ML19282A645
| ML19282A645 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 03/01/1979 |
| From: | Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 123, NUDOCS 7903050271 | |
| Download: ML19282A645 (3) | |
Text
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1 Ve co VIRGINI A ELECTRIC AND POWER COMP ANY, RICHMON D, VIRGINI A 23261 March 1,1979 Mr. Harold R. Denton, Director Serial No. 123 Office of Nuclear Reactor Regulation PSE&C/MLM:adw:mc Attn: Mr. O. D. Parr, Chief Light Water Reactors Branch No. 3 Docket No. 50-339 Division of Project Management U. S. Nuclear Regulatory Commission Washington, D.C.
20555
Dear Mr. Denton:
Mr. A. W. Dromerick and Mr. T. D. Murphy,of the NRC staff have re-quested that we address the effects of radiation-induced deterioration of the collar / saddle shield material which we will use for the supplementary neutron shield for North Anna Unit 2.
We have authorized a radiation-thermal test of the shield material to determine the combined effects an integrated gamma dose of 3.3(+10) rads at 400 *F will have on the integrity of the shield material. The neutron fluence shall be to the following levels:
1.
6.0(+18)n/sq cm (Less than 0.11 MeV) 2.
3.0(+18)n/sq cm (0.11 MeV - 1.1 MeV) 3.
1.4(+17)n/sq cm (Greater than 1.1 MeV)
The integrated gamma dose and the neutron fluence levels are based on 32 effective full power years (EFPY).
Chemtrol Corporation, the supplier of the shield material, has provided us with a report entitled Test Report on the Effects of Combined Gamma and Neutron Radiation on Borated Silicon Matrix CT-40-NS for Use Inside the Containment Building of Almaraza, Unit 1 (October 31, 1977). The sample speci-mens were irradiated to an integrated gamma dose exceeding 3.0(+9) rads at 120 F.
The neutron fluence levels were:
1.
5.35(+17)n/sq cm (Greater than 1.0 MeV) 3.61j+18)n/sqcm(Lessthan0.625eV) 18)n/sq cm (0.625 eV - 1.0 MeV) 2.
3.
1.63s+
790305OJ4l s
VIRGINIA ELECTRIC AND POWER COMPANY TO Mr. Harold R. Denton, Director
$HEET NO. 2 Chemical analysis of the test sample revealed a slight reduction (0.005 g/cc) in the hydrogen content as compared to an unirradiated control sample (0.06 g/cc). Physical analysis revealed an increase in durometer as was postulateu prio.' to irradiation. The irradiated samples retained their physical integrity throughout the irradiation and post-irradiation period without any observable flaws or defects.
Based on existing test data, we foresee no potential for deterioration of the shield material during the first 4 years of operation.
Following completion of the radiation-thermal test, we will review the test data to determine whether a periodic testing program is warranted.
If after review of the test we decide to implement an inspection program of the saddle segments (Note: the collar portion of the shield is encased in a carben/ stainless steel can), we will inform you at that time of our inspection procedures and criteria.
Mr. T. D. Murphy was also concerned with the radiation levels outside the equipment hatch at Unit 2.
At his request, we are enclosing a map of the radiation fields in the vicinity of the Unit 1 equipment hatch from a survey taken February 26, 1979. As you will note, the highest dose rates at the outer surface of the missile shield is about 0.06 mrem /hr gamma and less than 0.5 mrem /hr neutron (the neutron detector did not register any neutron dose rate below 0.5 mrem /hr).
Based on these measurements, we expect the dose rates on the outside surface of the containment (in this case, the outer surface of the missile shield) to be less than 0.75 mrem /hr with the supplementary neutron shield installed in Unit 2.
The 0.75 mrem /hr limit was established in Section 12.1.1 of the FSAR for North Anna Units 1 and 2.
Please contact me if you require furth6r information.
Very truly yours, Y M,dE47 V
Sam C. Brown, Jr.
Senior Vice President-Power Station Engineer and Construction cc: Mr. James P. O'Reilly, Director Office of Inspection & Enforcement Region II
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