On the maxwellian + 1/E + fission-spectrum weighting function of NJOY 99.90 system’s GROUPR module

It is not possible to generate correct multigroup nuclear data with the GROUPR module of the NJOY system version 99.90 when the Maxwellian + 1/E + fission-spectrum weighting function is specified. It was detected that the calculation stops in the energy group that contains the break point between 1/E weighting and fission-spectrum weighting. A possible solution to bypass the error is proposed.