ML19332D156
| ML19332D156 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 11/22/1989 |
| From: | Creel G BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| RTR-REGGD-01.068, RTR-REGGD-1.068 IEIN-89-051, IEIN-89-51, NUDOCS 8911300094 | |
| Download: ML19332D156 (3) | |
Text
cr 9*, p,..x [ BALTIMORE L GAS AND ELECTRIC i F CHARLES CENTER. P. O. BOX 1475. BALTIMORE, MARYLAND 21203 b [ 0* ""',,C C" November 22,1989 i y, p.,,, O Hvett an [NEROV 400peo mass ( I U. S. Nuclear Regulatory Commission Washington, DC 20555 i ATTENTION: Document Control Desk { 4
SUBJECT:
Calvert Cliffs Nuclear Power Plant i Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 [ Concerns Involving a Potential Loss of Shutdown Margin at Pressurized Water Reactors
REFERENCES:
(a) Letter from G. C. Creel (DG&E) to Document Control Desk (NRC), dated March 15,1989,10 CFR 21 Written Report: Potential Loss of ShutGewn Margin (b) NRC Information Notice 89-51: Potential Loss of Required Shutdown Margin During Refueling Operations, dated May 31, 1989 o Gentlemen: In March, 1989, Baltimore Gas and Electric Company (BG&E) provided the Nuclear 1 Regulatory Commission (NRC) with information concerning the potential for a = loss of shutdown margin during refueling (Reference (a)). After review of the information provided, the NRC, issued an Information Notice (Reference (b)). Since issue of the i information Notice, we have become concerned that the Notice may not have fully represented the seriousness of the issue to the industry. We have identified additional information which we believe the NRC should consider in re-evaluating this issue. 1. While the NRC Information Notice stressed the potential loss of shutdown margin, and touched on the possibility of accidental criticality, we believe there is, in fact, a potential for prompt criticality. The possibility of experiencing a prompt critical excursion during core refueling operations was not discussed in the Notice. Given the potential consequences of such an event, we recommend the staff evaluate it further, i - 2. Regulatory Guide 1.68, which was used to provide a basis for the Calvert Cliff's refueling procedure, was vague in addressing fuel placement and reinforced the belief that monitoring suberitical multiplication. was sufficient to guard against reactivity excursions. The recent use of higher reactivity fuel could allow a prompt critical array to be formed with a single fuel move. This condition exists even though fuel movement is done while a large shutdown margin is ^9911300094 891122 FDR ADOCK 05000317 a... .-. ?
r a. e= ~. ' t Document Control Desk November 22,1989 Page 2 l maintained. Without new guidsoce from the staff, refueling procedures at other utilities may continue to contain deficiencies which would permit the formation of a prompt critical mass. 3. The NRC Information Notice (Reference 2) states that control rods and burnable poisons were not considered in BG&E's analysis. Even with these effects credited the worst case scenario could still iesult in criticality. This understatement in the' Information Notice may not s sequately received by other utilities. j s 4. During the fifth refueling of Calvert Cliffs Unit' 2 in 1984, a substantial number f of fresh unshimmed nuclear fuel assemblies were placed in unanalyzed, non-conservative interim core positions. In this instance, a batch of burned fuel was removed from the core and put into the spent fuel pool for modification prior to reinsertion, in order that modification could proceed in parallel with a reshuffle of fuel into final locations in the core, fresh fuel was moved into interim core locations simultaneous with removing the fuel to be modified. Our calculations show that during these moves the $% shutdown margin was not violated. 110 wever, the placement of fresh fuel in unanalyzed positions and placement of control rods on the core periphery proceeded in a manner which was logical for that out-in fuel management reload. In such a case, the systematic i nature of the fuel and control rod motion greatly increased the probability of forming a critical array. 5. EPRI is currently engaged in writing computer codes which will optimize the refueling process. It is our understanding that these codes do not include safety checks to guarantee fuel is placed in conservative positions. The systematic nature of fuel movement into unanalyzed positions, similar to Unit 2 fifth refueling, provides an opportunity to create critical arrays with a much higher probability than that associated with random chance. Small reload batches, in combination with high enrichment, enhances the opportunity for critical arrays. Any situation which encourages the inspection or modification of fuel assemblies simultaneous with reshuffling in the core creates an opportunity for systematically placing new fuel into unanalyzed positions. Under these reali,itic situr.tions, the probability of placing new fuel into critical arrays, with the last fuel assembly initiating prompt criticality, is too high. To address these concerns at our facility, BG&E has instituted additional refueling procedure controls which prohibit the placement of fuel in unanalyzed positions in the core. Should an accidental criticality occur under PWR refueling conditions, the effects would be extremely disturbing to the industry as a whole. Therefore, we strongly recommend that the NRC review our concerns again and establish firm guidance for the placement of nuclear material in a reactor core.
g. N' '5 'c ( Document Control Desk ' November 22,1989 Page 3 Should you have any further questions regarding this matter, we will be pleased to discuss them with you. Very truly yours, O t GCC/I5F/bjd cc: D. A. Brune, Esquire J. E.. Silberg. Esquire R. A.Capra, NRC S. A.McNeit,NRC W. T. Russell, NRC J. - E. Beall NRC T. Magette, DNR ,}}