ML20133D216

Submits Corrected Paragraph of ,Page 3,to NRC Re Reportable Occurrence Involving Reactor Control Rod Calibr

ML20133D216
Person / Time
Site:	Pennsylvania State University
Issue date:	01/06/1997
From:	Randy Erickson PENNSYLVANIA STATE UNIV., UNIVERSITY PARK, PA
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9701090069
Download: ML20133D216 (2)

Text

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(814) 863-9580 i PENNSTATE Fax: (814) 863-9659 l

l Vice President for Research The Pennsylvania State University 207 Old Main l University Park, PA 16802-1503 l

l January 6,1997 Nuclear Regulatory Commission Document Contml Desk Washington, DC 20555 Re: Correction to a July 7,1995 Letter, Page 3, to the NRC for a Reponable Occurrence for the Penn State Breazcale Reactor License Number R-2, Docket Number 50-05

Dear Sir or Madame:

During NRC inspection 50-59601 by Mr. Marvin Mendonca of NRC Headquarters on fxecmber 10 to December 12,1996, Mr. Mendonca noted an error in a July 7,1995 letter to the commission . Hat Ictter fulfilled reporting requirements for a reportable occurrence involving reactor control rod calibrations. The paragraph entitled " Consequences of the Incident" on page three of that letter contained the error. He conclusion in that paragraph that the consequences of the excess reactivity being $.06 over the Tech Specs limit are within the accident analysis in the Safety Analysis Repon remains intact. However, the analysis was based on using the wrong reference in the Tech Specs conccming the pulse reactivity ($3.40 was used rather ,

than $3.00). A corrected paragraph for the paragraph in error of the 7/1/95 letter follows:

Corrected Paragranh of.Tulv 7.1995 Letter. Pace 3 Consequences of the Incident Here is a limiting condition for operation (LCO) which states that the maximum excess reactivity above cold, clean, critical plus samarium poison of the core configuration with experiments and experimental facilitics in place shall be 4.9% Ak/k (~$7.00). The basis is that by limiting the excess reactivity of the core to 4.9% Ak/k prevents the fuel temperature in the core from exceeding 1150 *C under any assumed accident condition as described in the Safety Analysis Repon,Section IX - Safety Evaluation (Technical Specification, Section 3.1.2-Reactivity Limitation).

On 7/6/94 the core excess reactivity was measured for the existing core (47) to be $6.03 using the rod calibration data taken that day; this is the normally desired excess. However,it has been shown that the rod worths measured that day were low. The rod calibration curves measured for the same core on 6/14/95 showed core excess reactivity to be $6.66. The core is worth an additional $0.26 against the heavy water tank (i.e. our most reactive experimental facility in place). During a cycle the core loses about $0.14 from bumup, making it conceivable that this LCO was violated early in the cycle by operating with an excess reactivity of

$7.06.

TM above LCO basis is the Reactivity Accident that is analyzed in part F of the Safety Analysis Report,Section IX. In this accident, it is assumed that the reactor is taken to a 1.15 MW power level with the transient rod inserted in the core and then the reactor is pulsed with a $3 reactivity insertion. His accident requires a violation of the PSBR Standard Operating Procedures, failure of the overpower scrams, and a failure of the interlock that prevents pulsing if the reactor power exceeds 1 kw.

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Nuclear Regulatory Commission Page 2 January 6,1997 With the core operating at 1.15 MW, the measured fuel temperature in the B-ring (using extrapolated experimental data for core loading 47 with 95.5 elements ) would be 630 *C in the 12 wt% instrumented fuel element,1-15. Ec maximum fuel temperature during steady state will be slightly higher (no most than 10%),

but the fuel temperature near the cladding will be approximately half this temperature. To this steady state fuel temperature, the temperature increase due to the pulse must be added to determine the fuel temperatme for this case.

Ec maximum allowed core excess icactivity is $7. %c reactivity loss for core loading 47 (the loading that was in use during June 1994 to July 1995) would have been - $4.62 at 1.15 MW, leaving only $2.38 remaining reactivity for a pulse. If a $3.00 pulse had occurred while the reactor was at 1.15 MW, the measured fuct temperature would have risen from 630 *C to 1122 'C. His was calculated using the maximum measured $3.00 pulse temperature data for I 15 and core loading 47 (i.e. pulse #6404 with peak l measured fuel temperature of 492 *C).

In the case, when the core is pulsed from an initial power of 1.15 MW, the maximum fuel temperature is the I I

measured fuel temperature. His is because the temperature rise during a pulse has a different radial shape than that attained during steady state operation. During a pulse, the increase in fuel temperature is a maximum j near the edge of the fuel. Superimposing this shape of the fuel temperature on that attained at a steady state  ;

I power of 1.15 MW produces, at the end of the pulse, a relatively nat radial temperature distribution of approximately 1122 'C. With the core loading that was in use from June 1994 to July 1995, the core scactivity excess would have had to have been $7.62 for there to be enough reactivity left to perform a $3.00 pulse. De maximum core reactivity excess possible from June 1994 to July 1995 was $7.06. De effect of )

being $0.06 over the limit was not significant because the consequences (if all of the assumptions were met i and the reactivity accident had occuned) would have been within the consequences of the accident as l analyzed. Namely the safety limit of 1150 C would not have been reached. l l

There are other mitigating circumstances which would have made the occurrence of such an accident evea 1 more unlikely. Administratively, if the reactor is operating above 900 kw all four control rods must be balanced. This implies that the transient rod would not be available for the $3.00 pulse. In addition, the Technical Specification icquired pulse interlock (section 3.2.4), which prevents imtiation of a pulse when reactor power is greater than 1 kw, will prevent the postulated accident. Also the Tecanical Specification required high power scrams will prevent operation at 1.15 MW.

Please replace the subject paragraph with the above information.

S' rely, l l

l Dr. Rodney A. Erickson Interim Vice President for Research RAE;TLF/DEH/WFW/ldb1001.97 pc. RegionI Administrator T. Flinchbaugh, PSBR Subscribed to the swom before me on this 4 Ab day of rW dW ,

1997, Notary Public in and for Centre County, Pc sylvania. # f

&f Notarial Seal Bonnie L Burris. Notary Public State College Boro. Contre County My Commission Spires Nov. 22.1999