ML20132D780
| ML20132D780 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 09/17/1985 |
| From: | Beall J, Kottan J, Pasciak W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | |
| Shared Package | |
| ML20132D767 | List: |
| References | |
| 50-278-85-31, NUDOCS 8509300287 | |
| Download: ML20132D780 (7) | |
See also: IR 05000278/1985031
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U.S. NUCLEAR REGULATORY COMMISSION
REGION I
Report No.
50-278/85-31
Docket No.
50-278
License No.
Priority
-
Category
C
Licensee:
Philadelphia Electric Company
2301 Market Street
Philadelphia, Pennsylvania 19101
Facility Name:
Peach Bottom Atomic Power Station, Unit 3
Inspection At:
Delta, Pennsylvania
Inspection Conducted:
August 6-7, 1985
Inspectors:
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J. J. Kottan ' Radiation Laboratory Specialist
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J . ~ E. B
,~ Project Engineer
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Approved by:
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7.Miasciak, Chief, BWR Radiological
idate
Protection Section
Inspection Summary:
Inspection on August 6-7, 1985 (Inspection Report No. 50-278/85-31)
Areas Inspected: Nonroutine, unannounced inspection of allegation RI-85-A-0084
involving a potential overexposure during an unplanned reactor shutdown of
Unit 3 on March 1, 1985. The inspection involved 20 inspector hours on-site by
two NRC regionally-based inspectors.
Results: No violations were identified.
No individual appeared to have
received doses in excess of regulatory limits.
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0509300287 850
ADOCK O
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DETAILS
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1.
Individuals Contacted
- R. Fleischmann, Manager, Peach Bottom Atomic Power Station
- A. Hilsmeir, Senior Health Physicist
- Denotes those present at the exit interview.
The inspector interviewed other personnel not identified in the report for
reasons of confidentiality.
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2.
Background
On August 2, 1985, Region I received an allegation regarding a potential
overexposure during an unplanned Unit 3 shutdown on March 1, 1985. A
regionally-based NRC inspector was dispatched to the site on August 6
and 7, 1985, in order to review the allegation.
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Two licensee and two licensee contractor personnel entered the Unit 3
recombiner offgas tunnel at approximately 1130 hours0.0131 days <br />0.314 hours <br />0.00187 weeks <br />4.29965e-4 months <br /> on March 1, 1985.
At initial entry, the general area radiation exposure survey meter
(Eberline Instrument Company Model R0-2A air tonization chamber) readings
were approximately 80-100 mR/hr as expected.
During the entry, the survey
meter went offscale on the 0-5 R/hr scale. When switched to the 0-50 R/hr.
scale, the survey meter registered approximately 5 R/hr. When the beta
shield of the instrument was opened, the instrument went offscale on the
0-50 R/hr scale. All four personnel evacuated the Unit 3 recombiner
offgas tunnel promptly. At approximately the same time, friskers through-
out the turbine building were alarming.
Licensee personnel present in the
turbine building were contaminated, and particulate air samples were taken
throughout the turbine building.
The air sample results indicated the
presence of noble gas particulate daughters:
Rb-88 and Cs-138.
Specific
areas of the Unit 3 turbine building were cleared of personnel by the
licensee and posted as airborne radiation areas.
Because the personnel
contamination was short lived, after sufficient decay and monitoring,
personnel could leave the area and the site.
The gas releases and the changes in radiation fields were caused by a
Unit 3 plant transient which occurred at 11:50 a.m. on March 1, 1985 due
to the failure of the 38 offgas recombiner compressor.
The equipment
failure, together with air leakage into the main condenser, caused a loss
of condenser vacuum. Control room operators responded to the transient by
attempting to reduce power and recover condenser vacuum. These efforts
were unsuccessful and the unit scrammed on loss of main condenser vacuum
at 12:03 p.m.
A Licensee Event Report (LER) was submitted regarding this
unplanned reactor shutdown (LER No.85-007).
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3.
External Exposure
The personnel entering the Unit 3 recombiner offgas tunnel were wearing
two TLD badges, one which is read daily by the licensee., and one read
monthly by a vendor. On March 1, 1985, the daily TLD read less than
10 mR gamma for all individuals in the recombiner offgas tunnel. With the
exception of one of the four persons, the daily TLD surface dose results
of March 1, 1985, were also less than 10 mR.
The one exception had an
apparent surface dose of 12.5 mR.
The vendor TLDs for three of the four
individuals were sent to the vendor on March 6, 1985, and indicated
0 surface dose and 0 gamma dose. The radiation survey meter indicated
an exposure of approximately 5 R/hr, and with the beta shield open, the
instrument went offscale (0-50 R/hr).
Based on interviews with personnel who were in the offgas recombiner
tunnel, the inspector determined that at least one person was concerned
about the discrepancy between the survey meter and the TLD results, and the
potential for an overexposure.
The inspector reviewed a licensee discrep-
ancy report (85-087) which was issued regarding the difference between the
survey meter and the TLD results.
The instrument calibration was checked
on March 5,1985, and found to be within calibration and functioning
properly. The H.P. technician who used the survey meter stated that the
meter responded to a radioactive source before entry into the Unit 3 offgas
recombiner tunnel.
The licensee's resolution of the discrepancy report concluded that the
instrument was in error as a result of moisture and high humidity which
caused the instrument to temporarily malfunction. The instrument cali-
bration performed on March 5, 1985, was acceptable because the instrument
had " dried out" by that time. The inspector could find no evidence to
support this conclusion, such as moisture found inside the instrument
which would cause the instrument to over-respond.
An NRC Inspection Report, (Report Nos. 50-277/85-19 and 50-278/85-15)
which contained the results of performance tests of the licensee's inhouse
and vendor TLDs used in their personnel dosimetry program, indicated that
both the inhouse and vendor TLD systems underrespond to lower energy
(T1-204) beta radiation.
Licensee personnel stated that a large part of
the noble gas mixture beta energy spectrum would fall into this lower
energy category.
The licensee would, therefore, multiply the surface dose
by a correction factor to obtain a corrected surface dose. At the time of
this inspection, the licensee had yet to determine the correction factor
to be used in this calculation.
The NRC inspector performed calculations based on an offgas sample taken
on March 4, 1985, at 90% power.
(On March 1, 1985, Unit 3 was at approxi-
mately 25% power prior to shutdown.) The calculated beta dose and the
gamma dose bracket the licensee's TLD values.
See Appendix A.
The
assumptions made by the inspector were based on the following:
(1) No
radioective decay of the offgas sample, (2) dilution based on the ratio of
the gamma survey meter (approximately 5 R/hr), with the beta shield closed,
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to the calculated body dose of approximately 450 R/hr, and (3) dilution
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based on the ratio of Cs-138 concentrations in air samp.les taken in the
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turbine building to the Cs-138 concentration in the offgas sample.
These
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ratios are approximately 100 and 100,000 respectively. Although not in
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equilibrium with Xe-138 (the daughter half life is greater than the parent
half life), the Cs-138 air sample data was decay corrected to the counting
time of the offgas vial, approximately one hour after sample time in order
to approximate the dilution factor.
The dilution factors give boundary
conditions for the dose calculation.
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4.
Conclusion
Based on the results of this inspection, it appears that no licensee
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personnel were exposed in excess of NRC regulatory limits. The TLD gamma
dose results appear to be a valid estimate of the gamma dose obtained by
the individuals in the recombiner offgas tunnel.
The beta doses have yet
to be finalized by the licensee since the licensee has not yet decided on
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- a final correction factor for the system underresponse.
NRC calculations,
based on conservative dilution factors and no radioactive decay, bracket
.the TLD results.
The radiation survey meter appears to have been working
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correctly in the offgas tunnel, and the licensee's resolution of the dis-
crepancy report appears to be incorrect. The licensee, at the time of
this inspection, had no information regarding the survey instrument
. response in noble gas clouds including the potential for leakage into the-
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instrument by the noble gases. The inspector stated that this issue would
be an inspector follow-up item (50-278/85-31-01) until the beta dose had
been finalized, the instrument response to noble gases was determined, and
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the release points of offgas into the offgas tunnel and the turbine build-
ing was determined.
The inspector also reviewed the results of air samples taken in the Unit 3
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turbine building and noted that these values were below 10 CFR 20 MP,C
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values. A review of the Unit 3 roof vent effluent release point for-
March 1, 1985,. indicated an elevated release for approximately two' hour
period, 1230 hrs to 1430 hrs., but within Technical Specification limits.
In addition, the inspector note'd that interviewed individuals expressed
concern regarding the difference between survey instrument beta results
and beta results from TLDs used to measure beta dose rates for various
maintenance jobs in contaminated areas. The inspector discussed the
method of calibration versus the actual method of use for the survey
instruments with the licensee. The inspector stated that this area would
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be an inspector follow-up item until the discrepancy could be resolved.
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(50-278/85-31-02)
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5.
Exit Interview
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The inspector met with the licensee representatives denoted in Paragraph 1
at.the conclusion of the inspection on August 7, 1985. .The inspector
summarized the purpose and scope of the inspection and the inspection
findings.
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APPENDIX A
Offgas Sample
uCi/ml
pCi/m8
Kr-85m
2.04E-2
2.04E+10
=
Kr-87
5.37E-2
5.37E+10
=
Kr-88
5.41E-2
5.41E+10
=
1.06E-2
1.06E+10
=
Xe-135
8.80E-2
8.80E+10
=
Xe-135m
1.47E-1
1.47E+11
=
2.51E-1
2.51E+11
=
S Skin Dose (rem /hr)
1r Body Dose (rem /hr)
Kr-85m
3.40
2.72
Kr-87
59.57
36.24
Kr-88
14.62
90.66
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0.37
0.36
Xe-135
18.66
18.16
Xe-135m
11.91
52.28
118.18
252.f3
226.64
453.08
Dose factors taken from Reg. Guide 1.109. Stay time is 1 min.
This assumes a semi-infinite cloud of offgas.
This is not the case.
A dilution factor must also be considered.
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Oilution factor of ~100 based on gamma survey meter readings. (See Paragraph 3)
Dilution factor of ~105 based on Cs-138 air particulate values.
(See Paragraph 3)
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226 Rad
I hr
1 min
1
Therefore beta skin dose =
hr x 60 min x
x 100
= 38 mrem
to
226 Rad
I hr
1 min
1
=
hr x 60 min x
x 100,000 = 0.04 mrem
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Appendix A
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453 Rem
I hr
1 min
1
Gamma body dose =
hr. x 60 min x
x 100
~= 76 mrem
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453 Rem
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1 min
1
=
hr x 60 min x
x 100,000 = 0.08 mrem
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