Working Group on Operating Experience/Fuel Cycle Safety

The Working Group on Operating Experience is mandated to analyze and develop insights from operating experience and to communicate these insights to the CSNI and interested government and industry bodies. On an annual basis, the WGOE reviews and assesses the safety significance of operating events using information from probabilistic safety assessments of these events when possible. The WGOE is to promote the development of improved techniques and methods for the review of operating events and will utilize these improved practices and methods as they are available. The Fuel Cycle Safety (FCS) expert group has operated since 1976 and since 1999 has functioned as a subgroup to the WGOE.

The FCA mission is to advance the understanding of relevant aspects of nuclear fuel cycle safety in OECD Member countries. In pursuing this goal, the FCS meets to:

 exchange information on relevant matters including licensing systems, safety philosophy and safety standards to improve mutual understanding;

 maintain a database on incidents involving fuel cycle facilities (FINAS);

 indicate where further research is needed;

 review and prioritize safety issues;

 prepare state-of-the-art fuel cycle safety reports and

 collaborate with other groups as necessary.

The WGOE/FCS has recently proposed and is currently seeking approval from CSNI for a new activity related to BUC. The proposal is related to the examination of the regulatory situation for BUC and incorporates an internal survey performed by WGOE/FXCS and the CSNI High Level Safety Issues on Spent Fuel Management and Criticality Safety in Fuel Reprocessing. In accordance with the recent increase in burnup of nuclear fuel including increasing initial enrichments, it is apparent that the necessity of adopting BUC in the

criticality safety design is becoming larger and larger. The WGOE/FCS has noted that BUC has already been adopted in several countries by the regulatory authorities. The regulatory basis and content appear to differ from country to country. Given the wide-scale research and development activities advancing the understanding of BUC, the WGOE/FCS has determined to make an effort to prepare the regulatory side to incorporate the results of these programs.

This concern is similar to that which has prompted the IAEA to organize and host meetings such as this one.

The primary difference between the activity proposed by the WGOE/FCS and that of the IAEA TCM is that the ultimate objective is to determine if it is possible to standardize BUC.

Since BUC is complex and will advance in the near future, standardization of the fundamental conditions is preferable. The resulting standardization is expected to be applicable to storage pool, transportation cask, interim storage and reprocessing. The specific activity under consideration is to collect information via the questionnaire given in Table II. The second step will be to use nuclear fuel cycle experts to summarize and analyze the replies to extract items to be used to proceed towards standardizing BUC from a regulatory viewpoint. Care will be taken to proceed with the cooperation of other groups such as the WPNCS/EGBCC and the IAEA TCM to avoid duplication of work.

Information about the current activities and links to publications of the OECD/NEA WGOE/FCS may be found at http://www.nea.fr/html/nsd/csni/wgoe.html. The OECD/NEA Secretariat for this work is Mr. Barry Kaufer(Barry.KAUFER@oecd.org) who may be contacted for additional information.

Table II. WGOE/FCS BUC Questionnaire

Have you adopted the burnup credit already in the regulation?

1. Facilities where the burnup credit is adopted.

In which facility or equipment is the burnup credit adopted in your country?

2. Burnup data There are two kinds of burnup data; one is the reactor management data that is attached to each spent-fuel assembly and the other is the data measured by use of the burnup monitor. Which of these two kinds of data do you use in the regulation for burnup credit implementation.

3. Precision and accuracy of burnup data

How do you evaluate the precision and accuracy of each burnup data, i.e., reactor management data and measured data? If two data differ beyond the sum of each expected error, how do you treat this assembly?

4. Maximum allowable

multiplication factor What value is used as the maximum allowable multiplication factor for criticality safety design at facilities where the burnup credit is adopted?

5. Level of burnup credit adoption

Which level of burnup credit is adopted in your country, actinide only or actinide plus fission products and/or gadolinium effect?

6. Method to derive multiplication factor from the burnup data

(In order to derive the multiplication factor it is necessary to know the initial enrichment, cooling time and so on of the spent-fuel in addition to the burnup data. How do you know these values and how do you derive the multiplication factor from these values)

All BWR and some PWR fuel assemblies contain gadolinium. Therefore, in order to evaluate the burnup credit, decreasing effect of gadolinium with increasing burnup may also be evaluated. Do you take into account this gadolinium effect when you evaluate the burnup credit?

8. Issues to be solved Do you have any issues for the burnup credit from the regulatory view point?

9. Adoption or

improvement

Do you have any plan to adopt newly or improve the burnup credit in the regulation in the near future? In order to eliminate the back-up confirmation of burnup monitor what conditions do you consider are necessary to be met?

10. R&D What kinds of R&D are being carried out to improve the burnup credit?

11. Other Comments?

REFERENCES

[1] M. TAKANO, “OECD/NEA BUC Criticality Benchmark-Result of Phase-1A,” JAERI-M 94-003, NEA/NSC/DOC(93)22, January 1994.

[2] M. D. DEHART, M. C. BRADY, and C. V. PARKS, “OECD/NEA Burnup Credit Criticality Benchmark-Phase I-B Results,” ORNL/TM-6901, NEA/NSC/DOC(96)06, (June 1996).

[3] M. TAKANO and H. OKUNO, “OECD/NEA BUC Criticality Benchmark - Result of Phase IIA,” JAERI-Research 96-003, NEA/NSC/DOC(96)01, February 1996.

[4] A. NOURI, “BUC Criticality Benchmark: Analysis of Phase II-B Results of a Conceptual PWR Spent Fuel Transportation Cask”, May 1998, IPSN/98-05,

NEA/NSC/DOC(1998)1.

[5] H. OKUNO, Y. NAITO AND Y. ANDO, “OECD/NEA Burnup Credit Criticality Benchmark Phase III-A: Criticality Calculations of BWR Spent Fuel Assemblies in Storage and Transport”, September 2000, JAERI-Research 2000-0441, NEA/NSC/DOC(2000)12.

[6] H. OKUNO, Y. NAITO, K. SUYAMA, “OECD/NEA Burnup Credit Criticality

Benchmark Phase III-B: Burnup Calculations of BWR Spent Fuel Assemblies in Storage and Transport”, February 2002, JAERI-Research 2002-001, NEA/NSC/DOC(2002)2.

TECHNICAL TOPICS