ML20127H614
| ML20127H614 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 11/11/1977 |
| From: | Cwalina G Office of Nuclear Reactor Regulation |
| To: | Grimes B Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9211180560 | |
| Download: ML20127H614 (12) | |
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MEMORANDUM FOR: B. Grimes. Chief. Environmental Evalaation Branch i
FROM: G. Cwelina Environmental Evaluation Branch THRU: L. Barrett, Section Leader Envimnmental Evaluatica --
Branch
SUBJECT:
MONTICELLO TRIP REPORT On October 7,1977 I visited the Monticello Nuclear Plant to observe the i licensee's effort to maintain occu i as reasonably achievable" (ALARA) pational during repairradiation of the feedwater exposures to "as low nozzles.
The licensee was engaged in repair of the nozzles utilizing a milling ma-chine designed by GE. Because of the generic nature of the pmblem (see N1' REG-0312, " Interim Te .hnical Report on BWR Feedwater and Control Rod Drive Return Line Nozzle Cracking") and high occupational exposures asso-ciated with past repair efforts, the staff is concerned with licensees' efforts to reduce these exposures to ALARA values. There are several methods used to keep occupational exposures ALARA, such as training, de-cor.tamination, shielding and development of special tools which reduce ex-posure time. These techniques, as utilized by Monticello, are discussed in the following paragraphs.
The majority of work performed was done by contract (GE) personnel. These workers were trained on a full scale mockup using the actual tool which was used to remove the cladding from the nozzle. In addition, any local workers must view a videotape of the training session before they are allowed to en-ter the work area. Daily meetings are held to plan all activities in order to keep occupancy times in high radiation areas as short as possible.
The work area was decontaminated using a "hydrolasing" (high pressure water spray) technique. The decontaminated areas include the reactor vessel walls, reactor cavity and the operating floor in the vicinity cf the reactor cavity.
Radiation surveys indicated dose rate reduction factors of 2-5 were achieved by hydrolasing.
Extensive shielding was used to reduce dose rates in the work area. (The work was performd with the core in place.) GE designed the shield plug to be used over the core region. This plug consisted of 33 inches of concrete with a 1 1/4 inch steel plate on each side. The plug is a single unit and weighs about 50,000 pounds. The licensee stated that an analysis was done to determine the consequences of dropping the shield plug on the core. The result was the consequences would not exceed those of dropping the steam separators and drnrs. The analysis was reviewed by the plant safety com-mi ttee which concluded that dropping the plug would not
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en ursmn -a-unnviewed safety question. We understand P58 pIrkennel' informally M-viewed the plug design, handling and support systemsE The shield was 3 y
supported by a series of small beams which mst on the core shroud. The top of the plus was about 74 inches above the top of the active fuel. I Shielding of the core sprey Itne was accomplished by setting lead shields i
vertical'y in front of the lins, placing a board resting on the vertical shieldiag5arran shielding the spray line and covering the boani with lead blankets. This water nozzles. gement was about 12 inches below the centerline of the feed- 3 The nozzle area, including the feedwater spargers, was shielded support lugs. Theselead by hanging shields by pulleys attached to the steam dryer shields are suspended around the entire circumference of the vessel. In order to work on a nozzle, the shields in that nozzle
' 1 area only are raised so that the remaining nozzles and vessel walls are still shielded.
F factor of 8-10. The shielding techniques lowered the dose rates in the area by a The dose rate at waist level on the shield plug was 500 mr/
hr after shielding and before sparger removal whereas before shielding and
' af ter hydrolasing the level was in excess of 4 R/hr. After sparger removal, the level dropped to 300 mr/hr. A sketch of the shielding arrangement is
- included as Fig"re 1.
The milling tool in use was developed by GE specifically for the BWR feed-umr nozzle cracking problem. Past repairs were made by flapper wheel i
grinding the nozzles to remove all the cladding. This method required long exposure times.
late activity due to the small sized particles. Flapper wheel grinding als i requires a minimum of flapper wheel grinding to only smooth the nozzle sur-l The machine operates at 5-10 RPM using either a rou The resultant chips are about 10 mils thick and arc collected in s basket lo-cated under the nozzle.
set the machine and change the cutting heads. Occupancy in the grinding z ally, thus greatly reducing occupancy times in the zone.Ali grinding is done In addition, automatic-a con-tinuous water grinding residue. spray inninges on the nozzle which will wash out any small The area was ventilated by a portable air hose which drew t
l 4000 cfm passing of airafrom it through HEPAthe andwork charcoal area and exhausted it to the containme filter.
were carefully monitored for radiation exposure and Workers in thetime.
occupancy radiation area tective clothing including respirators equipped with particulate filters, wasFull pro-l required at all times in the work zone.
The work monitored. areas on the refueling floor and inside the vessel were continuousl The refueling floor area was monitored using ti,e instrumentation
!. as desigMd for the plant during normal operations.
l The vessel work area was i monitored by an area radiation monitor located inside the vessel with a read- ,
l, out on the refueling floor and by a continuous air monitor which d ew air from the work area near the nozzle at approximately head level. During milling i
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B. Grimes .l @g operations, the aree radiation monitor was reading from 150-200 mr/hr in the vessel. During the flapper wheel grinding the airborne activity $n the ves-sel work area increased to about 90 FC and the refueling floor airtorne ac-tivity.was about 1 1/2 F C.
) Radiation protection procedures were formulated in advance of all work and distributed to the plant radiation protection group. A copy of the memos
, sent to personnel are included as Enclosure la and Ib.
A copy of the outage timetable, including the nozzle repair vork, is included as Enclosure 2.
The overall plant ALARA pn> grams seems to oe well planned and executed. Simi-lar type work was performed at Monticello in 1975 consisting of replacement of the feedwater spargers and examining the nozzle areas for cracks. The early work was done without a core shield and required considerably less work than the recent maintenance. Plant personnel estimate exposure of the present work will be about 1/3 of that previously experienced. It is hoped that experience i gained from the Monticello repair can be utilized at other facilities to aid in reducing their occupational exposures during this and other repair jobs.
G. Cwalina Environmental Evaluation Branch i
, Division of Operating Reactors
Enclosures:
As stated cc:: w/ encl DISTRIBUTION V. Ste110 Central files EEB Rdg D. Eisenhut R. Snaider GCwalina JGuibert cc: w/o enc 1. RCudlin E. Case T. Murphy
- i K. Goller J. Collins P. Nelson, Region I D. Davis R. Alexander J. Sutherland, Region II IL.,E. Adensam R. Muranaka J. Allan, Region 11!
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H. Book, Region V OR Br. Chiefs
[yf)DPM, DSS, DSE Br. Chiefs J. Long i W. Kreger R. Fraley, ACRS (16)
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. INT.E.RN,AL CORRESPONDENCt:
Enclosure la o' Arc July 29,1977 P3;OM F. L. Fey, Radiation Protection Supervisor tocanoa Monticello .
To M. H. Clarity, Supt. , Plt. Engr. 4 Rad. Prot. Locanoa Monticello sucact Radiation Exposure Considerations for the Feedwater Sparger Work In the interest of maintaining radiation exposures ALARA during the feedwater ,
s aarger work to be performed during the Fall 1977 Refueling Outage, I am r'. king the following recommendations:
1 The vessel walls should be deconned with a high pressure "hydrolazer".
A rig should be fabricated which will allow a person to be lowered into i the vessel on the center line with equipment which will allow him to maintain the hydrolazer nozzle within 150 cm of the vessel wall. This ,
will require an extension and outriggers to counteract nozzle thrust. '
- 2 The contamination flushed from the walls will accumulate in the reactor water some of which may tend to float. This " crud" should be removed inorder-to reduce the expesure from this source. The reactor cleanup is not very effective in cleaning up this activity. A pump should be provided to pump this water to the fuel pool sMimmer surge tanks.
- 3. The work platfom should be constructed as to provide a minimum of 6 feet of water above active fuel and 2" 3of lead or equivalent to shield workers from the fuel. & ep >*lemh , q 4 'Ihe walls of the vessel should be provided with 2.5 cm of lead (or equivalent) over approximately 90t, of the circumference from the work platform to a height of at least 6 feet. (/"OAceQ,,Cw.im h ede, uy Ao 4 * ) h
- 5. The exposed portion of the core spray lines should be provided sth 5 cm lead (or equivalent) shielding. Q ~\y >,4 L,(e,, y ,
6 The core spray lines must be thoroughly flushed to remove contaminated crud.
Larry Nolan is pursuing items 1 and 2 Items 3, 4, and 5 should be incorporated in the platfonn design. Number 6 should be handled by procedure.
id ( 0 4 F. L. Fey Radiation Protection Supervisor
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N F. L. Fey, Radiation Protection Stpervisor Locario* k nticello q.gu:y-iMO to Itadiation Protection Group LOC ATION %gt{CgQ
- Radiation Protection Memo #77-11 w*act Radiation Protection Requirements for Peedwater Sparger Work 1.0 PURPOSE, 1 This memo establishes radiation protection requirements for feedwater sparger work.
2.0 APPLICABILITY This wmo applies to all personnel working inside' the reactor vessel belco the head flange. 3.0 DEFINITIONS 3.1 Radiation Protection Group Radiation Protection and Chemistry Specialists employed by Northern States Power Company or contract Health Physics Personnel assigned to the NSP Radiation Protection Department. 3.2 Health Physics Personnel Same definition as defined in Step 3.1. 4.0 RESPONSIBILITY
. 4.1 The Radiation Protection Supervisor has the overall responsibility and authority for insuring that adequate radiation protection pre-l cautions and instnictions are provided to personnel during feed- .
water sparger work. 4.2 Health Physics personnel have the responsibility to insure all per-sonnel are provided with the protective equipment / clothing and person-nel monitoring devices prescribed on the Radiation Work Pemit (RWP) issued for the job. 4.3 The NSP Lead Plant Equipment Operator on the floor has the authority and responsibility to stop the job and require evacuation of the work area if an unsafe condition exists.
, 4.4 Each individual working on the feedwater'sparger job has the responsi-I bility to comply with all verbal and written instructions provided to.him by the Health Physics personnel.
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- x Y Radiction Protection Memo f 77-11 September 29, 1977
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q; J' 5.0 RBQUIRDMS 9 5.1 All personnel shall be assigned and required to wear high range self-reading pocket dosimeters (0-1R and 0-10R) in the work area. 5.2 All personnel shall be required to wear a finger TLD badge, wy 5.3 %:t Personnel sher 1 be required to wear a versonnel TLD badge. u d v Aer wm t e b y WP ch t:4 5.4 All personnel shall be timed by individual stop watches by a HP timekeeper. All personnel shall leave the work area when directed by the HP techanician without question. 5.5 No more than six (6) individuals should be in the work area (below the head flange) at any time. . 5.6 Each individual shall obtain a "Sparger Exposure Control Log" from RP Cotnrol Office prior to each entry to the Refuel Floor and return it to RP Control Office upon return from Refuel Floor. 5.7 'Ihe crane shall be manned any time per:,onnel are below the head flange. An alternate escape route / method shall be provided. 5.8 5.9 An Area Radiation hbntior shall be located within the vessel work area and op% ting any time personnel are working below Jie head flan;;e. 5.10 At least two (2) Health Physics Technicians shall be present on the refueling floor when personnel are entering, working in or exiting the work area below the head flange. One will be assigned to keep time and provide warning when an individual should leave the work area. 5.11 All personnel should have completed current hhole Body count before entering the work area. 5.12 All personnel shall have completed respirator training within the past year. 5.13 A Whole Body count should be perfomed for all personnel involved in feedwater sparger work (below the head flange) prior to leaving the site (upon temination). 5.14 A CM4 shall be monitoring airbome radioactivity within the vessel anytime personnel are working below the head flange. 6.0 INSTmy rIONS i
.1 Hea-th Physics personnel shall complete the " Radiation Protection ; S4 c. off Sheet" prior to each entry irto the work area (at least
[ o* a per shift). t l
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6.2 Health Physics personnel shall periodically'sonitor the work area and .:-
.f/ establish the alann point for area radiation monitor and CAM being .@~~N
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l 6.3 Health Physics personnel shall provide timekeeping for all . personnel in the work area. Timekeeping shall be based on using a factor of 1.5 times the dose rate as read from the self-reading pocket dosi . meter. 6.4 Health Physics personnel shall collect and count air samples at least twice per shift, in the reactor vessel and the refueling floor. 4 6.5 Health Physics Personnel shall survey the work area for exposure rate and smearable contamination at least once per 12 hour shift and should perfonn surveys following any change in shielding or contamin-ation until they are familiar with effects of changes. J - 4 i y N
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- 1. An alternate escape route is available.
- HP Technician.
- 2. An Area Radiation hbnitor is operable and operating.
with the instrument detector in the work area. - HP Technician
- 3. At least two (2) Health Physics Technicians are pre-
- sent on the refueling floor.. ,,
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- 4. Air Sample has been collected and counted as indi- .
cated by 6.4 of pincedures. IP Technician
- 5. A Continuous Air hbnitor is operating and sampling ,
the air in the work area. i , HP Technician I
- 6. Smear and Exposure Survey is taken once per shift in work area.
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- REVISION 2
.N0fs j: PAGE 1 OF 2 MONTICELLO FALL '77 REFUEL OITIAGE AUGUST 23, 1977 $
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