ML17202G793
| ML17202G793 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 03/01/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17202G792 | List: |
| References | |
| NUDOCS 9003070056 | |
| Download: ML17202G793 (3) | |
Text
UN.ITED STATES NUCLEAR RE'GULATORY COMMISSION WASHINGTON, D. C. 20555 ENCLOSURE 1 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO ABB-ATOM CONTROL ROD DEMONSTRATION PROGRAM COMMONWEALTH EDISON COMPANY DRESDEN NUCLEAR POWER. STATION UNIT 3 DOCKET NO.
50~249
1.0 INTRODUCTION
By letter dated January 4, 1990, Commonwealth Edison Company submitted justification of continuous use of ABB-ATOM control rods for Dresden Unit 3 Cycle.12 operation. *The use of ABB-ATOM *control rods is an on-going EPRI/A~~-ATOM control rod demonstration program.
This p~ogram tnvolves the.
irradiatitin of eight lead test control blades, four_all-B4c control rods and four B4C-with-hafnium tips control rods.
During the Cycle-11 outage, the licensee discovered various cracks involving one all-B4t control rod and two hafnium tipped control rods. A visual examination was performed in the spent fuel pool using high reso*lution color.video monitor.
The affected al1-B4C control rod had three minor crack indications while the two affected hafnium tipped control rods showed four-and eight crack indicati~ns, respecti~ely.
This information has prompted the manufacturer ABB-ATOM to schedule a post-irradiation examination on the two discharged control rods.
The licensee will provide the staff :esults when new information becomes.available.
For Cycle-12 operation, the licensee proposes-to discharge the two cracked hafnium tipped control rods, and to place the cracked all-B4c control rod a_nd *one non-cracked all-B4C control rod in a non-control Cell location. The remaining fou~ nori-cracked (two all-B4c and two hafnium tipped) control rods will be positioned into symmetric control cell location. The licensee will p~rform visual inspection for this affected a11-B4C control rod during the next outage.
The licensee.provided justification for the us~ of this aff~cted all~B4 c control rod in Cycle 12.
Our evaluation follows..
~oO 307 9 Os:(;.
2 2.O EVALUATION One of the major concerns on t~e cracked s4c ~ontrol rods is the loss o~
reactivity through B4C leaching -into the. coolant.
The ABB-ATOM design of control rod consists of 454 absorber holes pe~ control blade wing (1816 absorber 'holes in total per control rod). The licen*see contende~ that t!le cracks of the affected all-B4c control rod were loca~ed near the tip of one of the wings, and the potential loss of B4C in a few holes would have a minimal effect on reactivity* worth. *Based on the on~going *EPRI/ABB-ATOM examination program and continuous inspection of the affected control rod, we conclude that there is adequate assurance that the affected.control rod will maintain enough reactivity worth during plant~peration~
The licensee also addressed the concern of new control rod arrangement for rod drop accident and the rod withdrawa 1 error..
The licensee determined that the new control rod patterns.are consistent with the over~11 neutronic design* and the analytical results are bounded by the current analyses for rod drop accident and ro'd wi thdrawa 1 error. Based on the *licensee analyses, we agree that the new control rod patterns are acceptable.
- 3. 0 CONCLUSION We have reviewed the.licensee submittal of continued irradiation of.ABB-ATOM control rods for Dresden Unit 3.
Based on the acceptable analyses and design featu.res, we co_nclude that the risk associated with the cracked contr.ol rod is very minimal,.and the new control rod patterns present no major safety concern for Dresden. 3 Cycle 12.
- Therefore'. the submittal is acceptable. It is our understanding that examination results of the.two discharged hafnium tipped control rods will be made available to NRC.in th~ near future.
Pricipal Revie~er: S. Wu, NRR/SRXB Dated:
j "J
~..
FOLLOWUP A~~ ~tom. Inc. ~ade a 10 CFR Part 21 notification.
Also, the licensee plans to discharge the two cracked hafnium tipped control rods and place the cracked all boron carbide control rod in a non-control cell location.
The R~actor Systems Branch (RSB) has reviewed the infarmation submitted bY Dresden on this matter under TAC 75600, D!esden 3 -
ABB Atom Control Rods.
RSB has concluded that the risk associated the the cracked control rod is very minimal, and that the new control rod patterns pres~nt no major safety concern.
The SER for this matter was issued on March 1, 1990.
Since the three crack control rods are part of a demonstration program, there seems be be no*m~jor generic safety concern and no further EAB action is required *.
Enc lo sure:
Thomas Greene BWR Section Event Assessment Branch Event Notification 17372, December 17, 1989 10 CFR 21 Notification, December 20, 1989 SER. March 1, 1990 cc:
- c. Rossi B. Siegel C. Berlinger L. Phillips
. M.A. Ring, Rgn III J. Ramsey S. L. Wu
".