ML19221A267
| ML19221A267 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/11/1979 |
| From: | Slobodien M NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Galen Smith NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| References | |
| NUDOCS 7905210108 | |
| Download: ML19221A267 (4) | |
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.N April 11, 1979 MEMORidiDUM FOR: George H. Smith T11RU:
Alan Gibson FRCM:
M. J. Slobodien
SUBJECT:
EVALUATION OF TMI PERSC'iNEL DOSIMETRY I.
Purpose To determine whether the 'IMI inplant personnel dosimetry system provides an accurate assessment of whole body and skin deses.
The system should be responsive to both penetrating radiation and bata components, and the calibration should reflect a proper evaluation of beta sensitivity resulting in a correction factor applied to TLD data.
II.
Dosimetry Sydtem
'Ihe licen: ee uses a Harshaw TLD system employing two 1/8" x 1/8" x.035" LiF chips. The badge has an open window with a 7 mg/cm-2 absorber and a shielded window (Al & plastic) with a total of 283 mg/cm-2.
Wearing of TLD badges i.s mandatory.
Self reading pocket dosimeters are available and are required only if indicated on the RWP.
Pocket docimeters are read and logged in by the individual uearer.
III.
Calibration of Dosimeters A.
The TLD badges are calibrated in accordance with TMI health Physics Procedure 1642, Revision 1, 9/28/77 (copy attached).
B.
Car:na Doses TLD badges are exposed annually to a nominal 100 mC4 137-Cs source which has a calibration traceable to N63.
The exposure rate from the source is confirmed by decay calcu -
lacion and by measurement with Victoreen condenser meter
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. and R chambers with calibration traceable to BS through the Victoreen Instrument Company.
The TLD badges are then read out on the Harshaw 2271 reader-integrator after 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> to allow for a fade correction factor to be calculated.
In normal operations, TLD badges are read out within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> of exposure.
The Harshaw unit has been set up so that an accu =ulated charge of one nanocculomb is equivaler t to one mil 11 roentgen.
Thg system has been tested ar.d is line ir to at least 10 nC (100R).
C.
Beta Doses The licensee has evaluated beta doses and the TLD correction f actor by exposing badges to a "se=1 infinit' depicted uranium slab.
The beta correction factor 1.
determined by (0{1) b=R1 - 1.15 R2 Da u
where b = beta correction factor R1 = the dose to the open window due to 3 and components R2 = the dose to the shielded window due to the component D3 = the dose due to the uranium B slab The licensee calls the factor 1.15 in eg.1 a correction for lack of electronic equilibrium at the chip in the "open" window.
'.his is not correct. With the 0.662 MeV photon from Cs-137 there is essentially no difference in dose due to electronic inequilibrium from a bare dosimeter or dosimeter with buildup material.
The 1.15 factor is, in fact, the correction which should be applied to the chielded (283 cg/cs-2 Al) chip to account for the small absorption of Cs-137 energy in the aluminum B shield.
Although the licensee's reason for applying the equation 1 correction
' factor to R 2 is incorrect, the use of the facter is proper and reasonable.
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- The factor b has been found b = 4.0.
This is in fact quite conservative.
Dr. Donald E. Jones, HSL DOE, Idaho Falls was contacted by phone on 4/9 to discuss the
@ correction factor.
He indicated that careful studies with pure B sources demonstrated a [5 correction factor of 2.0.
He felt that 4.0 was conservative.
The correction factor of 1.15 is reasonable given the 2
283 mg/cm Al shield.
D.
Quality Contrc' l.
Prior to 3/28/79 The licensee conducts a routine QA check of TLD badges on a monthly basis.
Eleven dosimeter badges are removed from the general supply at random.
10 are exposed to a calibt ated 100 mci Cs-137 t ource.
These along with a control are sent to Harshaw for reading.
These are read at Harshav then reirradiated and returned to Met Ed for comparison.
The licermee usec as acceptance criteria f 257. discrepancy between indicated dose Eo' licensee irradiated TLD El Harshav irradiated TLD.
2.
Sr-90 check newly instituted since 3/28/79 The licensee now maintains an 0.5 cCi Sr-90 TLD card irradiator supplied by the Harshaw Company.
The output of this irradiator is expressed in terms of exposure to Cs-137.
The irradiator is used to expcse TLD cards for each run period as a cons.ancy check.
The TLD reader settings are adjusted to maintain a constant response per mR received to the chips from the Sr-90.
This system will be used as an interim measure.
3.
The. licensee's corporate HP (Buring) stated that no spike tests are conducted as part of the QC program.
E.
Low Energy Correction Factors Discussions with Douald E. Jones at HSL, DOE, and Barbara Golby on site from Harshaw indicate that studies conducted with 80 kev ef fective X-rays show no correction factor need be applied to the LiF TLD-100 when low energy photons are present.
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Inspector's Evaluation P
ysourcesis The licensee's calibration method for both p and deceptable. The correction factors in use - 1.15 for Cs-137 photen en shielded chip is apnropriate.
The 4.0 correction factor used for skin dose assessment is conservative by approximately a factor of 2.
Questions still remain as to adequacy of the licensee's QA program, h,owever it appears that the ability to asser: doses to personne1J'12* adequate and conservative.
The QA questions which have already been looked into are as follows:
A.
Does the Met Ed TLD computer system have a way to identify dis repancies between open wEdew and shielded window which are unexpected?
Ans: No such capability.
B.
Is any effort made to reconcile pocket dostmeter and TLD data?
Ans: None.
C.
Is ny attempt made to correlate K' P data, specifically J
estLsated doses and pocket dosimeter data with ILD results?
Ans:
No.
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