ML20235X037
| ML20235X037 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 10/12/1987 |
| From: | Shelton D TOLEDO EDISON CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| 1-760, NUDOCS 8710190176 | |
| Download: ML20235X037 (3) | |
Text
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3 USHRC-DS IWI 00119 A D 02 EbYSON-DONALD C. SHELTON Vcs prender*~Nucienr Docket No. 50-346 -
(4'818498
- License No. NPF-3 Serial-No. 1-760 October 12, 1987 i
Document Control Desk United States Nuclear Regulatory Commission Washington, D.C.
20555
Subject:
Response to Inspection Report 87023 Gentlemen:
Toledo Edison has received I spection Report 87023 (Log No. 1-1664, dated September 11, 1987) and provides the following response.
Violation 87023-01:
Technical Specification 4.11.1.1.1 requires that radioactive liquid wastes be sampled and analyzed according to the sample and analysis program of Table 4.11-1.
Table 4.11-1 requires that certain named principal gamma emitters, including Cs-134, be detected at a concentration greater than 5 x 10-7 pCi/ml (Lower Limit of Detection).
Contrary to the above, on July 22, August 4 and 9, 1987, i
the licensee spectroscopy system failed to identify and quantify Cs-134, present in liquid waste samples, at concentrations greater than 5 x 10-7 pCi/ml.
Acceptance or Denial of the Alleged Violation a
i Toledo Edison denies the alleged violation.
tu Q Reason for Violation 58a-y Inspector examination of Davis-Besse data revealed that Davis-Besse's ro o spectroscopy system did not identify the Cs-134 peak in the presence of l
other nuclides in the 600 key energy range.
Since the system did not eg
. Q identify the Cs-134 604 key peak, it could not satisfy the system software on requirement that both the 604 key and 795 key peaks of Cs-134 be identified before the nuclide could be quantified.
The NRC reviewed the Davis-Besse o
liquid release analyses for December 31, 1986 through August 9, 1987 and g
'We p
i THE TOLEDO EDISON COMPANY EDISON PLAZA 300 MADISON AVENUE TOLEDO, OHIO 43652 Ci___________._
1 Docket No. 50-346' License No. NPF-3
-Serial No. 1-760 October 12, 1987 Page 2' determined that Cs-134 was present in quantities greater than 5 x 10 pCi/ml on July 22, August 4 and 9, 1987.
Inspection Report 87023 states that the failure to quantify Cs-134 in radioactive liquid wastes at a _
concentration greater than 5 x 10-7 pCi/ml-is a violation of Technical j
Specification 4.11'1.1.1 and referenced Table 4.11-1.
Prior to the end of the subject inspection, Toledo Edisan changed the Cs-134 measurement so i
that. it quantifies without th. 604 key peak confirmation.
Reason for Denial Davis-Besse Technical Specification 4.11.1.1.1, Table 4.11-1, Notation "a" states that "... the LLD'is defined as an e priori (before the fact) limit representing the capability of a measurement system and not as an a posteriori (after the fact) limit for a particular measurement". This
. definition of Lower Limit of Detection (LLD) requires that the gamma spectroscopy. system have the capability to detect principal gamma emitters (including Cs-134 as specified in Table 4.11-1., Notation "b") at a' level of 5 x 10-7 pCi/ml, without interference.
It does not require that this level of detection be achieved on actual samples.
The equation for LLD as presented in Table 4.11-1, Notation "a",
further supports this position.
The LLD is a function of s, which is defined as "... the standard deviation b
of the background counting rate or of the counting rate of a blank sample...".
Radioactivity levels, interfering gamma energies, and Compton scatter all contribute to the complexity of gamma spectroscopy and affect the actual detection capability for a particular sample analysis. Toledo Edison's practice has been to evaluate the capabilities of the gamma spectroscopy system to achieve the LLD using a blank sample. This approach is supported by the Technical Specification definition and has been an industry-wide l
accepted method. Our past evaluations of the gamma spectroscopy system capabilities demonstrated an LLD of 5 x 10-7 pCi/ml which met our Technical Specification requirements.
The use of multiple peak identification to confirm the presence of a radionuclides is a common practice in gamma spectroscopy. A primary peak used for identification may coincide in energy with other gamma peak;, leading to misidentification.
Confirming peaks is one of the key checks in the gamma spectral analysis.
For the situation cited, Toledo EdisGa acknowledges cMt the use of confirming peaks for Cs-134 detection did not yield the most sensitive i
results. Several radionuclides have gamma energies in the region of the Cs-134 604.7 key gamma (e.g., Sb-125 and Xe-135). These competing peaks could mask the identification of the Cs-134 peak and raise the detection capability for Cs-134.
Toledo Edison agrees that the 795.8 key Cs-134 gamma peak exhibits less interference from other radionuclides. Use of single peak identification (rather than requiring identification of both peaks) should provide more r*1iable identification of Cs-134 with inter-fering peaks present.
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I Docket No. 50-346 l
License No. NPF-3 Serial No. 1-760 I
October 12, 1987 Page 3 Toledo Edison reviewed liquid release data back to August, 1985 and found no additional cases where Cs-134 was not quantified above the LLD.
Our gamma spectroscopy systems are evaluated on a routine basis and changes are made as needed. Prior to the NRC confirmatory measurements, the problem.with the interfering SB-125 peak had just. began and had not been identified by Toledo Edison. Toledo Edison first-became aware of the interfering peak as a result of the NRC's confirmatory measurement during the subject inspection. Since the spectroscopy system was capable of identifying and quantifying Cs-134 at the LLD limits (before the fact, without interference) prior to confirmatory measurements, the requirements of Technical Specification 4.11.1.1.1 were met.
The a posteriori (after the fact) limit for a particular measurement is'not a Technical Specification requirement. Therefore, Toledo Edison denies the alleged violation.
l Very truly ours,
.[gjss EBS:dem cc: DB-1 NRC Resident Inspector 1
A. B. Davis, Region III Regional Administrator I
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