IR 05000029/1987010
| ML20238A041 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 08/21/1987 |
| From: | Shanbaky M, Sherbini S NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | |
| Shared Package | |
| ML20237L768 | List: |
| References | |
| 50-029-87-10, 50-29-87-10, NUDOCS 8708280284 | |
| Download: ML20238A041 (8) | |
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{{#Wiki_filter:..... ..... .. .. .. .. .. . .. l i - U.S. NUCLEAR REGULATORY COMMISSION
REGION I
Report No.
50-29/87-10 ) Docket No.
50-29 l l License No.
DPR-3 Category C l Licensee: Yankee Atomic Electric Company 1671 Worcester Road ) Framingham, Massachusetts 017dl l Facility Name: Yankee Rowe
Inspection At: Rowe, Massachusetts l Inspection Conducted: June 15-19, 1987 !
D'!37 Inspectors: N (A tu c. v d'L S.Sherbini, Radiation [lSpecialist date Approved by: bkd @,l2: l 8 7 e M. M. Shanbaky, Chief, Fadilities date Radiation Protection Section ! Inspection Summary: Inspection on June 15-19, 1987 (Report No. 50-29/87-10).
i Areas Inspected: Special announced Radiological Controls Inspection. Areas reviewed included the program to control exposure from radioactive, or " hot", particles,and to prevent their spread within and outside the radiological controls area.
The circumstances connected with a hot particle contamination incident that occurred on May 30, 1987 were also reviewed.
Results: Two apparent violations of NRC requirements were identified (failure to perform an adequate survey and exposure of the skin of the whole body in excess of the regulatory limit).
8708280284 B70824 PDR ADOCK 0000
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- _ _ _ _ _ _ - - & . . DETAILS 1.0 Persons Contacted 1.1 Licensee Personnel
- G. Babineau, Radiation Protection Manager j
- B. Drawbridge, Assistant Plant Superintendent
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- T. Henderson, Technical Director
{ S. Litchfield, Site Nurse j
- R. Mellor, Assistant Technical Director N. Stanford, Dosimetry Group Manager, Yankee Environmental Laboratory
- N. St. Laurent, Plant Superintendent 1.2 NRC Personnel q
- H. Eichenholz, Senior Resident Inspector
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- Denotes attendance at the exit meeting.
2.0 Review of A Skin Exposure Suspected to Be Above the Regulatory Limit.
Contamination was discovered on a member of the licensee staff as that person frisked at the containment check point on the morning of May 30, 1987 (Saturday).
The contamination was on the back right region of the scalp. The frisker reading at that time was 8000 cpm.
Repeated attempts at decontamination failed to reduce the count rate.
The person was then
allowed to go home after applying a bandage to the contaminated area.
Upon his return to the site on the evening of the same day, the whole body counter was used to determine the isotopic composition of the contaminants.
A dose assessment was subsequently made and the dose rate was estimated to be about 8 mrem /hr.
Based on this estimate, and also on the fact that i continued decontamination efforts failed to reduce the count rate, the licensee decided that surgical removal of the contaminant was advisable.
However, in view of the relatively low calculated dose rate, it was decided not to handle it as an emergency situation.
Several discussions with the physicians at a local hospital resulted in arrangements being made for a physician to go to the site on the morning of June 2 (Tuesday) to perform the surgical removal.
During shaving around the contaminated area on the morning of June 2, in preparation for surgical removal, the hot particle came off on a piece of dry skin.
The particle was analyzed on the site gamma spectrometer and was al.;o sent to the Yankee Atomic Environmental Laboratory (YAEL) for further gamma analysis and also for strontium yttrium analysis.
Based on these analyses, the licensee calculated a dose to a one .itimeter square of the skin of the contaminated worker of approximately 10 rem.
The YAEL also performed a series of measurements.in an attempt to measure the skin dose directly using thermoluminescent dosimeters. These measurements yielded a dose estimate of 6.5 rem.
It is the licensee's position that the measure-ments represent a more reliable estimate of the dose than the calculations.
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l The inspector's assessment, however, indicated, that the calculations ' provided a more reliable estimate.
One of the reasons for this assessment is that the licensee did not allow for the fact that the dosimeters used { in the experiment under-respond to several of the beta spectra known to be emitted by the hot particle. The inspector's calculations estimate this ( under response to be of the order of a factor of'1.2.
If allowance is j made for this effect, then the measured dose is raised from 6.5 rem to 7.8
rem.
Thus, by including this necessary correction, the measured dose exceeds the regulatory limit.
Finally, the licensee made a number of
assumptions in arriving at the equations used to convert the experimental data to a dose estimate. Although these assumptions appear reasonable, they are not supported by data, and equally reasonable assumptions can be made that would result in a significantly higher dose estimate than that
obtained by the licensee.
For the above reasons, and in view of the fact ' that the model used in calculating the dose is supported by an extensive body of experimental data, the model will be considered a more reliable method for estimating skin doses resulting from hot particle contamination unless the licensee can demonstrate through very carefully conducted I experiments that the model does not give reasonable dose estimates.
The model used in the calculations is the same as that used in the computer ' progrcm "Varskin" that is currently widely used in the industry for skin . , l dose calculations. Based on calculations using the theoretical data i developed by Berger of NBS, the inspector estimates that the contamination i produced a dose to the skin of approximately 10.5 rem.
If the previous exposure of 0.5 rem for the quarter is added, then the skin dose for the second quarter of 1987 is 11 rems.
This is in violation of the require-ments of 10 CFR Part 20, Section 20.101(a), which sets a limit to the quarterly exposure of the skin of the whole body of 7.5 rems.
(50-29/87-10-01).
The main factor that lead to the high skin exposure resulting from the hot particle contamination was the fact that the particle was allowed to i irradiate the skin for a period of 75 hours.
Soon after discovering the j contamination, the licensee estimated the dose rate to be 8 mrem /hr.
Based on that estimate, the total dose after 75 hours of irradiation would be about 600 mrem.
However, the actual dose rate was close to 140 mrem /hr.
The licensee stated that, had they known that this was the actual dose rate, their response would have been different. Thus, although the licensee's response may have been appropriate for what they believed to be a low dose rate of 8 mrem /hr, this dose rate estimate was in error by a factor of over 10. The root cause of the high skin exposure in this case was therefore the erroneous dose rate estimate.
A review of the calculations used to make the initial dose rate estimate indicated that the licensee had made the assumption that the observed activity was spread out over an area of approximately 15 square cm, which is presumably the , area of the pancake probe used in the frisk.
This assumption is in con-tradiction to the known facts at the time, based on licensee accounts.
These accounts indicate that it was believed at the time that the area of contamination was at most 2 square cm, or " dime size".
It is thus _ _ _ - _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.
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apparent that the survey performed to assess the hazard resulting from the contamination was inadequate.
This is in violation of the requirement of , 10 CFR Part 20, Section 20.201(b) (50-29/87-10-02).
3.0 Findings i The inspector examined the licensee contamination control program including i "bct particle" controls and dose calculations methods.
Several program i upgrades were made subsequent to the May 30, 1987 contamination incident.
3.1 Origins and Distribution of the Hot Particles Isotopic analysis of a number of hot particles found on individuals on site indicated the presence of fission fragments. The hot particles are thus of fuel origin.
Licensee representatives believe that the appearance of hot particles on site is a recent occurrence, and that the problem was not observed during previous outages.
It is believed to have been caused by damage observed in a fuel element that was found to have three broken fuel pins.
This was discovered during the current oute. The licensee n stated that hot particles started to appear on personal during transfer of the camaged fuel from the reactor to the spent fuel pool.
The licensee i noted that the distribution of the particles is currently confined to the i vapor containment.
For this reason, a health physics auxiliary check i point has been established inside the containment air lock.
Protective l clothing is donned at the primary check point in an annex to the Turbine Building.
Personnel working in the containment must go through the air lock and then through the auxiliary check point.
They are assigned a stay time of up to a maximum of two hours.
At the end of this time, the worker I removes the protective clothing at the auxiliary check point, frisks with , a hand f-isker, and then exits the air lock. A second hand frisk is ! conducted at the primary check point, as well as a whole body frisk by a ! whole body frisker.
The licensee stated that the two hour work limit in the vapor containment was instituted to ensure that if a worker is contaminated, the exposure time will be limited to a maximum of about two hours, thus reducing the l total dose received.
The inspector pointed out that this two hour time limit did not apply to people working outside of containment. The licensee stated that they did not believe that this constituted a significant exposure risk because the probability of contamination by a hot particle
outside of containment is very small.
In an effort to limit the spread of hot particles, the licensee has made extensive use of tents constructed around jobs that are potential sources of contamination. Areas that had become contaminated as a result of contact with the primary coolant were cleaned and then covered with masslin, where possible.
Work in highly contaminated areas, such as in and around steam generators, is conducted in full protective clothing and respirators or supplied air hoods. The licensee stated that although these measures have not eliminated hot particle contamination, they appear to have reduced the rate of such contamination.2 Area and Personnel Surveys.
I The licensee stated that in addition to the standard area contamination surveys using filter paper and masslin smears, they have instituted " sticky tape" smears.
Sticky tape is attached to paint rollers and the rollers are then troyed over the surfaces to be surveyed.
Personnel contamination surveys are performed using a hand frisker con-l sisting of an hP-210 or similar hand-held pancake probe attached to an " alarming rate meter.
In addition, three whole body friskers, model IPM-7, have been installed at a low background area at the main HP check point.
All personnel exiting the radiological controls area must pass through the wh'.le body friskers. A portal monitor has also been installed at the entrance to the radiological controls area.
The purpose of this monitor is to alarm in case a person wearing laundered but contaminated protective clothing passes through it.
The licensee indicated that they believe that . some of the incidents of hot particle contamination have resulted from I contact with laundered protective clothing that sti'll retained hot ' particles in them, such as in an inside seam or between the threads of the l cloth.
Discussions with the licensee regarding the sensitivity of the whole body l friskers and the portal monitor revealed that the capabilities and I'mi-l tations of these instruments have not been adequately quantified.
The ' inspector, together with a licensee representative, conducted brief tests that revealed that the whole body frisker has blind spots, particularly in the area of the arms, and also significantly reduced sensitivity if the contamination is on the inside of clothing.
Contamination in such areas . may go undetected.
The inspector indicated that the capabilities and ! limitations of the whole body friskers and portal monitors should be quantified so that potential weaknesses in the performance of these I instruments may be addressed by changing the sensitivity if possible, or i by supplemental frisking.
The inspector also indicated that the user's
manual for the whole body friskers requires that the friskers be checked I on a daily basis using special calibration sources. The licensee indicated ! that the sources have been ordered and that their use will become part of l required daily routine as soon as they arrive on site.
The licensee also indicated that since the whole body friskers had been installed only a i short time before this inspection, there has not been sufficient time to complete all the tests that they planned to perform. They indicated that these tests will be completed soon.
3.3 Laundn The licensee stated that the laundry is normally handled by an offsite contractor.
However, since the identification of hot particles during the , current outage, the licensee has discontinued this arrangement and the laundry is now handled.on site. A laundry trailer has been installed on site in the yard inside the radiological controls area. The trailer contains two freon washers with attached freon recycling systems and filters, and two dryers.
The laundry is segregated before washing.
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Laundry from areas with potential for hot particle contamination is handled separately from laundry coming from other areas of the plant. All laundered articles are frisked manually both inside and out before being released for use. Articles of clothing that are found to be contaminated l (over 3000 cpm with the frisker) are recycled through the laundry, Laundered clothing reading over 20,000 cpm are discarded.
Rubber gloves , used during execution of work in contaminated areas are discarded.
The licensee stated that they expect to return to contractor laundry pro-cessing after completion of the current outage because they expect the hot particle problem to diminish substantially upon completion of outage work.
3.4 Dose Assessment Procedure OP-8430 requires that personnel decontamination be performed , when the manual frisker registers over 100 cpm above backcround or when l an alarm is received on the whole body frisker.
The 100 cpm on the frisker is equivalent to approximately 1 mrem /hr to the skin of the whole body (0.007 cm depth) for a point contamination.
If the contaminant is a point, a skin dose assessment is performed regardless of the activity.
This assessment uses a dose conversion factor of 0.01 mrem /hr/ cpm. The inspector started that if an efficiency of 10% is assumed for the frisker, the conversion constant implies a dose rate conversion factor of approxi-mately 2.2 rem /hr/uCi.
This is low for point contamination resulting from . a mix of fission fragments, and may underestimate the dose to the skin, A l review of the basis for this factor in light of recent isotopic analyses
of hot particles should therefore be undertaken.
Procedure OP-8430 also i requires that if the estimated dose based on the above method exceeds 750 mrem then an isotopic analysis of the particle should be attempted, together with a more detailed dose assessment based on that analysis.
The threshold for dose assessment for uniform skin contamination is 6000 cpm above background.
This is equivalent to a dose rate of approximately 12
mrem /hr to the skin of the whole body.
The threshold for adding the assessed dose to the individual's record is 100 mrem.
Isotopic analysis of hot particles is performed on site using a gamma spectrometer. The spectrometer was calibrated for the hot particle geometry using a source that adequately approximates a point source at approximately 4.5 inches from the face of the detector.
Since this spectrometer cannot detect pure beta emitters, such as some strontium and l ' yttrium isotopes, the licensee has deviloped a technique to estimate the activities of these isotopes on the basis of the measured activities of certain gamma emitters.
The method is based on determining the ratios of strontium and yttrium and some gamma emitters normally found in the hot particles.
The raths were determined from the calculated core inventory for a core at the end of a typical fuel cycle.
Cesium and barium are two isotopes that may be used for this purpose.
This method was compared with analysis results for a hot particle and the accuracy was found to be reasonable.
The method is to be incorporated into the dose assessment procedures.
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i The inspector reviewed the above methodology and the dose assessment procedure (OP-8430 rev. 2) with licensee representatives.
The inspector j pointed out some areas of weakness in the procedure.
The licensee stated ] that the procedure will be reviewed and modified before being released for j general use.
{ ! 4.0 Multiple Hot Particle Problem During the inspection, the liceasee asked the inspector to clarify the { limitations imposed on the entry of personnel into radiological controls areas after receiving a skin dose from a hot particle that is close to, but below the regulatory limit.
Specifically, the if censee questioned whether a second hot particle contamination of the same individual but on a different area of the skin from the first contamination would be additive, and thus ny result in a skin dose that exceeds the regulatory l limit. The inspector directed the licensee to Information Notice 83-59: { Dose Assignment For Workers In Non-Uniform Radiation Fields.
This notice i stated that the dose received by each appendage may be separately deter-mined and compared to the applicable regulatory limit when irradiation l ' occurs in a non-uniform field.
Since hot particle irradiation is non- -{ uniform, the same principles promulgated in the information notice may ' apply to skin exposure by hot particles.
Specifically, separate areas of the skin exposed to hot particles may be individually compared to the l regulatory limit.
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5.0 Exit Interview ) The inspector met with licensee representatives at the conclusion of the inspection on June 19, 1987.
The inspector summarized the purpose, scope and findings of the inspection.
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