ML20045D887
| ML20045D887 | |
| Person / Time | |
|---|---|
| Issue date: | 06/30/1993 |
| From: | NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | |
| References | |
| TASK-DG-8006, TASK-RE REGGD-08.038, REGGD-8.038, NUDOCS 9306300172 | |
| Download: ML20045D887 (15) | |
Text
U.S. NUCLEAR REGULATORY COMMISSION June 1993 no aQ*g)
REGULATORY GUIDE
- e 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 proper 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 pendix B summarizes past experiences with very high Against Radiation," requires licensees to develop and and potentially very high radiation areas so that his-implement a radiation protection program appropriate torical, yet pertinent, information is readily accessible to the scope of licensed activiues 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-X 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, plcmenting these requirements.
unwarranted, and potentially dangerous overexpo-sures of m, dividuals at facibues 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 tion hazard during both normal operations and ab-procedures because of the potential for sigruficant normal operational occurrences.
overexposures from irradiated fuel elements and irra-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 rdGUIAToRY GUIDES Written comments may be submitted to the Regulatory Publications Branch, oFIPS, ADM. U.S. Nuclear Regulatory Commission, Washing-Regulatory Guides are issued to describe and make available to the pub-ton, oC 20555.
lic such information as methods acceptable to the NRC staff for imple-menting specific parts of the Comtnission's regulations, techniques The Quides are issued in the following ten broad divisions:
used by the staff in evaluating specifsc problems or postulated acci-
- 1. Power Reactors
- 6. Products dents and data needed by the NRC staff in its review of applications for
- 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 compilance 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 guldes may be purchased from the Govemment Print!ng Office at the current GPo price. Information on current GPo prlces rnay be obtained by contacting the Superintendent of Documents, U.S.
This guide was issued aftor consideration of comments received from
, " "O hg g g "[*
h2 5 p
the public. Comments and suggestions for improvements in these
/
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 mat 6on Service on a standing order basis. Detalls on this service may be experience.
obtained by writing NTIS, 5285 Port Royal Road, Springfield, VA 22161.
9306300172 930630 PDR REQCD
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08.038 R-ppg
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 Administ-ive procedures should address doses that resuh in a significant health risk.
the management ove.g t 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 arca 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-ccre 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 1.2.4 Procedures should provide for timely sur-that the radiation penetrates. An accessible area is defined as one that can reasonably be occupied by a veys to identify and post with precautionary notices the areas and systems that may become high or very major portion of an individual's whole body, which is high radiation areas, especially when in-plant changes defined in 10 CFR 20.1003.
(e.g., spent fuel transfer operations) could alter the C. REGULATORY POSITION 1.2.5 Procedures should be provided to verify, at 1.
PROGRAM ELEMENTS least on a weekly basis, that propcr 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 Train, g m
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 m licensees have effective programs for controlling ac-traimng for radiation workers (both imtial and re-cess to these areas. There have been instances of per-qualification trammg) Areas m the plant that are sonnel inadvertently entering these areas because of knewn 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 1.4 Communications plant procedures and practices for access control to be sure that personnel are protected in high and very Good communication is essential among all de-high radiation areas.
pr.rtments 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, fabn.cated walls) may be used to prevent unauthor-J 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, ens should be sufficient to prevent madvertent entry 4
- 5. Prework briefing, (e.g., a 2-meter [6-foot] fence, with worker training 8.38-2
- J O !, g
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-p area). Physical barriers should, to the extent practica-cess.
ble, completely enclose very high radiation areas suf-
[N ficient to thwart' undetected circumvention of the 1.
The shielding should not be readily removable.
barrier (i.e., fencing around very high radiation areas Blankets, bricks, or ser 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 point to a high radiation area is that the opening (or 3.
If the shielding is removable, local radiation portal) itself is accessible to personnel. Openings in monitors with audible and visible alarms should physical barriers around a high radiation area are not be installed to warn personnel of the high expo-regtned to be controlled as entrances if exceptional sure rates created by removal of the shielding.
measures are needed to access them. Examples of ar-eas that do not need to be controlled as entrances are 2.
IIIGil RADIATION AREAS the manway to a tank or vessel that has its cover 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 l
An acceptable method of excluding personnel
.CFR 20.1601(a), the most widely used procedure _ at from areas with dose rates greater than 1 mSv (100 nuclear pow;er plants is keeping high radiation areas mrem) in I hour 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 I
closes the area and has no openings or portals. This to reduce radiation levels when an individual enters
! (Q type of control is commonly called cocooning. Since the area or the use of an alarm to alert the individual l y 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 20.1601(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-
{
der 10 CFR 20.1601(c). See Regulatory Position 2.4 I'
Note: When an inaccessible portal to a high ra-below.
diation area is made accessible (e.g., a manway cover l
is removed or scaffolding is erected) or when a portal 2.2 Positive Access Control I
is created m a physical barrier (i.e., a cocoon is breached), the applicable controls for a high or very Positive control over each individual entry is re-high radiation area must be provided.
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-i nel from being locked in a high radiation area (10 trolled by bemg locked. In a large facility such as a CFR 20.1601(d)). For example, if chains and pad-melear 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 w rk permits (RWPs) or an equivalent program. Such j
i 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:
1.
Surveys that identify the radiation hazards in the Shielding may be used to make a high or very area should be made and the results docu-high radiation area, or a potentially very high radia-n mented; f
k
.' Determined circumvention of a physical barrier, with wire 2.
An appropriate level of supervision to determine cutters or other tools, cannot be prevented absolutely. Such instances should be addressed with appropriate disciphnary that exposure of the individual to the hazards is
- action, warranted; 8.38,.
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 e
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 e
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.
~
5.
Permission for only authorized individuals to en-Entry into such areas with this monitoring device ter the high radiation area with all entries and may be made after the dose rates in the area have been determined and personnel have been exits documented, made knowledgeable of them, 2.3 Direct or Electronic Sarveillance An individual qualified in radiation protection e
Direct or electronic surveillance is identified in procedures with a radiation dose rate monitoring device. This individual is responsible for provid-10 CFR 20.1601(b) as a substitute for the controls required in 10 CFR 20.1601(a). The direct or elec.
ing positive radiation protection control over the 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 entry so that action can be taken to correct the surface penetrated by the radiation, should be pro-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 The requirements in 10 CFR 20.1601(a) for ac-locked except during periods of access by personnel cess to hi h radiation areas may, in some instances, under an approved RWP that specifies the dose rates f
in the immediate work areas and the maximum allow-cause unnecessary restrictions on plant operations.
According to 10 CFR 20.1601(c), licensees may ap.
able stay time for individuals in that area. In lieu of a ply to the Commission for approval to use alternative stay time specification on the RWP, direct or remote methods for control. The following method is accept.
continuous surveillance (such as closed circuit TV able to the NRC staff as an alternative to the require.
cameras) may be made by personnel qualified in ra-ments in 10 CFR 20.1601(a) for the control of access diation protection procedures to provide positive ex-to high radiation areas.
posure control over the activities being performed within the area.
Each high radiation area as defined in 10 CFR Part 20 should be barricaded 2 and conspicuously Individual high radiation areas that are accessible posted as a high radiation area, and entrance thereto to personnel, that could result in radiation doses should be controlled by requiring issuance of a radia.
greater than 0.01 Sv (1.0 rem) in I hour, and that tion work permit (RWP) or equivalent. Individuals are within large areas where no enclosure exists to trained and qualified in radiation protection proced, enable locking and where no enclosure can be rea-ures (e.g., a health physics technician) or personnel sonably constructed around the individual area-continuously escorted by such individuals may be ex.
should be barricaded and conspicuously posted. A empted from this RWP requirement while performing flashing light should be activated as a warning device whenever the dose rate in such an area exceeds or is their assigned duties in high radiation areas where ra-diation doses could be received that are equal to or 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 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 em from the radiation source or from any surface 30 centimeters from any source of radiation) pro.
penetrated by the radiation.
vided they are otherwise following plant radiation pro-tection procedures, or a general radiation protection 2.5 Controls for Iligh Radiation Areas (Control Points and Barriers)
- RWP, for entry into such high radiation areas. Any-individual or group of individuals pennitted to enter Controls (e.g., locked doors, access control, and posting) for high radiation areas may be established at
'A barricade can be a rope, ribbon, or other firmly secured, conspicuous obstacle that (by itself or used with physical bar.
locations beyond the immediate boundaries of the riers such as existing walls or hand rallings) completely sur-high radiation areas to take advantage of natural or rounds the area and obstructs inadvenent entry.
ex sting barriers. The use of one locked door, or one 8.38-4 i
1 control point where positive control over personnel high radiation areas inside the containment, with the q
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-i ing conditions are met:
diation area within these areas should also be con-j spicuously posted and barrica %d separately. Controls 1.
The individual high radiation areas are barri-for personnel access to very high radiation areas caded and posted separately to ideuify the actual' should be established at the locked entrance, areas of concern,8 Authorized entries to very high radiation areas 2.
Control points are established sufficiently close iu 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 control point.d posted and barricaded very high radiation areas within the containment.
2.6 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 IIIGH 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 t, hat 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 j
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' 1
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-E mine the radiation exposure conditions at the time of entry and render assistance if necessary.
- Relatively small areas with several discrete high radiation ar-cas (i.e., near several valves or components) do not require l
separate barricades and posting for each if the whole room 4.-
SPECIAL AREAS (or area).ls considered a high radiation area.
Special. hazards.may arise in areas that usually 1 '[\\
' Protective measures for access to an area not posted and bar-6 4
ricaded as a high radiation area, but which is within a room are not verY hazardous but have' the Eotential to be-4 i
-(~f or area controlled as a high radiation area, may be relaxed come very high radiation areas during certam 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.-
l L
I a
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 is Written procedures for any diving operations into Admm.. trative procedures should be established pools, tanks, or cavities, or for access to plant compo-to identify these "special plant areas and ensure that nents that contain or may contain highly radioactive appropriate control measures for potentially very high materials, should be established to ensure proper ra-radiation areas are implemented prior to startmg any diological controls. Appendix A discusses some radio-operation that could create very high radiation areas.
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 liigh 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.1MPLEMENTATION 1.
Control measures are implemented to ensure that
. The purpose of this section is to provide m, forma-activated materials are not inadvertently raised above or brought near the surface of the pool ti n to applicants and licensees regarding the NRC staff s plans for using this regulatory guide.
- water, 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 Jrainage 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.
i O
8.38-6 i
' APPENDIX A PROCEDURES FOR DIVING OPERATIONS IN Il!GII AND VERY IIIGH RADIATION AREAS
?
i V
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 resume. 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-5.
When practical, physical barriers should be pro-cise this control function should be included in vided to prevent divers access to irradiated fuel-radiation protection and divmg procedures (see elements and other high radiation items or areas'.
additional discussion on diving in Appendix B).
Each diver should be equipped with a safety line and continuous voice communication with sur-3.
The location of the fuel assembh.es and other ir-face personnel. Emergency procedures for diver radiated objects that produce dose rates greater rescue. should be provided and understood by than 0.01 Sv (1 rem) per hour at their surface should be documented, and the location of these everyone involved in the diving operation.
items should be made known to the divers.
6.
Divers sh' uld be equipped with a calibrated do- -
o 4.
Radiation surveys of diving areas should be con-simeter that will function and provide an alarm -
ducted before all ' diving operations. Those underoater. 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, f%
'lv)
.l p\\
1 J
A-1 J
APPENDIX B EXPERIENCE WITil VERY HIGII AND POTENTIALLY VERY IIIGH 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 S me of the areas ment,oned in the above docu-historical information is readily accessible to users, es-pecially to newer personnel, ments have the potential to become high and very high radiation areas during certam 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 Poola 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 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 Storde 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-1.)-
. 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- -
-[
s-veys, or knowledge of the condition of the retractable
.1 i
An Electric Power Research Institute document in-core detectors and their thimble tubes. Personnel -
V also provides information on past incidents: " Residual have bypassed the lock systems and ignored posted
-B-1
TAllLE 111 Spent fuel transfer tube 100-500 Gy/hr (10,000-50,000 rads /hri)
Letdown IX/ filter 10-100 Gy/hr (1,000-10,000 rads /hr)
Spent fuel (in pool) 1000-10,000 Gy/hr (100,000-1,000,000 rads /hr)
Radwaste resin tank
-50 Gy/hr (-5,000 rads /hr)
Traversing in-core probe detectors (TIPS) and cables, source and intermediate range monitor detectors and cables (SRMs,lRMs)2 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)
Steam generator channel head 3 0.1-0.4 Gy/hr (10-40 rads /hr) 1This is the dose rate during spent fuel transfer.
2These 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.
aAlthough this is not a very high radiation area, it is important because it is an area frequently accessed by personnel.
1 l
l warning signs on the special conditions required for 1.
Personnel were not aware of the hazards to a l
l 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.
p"vsics technicians. There have been overexposures j
ex.eding 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 i
During certain spent fuel handling operations.
operators and pmonnel at radiological control i
very high dose rates can exist in BWR drywells. All points.
drywell containment types (Mark 1,11, and 111) 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 108 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 fuelin various con-ough planning. The use o proper underwater work r
figurations.
techniques can result in substantial savings of time and reductions in radiation doses.
In 1987 and 1988, the NRC conducted reviews of The gear that divers wear makes their out-of-the radiological controls for BWR drywells during water movements awkward and makes seeing and spent fuel movement. The licensees
- use of temporary shielding for transfer of spent fuel to the storage pool hearing more difficult, thereby hindering communica-tions. Control of a diver s location m the pool is im-(see Figure B-3), operational considerations (e.g., re-p ttant to keep the diver away from areas of high stricting access to the upper drywell or evacuation pr-radiation levels.
ocedures for the drywell during fuel movement), and 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 t o 104 -
11-2
Gy per hour (104 to 10( rads per hour) at close prox-from components that have been suspended at insuf-rnity. Other irradiated objects in the pool or cavity ficient depth in the spent fuel pool.
can produce contact dose rates from ten to hundreds Other mechanisms that can cause water losses in f rads per hour.
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 sornetimes 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 ca.ity 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 Resin tanks may accumulate large inventories of.
these areas have been inadequate in some cases. Visi, radionuclides from the processing of various coolants bility, lighting, and the performance of underwater r wastes. Resins may flow through piping in the reac-survey instrumentation in the fuel pool have been tor facilities because of improper valve lineups, mal-
- poor, 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 Iligh 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
. ool or uncover other highly radioactive objects in the loops, may become collection points for radionuclides l
g 'uel 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.
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NTHIMBLE
,s, s
m s
s y, - 'f GUIDES SUMP SEAL (a) Rad!ation Dose Rates With incore Instrument
-Thimbles Withdrawn s'
THIMBLE GUIDES LOWER CORE
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f) N REACTOR 7
VESSEL
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PENETRATION THIMBLE i.
TUBES GUIDES (b) Detail of Thimble Guides l
l l
l Figure B-1 Pressurized Water Reactor Cavity 9
- B-4
O WATER LEVEL FUEL-EGMENTS I
Q
_4p i
i A B p r FUEL ELEMENTS c
/
FUEL POOL l-
.--- 66' ELEVATION 0-1 p
4s REACTOR VESSEL.
g, ELEVATION '
r
/-
SACRIFICAL
-d BIOLOGICAL
- d
- --O' ELEVATI' N O
SHIELD 0
Dose Rates During Refueling
- (R/hr without/with moveable shield)--
' Fuel Position -
Location 1
2 -.
3 A-
-/-
- 30/0.3 -
8x10 /15
-- / - -
4 B1 10/-
-/-
-/-
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-- / -
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-/-;
-/_ -
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Foot Note:- 1. Measured 2 fL from reactor veessi _
- 2. Measured on contact with reactor veneel :
Figure B-2 Dose Rates in BWR'Drywell During Spent Fuel Transfer::
B-5 h
I.
O TOWARD SPENT FUEL POOL
.N I
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Figure B-3 Portable Radiation Shield O
B-6 i
1 1
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- l...
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, exaniines the costs and benefits of the rule as DC, as an enclosure to Part 20.
L on recycled paper Federal Recycling Program.
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