ML16341G687
| ML16341G687 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 09/04/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML16341G686 | List: |
| References | |
| NUDOCS 9209160078 | |
| Download: ML16341G687 (8) | |
Text
~p,g REGS 0
O
+~
~O
+p**W UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO SUPPLEMENTAL REACTOR VESSEL RADIATION SURVEILLANCE PROGRAM PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON POWER PLANT UNIT 1
DOCKET NO. 50-275 1.0 Introduction In a letter dated March 31,
- 1992, the Pacific Gas and Electric Company (the licensee) requested that the staff review and approve a proposed supplemental reactor vessel radiation surveillance program and a revision to the reactor vessel material surveillance capsule withdrawal schedule for Diablo Canyon Power Plant Unit 1
(DCPP-1).
The licensee stated that the current Unit 1
surveillance program was established before the issuance of Appendix H to 10 CFR Part 50, and was designed in accordance with the requirements of ASTM E
185-70, the standard in effect when the reactor vessel was manufactured.
2.0 Discussion Appendix H to 10 CFR Part 50 requires that the surveillance program meet the requirements of the edition of ASTM E 185 that was current on the issue date of the ASME Code to which the reactor vessel was purchased.
Appendix H also requires that the schedule for capsule withdrawal must be approved by the NRC staff prior to implementation.
ASTM E 185-70 requires that specimens be withdrawn at three or more separate times throughout the design life of the vessel and that specimens be taken from the following locations:
(1) the base metal of the heat from the high flux location of the reactor vessel that has the highest initial ductile-brittle transition temperature, (2) weld metal that is fully representative of fabrication practices used for welds in the highest flux location of the reactor vessel (weld wire and flux must come from one of the heats used in the highest flux region),
and (3) the heat affected zone of the weldment.
The current surveillance program consists of eight capsules:
three "Type II" capsules containing the limiting beltline weld metal, limiting shell plate, and weld heat affected zone from an intermediate shell plate, and five 9209160078 920'904 PDR ADOCK 05000275 P
"Type I", or "standby" capsules that do not contain limiting beltline material (weld metal).
The three Type II capsules will be removed to determine the effect of irradiation during the vessel's current design life of 32 effective full power years.
The three Type II capsules contain base metal, weld metal, and heat affected zone samples that meet the requirements of ASTN E 185-70.
In its Harch 31, 1992 letter, the licensee proposed to:
(I) add four supplemental capsules (A, B, C,
and D) to the surveillance
- program, (2) remove and store standby capsules T and Z,
(3) remove and test standby capsule Y, in accordance with the previously existing withdrawal schedule, (4) relocate capsule V, and (5) revise the capsule withdrawal schedule.
The four supplemental capsules (A, B, C,
and D) that are to be added to the program will contain weld metal fabricated using the same heat of weld wire as the limiting beltline weld and plate material from the limiting plate at 48 EFPY.
All four supplemental capsules will contain weld metal removed from a
reactor vessel nozzle dropout supplied by the vessel
- vendor, ABB Combustion Engineering.
Two of the supplemental capsules (B and D) will contain material from broken weld metal Charpy specimens that were previously irradiated in Capsule S.
After reirradiation, the capsule B and D Charpy specimens will be reconstituted and compared to samples removed from reactor vessel nozzle dropout.
The staff believes that it is essential that the process for reconstitution not effect the Charpy test results.
- Hence, the staff concludes that, prior to the removal of Capsules B and D, the licensee should develop a procedure that will ensure that the reconstitution process will not affect the Charpy test results.
The withdrawal schedule for the four supplemental capsules is as follows:
(I)
Capsule A will remain in the vessel as a standby capsule.
(2)
Capsule B will be removed and tested when the accumulated fluence is equivalent to the vessel inside surface at 48 EFPY.
(3)
Capsule C will be removed when the accumulated fluence is equivalent to the vessel inside surface at 32 EFPY, the design life of DCPP-I.
Half of the specimens will be tested before annealing and half will be tested after annealing to demonstrate the toughness recovery after thermal annealing.
I C
t (4)
Capsule D will be removed when the accumulated fluence is equivalent to the vessel inside surface at 32 EFPY.
The samples from Capsule D
will be annealed, reinserted into the vessel, and subsequently removed when the accumulated fluence is equivalent to the vessel inside surface at 48 EFPY.
This capsule will be used to demonstrate the degree of reembrittlement after thermal annealing.
All capsules, except for the standby capsules, will be withdrawn by approximately 19.2 EFPY.
These capsules will provide data for the license renewal period and will determine the effect of annealing on the reactor vessel.
The two capsules (T and Z) to be removed and stored contain only plate material.
Since the limiting material with respect to pressurized thermal shock is the weld metal, these capsules need not be tested.
Capsule V will be moved from its present location (184 degrees) to a location (320 degrees) which has a greater lead factor than its present location.
Hence, it will reach its planned accumulated
- fluence, a value equivalent to the vessel inside surface at 32 EFPY, earlier in the plant's life.
3.0 Conclusions The NRC staff has reviewed the proposed supplemental reactor vessel radiation surveillance program and revision to the reactor vessel material surveillance capsule withdrawal schedule for Diablo Canyon Power Plant Unit 1.
The results of the review are given below.
(1)
The licensee proposes to install the supplemental capsules in the DCPP-1 reactor vessel at the end of Cycle 5, during the September 1992 outage.
Capsules T and Z will be removed at that time and stored to make room for the supplemental capsules.
Capsule V will be moved to a
higher flux location (320 degrees).
The staff finds these changes acceptable because they augment the current program, and will provide additional data on the limiting reactor vessel materials.
(2)
The staff concludes that broken weld metal Charpy specimens may be reconstituted and compared to samples removed from the reactor vessel
- dropout, provided that the licensee develops a reconstitution procedure that ensures that the reconstitution process does not affect the Charpy test results.
(3)
The staff finds the proposed withdrawal schedule to be acceptable.
- However, the schedule should be reviewed by the licensee when test results from irradiated capsules become available or if the licensee significantly changes its fuel management program.
(4)
If at some future time the licensee decides to anneal the DCPP-I reactor vessel, all standby capsules should be annealed to a condition equivalent to the reactor vessel.
Principal Contributor:
B. Elliot Date:
September 4,
1992
~ly