measures are needed to access them. Examples of ar sure rates created by removal of the shielding.
eas that do not need to be controlled as entrances are the manway to a tank or vessel that has its cover
2. HIGH RADIATION AREAS
bolted in place or an opening in a shield wall that is physically difficult to access without a ladder or mo 2.1 Options for Access Control bile platform.
Of the options for access control provided in 10
An acceptable method of excluding personnel CFR 2 0.1601(a), the most widely used procedure at from areas with dose rates greater than 1 mSv (100
nuclear power plants is keeping high radiation areas mrem) in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> is to provide a substantial physical locked. Although licensees have the option to control barrier (e.g., chain-link fencing) that completely en high radiation areas with the use of a control device closes the area and has no openings or portals. This to reduce radiation levels when an individual enters type of control is commonly called cocooning. Since the area or the use of an alarm to alert the individual these areas are not accessible, the control of access and the supervisor to an entry into a high radiation and posting requirements in 10 CFR Part 20 for high area, experience has shown that these options have and very high radiation areas do not apply. However, limited practical application at nuclear power plants.
the requirements in 10 CFR Part 19 to instruct the In addition to the provisions of 10 CFR 2 0.1601(a), a worker on the radiological hazards in these areas are nuclear power plant licensee may apply for Commis applicable. sion approval of alternative methods for control un Note: When an inaccessible portal to a high ra der 10 CFR 2 0.1601(c). See Regulatory Position 2.4 diation area is made accessible (e.g., a manway cover below.
is removed or scaffolding is erected) or when a portal is created in a physical barrier (i.e., a cocoon is 2.2 Positive Access Control breached), the applicable controls for a high or very high radiation area must be provided. Positive control over each individual entry is re quired by 10 CFR 20.1601(a) (3) when access is re Controls must be established that prevent person quired to a high radiation area that is normally con nel from being locked in a high radiation area (10 trolled by being locked. In a large facility such as a CFR 20.1601(d)). For example, if chains and pad nuclear power plant, appropriate positive access con locks are used, the procedural controls must prevent trols can be instituted through the use of radiation the area from being locked with personnel in the work permits (RWPs) or an equivalent program. Such area. If doors are self-locking, personnel must be able a system ensures appropriate supervision through spe to open them from the inside without a key (10 CFR cific procedures that establish requirements for con
20.1601(d)). trol and delegate responsibility to qualified individu als. Procedures for establishing positive control over
1.6 Shielding each entry should provide for:
Shielding may be used to make a high or very 1. Surveys that identify the radiation hazards in the high radiation area, or a potentially very high radia area should be made and the results docu mented;
1 Determined circumvention of a physical barrier, with wire cutters or other tools, cannot be prevented absolutely. Such 2. An appropriate level of supervision to determine instances should be addressed with appropriate disciplinary that exposure of the individual to the hazards is action. warranted;
8.38-3
3. Communication of the nature and extent of the such areas should be provided with or accompanied radiation hazards to each individual entering the by one or more of the following:
area;
"* A radiation monitoring device that continuously
4. Protective measures (e.g., shielding, time limits, indicates the radiation dose rate in the area, protective clothing, monitoring) to protect the in " A radiation monitoring device that continuously dividual from excessive or unnecessary radiation integrates the radiation dose rate in the area and exposure; and alarms when a preset integrated dose is received.
Entry into such areas with this monitoring device
5. Permission for only authorized individuals to en may be made after the dose rates in the area ter the high radiation area with all entries and have been determined and personnel have been exits documented.
made knowledgeable of them,
2.3 Direct or Electronic Surveillance " An individual qualified in radiation protection procedures with a radiation dose rate monitoring Direct or electronic surveillance is identified in device. This individual is responsible for provid
10 CFR 20.1601(b) as a substitute for the controls ing positive radiation protection control over the required in 10 CFR 20.1601(a). The direct or elec activities within the area and should perform pe tronic surveillance should have the following capabili riodic radiation surveillance at the frequency ties as a minimum.
specified in the radiation protection procedures
1. Detect attempted unauthorized entry, or the applicable RWP.
In addition, areas that are accessible to personnel
2. Warn individuals that their attempted entry is un and that have radiation levels greater than 0.01 Sv authorized, and (1.0 rem) (but less than 500 rads at 1 meter) in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> at 30 cm from the radiation source, or from any
3. Alert the proper authority about an unauthorized surface penetrated by the radiation, should be pro entry so that action can be taken to correct the vided with locked doors to prevent unauthorized en situation. try, and the keys should be maintained under the ad ministrative control of the shift supervisor on duty or
2.4 Alternative Methods for Access Control health physics supervisor. Doors should remain locked except during periods of access by personnel The requirements in 10 CFR 20.1601(a) for ac under an approved RWP that specifies the dose rates cess to high radiation areas may, in some instances, in the immediate work areas and the maximum allow cause unnecessary restrictions on plant operations. able stay time for individuals in that area. In lieu of a According to 10 CFR 20.1601(c), licensees may ap stay time specification on the RWP, direct or remote ply to the Commission for approval to use alternative continuous surveillance (such as closed circuit TV
methods for control. The following method is accept cameras) may be made by personnel qualified in ra able to the NRC staff as an alternative to the require diation protection procedures to provide positive ex ments in 10 CFR 20.1601(a) for the control of access to high radiation areas. posure control over the activities being performed within the area.
Each high radiation area as defined in 10 CFR Individual high radiation areas that are accessible Part 20 should be barricaded 2 and conspicuously to personnel, that could result in radiation doses posted as a high radiation area, and entrance thereto greater than 0.01 Sv (1.0 rem) in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, and that should be controlled by requiring issuance of a radia are within large areas where no enclosure exists to tion work permit (RWP) or equivalent. Individuals enable locking and where no enclosure can be rea trained and qualified in radiation protection proced sonably constructed around the individual area ures (e.g., a health physics technician) or personnel should be barricaded and conspicuously posted. A
continuously escorted by such individuals may be ex flashing light should be activated as a warning device empted from this RWP requirement while performing whenever the dose rate in such an area exceeds or is their assigned duties in high radiation areas where ra expected to exceed 0.01 Sv (1.0 rem) in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> at 30
diation doses could be received that are equal to or cm from the radiation source or from any surface less than 0.01 Sv (1.0 rem) in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> (measured at penetrated by the radiation.
30 centimeters from any source of radiation) pro vided they are otherwise following plant radiation pro 2.5 Controls for High Radiation Areas (Control tection procedures, or a general radiation protection Points and Barriers)
RWP, for entry into such high radiation areas. Any individual or group of individuals permitted to enter Controls (e.g., locked doors, access control, and
2 A barricade can be a rope, ribbon, or other firmly secured, posting) for high radiation areas may be established at conspicuous obstacle that (by itself or used with physical bar locations beyond the immediate boundaries of the riers such as existing walls or hand railings) completely sur high radiation areas to take advantage of natural or rounds the area and obstructs inadvertent entry. existing barriers. The use of one locked door, or one
8.38-4
control point where positive control over personnel high radiation areas inside the containment, with the entry is exercised, to establish control over multiple reactor at power, may be controlled by locking the high radiation areas is acceptable provided the follow containment access port. However, each very high ra ing conditions are met: diation area within these areas should also be con spicuously posted and barricaded separatel
y. Controls
1. The individual high radiation areas are barri for personnel access to very high radiation areas caded and posted separately to identify the actual should be established at the locked entrance.
areas of concern, 3 Authorized entries to very high radiation areas
2. Control points are established sufficiently close to may be monitored by continuous direct electronic the high radiation areas that adequate supervision surveillance. Unauthorized entries to very high radia of access to the areas can be assured, and tion areas inside a PWR containment at power can be controlled by locking containment access. However,
3. The required protective measures and other re during authorized entry of the containment at power, quirements for entering the high radiation areas electronic surveillance is an acceptable method to en (e.g., dosimetry, monitoring) are enforced at the sure that unauthorized entries do not occur into
4 control point. posted and barricaded very high radiation areas within the containment.
2.6 Control of Keys
3.2 Control of Keys The shift supervisor or the radiation protection manager (or their respective designees) should ad The following procedures should govern the ad ministratively control the issuance of keys to person ministrative control of keys to very high radiation ar nel requiring access to high radiation areas and the eas.
return of the keys.
1. Procedures should be established so that
3. VERY HIGH RADIATION AREAS (1) there are stricter requirements for issuance of keys to very high radiation areas than keys to Because of the potential danger of life-threaten high radiation areas, and (2) the responsible op ing overexposures to individuals, extremely tight con erations and radiation protection supervisors are trol must be maintained over any entry to very high notified prior to personnel entry to very high or radiation areas. According to 10 CFR 20.1602, licen potentially very high radiation areas.
sees must institute additional measures to ensure that an individual is not able to gain unauthorized or inad 2. A key for access to a very high radiation area vertent access to very high radiation areas. To the ex should unlock only that area. Master keys that tent possible, entry should be forbidden unless there unlock more than one area may be established is a sound operational or safety reason for entering. for use during emergency situations provided Special consideration should be given to areas that their distribution is limited and they are not used become very high radiation areas when the plant for normal personnel access.
changes operational modes, such as shutdowns or startups. 3.3 Radiation Work Permits
3.1 Entrances Entries to very high radiation areas should be controlled by issuance of a specific RWP or equiva Entrances to very high radiation areas should be lent. General, standing, or blanket RWPs should not kept locked except during periods when access to the be used for controlling entries to very high radiation areas is required (see 10 CFR 20.1601(a)(3)). Post areas.
ing of very high radiation areas is required by 10 CFR 20.1902. 3.4 Radiation Protection Technician Multiple very high radiation areas may be con A person entering a very high radiation area trolled with one locked entrance to take advantage of should be accompanied to the entryway to that area natural or existing barriers. For example, several very by a radiation protection technician who can deter mine the radiation exposure conditions at the time of
3 entry and render assistance if necessary.
Relatively small areas with several discrete high radiation ar eas (i.e., near several valves or components) do not require separate barricades and posting for each if the whole room
4. SPECIAL AREAS
(or area) is considered a high radiation area.
4 Special hazards may arise in areas that usually Protective measures for access to an area not posted and bar ricaded as a high radiation area, but which is within a room are not very hazardous but have the potential to be or area controlled as a high radiation area, may be relaxed come very high radiation areas during certain normal commensurate with the radiological hazards existing in the plant operations. For example, a PWR reactor cavity area. sump can change from a radiation area to a very high
8.38-5
radiation area as a result of withdrawal of the retract very high radiation areas are incorporated into able incore detector thimble tubes (see Appendix B). plant procedures.
4.1 Administrative Procedures 4.3 Procedures Administrative procedures should be established Written procedures for any diving operations into to identify these "special" plant areas and ensure that pools, tanks, or cavities, or for access to plant compo appropriate control measures for potentially very high nents that contain or may contain highly radioactive radiation areas are implemented prior to starting any materials, should be established to ensure proper ra operation that could create very high radiation areas. diological controls. Appendix A discusses some radio logical considerations for conducting diving opera tions that should be incorporated into the plant pro
4.2 Materials cedures for diving operations.
Because of high radioactivity levels from activa 4.4 Potential Very High Radiation Areas tion and contamination, materials in the spent fuel pools, reactor vessel, and refueling cavities could cre Areas of the plant that are known to have a high ate a very high radiation area when unshielded. These potential for becoming very high radiation areas dur materials are normally covered with more than 10 ing certain operational occurrences should be con feet of water and are inaccessible to personnel per trolled to provide for ready evacuation of the area.
forming duties above the pool surface. Therefore, An example would be the upper drywell in a BWR if these pool areas do not have to be controlled as high an activated fuel bundle is dropped during fuel han or very high radiation areas solely because of the ma dling.
terials in them provided that:
D. IMPLEMENTATION
1. Control measures are implemented to ensure that activated materials are not inadvertently raised The purpose of this section is to provide informa above or brought near the surface of the pool tion to applicants and licensees regarding the NRC
water, staff's plans for using this regulatory guide.
Except in those cases in which the applicant or
2. All drain line attachments, system interconnec licensee proposes an acceptable alternative method tions, and valve lineups are properly reviewed to for complying with specified portions of the Commis prevent accidental drainage of the water, and sion's regulations, the methods described in this guide will be used in the evaluation of compliance with
3. Controls for preventing accidental water loss and 10 CFR Part 20 on control of access to high and very drops in water levels that may create high and high radiation areas in nuclear power plants.
8.38-6
APPENDIX A
PROCEDURES FOR DIVING OPERATIONS IN
HIGH AND VERY HIGH RADIATION AREAS
1. A special radiation work permit (RWP), or trained to perform such surveys. If irradiated fuel equivalent, containing detailed requirements for or other highly radioactive objects are moved, an the work should be written. underwater survey should be conducted before any diving operations resum
e. A survey map of
2. Continuous observation of diving operations the diving area should be prepared and updated should be provided by qualified radiation protec to reflect the current status.
tion (RP) personnel that have stop-work author ity. Clear management guidance on when to exer cise this control function should be included in 5. When practical, physical barriers should be pro radiation protection and diving procedures (see vided to prevent divers access to irradiated fuel additional discussion on diving in Appendix B). elements and other high radiation items or areas.
Each diver should be equipped with a safety line
3. The location of the fuel assemblies and other ir and continuous voice communication with sur radiated objects that produce dose rates greater face personnel. Emergency procedures for diver than 0.01 Sv (1 rem) per hour at their surface rescue should be provided and understood by should be documented, and the location of these everyone involved in the diving operation.
items should be made known to the divers.
6. Divers should be equipped with a calibrated do
4. Radiation surveys of diving areas should be con simeter that will function and provide an alarm ducted before all diving operations. Those underwater. This dosimeter should be checked prework surveys should be conducted using two for operability each day before diving operations independent radiation survey instruments. Conf begin. Each diver should also be equipped with a irmatory surveys of the work area may be per remote-readout radiation detector that is continu formed by the diver if the diver is properly ously monitored by RP personnel.
A-1
APPENDIX B
EXPERIENCE WITH VERY HIGH AND
POTENTIALLY VERY HIGH RADIATION AREAS
The following NRC documents provide informa Heat Removal Experience Review and Safety Analy tion on past incidents in high and very high radiation sis: Pressurized Water Reactors," NSAC-052, Janu areas and present means for preventing their recur ary 1983.
rence. They are summarized here so that pertinent historical information is readily accessible to users, es Some of the areas mentioned in the above docu pecially to newer personnel. ments have the potential to become high and very high radiation areas during certain periods of opera IE Circular 76-03, "Radiation Exposures in Re tion, most frequently during refueling outages. Poten actor Cavities" tial radiation fields for certain operations are listed in Table B-1 below. These are general ranges, and ac IE Bulletin 78-08, "Radiation Levels from Fuel tual numbers may be higher or lower because of Element Transfer Tubes" plant-specific factors.
IE Information Notice 82-31, "Overexposure of Without proper controls and monitoring, person Diver During Work in Fuel Storage Pool" nel entering these areas when the indicated radiation fields are present could receive radiation exposures IE Information Notice 82-51, "Overexposures in with severe or life-threatening consequences.
PWR Cavities"
A study of the above documents indicates generic IE Bulletin 84-03, "Refueling Cavity Water Seal" reasons for repeated incidents. In general, improper entry into these areas is caused by a lack of aware IE Information Notice 84-19, "Two Events In ness, indicating insufficient training and administra volving Unauthorized Entries into PWR Reactor Cavi tive controls. Some of the causes are discussed below.
ties"
Entry into Reactor Cavities When In-Core IE Information Notice 84-61, "Overexposure of Detectors Are Withdrawn Diver in Pressurized Water Reactor (PWR) Refueling Cavity" At times during refueling or maintenance, the re tractable in-core detectors and associated thimble IE Information Notice 84-93, "Potential for Loss tubes are withdrawn from the reactor. While in the of Water from the Refueling Cavity" reactor core, parts of the detector system such as the thimble tubes become highly radioactive. These parts IE Information Notice 86-107, "Entry into PWR can create radiation fields within the reactor cavity Cavity with Retractable Incore Detector Thimbles where annual occupational dose limits can be ex Withdrawn" ceeded within a few seconds. These extremely haz ardous areas can present life-threatening radiation IE Information Notice 87-13, "Potential for High situations in which acute exposures, sufficient to Radiation Fields Following Loss of Water from Fuel cause serious radiation injury, are possible after just a Pool" few minutes of exposure. This hazard is compounded by limited visibility and access to equipment within NRC Information Notice 88-63 and its supple the reactor cavity. The cavity is also a hostile physical ments, "High Radiation Hazards from Irradiated In environment in which accidents and mishaps can core Detectors and Cables" occur.
NRC Information Notice 88-79, "Misuse of In the vicinity of the thimbles, general area dose Flashing Lights for High Radiation Area Controls" rates can be greater than 20 gray per hour (2,000
rads per hour), with dose rates at the surface of the NRC Information Notice 90-33, "Sources of Un guide tubes as high as 200-400 gray per hour (20,000
expected Occupational Radiation Exposure at Spent to 40,000 rads per hour). Acute exposures to these Fuel Storage Pools" high dose rates are sufficient to cause clinical radia tion injury effects (or possibly death) within just a few These documents are available for inspection and minutes (e.g., 20 Gy/hr or 0.3 Gy/min [2,000 rads/hr copying for a fee from the NRC Public Document or 30 rads/min]). (See Figure B-i.)
Room, 2120 L Street NW., Washington, DC. The PDR's mailing address is Mail Stop LL-6, Washing In the past, personnel from the operations de ton, DC 20555; phone (202)634-3273; fax partments at several plants have entered the reactor
(202) 634-3343. cavity without radiation work permits, adequate sur veys, or knowledge of the condition of the retractable An Electric Power Research Institute document in-core detectors and their thimble tubes. Personnel also provides information on past incidents: "Residual have bypassed the lock systems and ignored posted B-1
TABLE B-i Spent fuel transfer tube 100-500 Gy/hr (10,000-50,000 rads/hrl)
Letdown IX/filter 10-100 Gy/hr (1,000-10,000 rads/hr)
Spent fuel (in pool) 1000-10,000 Gy/hr (100,000-1,000,000rads/hr)
Radwaste resin tank -50 Gy/hr (-5,000 rads/hr)
Traversing in-core probe detectors (TIPS) and cables, source and intermediate range monitor
2 detectors and cables (SRMs,IRMs) 0.01-1000 Gy/hr (1-100,000 rads/hr)
Reactor cavity with thimbles, withdrawn 2-20 Gy/hr (200-2,000 rads/hr)
Thimbles -500 Gy/hr (-50,000 rads/hr)
Reactor cavity (in core) >10 Gy/hr (>1,000 rads/hr)
3 Steam generator channel head 0.1-0.4 Gy/hr (10-40 rads/hr)
'This is the dose rate during spent fuel transfer.
2 These doses vary considerably depending on the time after withdrawal from the core. Immediately upon with drawal, dose rate of >100 Gy/hr (10,000 rads/hr) may be experienced, while decay can reduce the contact dose rates to -0.01-0.1 Gy/hr (1-10 rads/hr) after about 3 days.
3 Although this is not a very high radiation area, it is important because it is an area frequently accessed by personnel.
warning signs on the special conditions required for 1. Personnel were not aware of the hazards to a entry. These personnel include managers, shift engi worker in the drywell resulting from a dropped neers, shift supervisors, reactor operators, and health spent fuel element.
physics technicians. There have been overexposures exceeding established limits, and several near overex 2. Personnel were not aware of the special shielding posures. requirements.
3. Radiological controls, procedures, and personnel Fuel Movement in BWR Drywells training needed improvement.
4. There was a lack of communication between fuel During certain spent fuel handling operations, operators and personnel at radiological control very high dose rates can exist in BWR drywells. All points.
drywell containment types (Mark I, II, and III) lack complete shielding. Fuel handling must be controlled Divers in the Spent Fuel Pool and Reactor to prevent potentially fatal exposure to drywell work Cavity ers from mishaps with irradiated fuel. Unshielded ir radiated fuel can create radiation fields of 102 to 104 Divers are used for an increasing number of gray per hour (104 to 106 rads per hour) at a distance maintenance and inspection tasks. The operations of 1 foot. Figure B-2 shows dose rates in several areas these individuals perform require careful and thor of the drywell resulting from spent fuel in various con ough planning. The use of proper underwater work figurations. techniques can result in substantial savings of time and reductions in radiation doses.
In 1987 and 1988, the NRC conducted reviews of the radiological controls for BWR drywells during The gear that divers wear makes their out-of water movements awkward and makes seeing and spent fuel movement. The licensees' use of temporary hearing more difficult, thereby hindering communica shielding for transfer of spent fuel to the storage pool tions. Control of a diver's location in the pool is im (see Figure B-3), operational considerations (e.g., re stricting access to the upper drywell or evacuation pr portant to keep the diver away from areas of high ocedures for the drywell during fuel movement), and radiation levels.
employee training were all reviewed. Careful planning and execution of divers' work in the spent fuel pool, reactor cavity, and reactor vessel The following conditions have been found in the and piping are extremely important, as a single spent past: fuel element can create radiation fields of 102 to 104 B-2
Gy per hour (104 to 106 rads per hour) at close prox from components that have been suspended at insuf imity. Other irradiated objects in the pool or cavity ficient depth in the spent fuel pool.
can produce contact dose rates from ten to hundreds f rads per hour. Other mechanisms that can cause water losses in the spent fuel pool, fuel transfer canal, and reactor Past experience shows that surveys and- radiation cavity include certain misalignments of valves in the work permits have sometimes been inadequate for the residual heat removal system while the reactor is in special nature of the work environment for divers. the shutdown cooling mode (assuming shutdown cool Continuous readout dosimeters and dose rate survey ing is in use when the cavity is filled), leaking steam instruments have not been widely used. Dosimeters generator nozzle dams, and slow-draining lines at with alarms have failed for lack of proper controls tached to the refueling cavity.
and checks of instruments. Dose rate monitoring de vices that warn of unexpected changes in dose rates Resin Tanks, Systems, and Chemical in the work area have not been used. Procedures de Decontamination tailing special precautions for diving operations in these areas have been inadequate in some cases. Visi Resin tanks may accumulate large inventories of bility, lighting, and the performance of underwater radionuclides from the processing of various coolants survey instrumentation in the fuel pool have been or wastes. Resins may flow through piping in the reac poor. tor facilities because of improper valve lineups, mal functions, etc., and may result in new high radiation areas.
Loss of Water from the Fuel Pool, Fuel Transfer Canal, and Reactor Cavity Chemical decontamination of systems may result in the movement of large quantities of radioactive Complete or partial loss of water from the spent materials. Activities in these areas must be carefully fuel pool, fuel transfer canal, or reactor cavity can observed because of the potential for the areas to be result in very high radiation areas. In some instances, come very high radiation areas.
a refueling cavity water pneumatic seal and a transfer canal pneumatic seal have failed, causing a rapid Other Very High Radiation Areas drop in the water level in the spent fuel pool. These large water losses can expose spent fuel in the fuel Portions of the reactor piping, such as valves and pool or uncover other highly radioactive objects in the loops, may become collection points for radionuclides fuel pool (such as irradiated control rod blades and over time. Activities in these areas must be carefully neutron detectors) within a few minutes. These large observed because of the potential for the areas to be water losses could also result in high radiation levels come very high radiation areas.
B-3
>*2000 R/hr PLATFRM/ =50-200 R/hr PLATFORM/
GUIDES
(a) Radiation Dose Rates With Incore Instrument Thimbles Withdrawn THIMBLE
GUIDES
,CORE
PLATE
THIMLE i PEN ETRATION
TUBES
- GUIDES-7 (b) Detail of Thimble Guides Figure B-1 Pressurized Water Reactor Cavity B-4
.- 30' ELEVATION
0.*--
0' ELEVATION
Dose Rates During Refueling (R/hr without/with moveable shield)
Fuel Position Location 1 2 3 4 A 30/0.3 8x10 4/15 /
B1 10/- -1- -/- -I
C2 50/--/---
D -/- 3/3x10-2 2x10 3 /1.5 -
E -/- 0.13/lx1o- 4 5x10 2 /0.15 F -I- -1- 3/
Foot Note: 1. Measured 2 I
t. from reactor vessel
2. Measured on contact wit reactor vessel Figure B-2 Dose Rates in BWR Drywell During Spent Fuel Transfer B-5
TOWARD SPENT
FUEL POOL
FUEL CHUTE
SHIELD
Figure B-3 Portable Radiation Shield B-6
REGULATORY ANALYSIS
A separate regulatory analysis was not prepared implemented by the guide. A copy of the "Regulatory for this. regulatory guide. The regulatory analysis Analysis for the Revision of 10 CFR Part 20"
prepared for 10 CFR Part 20, "Standards for (PNL-6712, November 1988), is available for Protection Against Radiation" (56 FR 23360), inspection and copying for a fee at the NRC Public provides the regulatory basis for this guide and Document Room, 2120 L Street NW., Washington, examines the costs and benefits of the rule as DC, as an enclosure to Part 20.
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