ML20030D321
| ML20030D321 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 04/13/1981 |
| From: | Leasburg R VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | Clark R, Harold Denton Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20030D322 | List: |
| References | |
| 276, 810813, NUDOCS 8109010176 | |
| Download: ML20030D321 (4) | |
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August 13, 1981 Mr. Harold R. Denton, Director Serial No. 276 Office of Nuclear Reactor Regulation PSE&C: FCP ATTN:
Mr. Robert A. Clark Docket No. 50-339 Operating Reactors Branch No. 3 License No. NPF-7 Division of Licensing
'J.S. Nuclear Regulatory Commission Washington, D.C.
20555
Dear Mr. Denton:
In compliance with 10CFR50.55(e), NRC Region II was notified on April 28, 1978 that maximum dose rates on the containment opera-ting floor of Norti: Anna Unit 2 could exceed the values presented in the FSAR, resulting in the pote'itial for excess exposure to operating personnel. On May 25, 1978, an interim report was submitteo' to NRC Region II (Serial No. 300) stating that we were investigating severa' methods of reducing the higher than anticipated radiation levels.
In our final report submitted on January 31, 1979, (Serial No. 300A) we described the supplemental shield that had been installed in North Anna Unit 2.
Also, in this letter, we stated that we would ebtain experimental confirmation of the adequacy of the supplemental shielJ in reducing the Unit 2 containment dose rates.
In addressing the effectiveness of the supplemental shielding there are three areas or zones of concern. These zones are defined in Section 12 of the North Anna FSA3 and are as follows:
Zone I - Continuous access Maximum dose rate: 0.75 mrem /hr Applicable containmert location:
outside surface of containment including uncontrolled areas of the equipment hatch platform.
Zone II - Periodic access Maximum dose rate:
2.5 mrem /hr
/
Applicable containment location:
inside reactor k OC/
containment personnel lock.
y
//V0 8109010176 810813 PDQ ADOCK 0500033Q Pr PDR L
i Mr. Harold R. Denton Page 2 Zone IV - Controlled access Maximum dose rate: 100 mrem /hr Applicable containment location: Annulus between crane wall and containment wall.
Since the supplemental shielding was installed in Unit 2 prior to startup, there is no pre-shield dose rate data available.
Therefore, postulated dose rates based on a partial radiation survey conducted in the Unit 1 containment at 100% power prior to supple-mental shield installation will be used for Unit 2 comparisons. A copy of this survey, conducted on March 14, 1978, is provided as Attachment No. 1.
The post-shield dose rate data is from a 100%
power survey taken on October 15, 1980. A copy of this survey is provided as Attachment No. 2.
The results of the surveys are summarized below:
fiaximum dose rate per zone at 100% power - mrem /hr Zone Pre-Shield
- Post-Shield I
Not available
< 0.6 II Not available 3.0 IV 650 50
- Postulated values based on Unit 1 survey. During the Unit 1 survey, certain areas were not surveyed either because they were not included in the planned points or because radiation levels were prohibitive.
The survey values were taken in mrem /hr for neutrons and mR/hr for gammas. The dose rate values for neutrons being in mrem /hr were directly usable. The values for gammas being given as an exposure rate in mR/hr were converted to dose rates in mrem /hr.
This conversion was made by assuming a direct one to one relation-ship between R and rem. We feel this is a conservative assumption which is applicable over a broad gamma energy spectrum. After conversion, the gamma dose ~ rates were added to the neutron values giving total dose rates in mrem /hr.
It is these total dose rates that are presented above.
1 Mr. Harold R. Denton Page 3 The comparison of pre-shield and post-shield dose rate values indicates a significant decrease as a result of the installation of the supplemental shielding.
In one area, inside the personnel lock, the maximum post-shield dose rate was 3.0 mrem /hr as opposed to the FSAR maximum value of 2.5 mrem /br. All other areas were within the FSAR limits. We feel this higher value in the personnel lock was caused by an overresponse of the neutron survey instrument. The type of neutron survey instrument used for all surveys was the Eberline Model PNR-4 (nine inch remball).
Recent de': ailed studies conducted by the Environmental Measurement Laboratory of the Department of Energy (EML-376) at North Anna and seven other PWR power stations using bonner sphere neutron spectral analysis indicates the nine inch remball will give dose rate readings from 150 to 185 percent of actual.
If it is assumed the neutron dose rates from the survey are 150 percent of actual, the valuas for the reactor containment personnel lock will drop to within the FSAR limits. We feel this is a conservative assumption and is applicable to this situation.
In addition, our letter of March 1,1979, Serial No.123, stated that we would advise you following the completion of the radiation-thermal test if a period'c testing program is warranted for the saddle segments of the supplemental shield. The test results indicate that the shield material will maintain its struc-tural integrity during normal operation in excess of ten years.
In the unlikely event that the material begins to deteriorate, it would be detected through radiation surveys made of the containment during entries a power.
In addition, the shield material must be removed to complete the periodic inservice inspection of the reactor nozzles.
Should material defects be indicated at this time, the defective portion would be replaced at the next outage of sufficient duration.
A copy of the radiation-thermal test results is provided as Attachment No. 3 and completes the requirements of condition 2.C.(19) of Amendment No. 2 to License No. NPF-7, dated December 29, 1980.
O Mr. Harold R. Denton
[
Page 4 The results of our investigation indicate the adequacy of the supplemental shielding installed in Unit 2 in reducing the maximum containment dose rates to within the FSAR values.
Should any significant new information be developed, we will promptly inform l
you.
Vcry truly yours,
. Leasburg Vice President - Nuclear Operations FCP/jw Enclosures